The Weather Guide

A Weather Information Companion for the forecast

area of the National Weather Service in San Diego

4th Edition
2007

National Weather Service, San Diego

Prepared by Miguel Miller, Forecaster

Introduction
This weather guide is designed primarily for those who routinely use National Weather Service
(NWS) forecasts and products. An electronic copy can be found on our web page at:
www.wrh.noaa.gov/sgx/research/Guide/weather_guide.php?wfo=sgx.
The purpose of the Weather Guide is to:

! Provide answers to common questions

! Describe the organization, the people, and functions of the NWS - San Diego
! Explain NWS products
! Describe specific challenges local NWS forecasters face in producing accurate forecasts
! Create a better general understanding of the particular weather and climate of our region
! Provide numerous resources for additional information

The desired effect of this guide is to help the general public and journalism community gain a
greater understanding of our local weather and the functions of the National Weather Service.
We hope to improve relationships among members of the local media, emergency management,
and other agencies with responsibility to the public. With a spirit of greater cooperation, we can
together provide better services and understanding to our residents and visitors.

The National Weather Service in San Diego invites anyone with any interest to our office for a
free and informal tour. We especially encourage members of the weather community or
meteorology students to take advantage of this nearby resource and become familiar with the
science, our work, and the local weather. We have various training and educational resources for
those pursuing a career in meteorology or for those seeking a greater understanding of the
science and its local applications.

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Contents
The National Weather Service…………………………………………………….…………5
Mission
Brief History
Organization

The National Weather Service Forecast Office - San Diego…………………….…..……10

Our area of responsibility
History of the NWS - San Diego
The People of NWS - San Diego
Communications and Product Dissemination
Local programs: Aviation, Cooperative Observers, Fire Weather, Hydrology, Marine,
NOAA Weather Radio, Public, Weather Spotter

Products and Services offered by NWS - San Diego……………………………………...16

Climate, Current Observations, Public Forecasts.
Non-routine products and verification: hydrology, winter weather, severe weather,
weather without precipitation, marine forecasts and warnings, aviation products, fire
weather, news products
Weather Safety and Preparedness: Emergency Alert System, Stormready

Behind the Forecasts………………………………………………………………….…….22

Terminology and Forecast Language
Forecast Tools: Satellite, Radar, Observations, Forecast Models, AWIPS, IFPS
Forecast Challenges: Uncertainty, Scarce Data, Microclimates

The Weather of Southwest California: A Climate Overview……………………………37

Climate Zones
Winter Storms: Heavy Rain, Snow, Thunderstorms, Flooding, Wind
The Summer Monsoon: Thunderstorms, Flash Flooding
The Marine Layer: Fog, Sea Breeze, Coastal Eddies
Santa Ana Winds: Damaging Wind, Extreme Heat, Dust Devils
Tropical Connections: Hurricanes and Their Remnants
El Niño and La Niña
Global Warming, the Greenhouse Effect and Climate Change
Sun, Earth, Sea, Space and Optical Phenomena

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Appendices
Appendix A: A History of Significant Weather Events in Southern California (organized by
weather type)
Heavy Rain: Flooding and Flash Flooding, Mud Slides, Debris Flows, Landslides….53
Heavy Snow, Rare Snow at Low Elevations………………………………………....86
Severe Thunderstorms: Large Hail, Strong Thunderstorm Winds, and
Killer Lightning (See flash flooding in heavy rain section)…………………….…....93
Tornadoes, Funnel Clouds, Waterspouts, and Damaging Dust Devils………….…..101
Strong winds (For thunderstorm related winds, see severe thunderstorms)…….…..114
Extreme Heat…………………………………………………………………….….125
Extreme Cold……………………………………………………………………..…131
High Surf, Stormy Seas, Tsunamis, Coastal Flooding and Erosion……………...…133
Miscellaneous: Dense fog, barometric pressure, dry spells, etc………………….…138

Appendix B: Weather Glossary…………………………………………………….…140

Appendix C: Weather Education and Bibliography…………………………….…..203

Appendix D: Product Cross Reference.........................................................................208

Appendix E: Warning and Advisory Criteria………………………………….…….212

Appendix F: Climate Data and Records……………………………………….……..214

Appendix G: Weather Safety Tips for Southern California………………….……..215

Appendix H: Charts and Tables……………………………………………….…..….218

Appendix I: Weather Extremes………………………………………………….……232

Appendix J: Web Sites for Weather Information………………………….…...……236

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The National Weather Service
Mission

The National Weather Service (NWS) provides forecasts and warnings for weather, hydrologic,
and climate needs for the United States, its territories, adjacent waters and ocean areas. The
mission is to protect of life and property and enhance the national economy. NWS data and
products form a national information database and infrastructure which can be used by other
governmental agencies, the private sector, the public, and the global community.

This mission is accomplished by providing warnings and forecasts of hazardous weather,

including thunderstorms, flooding, hurricanes, tornadoes, winter weather, tsunamis, and climate
events. The NWS is the sole United States official voice for issuing warnings during life-
threatening weather situations.

Brief History

The National Weather Service was created as a branch of the Signal Service, later the Signal
Corps of the Army, by a Joint Congressional Resolution in 1870. It provided “for taking
meteorological observations at the military stations in the...United States, and for giving
notice...of the approach and force of storms.”

The benefits of the weather service were soon recognized

by business industries, the general public, and farmers
who demanded special forecasts and warnings applicable
to their needs. This led to the creation of a new
organization with a more scientific status. Congress
transferred the weather service of the Army to the
Department of Agriculture in 1891 and named it the U.S.
Weather Bureau.

Before World War II, technology and communications improved slowly, but the war accelerated
the need for aviation forecasts, and an increase in technology and participation by all sectors of
society, including women. More employees, training and resources were poured into the war
effort. Advances in satellite and radar technology soon followed. During the 1950s and 1960s
organizational changes took place, including the distribution of local forecast offices across the
country. In addition, numerous national centers were established to provide support for
numerical weather prediction, research, climate archives, climate prediction, hydrology, aviation
weather, marine weather, severe storms and hurricanes. In 1970 the Weather Bureau changed its
name to the National Weather Service (NWS) and became part of the newly formed National
Oceanic and Atmospheric Administration (NOAA).

Since then many more advances have taken place in computer technology, allowing for greater
power in producing numerical model guidance used by meteorologists. Satellites have become
more sophisticated in the weather features they can detect. In the 1990s a “Modernization and
Restructuring” effort was realized. Doppler Weather Radars were installed nationwide,
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representing a vast improvement over the old radars. New Advanced Weather Interactive
Processing Systems (AWIPS) were installed nationwide in 1999. These workstations provide
meteorological data, model guidance, satellite imagery and radar data with great flexibility in
data manipulation and analysis. In 2000 a massive computer upgrade was made to allow greater
speed and stability in generating numerical model guidance. In 2004 the NWS changed the
forecast landscape with new digital forecasts designed to offer more spatial and temporal detail
and to adapt to emerging digital technology. As the capacity of technology and understanding
increases, forecasts become more accurate and extend further into the future. The NWS is the
world leader for all operational weather forecasting and provides its basic infrastructure. For
more history and stories, click on: www.history.noaa.gov.

The Role

The National Weather Service is part of NOAA, the National Oceanic and Atmospheric
Administration, which is part of the Department of Commerce (DOC) in the U.S. Government.
As noted in the mission statement, the entire weather database and infrastructure in this country
(i.e. satellites, radars, weather monitoring stations, model guidance, etc.), is provided and
maintained by the NWS. Private weather companies, consultants, media outlets, and research
organizations all depend on this infrastructure.

It is easy to see why the NWS is part of the Department of Commerce. Numerous professions are
directly impacted by the weather and countless decisions are made in response to weather
forecasts. For example, anybody who works outdoors such as construction crews must monitor
the forecast and make cost-saving decisions. Industries of transportation, agriculture and
recreation depend heavily on weather information. Indirectly, some industries like the stock
market may be impacted as entire local economies can be affected by flood, drought, freezes, or
damaging weather. In fact, it is hard to find a profession not in some way affected by the
weather.

The global economy is also increasingly dependent on weather forecasts. As much as one-third
of the U.S. gross domestic product—three trillion dollars' worth of goods and services—is at
least partially dependent on weather, according to estimates. Obvious examples include road,
sea, and air transportation. Less obvious, perhaps, are power companies, which depend on
temperature forecasts to anticipate consumer demand, and school systems.

Most Americans get weather information from media sources, such as television and radio, the
Internet, and newspapers. These media sources are in effect weather retailers, selling weather
information to customers through advertising money or subscriptions to services. But there is yet
another layer in the process. For example, let’s say a local newspaper features a weather page.
To prepare this page and to do it every day, the newspaper employs a private weather company.
The newspaper gives the company its requirements for their weather page. The company fulfills
the requirements at the appointed times and sends the bill to the newspaper. This works in a
similar way for television and radio. The daily temperatures and rainfall amounts you see on the
evening news were probably first collected and disseminated by the NWS, then gathered by the
private weather company, then included in their weather package delivered to the paying
television station. The private company may have some weather infrastructure of their own, but
largely their data and guidance are provided as public access by the NWS, namely satellite and
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radar data, and weather model guidance. In this way the NWS serves as a sort of giant wholesale
weather warehouse, where the weather retailers can shop for free to produce their products and
services specific to their customers’ needs.

The Organization

The NWS is organized into headquarters, national centers, regional offices, and various field
offices. See www.weather.gov/organization.php. The headquarters offices are located in
Maryland (metro Washington DC) which oversee and administrate the entire agency. Nine
national centers provide guidance to offices in the field scattered across the country, comprising
the National Centers for Environmental Prediction (NCEP), most of which are also located in
Maryland. They include:

• Aviation Weather Center (AWC) provides aviation warnings and forecasts of

hazardous flight conditions at all levels within domestic and international air space. The
center is located in Kansas City, MO. See aviationweather.gov.
• Climate Prediction Center (CPC) monitors and forecasts short-term climate
fluctuations and provides information on the effects climate patterns can have on the
nation. They provide the official monthly and seasonal outlooks. They are the official
experts on climate altering mechanisms such as El Niño and La Niña. See
www.cpc.ncep.noaa.gov.
• Environmental Modeling Center (EMC) develops and improves numerical weather,
climate, hydrological and ocean prediction through a broad program in partnership with
the research community. See www.emc.ncep.noaa.gov.
• Hydrometeorological Prediction Center (HPC) provides nationwide analysis and
forecast guidance products out through seven days, including the official daily weather
map analyses. They compute quantitative precipitation guidance. See
www.hpc.ncep.noaa.gov.
• NCEP Central Operations (NCO) sustains and executes the operational suite of
numerical analyses and forecast models and prepares NCEP products for dissemination
as guidance essential for weather prediction by each Weather Forecast Office (WFO).
See www.nco.ncep.noaa.gov.
• Ocean Prediction Center (OPC) issues weather warnings and forecasts out to five days
for the Atlantic and Pacific Oceans north of 30 degrees North latitude. See
www.opc.ncep.noaa.gov.
• Space Environment Center (SEC) provides space weather alerts and warnings for
disturbances that can affect people and equipment working in space and on earth. The
Center is located in Boulder, CO. See www.sec.noaa.gov.
• Storm Prediction Center (SPC) provides tornado and severe weather watches for the
contiguous United States along with a suite of hazardous weather forecasts. The Center is
located in Norman, OK. See www.spc.noaa.gov.
• Tropical Prediction Center (TPC) includes the National Hurricane Center and
provides forecasts of the movement and strength of tropical weather systems and issues
watches and warnings for the U.S. and surrounding areas. The Center is located in
Miami, FL. See www.nhc.noaa.gov.

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Other specialized support centers, not part of NCEP include:
• National Severe Storms Laboratory (NSSL)
• Spaceflight Meteorology Group (SMG)
• Climate Diagnostics Center (CDC)
• Hydrologic Research Laboratory (HRL)
• National Climatic Data Center (NCDC)
• Pacific Tsunami Warning Center (PTWC)
• Central Pacific Hurricane Center (CPHC)
• West Coast/Alaska Tsunami Warning Center (WC/ATWC)

For hydrologic support, there are 13 River Forecast Centers (RFCs) across the country. For
aviation support, there are 22 Center Weather Service Units (CWSUs) across the country, co-
located with Air Route Traffic Control Centers. The country is divided into 122 forecast areas,
also known as County Warning Areas (CWAs), each serviced by the local Weather Forecast
Office (WFO) (see map below).

Regional offices in the Eastern, Central, Southern, Western, Alaskan and Pacific regions oversee
these field offices within their region of the country. The Western Region Headquarters directs
NWS operations in the western states from its office in Salt Lake City, Utah. This includes 24
WFOs, including the office in San Diego, three RFCs, and four CWSUs.

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The NWS in San Diego

The San Diego Forecast Office prepares forecasts and any necessary warnings for a sizable area
of Southern California, which is called a County Warning Forecast Area (CWFA or CWA). The
San Diego CWA comprises all of Orange and San Diego Counties, western Riverside County,
southwestern San Bernardino County and adjacent coastal waters off San Diego County. The
CWA is divided into forecast zones, each containing
roughly similar climates. A zone forecast is routinely
made for each zone, the text of which is generated from
a highly detailed graphical database. Forecast operations
run continuously 24 hours a day, 365 days a year,
providing its citizens a constant monitoring of the
weather and protection of life and property in the form
of timely warnings. In this way the NWS is the “weather
police.” The San Diego Forecast Office meteorologists
are the experts of local weather and climate. They keep
informed of research developments and the latest
discoveries and news that impact the weather, such as El
Niño and climate prediction, but do not conduct the
research themselves and therefore are not experts in
those research fields.

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A History of the NWS in San Diego
“A very great gale blew from the southwest; the port being good, we felt nothing,” commented
Juan Rodriguez Cabrillo in 1542, upon sailing into what is now San Diego Bay. It was probably
the first documented weather observation in California.

Officially, weather observations were first taken in San Diego from 1849 to 1871 at the San
Diego Mission de Alcalá and at Ft. Stockton, now part of Presidio Park, by the Medical Corps of
the Army. When the Army’s Signal Service assumed the task in 1871, the weather observing
station was moved downtown to Horton Square at present day Broadway between 3rd and 4th
Avenues. In 1909 a city ordinance allowed the U.S. Weather Bureau to install a weather kiosk to
be placed in the San Diego Plaza containing weather instruments, posted forecasts, and weather
charts. It is not known when the kiosk was discontinued. The official station moved around the
Horton Square area several times from 1871 until 1940, but always remained within a stone’s
throw of present day Horton Plaza. In 1890 the first Weather Bureau Office was located on 5th
Avenue between E and F streets. In 1930 the office and a second weather observing station were
relocated to the Lindbergh Municipal Airport 1 ½ miles northwest of the city office, but
observations were continued downtown. In 1940 observations became official at Lindbergh
Field. This new site was considered close enough and sufficiently similar in climate to the
downtown location that the climate record was continued uninterrupted rather than starting a new
separate record for the new location. In 1969 the weather equipment was moved to its current
location at the General Aviation Building at Lindbergh Field, now San Diego’s International
Airport. A history of the early observations in San Diego has been published and can be found at:
www.wrh.noaa.gov/sgx/cpm/SanDiegoHistory.pdf.

In 1970 the Lindbergh Field office

became a National Weather Service
Office with limited forecasting
responsibility. The NWS office in Los
Angeles provided the general
forecasts for all of Southern
California. The San Diego office
adapted these forecasts for local use
and issued warnings for San Diego
County in addition to the regular
duties of taking weather observations
at Lindbergh Field. In October 1995, the office at Lindbergh Field moved to Rancho Bernardo in
the northern reaches of the city and discontinued taking the weather observations, but still
maintained the climate record at Lindbergh with the help of automated equipment and contract
observers installed in 1996. In 1997 the San Diego Office made a gradual transition to full
forecast office capacity. Orange, western Riverside, and southwestern San Bernardino Counties
were added to San Diego County. Since 1997 all forecasts and warnings for our area originate
from the office in Rancho Bernardo. Marine forecast and warning responsibility for adjacent
coastal waters were added in 1999. In late 2002, the Interactive Forecast Preparation System
(IFPS) was implemented. This bold new forecasting system provides NWS forecasts in a
graphical format and with a great amount of detail. In January 2003, the office assumed fire
weather forecast responsibility in an area with virtually a year-round fire season. In November
10
2004, the northern borders of the CWA were adjusted. The community of Yucca Valley joined
Twentynine Palms and other Morongo Basin communities as part of the Las Vegas area of
responsibility. In exchange, the San Diego Forecast Office added an area north of Victorville
almost to Barstow, including the city of Helendale.

The function, purpose and importance of the NWS were stated eloquently by Ford A. Carpenter
in The Climate and Weather of San Diego California, published in 1913. “A few years ago a
member of the French Academy of Science visited the San Diego Weather Bureau office, and
having being shown the meteorological apparatus and informed as to the application of the data
to the everyday needs of commerce and agriculture, exclaimed, “You Americans are a wonderful
people. You not only equal the French in the use of delicate instruments from which theories are
evolved, but you excel us in making the results worth dollars and cents.”
Carpenter also observed, “An article in the Century magazine a few years ago stated that the
Weather Bureau costs the United States a million and a half dollars a year, but that a
conservative insurance company figured that on an average the people of the United States saved
annually $30,000,000 because of their weather service, and this in addition to thousands of
lives.”

The People of the NWS in San Diego

The current staff at the NWS in San Diego consists of 25 employees. Four managers and one
assistant (three of which are degreed meteorologists) direct the work activities and administrative
duties of the office. An Information Technology Officer maintains computer systems. 11
forecasters (all of whom are degreed meteorologists) prepare and disseminate forecasts and
warnings, and attend to focal point duties and other projects. Three hydrometeorological
technicians (HMTs) and two meteorologist interns collect and disseminate data, operate the
NOAA Weather Radio, manage the climate observer program, and answer phone calls from the
public and media. The interns (who are degreed meteorologists) also perform forecaster duties
occasionally. Three electronic technicians maintain and repair observational equipment, the two
Doppler Radars and NOAA All-Hazards Radio.

The Meteorologist-in-Charge (MIC) is Jim Purpura. He ultimately oversees all operations and
work in the office and implements changes in policy or practices when needed. Questions about
policy, funding, employment, technology, and the future are best directed to the MIC.

Ed Clark is the Warning Coordination Meteorologist (WCM). He maintains relationships with

our partners in service, i.e., emergency management within cities and counties, agencies of flood
control and law enforcement, fire departments, and the media. He keeps the staff current and
proficient in correct warning practices, completes verification studies, and conducts a variety of
outreach activities.

Ivory Small is the Science and Operations Officer (SOO). He ensures that good forecasting
techniques and good science are used by meteorologists through training and development. He
implements the latest technology and meteorological theory from the research community and
produces some of the research himself. He can answer questions regarding student volunteer and
employment programs. He is the best resource for questions about the meteorology behind the
weather.
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The first line of phone communication is usually with a hydrometeorological technician (HMT).
They answer general questions about the weather, climate, or forecast, or can point you in the
right direction for the answer. Forecasters on duty can provide greater detail about the reasons
behind the current weather or forecast. Many questions of this nature can be answered by
consulting the latest Area Forecast Discussion, updated at least four times a day.

When not working basic operations directly, each member of the staff completes focal point
duties. These include directing local programs, conducting special projects or overseeing other
areas of responsibility. A list of the entire staff and the numerous duties they perform in addition
to operational duties can be found on our staff web page:
weather.gov/sandiego/office/staff.php?wfo=sgx.

Communications and Product Dissemination

Text products and information disseminated from the NWS are transmitted in a coded format.
Each product name is identified, for Weather Wire and EMWIN (Emergency Manager’s source)
purposes, by its code containing nine letters. The code formula is cccNNNxxx, where ccc is the
regional node, NNN is the product identifier, and xxx is normally the code of the originating
forecast office. For example, LAXZFPSGX indicates Los Angeles (LAX) is the regional node,
the Zone Forecast Product (ZFP) is the name of the product, and San Diego-Rancho Bernardo
(SGX) is the originating office. When a product is sent from the office, it goes to Gateway, the
communications center for the NWS. From there, the products are disseminated to the world.
Subscribing news services and private weather information companies then pick up these
products and send them to users. The NWS maintains the largest meteorological
telecommunications switching center in the world, sending and receiving nearly half a million
meteorological bulletins each day.

The NWS relies heavily on its partners in emergency management and the media to keep
communities safe and well informed. Emergency managers and the media have timely access to
severe weather information through a number of systems and services listed below. For
information on how to set up a service to receive real-time weather information, contact our
Warning Coordination Meteorologist, Ed Clark, at 858-675-8700 ext. 223.

The Family of Services includes the NOAA Weather Wire Service, NOAAPort and news
agencies such as AP, UPI and City News Service. These systems provide paying subscribers
consistent and timely weather information in real time. For more information, visit:
www.weatherwire.net and www.noaaport.com.

Private commercial information vendors supply numerous paying customers with weather
information packages tailored to their needs. These are easily found on the Internet by doing a
search for weather software.

Emergency management and flood control agencies in California can receive timely information
through the California Law Enforcement Telecom System (CLETS). This originates from the
State Office of Emergency Services in Sacramento. The Emergency Manager’s Weather
12
Information Network (EMWIN) provides real time information for a one-time cost for
equipment and installation. Email and pager notification can be easily set up. However, this
information may not be as reliable or timely as that found with the Family of Services. You can
always consult the NWS web page (www.weather.gov)for up to date information from a
national perspective. However, it is subject to the availability and connection limitations inherent
to the Internet.

Weather information can also be obtained from the National Weather Service anywhere and
anytime using a wireless device. All you need is a wireless device that can surf the Internet along
with a wireless Internet service provider. For more details, visit www.srh.noaa.gov/cte.htm.
RSS feeds and podcasts are also available, see www.nws.noaa.gov/rss.

Please note: The Internet is not the primary means of disseminating weather information from
the NWS and should not be solely relied on at any time, especially during significant weather
events. The clickable map on the home page is not the official means of communicating
current watches, warnings or advisories in effect. A backup source of information is
recommended, such as NOAA weather radio or other systems mentioned above.

Local Programs
The Aviation program encompasses the preparation,
transmission and verification of Terminal Aerodrome
Forecasts (TAFs) and Transcribed Weather Broadcasts
(TWEBs). TAFs are coded 24-hour forecasts updated at
least every six hours. TAFs give detailed weather
conditions expected at six area airports: San Diego-
Lindbergh Field (SAN), McClellan-Palomar Airport
(CRQ), Orange County-John Wayne (SNA), Ontario
(ONT), Palm Springs (PSP), and Thermal (TRM). Soaring forecasts are also generated daily.
Airport weather warnings are issued when severe weather threatens Lindbergh Field. Aircraft
accident reports are issued for fatal accidents.

The Cooperative Observer Program is a vast network of

thousands of weather stations across the nation. Local
volunteers keep a daily climate record with data collected
from equipment provided and maintained by the NWS. San
Diego’s Cooperative Program Manager directs this work at
more than 90 official weather stations in our region. Data
from some of the stations are used for hydrology and
forecasting purposes. Climate data are forwarded to the
National Climatic Data Center and become part of the
official climate record.

The San Diego Mesonet is a network of public and private providers of weather data. Using
existing weather stations, providers can transmit data from their own weather stations to the
NWS in real-time. See www.wrh.noaa.gov/sgx/cpm/sdm.php?wfo=sgx.

13
 Fire Weather forecasts are essential for fire fighting
efforts by a number of agencies. Routine Fire Weather
Forecasts are issued detailing sky condition, winds,
relative humidity, and lightning potential. Specific spot
forecasts are given by request for particular fire fighting
or controlled burn situations, and also for hazardous
material incidents. Fire Weather Watches and Red Flag
Warnings are issued when dangerous fire potential
exists.

The Hydrology program provides guidance and data for

forecasting rainfall amounts and flooding. The hydrology
focal point works closely with flood control agencies,
NWS hydrologists and River Forecast Centers to ensure
data that is correct, useful and timely gets into the hands
of forecasters during possible flooding events. Networks
of instrumentation such as rain gauges and stream gauges
are maintained to monitor rapidly changing hydrological
events. Computer models and software are developed and
maintained to enable accurate and timely issuance of
hydrological products such as flash flood warnings.

The Marine program oversees the quality

preparation of marine forecasts. The Coastal Waters
Forecast describes wind and sea conditions out to
five days; the Surf Forecast provides details about
the next day’s surf. Relationships with the marine
community are maintained, along with a network of
coastal observation equipment for frequent
observational data. Warning systems are ready to be
used in the event of large surf, coastal flooding,
tidal overflow, tsunamis, or severe weather of any
kind over the coastal waters.

NOAA All-Hazards Radio continuously broadcasts a cycle of

warnings, forecasts and current conditions on six separate
frequencies on the VHF band, originating from the San Diego
office. Specially designed receivers have the capability to alarm
and play a warning at the moment it is issued. This is possible
due to ever-improving computer-synthesized voice technology.
A Spanish language transmitter was installed in June 2004 in the
Coachella Valley and provides Spanish broadcast of all products.
It is the first transmitter of its kind in the west. The following
table includes transmitter locations, names, and frequencies:

14
San Diego (east of Poway) KEC-62 162.40 MHz
Santa Ana Mountains (south of Corona) WWG-21 162.45 MHz
Coachella Valley (east of Indio) KIG-78 162.40 MHz
Strawberry Peak (south of Lake Arrowhead) WXM-66 162.50 MHz
Mt. Soledad Marine (La Jolla) WNG-637 162.425 MHz
Coachella Valley Spanish (east of Indio) WNG-712 162.525 MHz

The Public Forecast Program is a suite of forecasts and warnings designed for the entire public
community. The traditional flagship product of the NWS has been the Zone Forecast, the routine
forecast issued at least twice daily. The forecast is text generated from our digital forecast
database. Forecasts of sky condition, temperatures, precipitation and significant winds are
included in the forecast which extends to seven days. Area Forecast Discussions are issued at
least four times a day. They give the current reasoning behind the forecast and explain any
additional action taken. Quantitative Precipitation Forecasts are issued during the wet season and
as needed during the dry season to indicate expected rainfall amounts. Hazardous Weather
Outlooks are issued when any hazardous weather is expected for the upcoming week and contain
flash flood potential indices during the monsoon season. Any necessary watches, warnings,
advisories, and other statements are issued under the direction of the Public Forecaster on duty.

The Weather Spotter Program is a network of volunteers. A weather spotter is a person who
observes significant weather and relays the information to the NWS. With this information,
forecasters can issue warnings and update forecasts if necessary in a more accurate and timely
manner. Around 1300 weather spotters are keeping an eye to the sky in our forecast area.
Information about the program, including the quarterly newsletter can be found at:
www.wrh.noaa.gov/sgx/spotter/spotter.php.
Skywarn is a more proactive spotter network involving ham radio communications to relay
weather information during active weather events. When forecasters deem appropriate, Skywarn
is “activated” and a Skywarn member operates radio communications from the San Diego office.
Reports of significant weather or damage are actively solicited from the Skywarn community.
The reports are then immediately forwarded to the forecasters on duty to aid in the forecast and
warning process. For more information on the local Skywarn organization, visit
www.swskywarn.org.
Spotter and Skywarn training presentations are held occasionally to recruit and train weather
spotters.

15
Products and Services Offered by the NWS in San Diego
The NWS prepares a large number of various products that provide specific information. Each
product name is identified by its code containing nine letters. The code formula is explained
under “Communications and Product Dissemination” above. For a listing of NWS products, see
Appendix A. The products are organized and described in the following categories. Note: All
products originating from San Diego begin with the LAX identifier. For simplicity, the products
below will be identified only by the following six letter code.

Climate - click on “Climate - Local” on our homepage for more information.

The Daily Temperature and Precipitation Summary (RTPSGX) reports the daily maximum
and minimum temperatures and precipitation for numerous cities in our forecast area from a
variety of weather stations, such as airports, cooperative observers, and remote weather systems.
The RTP is issued at 430 am/pm and again at 530 pm largely to provide the data to local news
media for early morning and late afternoon broadcasts. Updates may occur during the evening if
and when additional data arrives. Note that these temperatures are the 24 hour high and low,
which may not necessarily agree with the calendar day because thermometers are reset at the
time of the 4 pm observation. This can lead to a problem. For example, let’s say the high in
Anaheim was 80 degrees one day. The 4 pm report gave the high of 80 and the current
temperature of 77. The next day is much cooler; Fullerton and Santa Ana each report a high of
65 degrees. The report from Anaheim is a high of 77. Clearly, this is what we call a “carry-over”.
The high of 77 occurred at the time the thermometer was reset around 4 pm the previous day.
Stations that report once daily are susceptible to carry-overs when the following day is cooler.
Other problems are more rare, but also possible. An observer may not have reported for multiple
days for a variety of reasons and the thermometer would not have been reset. The data given may
then be the highest and lowest temperatures for the period, not the current day. Also, the high
temperature may actually occur after the 4 pm observation. Please take special note of the
disclaimer on the product and understand that some highs that appear abnormally high may be
carried over from the previous day.
The Climate Report (CLIxxx) shows the updated climate values for the day for a number of
cities in our area. Daily climate reports are prepared for many sites with automated weather
equipment. In the product’s header, xxx represents the three-letter identifier, normally an airport.
Each CLI product is a daily almanac of temperature, precipitation, and several other weather
conditions displayed with daily normal values, updated totals and records. These products are
updated twice daily early in the morning and in the afternoon.
The Local Climatological Data (CF6) chart is a look at the current month of daily records. This
is not an issued product, but is available on our web site. These are prepared for all cities for
which there is a climate report (CLIxxx).
The Monthly Weather Summary (CLMSAN) is updated on the 1st day of each month, detailing
the previous month’s statistics for these same cities/airports that have a CLI report. This product
summarizes the weather of the previous month.
The Record Report (RERSGX) is a report of daily record temperatures or rainfall amounts met
or exceeded at many cities in the area. This product is automatically headlined on the home page.
Only some of the cities that report daily on the RTPSGX keep a history of daily records. Some of
these cities have a short history dating back only to the 1970s. This makes the records easier to
reach, and therefore less than remarkable. San Diego, Santa Ana, and Riverside are three stations
16
with a much longer climate record.

Current Observations - click on “Current Conditions - Observations” on our homepage for

more information.

The Regional Weather Roundup (RWRSGX) is a collective of current automated observations

in the region including sky condition, temperature, dew point, relative humidity, wind speed and
direction, barometric pressure and trends. When applicable, the remarks column shows very low
visibilities, heat index or wind chill index values.
The Coastal Weather Observations (CGRSGX) product lists the current weather and sea
conditions at several coastal stations, and is updated every three hours, but is very limited
overnight.

Public Forecasts

The Zone Forecast Product (ZFPSGX) has traditionally been the most well known and used
product we prepare. It is issued at 330 am and 230 pm every day and as necessary (when the
forecast does not match current or expected conditions). It is generated from a digital database
maintained and updated by forecasters. Graphical digital forecasts are also available providing
spatial and temporal detail not previously available with text products, see Forecasts – Digital for
more on these increasingly popular forecasts.
The Hazardous Weather Outlook (HWOSGX) is a product issued when any expected weather
in the following week may need the issuance of an advisory or a warning. It is issued by 6 am on
days when these expected conditions exist, and updated as necessary. The outlook also presents a
flash flood potential rating during the monsoon season in each mountain and desert zone as none,
low, moderate or high.
The Short Term Forecast (NOWSGX), also called the “nowcast”, is a brief detailed forecast
usually covering two hours, but no more than six hours. These forecasts are issued to add
beneficial detail, for example, describing location, movement, and possible impact of
thunderstorms.
The Area Forecast Discussion (AFDSGX) is a discussion of the reasoning and thinking behind
the forecast. A simple explanation of the general weather pattern for the coming week is given in
the synopsis. The discussion portion contains a wealth of information about the current and
future weather developments and the particular challenges involved in the current forecast. It is
routinely updated four times daily, at 330 am, 930 am, 230 pm, 930 pm and other times when
needed. The discussion on the web contains links that go to the non-routine products in effect
and links that explain some of the more complex meteorological terms that may be used.
The Tabular State Forecast for California (SFTSGX) and the Point Forecast Matrix
(PFMSGX) are part of the digital suite of products generated by the gridded digital database. The
SFTSGX is a forecast of specific temperatures and chances of precipitation for selected cities
across Southern California. The PFMSGX is a highly detailed forecast of numerous weather
parameters in three hour increments for the next two days for a select few cities. Both these
products are issued at least twice daily at 330 am and 230 pm.
The Quantitative Precipitation Statement (QPSSGX) is a routine forecast of rainfall amounts
during the wet season, roughly November through April, but also during other times of the year
when a significant precipitation event is expected. The product shows in table format expected
rainfall amounts in 6-hour intervals for the coming three days for numerous locations in the
17
forecast area. This product is issued twice daily by 4 am/pm.

Non-routine Products

A Watch is issued well in advance when conditions are favorable for a weather event to occur
that can threaten life and/or property in the watch area.

A Warning is issued when a weather event that can threaten life and/or property is imminent or
already occurring in the warned area. Emergency Alert Systems (EAS) are activated for short-
fused warnings, such as a Severe Thunderstorm Warning.

An Advisory is issued when serious conditions are present and cause significant inconvenience.
It may lead to a watch or warning.

Warning and Advisory criteria are found in Appendix D.

Verification

Observed weather conditions are essential to help the NWS determine which non-routine
products to issue. When warnings are issued, weather reports are collected to verify the warning.
A collection of these reports will be issued as a Local Storm Report (LSRSGX). With the
verification data, studies can be made to learn how well the forecast team warns correctly or
creates a false alarm. In this way the NWS takes responsibility for its warnings. Verification is an
important part of the ongoing improvement of the warning process.

Hydrology – Flash Floods and Floods

Flash floods are defined as a rapid rise in water flooding a local area, followed by a rapid drop in
water level. Any small stream, creek, arroyo, wash or paved urban areas can be briefly inundated
by a flash flood. Flash floods should be water flowing rapidly at least six inches deep. Dam
breaks or breaches cause flash flooding downstream. When any of these are expected a Flash
Flood Watch (FFASGX) and subsequently a Flash Flood Warning (FFWSGX) are issued. A
Flood Advisory for Urban and Small Stream Flooding (FLSSGX) informs of inundation
conditions not threatening life and property, but can be dangerous if not taken seriously.
Examples of advisory conditions include a flooded intersection or onramp to a freeway that is
blocked by water and disrupting traffic flow. The Flash Flood Statement (FFSSGX) is issued to
update or cancel Flash Flood Warnings (FFWSGX).

A Flood Watch (FFASGX) and subsequently a Flood Warning (FLWSGX) are issued when a
mainstem river is expected to overflow its banks. A Flood Statement (FLSSGX) updates a
warning and may update and summarize more than one warning. The NWS defines a flood as a
normally dry area inundated with water along an established watercourse such as a mainstem
river. In San Diego’s forecast area, there are four rivers that qualify as such watercourses: The
San Diego River at Fashion Valley, the San Luis Rey River at Oceanside, the Santa Margarita
River at Ysidora, and the Mojave River at Victorville (Mojave Narrows). The River Statement
(RVSSGX) provides specific forecast levels at these flood gages during flooding events.

18
Winter Weather

All of the following winter weather watches, warnings and advisories come under the product
header WSWSGX. The Winter Storm Watch and Winter Storm Warning are issued when a
significant winter storm will impact the region. These detail the adverse impacts caused by heavy
snowfall combined with strong winds. When the snowfall and winds are not expected to reach
warning criteria, a Snow and Blowing Snow Advisory is issued to communicate the lesser
impact. If heavy snowfall is expected without strong winds, a Heavy Snow Warning is issued.
If the snow will be heavy, but not reach warning criteria, a Snow Advisory is issued. When
snowfall and strong winds combine to create white-out conditions and near zero visibilities, a
Blizzard Warning is issued. Although unheard of in Southern California, ice storms or freezing
rain events would be covered by an Ice Storm Warning and a Freezing Rain (or Drizzle)
Advisory, respectively. Several different winter weather hazards can be in effect at once under
one WSWSGX product.

Severe Weather

Severe weather is associated with thunderstorms, which can bring any combination of deadly
lightning, tornadoes, large hail, heavy rain (with associated flooding), and any other strong
damaging winds. When conditions are favorable for severe thunderstorms or tornadoes, the
Storm Prediction Center issues a Severe Local Statement (SLSCA). This becomes a Severe
Weather Watch for Southern California in a redefining statement issued by the Oxnard office.
A Severe Thunderstorm Warning (SVRSGX) is issued when severe thunderstorm warning
criteria are met or are imminent. It is not mandatory that a local statement or a watch be in effect
before a warning is issued (in fact, it is rare). When a tornado is detected by weather spotters or
Doppler Weather Radar, or the forecaster strongly believes a tornado is about to develop, a
Tornado Warning (TORSGX) is issued. Updates are made to either or both of these warnings
with a Severe Weather Statement (SVSSGX). Flash floods occurring with severe
thunderstorms are detailed in their own separate Flash Flood Warning (FFWSGX). Severe
weather over coastal waters is covered by a Special Marine Warning (SMWSGX), which
warns of waterspouts and other severe and hazardous boating weather. Severe weather is often
extremely localized in time and space. Accordingly, these products are very short-fused and
cover a small area.

Weather without Precipitation

A Non-Precipitation Weather product (NPWSGX) covers a great variety of weather events that
do not include precipitation. This product can be an advisory, a watch or a warning. A High
Wind Watch and subsequently a High Wind Warning are issued when strong winds causing
potential damage are expected. A Wind Advisory is issued when strong winds are expected, but
fall below warning criteria. A Wind Chill Warning or a Wind Chill Advisory is issued when
strong winds combine with very low temperatures. Blowing dust and/or sand that reduce
visibility may prompt a Blowing Dust/Sand Advisory. When dense fog develops in more than
just a localized sense, a Dense Fog Advisory is issued. Extremes in temperature are also covered
by the product. High temperatures and humidity may warrant an Excessive Heat Warning when
the Heat Index becomes dangerous. A Freeze Warning is issued when freezing temperatures
present a serious threat to crops. A Frost Advisory is issued when a freeze is less serious.
19
Marine Forecasts and Warnings

The Coastal Waters Forecast (CWFSGX) is a routine forecast of winds and sea state on the
coastal waters out to five days. It is issued four times daily at 230 and 830 am/pm PST and 330
and 930 am/pm PDT. The forecast covers the coastal waters from the San Diego County shore
out to 60 nautical miles (about five nm beyond San Clemente Island). The area is divided into
two zones by a line 30 nautical miles off the coast parallel to the coast. Within the body of the
forecast a Small Craft Advisory may be headlined when winds begin to present a hazard for
small vessels. If seas are especially hazardous, it will be specified as a Small Craft Advisory for
Hazardous Seas. The following rare warnings, Gale, Storm, Tropical Storm, or Hurricane,
may be headlined when very strong winds and/or stormy seas are expected. The Surf Zone
Forecast (SRFSGX) is issued twice daily at 2 am/pm and contains surf and rip current risk
information for the beaches of Orange and San Diego Counties. A Marine Weather Statement
(MWSSGX) describes potentially dangerous boating conditions such as waterspouts or non-
severe thunderstorms on the open water. A High Surf Advisory (CFWSGX) is issued when
large and dangerous surf is widespread along the coast or when minor tidal overflow occurs.
When the weather over the water becomes severe with strong thunderstorms, a Special Marine
Warning (SMWSGX) is issued. Coastal flooding caused by very high tides and/or large surf is
covered by a Coastal Flood Watch and subsequently a Coastal Flood Warning (CFWSGX). If
an earthquake occurs along the Pacific Rim that will generate a tsunami along the coast, a
Tsunami Warning (TSUWCA) will be issued by the West Coast and Alaska Tsunami Warning
Center. A Tsunami watch, Tsunami Advisory, or Tsunami Information Statement
(TIBWCA) may be issued. If Southern California impacts are expected, these products are
reissued with more local details by the San Diego Forecast Office.

Aviation Products

Aviation products are coded and disseminated to the aviation community, not through the
standard media to the public, but are available on our web site. A Terminal Aerodrome
Forecast (TAF) provides detailed changes in wind speed and direction, visibility, cloud
coverage, cloud ceiling height and precipitation for local airports out to 24 hours. These airports
include San Diego-Lindbergh Field (TAFSAN), McClellan-Palomar in Carlsbad (TAFCRQ),
Orange County-John Wayne in Santa Ana (TAFSNA), Ontario (TAFONT), Palm Springs
(TAFPSP), and Thermal (TAFTRM). A Transcribed Weather Broadcast Text (TWB432) is
the 12-hour air-route corridor forecast encompassing the route between SNA and SAN, including
the mountains of San Diego County. This describes weather conditions to be expected along the
route. All forecasts are updated every six hours or updated more frequently as necessary.

Fire Weather

A Fire Weather Forecast (FWFSGX) is similar to the public zone forecast, but gives more
detail regarding relative humidity, winds and lightning potential. A Fire Weather Watch and
subsequently a Red Flag Warning (both RFWSGX) are issued when dangerous wildfire
potential exists, i.e., when strong winds combine with low relative humidity and low fuel
moisture. Spot weather forecasts, which are site specific for wildfires, controlled prescribed
burns, hazardous material spills, or for any other public agency support, are issued upon request.
20
News Products

A Special Weather Statement (SPSSGX) is a description of an upcoming significant weather

event, such as a winter storm. It is usually allowed to expire once the weather event is occurring
and is covered by a warning or advisory, such as a Winter Storm Warning. The Rainfall Storm
Total Summary (RRMSGX) is a periodic update to storm precipitation totals during or after a
given storm. This product is automatically headlined on our home page. The Local Storm
Report (LSRSGX) is issued during and after an intense weather event, documenting the impact
of heavy rain, hail, flooding or severe weather of any kind. Several reports may be issued during
the event as information becomes available. A summary report is issued at the end of the event.
A Public Information Statement (PNSSGX) is a multi-purpose news product. Its information
can range from a summary of a weather event, an update to new technology, a change in the
format of a product, a change in local policy, or other purposes.

Weather Safety and Preparedness – Click on “Weather Safety – Education” on our homepage
for more information.

The primary mission and responsibility of the National Weather Service is to protect life and
property. The goal is to warn for all potentially dangerous weather events with sufficient lead
time so emergency personnel and the public can take action to eliminate or minimize the loss of
life and/or property. However, for many reasons a dangerous weather event may strike without a
warning being issued, or the public may not be otherwise prepared. Weather awareness and
preparedness are vitally important especially in our region where residents can become
complacent because dangerous weather is relatively infrequent and the population is dense.

Upon the initial issuance of a warning, the Emergency Alert System (EAS) is activated. Local
news radio stations with this responsibility receive this alert of three tone bursts and proceed to
broadcast the warning over their station, in accordance with regulations of the Federal
Communications Commission (FCC). On television the warning message scrolls across the top
or bottom of the screen. NOAA weather radios broadcast the warning direct from the NWS
office (specially designed receivers kick on automatically when a warning is issued). The NWS –
San Diego web site will indicate the warning on a color coded map. Sadly, these efforts are
sometimes not sufficient to inform all endangered parties in a timely fashion. We encourage all
residents and visitors to become aware of the potential weather dangers associated with the area
in which the live, work, and visit, and the means to receive these warnings, and to prepare
accordingly.

Two programs of the NWS help communities to better prepare themselves for disasters.
Stormready communities are better prepared to save lives from the onslaught of severe weather
through better planning, education, and awareness. The TsunamiReady program is designed to
help coastal communities reduce the potential for disastrous tsunami-related consequences. For
more information about how to become involved, see www.stormready.noaa.gov and
www.tsunamiready.noaa.gov. See Appendix E for weather safety information.

21
Behind The Forecasts
Terminology and Forecast Language
The NWS has a unique way of describing expected weather. Some of the terms used to describe
time periods and weather conditions may seem arbitrary, but there are rather specific meanings
attached to them.

Forecast Time Periods

Time Period Definition

today sunrise to sunset

tonight sunset to sunrise

morning or in the morning sunrise to noon

afternoon or in the afternoon noon to around 6 pm

evening or in the evening from 6 pm to midnight

In the forecast the days are divided into both day and night periods. A night period crosses over
midnight as outlined above. For example, “Sunday night” means from sunset Sunday evening
until sunrise Monday morning. Lows for Sunday night most of the time would technically occur
early Monday morning around sunrise, but are mentioned in the Sunday night period.

Sky Conditions

Sky conditions are described depending on how many tenths of the sky is covered by opaque
clouds (clouds that completely block the sun).

clear or sunny less than 1/10 opaque clouds

mostly clear or mostly sunny 1/10 to 2/10 opaque clouds

partly cloudy 3/10 to 6/10 opaque clouds

mostly cloudy 7/10 to 8/10 opaque clouds

cloudy 9/10 to 10/10 opaque clouds

High cirrus clouds are often somewhat transparent, so even if the sky is full of them the term
mostly clear or partly cloudy may be used. In contrast, a small patch of fog can entirely obscure
the sky from an observer’s point of view. It may be cloudy or foggy at that point, but only a mile
or two away the skies are completely clear. That patch of fog is so low it is below the horizon
from an outside observer’s perspective. This is often the case with varying terrain, a shallow
22
marine layer, and dense fog. Fog may persist at the beaches while only a quarter mile inland it is
clear. Forecasters attempt to include language to specify the range of possibilities, but cannot
describe every possibility without becoming entirely too wordy. A mostly sunny forecast may be
a bad forecast to the few people underneath a tiny isolated patch of fog, but a correct forecast to
the other 99% of the population. By contrast, high clouds can be seen hundreds of horizontal
miles away.

Winds

Wind direction is described as the direction from which the wind is blowing (e.g., a northwest
wind is a wind coming from the northwest). Wind speeds are given in miles per hour. Terms that
may be used to describe wind speeds are defined in the following table.

0-5 mph light or light and variable

5-15 mph none used

15-25 mph breezy (for mild weather)

brisk or blustery (for cold weather)

20-30 mph Windy

30-40 mph very windy

40 mph or greater strong, damaging, dangerous

Since winds are highly variable in time and space, usually the strongest winds expected
anywhere in the zone are mentioned. For people in areas normally protected from the wind, this
understanding is important. “Local” is a term often used to imply that indicated winds will not
blow over the entire area, but at some unspecified locations that may differ in time and space.
Often, winds are influenced by terrain creating a predictable wind pattern. If there is enough
confidence about exactly where and when the winds will take place, a better description is given.
For example, phrases such as “mainly below Cajon Pass in the morning” are often included to
add beneficial detail.

Temperatures

Temperatures are given in simple numerical ranges such as “lows 42 to 50”. In many weather
situations temperature ranges can be very large; a forecast of the entire range would not be
useful, and a detailed description would be too wordy. In these cases, extreme temperature
outliers are simply left out of the range and the forecast is made for the majority of the area. For
example, on a clear morning in the San Bernardino Mountains low temperatures may range from
29 degrees in a high mountain valley to 51 degrees on a foothill slope. A forecast covering that
entire range (28 to 52 for example) is not very useful, so a judgment is made that most lows
within that zone will be 33 to 47. Observers over time will come to know where their local
temperatures fit with respect to the standard forecast ranges. The details can still be found using
the point-specific digital forecast, however.
23
Precipitation

The idea to use probabilities for whether it was going to rain began with the National Weather
Service in 1965. The original concept was to provide a risk-benefit assessment for people to
whom the occurrence of rain was critical. For example, a contractor might decide to pour
concrete if the chance of rain is only 30 percent, but might decide not to pour if it's 60 percent.
Probability of Precipitation (PoP) is the likelihood (expressed as a percent) of measurable
liquid precipitation (or the water equivalent of frozen precipitation) during a specified period of
time for any point in the forecast zone. Measurable precipitation is defined as 0.01 inch or
more. PoPs accompany expressions of uncertainty or areal qualifiers within the forecast
narrative. For example, a slight chance of rain (20%) is an expression of uncertainty that means
at least one location in a zone should receive measurable precipitation 2 out of 10 times (20%)
given a similar weather situation. Or, to state the converse, rain is NOT expected 8 out of 10
times. The probability has nothing to do with the amount, duration, or the percentage of the area
that will get rain. When showers are mentioned in a
forecast, there is a high likelihood of them
occurring somewhere in the area, and thus the
probability refers to the amount of the area in the
forecast that will receive measurable rain, and
receive an areal qualifier. “Scattered showers”
means that 30 to 50 percent of the zone’s area gets
hit by at least one shower and receives measurable
precipitation. Below is a table of these two
descriptive methods and their relationship to PoPs.

PoP Percent Expression of Uncertainty Equivalent Area Qualifiers

10-20 percent slight chance isolated

30-40-50 percent chance scattered

60-70 percent likely numerous (or none used)

80-90-100 percent (none used) (none used)

Other qualifying terms may be used with the above non-numerical expressions.
Terms of duration: brief, occasional, intermittent, frequent
Terms of intensity: Very light: less than 0.01 inch per hour
Light: 0.01 to 0.10 inch per hour
Moderate: 0.10 to 0.30 inch per hour
Heavy: greater than 0.30 inch per hour
For trace events (precipitation of less than 0.01 inch), the terms “drizzle,” “light rain” or
“sprinkles” will be used, often with a PoP of 10%. Our marine environment can bring dense fog
(which can be very misty), heavy condensation, and drizzle. Most of the time these marine layer
precipitation events result in a trace, even when road surfaces become completely wet. For more
on the philosophy of probabilities, see the Uncertainty section under Forecast Challenges below.
24
Forecast Tools
Today’s forecaster has a large variety of tools available. Many advances in technology and the
understanding of meteorological principles in recent decades have added a great deal to the
science. Seven day forecasts today are about as accurate as three day forecasts were 20 years
ago. Meteorologists blend their own knowledge and experience with the data provided by these
tools to make a forecast.

Satellite

Satellite data is one of the more essential forecasting tools. The satellite in use over the western
U.S. is the GOES - West Satellite. This satellite is geostationary, meaning that it rotates along
with the earth so that it is always over the same place on the earth. Three basic images are
generated from this satellite: visible, infrared and water vapor imagery. Polar-orbiting satellite
data are also used. These satellites orbit the earth crossing the poles. Several additional
specialized images are also available.

Visible imagery is like a camera snapshot

from space, recording reflected visible light
from the earth’s surface. All clouds are
white. The image goes black as the sun sets.
Since all clouds are white, it is sometimes
difficult to tell at what levels these clouds
exist.

Infrared images are actually measurements

of temperature, rather than reflected light as
in visible satellite images. Warmer objects
appear darker than colder objects. Cloud
temperatures are related to cloud height, and
relative cloud height can be readily inferred.
The color spectrum on the gray scale is
converted to colors to more easily discern
the temperature differences.

25
Water vapor images are useful for identifying
regions of moist and dry air. Dark colors such as
black and dark grey indicate dry air while bright
colors such as white or light grey indicate moist
air. Swirling wind patterns in low pressure
systems and jet streams are easily identified.
Colors have also been added to these images to
more easily discern the moisture differences.

Other derived satellite products have been

developed, such as the fog product. In San
Diego this is commonly used at night to easily
detect the low clouds and fog common to our
region. For more background on satellite imagery, click on:
www.srh.weather.gov/jetstream/remote/satellite.htm.

Radar

Doppler Weather Radars were installed during the early 1990s and marked the beginning of a
new era in detecting and forecasting weather. The official name is NEXRAD WSR-88D,
meaning NEXt Generation Weather Service RADar-1988 Doppler.
Technicians at the San Diego office maintain two Doppler radars: one
east of Scripps Ranch in San Diego, and one in the Santa Ana
Mountains south of Corona. While some media outlets claim ownership
of WSR-88D Doppler Radars, only the National Weather Service owns
and maintains weather radars in our area. In addition to detecting areas
of precipitation called echoes, the Doppler Radar also detects
movement and intensity of the precipitation. The radar also detects
wind velocity and direction, useful for detecting rapid shifts in wind
direction, including tornadoes. These data alert forecasters to the
possible need of warnings or advisories.

How does it work? The radar sends out a beam of energy that
strikes an object. Some of that energy is reflected back to the
radar. The velocity of the object can be derived from the phase
change of the beam’s wavelength as it returns to the radar. The
radar has many limitations. Due to occasional atmospheric
conditions, the beam is bent toward the ground and detects
ground effects (hills, trees, structures) called “clutter.” The
beam scans the atmosphere in slices, one angle at a time. As the beam angles upward, the beam
may be over 20,000 feet high at a distance beyond 100 miles. Significant weather can occur
below the beam completely undetected. In addition to raindrops and ground effects, the radar can
detect birds, insects, dust, etc. Military operations often include spreading chaff (tiny, fine metal
strips) into the atmosphere. Chaff is a very good reflector for the radar beam and shows up on the
radar display as an intense radar echo. Often, a quick look at the satellite image can help verify
that this is not precipitation. Echo signatures of chaff look quite different in appearance than
26
actual precipitation and can be easily identified by the trained eye, but it becomes more difficult
when echoes of legitimate precipitation are also present. For more information about Doppler
Radar, click on: www.srh.weather.gov/jetstream/remote/doppler.htm.

Observations
Surface observations are current weather conditions measured at a point on the earth’s surface.
The most reliable and accurate source of hourly weather observations are automated surface
observation systems, called ASOS
stations, a network of standardized
equipment funded and maintained by the
NWS. This equipment, usually located at
airports, transmits at least one hourly
observation called a METAR
(METeorological Aviation Routine
weather report). METARs are written in
METAR code, an international weather
descriptive code.

A network of ALERT (Automated Local Evaluation in Real Time) equipment is used primarily
for hydrological purposes, measuring rainfall and river levels, but also temperature and wind in
some cases. This equipment is maintained by flood control agencies in cooperation with the
NWS.

Another network of weather instrumentation is RAWS (Remote Automated Weather Station)

data, used primarily for fire weather forecasting support. The network is maintained by several
other federal and state agencies, such as the California Department of Forestry and the Bureau of
Land Management.

The San Diego Mesonet is a relatively new network comprising private citizens or external
agencies providing real-time data to the NWS in San Diego from their own privately funded
equipment. Participants collect their data on a data logger installed on their computer. Using high
speed Internet and the ftp process, the data is transmitted automatically to workstations at the
NWS in San Diego. The siting, placement, and accuracy of the equipment of these sites have
been verified and approved by NWS personnel, so forecasters can trust them. For more
information, click on “San Diego Mesonet” on our home page. The Mesowest is a collective of
numerous observational data maintained by the University of Utah. It is a useful tool used by
NWS forecasters to monitor all observational data at once.

A large variety of other weather data sources are available, mainly on the Internet. These
include school networks, resorts, businesses and private citizens with weather equipment. We
use these sources only as a last resort and with caution due to their occasional low levels of
accuracy and reliability. On occasion we invite these providers to join the San Diego Mesonet.

27
 Upper Air Observations provide valuable data for a lot of
reasons. Forecasters need to know the behavior of the
atmosphere in three dimensions, not just at the earth’s
surface. Observations of the upper air are taken by weather
balloons with an attached radiosonde, a small packet of
weather instruments. As the radiosonde rises, it sends a
constant stream of data, which is crucial for understanding
the current state of the atmosphere. The data is collected
by radio receivers on the ground and plotted as a vertical
trace called a sounding, on a thermodynamic diagram
called a “Skew-T.” This snapshot of temperature, dew
point and winds in the atmospheric column is a most
valuable set of data. A forecaster can identify temperature
inversions common to our region, levels of instability and
moisture, changes in wind speed and direction, and infer
many other atmospheric behaviors. More than 2,000 of
these balloons are launched around the world at 00z and
12z universal “zulu” time (locally 4 am/pm PST and 5
am/pm PDT). In this way the world is synchronized with
an accurate three dimensional picture of the weather
conditions twice a day. These data are among the most
important input to computerized numerical weather
models. It's only by getting a complete picture of what the
weather is doing now that forecasters can hope to say what
it will do next. Unfortunately, the sounding network is
rather sparse and soundings are taken only twice a day.
Locally, soundings are taken at Miramar MCAS (pictured
at right, below). Around the region, other soundings are
taken at Vandenberg AFB, Oakland, and occasionally at
Edwards AFB, Yuma, Arizona, and Guaymas, Mexico.

The typical weather balloon is about six feet in diameter (two

meters) and is filled with either helium or hydrogen. It carries a
one-pound (half a kilogram) package of weather instruments and
transmitters. Flights may last over two hours, reaching altitudes
of 22 miles (35 kilometers), where the temperature drops to
minus 130 degrees F (minus 90 degrees C). At that height the
balloon, having swollen to about 20 feet (six meters) in diameter
due to the low air pressure, tends to pop, cutting short the flight.
The one-pound radiosondes do not hurtle to the ground,
however—little parachutes bring them back down safely,
complete with mailing instructions. Returned instrument
packages can be retooled and reused. But even now, with GPS
tracking, the NWS recovers only about 20 percent of the
radiosondes.

Satellite Sounders are becoming more adept at correctly inferring temperatures and winds at all
28
levels of the atmosphere from GOES Satellites. Satellites have equipment that will acquire
profiles of temperature and moisture for clear or partly clear fields of view. In addition, cloud
tracking allows for the measurement of wind in the atmosphere. This information is used for
input to the weather models which result in improved weather analysis and forecasting.

Wind Profilers are surface based instrument grids that detect winds and temperatures in the
atmospheric column. Most of these are maintained by the military, universities, or other research
institutions.

ACARS (Aircraft Communication Addressing and Reporting System) data are vertical traces of
weather data taken by commercial airliners during ascents out of and descents into major
airports. The frequent upper air observations are valuable because they often fill in the gaps of
time and space between weather balloon soundings.

Forecast Models - Numerical Model Guidance

Once meteorologists have an accurate
picture of the current atmosphere, the
process of forecasting can begin. Scientists
through the ages have come to understand
some of the movements of the atmosphere
through the study of physics, fluid
dynamics, and thermodynamics.
Mathematical equations called equations of
motion have been developed to describe the
movement of air in the atmosphere. By
modifying these equations, removing the
less important components, and inserting
the weather data into the equations, a solution can be calculated for a future time. For example, if
we know the temperature for a certain place at midnight, we can enter that value into the
equation to get the temperature for that place at noon. This can be done for many time steps (i.e.
24, 36, 48 hours) into the future and for numerous points on the map. These equations of motion
are non-linear, meaning they cannot be solved by hand in a timely fashion; if we attempted to
solve the equation by hand, the weather event
would occur before we could produce a
forecast for it! This is why powerful computers
are essential. The computer can make
iterations, a long sequence of approximations
which increasingly get closer to the solution.
After numerous iterations, an acceptable
solution arrives. The process is repeated for
every weather parameter and for every grid
point on the map. The plotted values can then
be connected by interpolating values between
the points, like connecting the dots. The whole
process works like baking bread as follows:
29
 Data is collected: upper air, satellite, radar, Ingredients are gathered.
surface observations, buoys, etc.

Data is input into mathematical equations of Ingredients are mixed and put in the oven.
motion to be solved by powerful computers.

The computer generates a numerical solution The bread is baked.

in future time steps.

The solutions are checked for quality and The warm bread is sliced and served.
plotted graphically on maps.

In its finished form, the numerical model guidance arrives at each forecast office a few hours
after the “run time”: 00z, 06z, 12z, and 18z universal time (a few models are run more
frequently, but do not extend very far into the future). The main supercomputer in use by the
NWS is named Blue and is located at an IBM facility in Gaithersburg, Maryland. Weather data
arrives from an array of sources, including observation stations, ocean buoys, and global weather
balloons. Some aircraft even carry sampling instruments. But satellites increasingly provide
extensive coverage that can penetrate and monitor different layers of the atmosphere. The
number of daily weather observations crunched by NOAA's supercomputers is around 200
million. After the guidance is computed and post-processed, it is sent to each forecast office
where the data is ingested by AWIPS equipment. The guidance packages are then available to
the forecaster to analyze and formulate a forecast. It comes in graphical format or statistically
generated text format. Just like bread, the model guidance package becomes stale with time, and
obsolete with the arrival of the new model guidance run.

Some guidance is received from national or regional centers regarding rainfall amounts, flooding
and flash flooding potential, severe thunderstorms, hurricanes, hazardous fire weather, etc. For
example, if a big storm is coming and forecasters need to figure out how much rainfall is
coming, the San Diego office will receive guidance from the Hydrometeorological Prediction
Center (HPC) in Maryland and the River Forecast Center (RFC) in Sacramento. They will
provide valuable input for deciding how much precipitation will fall and what flooding impacts
may occur. The Storm Prediction Center (SPC) in Oklahoma provides guidance on the
probability of severe thunderstorms. The National Hurricane Center (NHC) in Miami projects
tropical cyclone tracks and intensities in the Atlantic and eastern Pacific Oceans. In the end, final
decisions regarding local warnings and forecasts rest with the forecasters in the San Diego office.

Advanced Weather Information Processing System (AWIPS)

AWIPS is a workstation that provides one-stop shopping for weather data and guidance used by
the forecaster. Numerical model guidance, satellite imagery, radar data, and analyses can be
viewed graphically. AWIPS offers the capability of viewing the model guidance in a variety of
ways to get a four-dimensional understanding of the atmosphere’s behavior. NWS alphanumeric
guidance, observations, and text products nationwide are also available.

30
Interactive Forecast Preparation System (IFPS)

IFPS is the system that forecasters use for

preparing and issuing forecasts. With this
system, located in AWIPS, forecasters
manipulate a high-resolution digital
database that represents the expected
weather, rather than writing text. Forecasters
edit grids of numerous weather parameters,
such as maximum and minimum
temperatures, hourly temperatures and dew
points, three-hourly winds, chances of
precipitation, sky cloud cover, and so on. IFPS then generates a suite of graphical and text
forecasts from the digital database. The resulting digital forecasts offer a much higher degree of
temporal and spatial detail, with additional weather elements not available previously, such as
relative humidity and rainfall amounts. Now you can literally get a forecast specific to your
neighborhood and see how the weather will change during the day. Explore the available
information by clicking “Digital” on our home page.

The grids generated by each local NWS forecast is collected and merged into one seamless
National Digital Forecast Database (NDFD). To ensure consistency and quality along forecast
office boundaries, weather elements are coordinated between offices. The NDFD database is
made available to all customers and partners (public and private) who can then create a wide
range of text, graphic, and image products of their own. Any individual user with a computer and
access to the internet can download information from the NDFD to suit his or her needs.

Forecast Challenges
Regarding Southern California weather, some observers may joke, “What weather?” Our climate
and our profession have often been the target of jokes (e.g., “why don’t you get a real job?!”, “if
I were wrong as often as you are, I’d be fired!” or “isn’t this where they send the junior
meteorologists?”). It is true that our climate does not suffer the extremes of temperature, wind,
and precipitation that many other climates do. The challenge of predicting our weather lies in the
uncertainties, subtleties, and relatively infrequent extremes, not often in the severity. Our
enormous population base is largely unfamiliar with severe life-threatening weather is less
prepared for it when it comes, and that presents a new risk. For these reasons Southern California
is prone to low-probability yet high-impact weather events. Dense fog, drizzle, or light rainfall
can be a killer. Compare traffic accident reports in Southern California when it rains with those
reports when it does not rain, then look at the same figures for Seattle. Additionally, expectations
differ with professions. A surgeon is expected to be perfect or very near perfect all the time, but
baseball players are considered successful when they get a hit in only one third of their attempts.
Stock market analysts are much less accurate and far more ambiguous than are weather
forecasters.

Despite popular belief, forecasting the weather in our region is not as easy at it seems. “You guys
have it easy, it’s always nice here” is an often heard comment. A common misconception is that
31
difficulty to forecast corresponds to severity of the weather, and conversely, it is easy to forecast
for benign weather. For example, it is very difficult to forecast tornadoes and hurricanes and easy
to forecast coastal fog. Understandably, more research has been conducted on severe life-
threatening weather (because that’s where the funding goes) and better model guidance has come
from it. Much less model improvement has been made for coastal fog, Santa Ana winds, and
terrain issues common to our region. Therefore, forecasting for weather that is not severe can
often be more difficult, but is overlooked because the weather remains benign and low impact.
However, when active weather occurs very locally, but in a very sensitive area, it can be
catastrophic. For example, only one hour of strong wind on only one hillside can make a wildfire
explode. Advances in the science have led to greater forecast accuracy, and that has increased the
public’s expectations of weather forecasters to get the forecast right. While forecasters may
claim and promise greater forecast accuracy, the weather is still the weather: chaotic, complex,
and inherently unpredictable.

There are a number of questions to answer and puzzles to solve each day. These puzzles may be
as innocuous as determining when the coastal clouds will clear or what the high temperature will
be, but most of the time there are more significant issues. These issues are mentioned in the
forecast discussion. Reasons, opinions, clarifications, and expressions of model performance
and preference are included in the discussion. Formerly, discussions were meant only for
coordination purposes within the NWS meteorology community and transmitted through
equipment that required extreme brevity. For these reasons, many complex meteorological terms,
abbreviations, contractions, and jargon were used. In recent years discussions have become much
more public (and posted on the Internet) and have become much more readable for non-
meteorologists. One who reads the discussions day after day will quickly gain an understanding
of the particular challenges the forecasters are facing, even when the weather is benign. A
glossary is linked to select terms often used in the discussion, providing explanations of these
complex terms. Click on “Discussion” on our home page for the latest update.

Uncertainty

“To the often-heard question, ‘Why can't we make better weather forecasts?’ I have been
tempted to reply, 'Well, why should we be able to make any forecasts at all?’”
- Edward N. Lorenz, MIT researcher, in The Essence of Chaos.

Chaos Theory is very real in meteorology. The tiniest errors in the initial conditions become
very large errors in the solution. If a computer model does not initialize well, it is like a golf club
swinging through the ball at an angle only slightly off perfection. The result, as many golfers
know, is a large error in where the ball ends up.

Some uncertainties in our forecasts arise because of the lack of essential information. With our
current knowledge and technology, it is impossible to account for all the possible variables that
impact the weather. Our data networks may not be dense enough to detect some significant local
effect. The leading researchers in the field may not have discovered the meteorological theory
behind an event and forecasters may not even understand everything that is actually taking place.
The forecaster may not be fully aware of the situation or sufficiently experienced to detect
something important. Sometimes the weather simply defies explanation, or at least an
explanation that forecasters can come up with. For example, if we look at two identical low
32
pressure systems with the same dynamics, moisture, temperature profile, structure, etc., we often
see different results, like rain with one system, but not with the other. We often ask how and
why. After the event forecasters can speculate on why it rained or didn’t rain, and even come up
with an acceptable explanation, but that’s after the fact. Forecasters keep that in their records and
in their brains for future reference. If the event is rather significant, forecasters may even collect
the data surrounding the event, analyze and study it in depth, and write and publish a paper as a
case study.

Our climate and global position add to the uncertainty in our forecasts. San Diego is located just
far enough south to be on the southern edge of the normal winter storm track. We may be on the
edge of the area of expected rain. Promising weather systems may not maintain strength as they
approach us. The weather system may bring local showers where some spots measure rain while
the rest of the area remains dry.

Comparisons of satellite data to model guidance can be done on AWIPS to determine the quality
of the guidance. This is called model initialization. For example, if the model guidance at 00z
does not match closely to the observed atmosphere (model data and observations can be overlaid
on a satellite image) at 00z, then the initialization was not good. The forecaster may conclude
that since this particular model did not initialize well (does not have a good handle on the current
weather pattern), there is no way its prognoses will have a good handle on it for future time
periods; the forecaster will then discount or ignore its solutions. The model guidance may give us
different solutions with each new model run, or the models’ solutions differ from one model to
another. When the models seem to disagree from run to run and/or with each other, forecaster
confidence lowers. At times with a particular feature such as a storm, the models are very tardy
to come into agreement, perhaps less than one day before the storm. When the confidence is low,
the forecaster relies more on experience and the observed weather data than the guidance, and as
a result the forecast may become less specific.

In contrast to our challenges, the Seattle forecaster has it relatively simple: A storm approaches,
forecast rain. It is only a question of when and how much. Many local folks demand that
forecasters could be so certain: “Just tell us, is it going to rain or not?” The science of
meteorology is young. Many
discoveries in meteorology
theory and improvements in
numerical model guidance are
taking place, but there are still
numerous hidden variables or
nuances that can go undetected
and change the weather. Our
efforts to correctly define
atmospheric motion in real
time are clumsy at best. The
NWS prefers to avoid giving an
irresponsible and possibly
misleading forecast of certainty
when no such certainty exists.
This is why forecasters use
33
terms of probability. The following true example is illustrative. One day the NWS issued a
forecast with a 40% chance of rain for the next day. When the next day arrived, a radio
personality reported rain where he was and questioned on the air: “Does this mean that the
chance of rain was really 100%?” No. If we were to flip a coin, we know the chance of it coming
up heads is 50%. If it comes up heads, it does not mean the chance of coming up heads before
the coin flip should have been 100%. The chance is again 50% before the next coin flip. Failure
of the broadcast media to grasp the probability concept can unintentionally change the meaning
of the forecast that much of the public receives. Broadcasters are often heard to report a chance
of rain, or even a slight chance, as “rain in the forecast,” significantly altering the meaning. It is
human nature to add certainty where there is little.

Forecasts can be misinterpreted or trusted too much. “A chance of showers” would have been a
good forecast if only some areas get measurable rain (in the radio personality example above, the
shower he experienced may have been the only one in the area). “Mostly sunny” is a good
forecast if most coastal areas are sunny, even if a few beaches experience fog all day. “Locally
windy” is a good forecast if a few spots are windy, even if most areas are not. Conditions change
in both time and space. “Partly cloudy” may mean mostly cloudy at times or mostly sunny at
times during the day, but for brevity’s sake the forecaster chose to simplify the wording. With
the common low clouds, it may be completely cloudy in some spots and completely sunny in
other spots, then the reverse occurs, all within the same zone; for this, “partly cloudy” might be
appropriate forecast wording as well. It should also be remembered that forecasts are refreshed
often. A forecast is routinely issued every 12 hours. Often, the forecast is updated between those
routine issuances. By the time the morning newspaper reaches your door, there may already be
two or three updates made to the forecast you are reading.

Forecasts for future time periods become more and more uncertain with each future forecast day.
The NWS issues seven-day forecasts as part of the routine public forecasts. On average, NWS
forecasters accurately predict the next day’s weather 90% of the time. Today's four-day forecast
is as accurate as the two-day forecast was in 1985. The accuracy deteriorates as the forecast goes
further out; the day seven forecast is just over 50% accurate. Beyond seven days, let’s be frank,
the forecast is a flip of the coin, but some extended models can indicate which way to lean, warm
or cool, wet or dry. Actually, the climatological normals become the best forecast much beyond
about ten days. When someone calls requesting a forecast for an outdoor wedding two months
away, we give them the climatological normal high, low, and chance of rainfall for the date.

Long Term Prediction is fraught with uncertainty, but significant advances have been made in
understanding the global climate and today there are more data available for analysis. In recent
decades the climate altering mechanism El Niño has been a catalyst for these advances (for more
on El Niño, see
“The Weather of
Southwest
California - A
Climate
Overview”). The
Climate
Prediction
Center (CPC) is a
34
national agency and world leader in climate studies and long term predictions. They produce
monthly and seasonal outlooks for the entire country. The outlooks are not exactly forecasts, but
graphical outlooks of whether temperature and precipitation will be above normal, near normal,
or below normal. Sophisticated climate models take into account all important effects on global
weather such as sea surface temperatures, pressure patterns, upper level winds, and solar
radiation. Occasional press releases on outlooks of significance are one way the CPC informs us
of the weather trends in the weeks and months ahead. Many of these press releases are headlined
on our home page when they occur.

Scarce Data on the Edge

To the west and south of California lies the vast, open Pacific Ocean. There are a few buoys and
ship reports, but it is largely devoid of data. To the south and east is Mexico with very few
reliable data sources. Because much of our weather comes from the west or south, it is difficult
to know just what kind of weather is headed our way. By contrast, most of the country has the
advantage of looking west (where most of their weather comes from) to learn exactly what kind
of weather is headed their way. An old axiom states that if you want to know what weather to
expect in New York City tomorrow, just look at the weather in Chicago today. The lack of
upstream observations hurt California forecasters in another way. Numerical model guidance
depends on initial data to get a correct start on the forecast. With very few data points over the
ocean, the model has only a vague idea of the weather conditions before they reach land.
Accordingly, the model often has trouble ascertaining the strength, position and/or timing of
approaching weather systems. Yet another problem arises. Several model domains (areas
covered by the model) have a western boundary not far out to sea. So these models do not “see”
a weather system before it enters the domain. Once it sees the system, it may struggle to
correctly represent and define it before it reaches land.

Even in our highly populated area

with numerous data points, there Other radar limitations
never seem to be enough data points Radar Horizon

when they are most needed. That is

because many weather phenomena A B
are highly localized and very brief.
California tornadoes provide a good
example. It is nearly impossible to
forecast a Southern California
Radar
tornado before it touches down. The
Doppler Radar scans a slice of the
atmosphere every six minutes at
each beam angle. A tornado can
touch down, do its damage and lift
back into the cloud in much less Radar beam cannot see lower portion of storm “B”

time than the six minutes between

radar scans. Additionally, a tornado may be distant from the radar, occur below the beam, and go
undetected. Doppler Radars were built and tested for the severe weather of the plain states and
are more attuned to detecting those larger scale severe storms. Luckily, California tornadoes are
usually not as severe or damaging as those in the Midwest. In an effort to better detect these
35
localized weather phenomena, we have around 1300 volunteer weather spotters across the region
that help fill in the gaps in data. We also appreciate it when our partners in the media and public
agencies pass along a significant report to us.

Microclimates

Microclimates are very small scale climate zones. Southern California’s highly complex terrain
and proximity to the ocean create a variety of microclimates. The weather can be very different
between canyons and mesas, beaches and inland areas, mountain tops, slopes and valleys, urban
and rural areas, and a number of other variables. On a clear night, overnight low temperatures
may be 15 degrees lower in a canyon compared to a neighboring mesa. High temperatures at a
foggy beach may be 15 degrees lower compared to the temperature under the sun only a mile
inland. Winds may be strong through certain corridors, while neighboring areas are nearly calm.
A mountain area may receive significantly more precipitation from a storm than that received in
the valley at its foot.

The digital forecasts generated by the IFPS (Interactive Forecast Preparation System) are our
way to provide this kind of microclimate detail to our users. But even with this cutting-edge
IFPS technology, more weather instrumentation and weather spotters, these slight nuances
continue to be very difficult to pinpoint.

36
The Weather of Southwest California: A Climate Overview
Climate Zones

“In enumerating the peculiar advantages of San Diego, there seems to be one which is of very
great importance. Perhaps, as a scientific man, I may lay more stress upon it than is necessary,
but I hardly think it possible; I have seen many parts of the world, and have made some study of
this subject. It is the question of the climate of your latitude that I refer to. You have a great
capital in your climate. It will be worth millions to you. This is one of the favored spots of the
earth, and people will come to you from all quarters to live in your genial and healthful climate,
a climate that has no equal.” – Alexander Agassiz, 1872.

The agreeable coastal California climate is the stuff of legend and lore. It has inspired artists and
writers. Most people visualize the mild coastal climate when asked about the climate of Southern
California, forgetting for a moment that there are coastal, inland, mountain and desert climate
zones that are highly distinct and very close together. These climate zones are determined by
several factors: proximity to the ocean, terrain, elevation and latitude. Using the Koppen climate
classification system, the metropolitan areas of Southern California have a Mediterranean
climate, characterized by mild, sometimes wet winters and warm, very dry summers. The climate
types in the mountains range from Mediterranean, to Subtropical Steppe (not as mild as
Mediterranean with more precipitation in all seasons) to Highland (more extreme and variable
due to elevation). Desert climate types include Mid-latitude Desert, a dry climate with hot
summers and cool winters, and
Subtropical Desert, relatively
hotter and drier. The
Mediterranean climate includes
all coastal areas, valleys and
foothills. Subtropical Steppe
climates would include the
mountains between the foothills
and the higher peaks. Highland
climates would encompass the
mountain tops, probably above
7,000 or 8,000 feet. Mid-latitude
Deserts include the Mojave
Desert, at elevations above 2,000
feet. Subtropical Deserts include
the Colorado Desert, at elevations
below 2,000 feet.

Annual precipitation amounts increase gradually from the coast to the mountain crests, then drop
dramatically into the deserts.

California owes its agreeable climate to a semi-permanent high pressure area located over the
eastern Pacific Ocean, which deflects storms northward and secures fair weather for the region.
During the winter months, this high breaks down allowing the jet stream to steer mid-latitude
weather systems along a more southern track of the prevailing westerly winds. For this reason,
37
the vast majority of precipitation comes from winter storms between November and March.

“The American public is familiar on all sides with elaborate and detailed statements of the
weather at a thousand and one resorts. If we may believe all we read in such reports, the
temperature never reaches the eighties, the sky is flecked with just enough of cloud to perfect the
landscape, the breezes are always balmy, and the nights ever cool. There is possibly one place in
the United States where such conditions obtain, a bit of country of about forty square miles at the
extreme southwestern part of the United States, in which San Diego is situated; but even here,
perhaps, once in two or three years, the sultry blasts of the Mojave Desert pass over the low
mountain range and parch this favored district.” - General Greely, Chief Signal Officer of the
United States, in an exhaustive article on summer climates appearing in the magazine Scribners
in April, 1888.

Winter Storms

“The wind [the southeaster] is the bane of the coast of California. Between the months of
November and April, including a part of each (which is the rainy season in this latitude), you are
never safe from it; and accordingly, in the ports which are open to it, vessels are obliged during
these months to lie at anchor at a distance of three miles from the shore, with slip-ropes on their
cables, ready to slip and go to sea at a moment’s warning. The only ports that are safe from this
wind are San Francisco and Monterey in the north and San Diego in the south.” – Richard
Henry Dana in Two Years Before the Mast, 1835.

Winter storms bring a great variety of weather

phenomena: strong winds, flooding rains, heavy
snows, large surf, and thunderstorms with their
damaging lightning, hail, winds and the occasional
tornado. In Southern California, cold fronts arrive
with little resemblance to those described by weather
textbooks. The cold air associated with deep troughs
of low pressure becomes modified by the mild ocean
waters and the front becomes less distinct. Winter
storms often have a leading band of rain ahead of the

colder air of the system. With the warmer

storms, the majority of the rainfall occurs in
these initial bands. Cold storms bring a pool
of cold unstable air aloft that follows behind
the initial rain band, bringing showers
and/or thunderstorms. In these colder storms
the majority of precipitation often falls from
the showers and thunderstorms rather than
38
the initial band of rain. At times there is a high variability of rainfall distribution. For example, a
big winter storm may bring three inches of rainfall to Anaheim, but less than an inch to San
Diego. In showery situations, one thunderstorm can drop over an inch of rainfall over one
neighborhood, leaving the rest of the area dry. The direction of flow of the lower level winds can
indicate favorable areas for more rain than others. If the flow is from the south or southwest, we
expect relatively greater rainfall in Orange County, the northern Inland Empire and especially the
San Gabriel Mountains and the San Bernardino Mountains. West or northwest flow will bring
relatively greater rainfall to San Diego County.

The mountains usually receive more rainfall than the

lowlands because of the orographic effect. This effect
is when the air directed at a mountain is forced upward,
enhancing the upward motion already within the low
pressure system. More moisture is able to condense and
grow into raindrops. For this reason San Diego area
beaches annually receive around 10 inches of
precipitation, while Palomar Mountain receives
annually over 40 inches.

On rare occasions, the subtropical jet stream

can direct warm, moist air into California
originating from the central Pacific. This
stream of moist air is sometimes called the
Pineapple Connection or Pineapple Express,
because the track often comes from the
direction of Hawaii. The air has greater
available moisture than the air contained in
colder storms, so they tend to bring heavy
rain, but little if any snow. When the long
wave pattern, or general global circulation,
steers this moisture into our region, a wet
pattern develops and there can be many days
of rainfall. Once the soil becomes saturated, most of the rainfall immediately becomes runoff,
which causes flooding and flash flooding. If the rainfall is intense enough, such as in heavy
prolonged thunderstorms, the soil need not be saturated, as the water will run off regardless and
produce flash floods. This is a serious problem in California. The state ranks second (behind only
Texas) in the number of flood related fatalities in the last 40 years. During roughly the same
period of time, California also ranks second (behind only Pennsylvania) in the costs of flood
related damage.

Southern California’s wildfires create burn areas that are ill-suited to absorbing rainfall for a
number of reasons. Vegetation helps mitigate flash flooding in two ways. Leaves and branches
intercept and absorb some of the rain falling before reaching the ground. Root systems absorb
some of that water as it percolates below the surface. If the vegetation is destroyed by a fire, the
important component of vegetation in reducing some of the runoff is taken away. Southern
California’s soils contain a high content of clay, a soil type that is very slow to absorb water. It
also dries into a hard packed surface resembling concrete. The soils dry out and compact even
39
further from the heat of a fire. As a result, a high percentage of the rainfall becomes runoff;
therefore, much less rain is needed to produce a flash flood. Rain falling on these burn areas can
gather mud, ash, and debris (trees, rocks) on its way downhill. These debris flows can be very
dangerous and damaging, like an extra thick flash flood with the additional mass of the debris
within the channel.

Strong winds accompany especially strong

winter storms and can cause damage particularly
along the coast and in the mountains. At the
coast the wind can move across the water with
little friction to drag the wind down. In the
mountains, the terrain rises up into the stronger
winds aloft. As the winds smash into the
mountains, lee side waves form and often
surface in the deserts, which can cause strong
damaging winds there as well.

The phenomenon of El Niño makes its presence known during winter by altering the traditional
path of the jet streams and directing frequent storms into California. Occasionally, the polar jet
stream brings a cold front that coincides with the subtropical jet stream and produces massive
amounts of rain. Any strong individual storm during the wet season can bring disaster, but the
real problem with El Niño comes from the frequent arrival of strong storms. They simply
continue to exacerbate the problems left by the previous storm(s) and do not allow enough time
for people or the environment to recover. See El Niño and La Niña later in this chapter.

A storm originating from the Gulf of Alaska or

Canada obviously will have much more cold air
associated with it than a storm from farther south.
Cold air aloft contributes to instability, a strong
decrease between temperatures at the surface and
temperatures aloft. If instability is great,
thunderstorms develop. On occasion these
thunderstorms are severe, meaning there is some
combination of intense flooding rain, large
damaging hail, and/or strong damaging wind.

Thunderstorms pose a number of problems. They bring intense rain, which can cause flash
flooding. They contain lightning, hail, and very strong wind gusts, which can kill or injure
people and damage property and crops. Thunderstorms also develop in warm air masses when
tropical moisture is introduced from the southwest
monsoon or a decaying tropical cyclone. A
thunderstorm is considered severe when winds are
strong enough and hail is big enough to produce
damage.

Winter storms also bring snow mainly to the

mountains. One strong storm can bring a few feet of
40
new snow to the higher mountains. While most Southern California residents do not have to
worry about snow at home, we do often have to drive through winter conditions to leave the
region. On very rare occasions, an especially cold storm can drop the snow levels to some of the
densely populated lower elevations.

When the atmosphere is moist and unstable,

convergence of the air at lower levels can
produce lines of rising motion called
convection. This convection is a circulation
of air in the vertical plane and can produce
showers and thunderstorms. Topographical
barriers such as islands or mountains can
induce these convective lines in the proper
conditions. Low level winds flow around
surface barriers, such as islands or mountains,
and converge on the lee side in the same
fashion that water in a stream flows around rocks and converges on the opposite side. As the air
converges, eddies form and the air is forced upward because it cannot sink into the ocean or the
ground. The result is a line of convection containing showers and/or thunderstorms parallel to the
mean flow extending downwind. We call this lee side convergence. For example, westerly winds
flowing around the Palos Verdes peninsula can
produce a line of convection from Long Beach
into northern Orange County. This area is also
Land Spout
Southern California’s “tornado alley.” In fact,
the area of southern LA County and northern diagram
Orange County receives a greater frequency of
tornadoes per unit area than does Oklahoma.
Luckily most of these California tornadoes are
not as violent. Winds flowing around the Santa
Ana Mountains form the “Elsinore
Convergence” from Lake Elsinore to Hemet.
Smaller similar convergence zones can develop
on the north and east sides of all the mountains
from Victorville to Mexico.
Land Spout

In addition to showers and thunderstorms,

waterspouts and landspouts can result. These are
small scale weak tornadoes, not caused by supercell
thunderstorms like their powerful Texas relatives, but
by low level wind shear as winds from opposite
directions collide and form tightly wound eddies in
these convergence zones. Waterspouts and landspouts
can cause damage, but are always identified among
the weak tornado class (EF-0 or EF-1 on the
Enhanced Fujita Scale). Indeed, most California
tornadoes on record have probably actually been
tornadoes of the landspout variety. There are
41
supercell thunderstorms each year in Southern California that produce the classic style tornadoes,
but they are relatively few.

Winter storms also bring large ocean swell,

which translates into large surf at the beaches.
Large swell is generated by strong persistent
winds that blow across a long swath of ocean
surface called a fetch. Large swells result and
propagate toward the shore. Large scale winter
storms bring Southern California the largest
swell and surf. In addition to the obvious
dangers for beach visitors and water sports
enthusiasts, tidal overflow and erosion of sand
and coastal bluffs present many more dangers
to life and property.

The Summer Monsoon

The Southwest Monsoon season

occurs from July through September
over the southwestern U.S., generally
more prominent from Arizona
eastward. Occasionally, episodes of
monsoonal flow reach Southern
California during late summer and
bring thunderstorms (sometimes called
“Sonoran” storms) mainly to the
mountains and deserts.

The monsoonal flow develops as a

strong upper ridge builds over the four
corners region or the Great Basin. The
resulting easterly or southeasterly flow on
the south side of this high draws warm moist
air from Mexico into the Southwest U.S.
Perturbations or disturbances in this flow
such as an easterly wave trigger convection
and thunderstorms. An easterly wave is an
inverted low pressure trough within the
monsoonal flow that moves from Arizona or
Sonora westward into California. At times
moist air flows northward from the Gulf of
California (Sea of Cortez) further
destabilizing the atmosphere. This is called a
gulf surge. At times, even when the
monsoon is absent, the moist air layer of the
gulf surge is rather shallow and does not
42
produce thunderstorms; it becomes a sort of hot, humid, desert marine layer. For thunderstorms
to develop, the moist air moving into the region needs to be rather deep in the atmospheric
column. The heating of the earth’s surface further destabilizes the atmosphere and convection
results; columns of locally heated bubbles of air
(thermals) rise in the moist atmosphere and grow into
towering cumulonimbus clouds and thunderstorms.
Sometimes the monsoonal flow spreads a shield of
opaque cloudiness over the region. When this
happens, convection may be inhibited because the sun
is not able to effectively heat the earth’s surface,
creating the instability sufficient to produce these
rising thermals.

In the mountains and deserts, the air from

the surface to the cloud level is usually
very dry. As the thunderstorm produces
rain, the drops fall into this drier layer and
may completely evaporate (if falling rain
does not reach the ground, it is called
virga). This evaporation cools the column
of air. Because cool air is heavier than
warm air, the cool air in the warm
environment will sink and accelerate as it
descends. This downburst of air can reach
the ground with damaging force. A highly
localized downburst (covering less than 2.5 miles)
is called a microburst. Upon impact with the
Gustnado ground, the winds rapidly spread across the earth’s
diagram surface as a gust front. Some gust fronts, or
outflow boundaries, can converge with
neighboring thunderstorm outflows. These
colliding gust fronts, often called outflow
boundaries, can create new lines of convection.
When a strong outflow meets with relatively calm
air or with other outflows, tightly spinning eddies
of wind called gustnadoes can result and can
Gustnado cause damage.

Flash flooding in rough terrain can be very deceptive. A mountain thunderstorm can flood desert
areas with water, mud and rock, even if no rain falls in the desert. Flash floods in areas of steep
terrain, impenetrable rocky soil, and little vegetation are the most volatile.

Normally, monsoon thunderstorms are relatively rare west of the mountains, but can occur under
the right conditions. If the winds from the mountain top level upward are rather strong from the
east or southeast, thunderstorms can drift from the mountains to the valleys, and even to the
coast.

43
The Marine Layer

The marine layer is perhaps coastal California’s

most dominating weather feature. It all starts with
the semi-permanent high pressure over the eastern
Pacific Ocean, which produces persistent northwest
winds that parallel the west coast. These winds pull
cool waters from the Gulf of Alaska southeast along
the west coast, producing the ocean current called
the California Current. In addition, the Coriolis
force pushes surface waters away from the coast,
allowing cooler waters from the ocean depths to
surface. This is called upwelling. The cool current
and upwelling combine to provide consistently cool
waters along the west coast. When the air well above the water is warmer than the water, as it is
normally for all seasons except winter but most common in late spring and early summer, a
temperature inversion develops. Instead of the air cooling with increasing elevation the air
actually increases in temperature with height, the inverse of the standard atmosphere. The cooler
air below the inversion is called the marine layer and is cooled by conduction to the point that
condensation occurs and stratus clouds form. Because of its persistence in late spring and early
summer, we often refer to it as the “May Gray” or “June Gloom”.

The downward force of air under very

strong high pressure aloft presses down on
the marine layer keeping it confined near
the coast where very cool, foggy weather
is typical. Inland, temperatures rise under
the same high pressure. We often call this
a shallow marine layer, squished by high
pressure aloft.

As high pressure aloft decreases in

strength, the downward force decreases
allowing the marine layer to penetrate
farther inland. The clouds are located near
the top of the marine layer so at the beach
the fog lifts to a lower cloud deck. Further
inland, fog is located at the leading edge
of the inland push of the cooler air.

Low pressure aloft allows the marine layer

to deepen to as much as 6,000 feet (2000
meters). The fog is confined to the
mountain tops and passes. In the lower
elevations, the marine air begins to warm
as it is modified by the heat rising from
the ground. The cooler air moves over the
44
coastal mountains and through the passes into the interior valleys.

However, if the low pressure has enough cold air aloft, it can wipe out the inversion; the cold air
replaces the warm air above the marine layer. This “busts up” the marine layer, the warm dry
layer and the cool moist layer mix, and the low clouds clear. When the inversion is very strong
and relatively shallow, the coastal clouds can stick to the beaches all day, which occasionally
happens during June and July, just when schools get out and locals and tourists hit the beaches.

The common cloudiness near the coast occurs mainly during the night and early morning, and
then evaporates during the day. The clouds normally clear during the morning as a progression
from inland areas to the coast. As the sun begins to warm the land surface (even through the
cloud layer), the cloud layer begins to evaporate from the ground upward until the clouds
completely evaporate. At dusk, the sun has set and the evaporation slows, so the onshore flow
can move the clouds over land without evaporating. Very little mixing takes place between the
cool moist marine layer and the warm dry layer above it due to stability. Cold air is denser than
warm air and finds stability or equilibrium at lower levels. As an analogy, the cool marine air is
like water in a bathtub,
content to stay at the
bottom and not mix with
the air above it. The clouds
will not rise over the
mountains without
evaporating. If you hike in
the sunny dry foothills
early on a summer morning
you can see an “undercast”
sky condition, a solid cloud
layer below.

A coastal eddy is a counter clockwise

circulation of low level winds in the
California Bight (the California Bight is
comprised of the ocean waters fronted by the
concave Southern California coastline).
Because these coastal eddy circulations are
often centered near Santa Catalina Island, it is
often called a Catalina Eddy. It forms when
the air flow aloft becomes cyclonic (counter-
clockwise) and when strong northwest winds
blow off Point Conception. Those winds
continue blowing toward the southeast and
naturally curve into the bight. Imagine a
pinwheel in the vicinity of Catalina Island.
The stronger winds over the outer waters would spin that pinwheel counter clockwise because
the winds in the inner waters are weaker. Eddy formation is characterized by a southerly shift in
coastal winds, a rapid increase in the depth of the marine layer, a thickening of the stratus cloud
layer, and often some drizzle. The marine layer can deepen to 6,000 feet and extend well inland
45
along the slopes of Southern California’s larger mountains and even through the lower passes
into the deserts near Hesperia and Palm Springs. These occasions are almost always
accompanied by drizzle or even light rain. Because the cloud layer is thick and the circulation
produces more clouds, it takes much longer to evaporate the cloud layer. Over land the
cloudiness can persist into the afternoon or even all day near the coast. Coastal eddies occur
predominantly during the “stratus season” – late spring and early summer.

At times with a deep marine layer, probably at least 2000 feet deep, the atmosphere below the
inversion can become unstable as the sun warms the land surface. The initial stratus clouds clear,
but the warm and moist surface air rises to produce shallow convection and cloud development
capped by the inversion. Meanwhile, at the beaches the sea breeze is drawing cool surface air
onshore, which stabilizes the atmosphere. In these situations, the coast clears while clouds
continuously redevelop inland. This is what we call “reverse clearing” because clearing occurs
from the beaches toward inland areas, the reverse of the standard clearing pattern.

Dense Fog can form when the stratus cloud

layer comes in contact with the ground, usually
along the inland edge of the cloud deck. When
the marine layer is deep, dense fog will develop
in the mountains and foothills. Fog can also
develop as air ascends a mountain slope and
condenses. When the marine layer is shallow,
the clouds will not penetrate very far inland,
staying near the coast. In these cases lower
elevations may get dense fog. This kind of fog is
called advection fog because the fog advects, or
moves horizontally from one location to another.

Radiation fog, also called ground fog, is not

usually related to the marine layer. It can
develop on clear, cold, and calm nights when
the air near the surface is moist, such as after a
rainstorm. The moist air has a high dew point
temperature, the temperature at which the air
becomes saturated. As the ambient
temperature falls in the evening, it will reach
the dew point and fog can develop. This is
more common in inland valleys because they
are sheltered from the modifying effect of the
mild ocean.

The Sea Breeze

At the surface, the sun warms both the ground and ocean at the same rate. However, since the
heat in the ground is not absorbed well it returns heat to warm the air. The warmed air, with its
decreased density, begins to rise (1, see diagram). The rising air creates a weak low pressure area
(called a thermal low) due to a decrease in air mass at the surface (2). Typically, from 3,000 to
46
5,000 feet above this low pressure, as the air cools, it begins to collect resulting in an increase in
pressure, creating a “high” (3). These differences in pressures over land, both at the surface and
aloft are greater than the differences in pressures over water at the same elevations (4 and 5).
Therefore, as the atmosphere seeks to reestablish the equal pressure both on land and on the sea,
two airflows from high pressure to low pressure develop; the offshore flow aloft (6) and the
onshore flow at the surface, called the sea breeze (7). The prevailing wind flow with a present
marine layer is from the ocean to
the land, or onshore flow. The
strength of the onshore flow is
determined and measured by
pressure differences (gradients)
between higher pressure over the
ocean and lower pressure over the
desert. If the gradient is steep, the
onshore flow is strong, and vice
versa. In our forecast discussions
we often refer to the pressure
gradient between Lindbergh Field
(SAN) and the Imperial Airport near
El Centro (IPL) as a local
benchmark.

Santa Ana Winds and Hot Weather

Santa Ana winds are strong, dry offshore winds that

blow from the east or northeast. These winds are
strongest below passes and canyons of the coastal
ranges of Southern California. The name is derived
from the Santa Ana Canyon, which is susceptible to
these winds. The complex topography of Southern
California along with various atmospheric conditions
create numerous scenarios that may cause widespread
or isolated Santa Ana events. Santa Ana winds
develop when a region of high pressure builds over
the Great Basin (the plateau east of the Sierra Nevada

and west of the Rocky Mountains

including Nevada and western Utah).
Air moves from high pressure to low
pressure; in this case, from the Great
Basin to the coast. This pressure pattern
often follows the passage of an upper
low through the interior west. If the
47
upper low moves into northern Mexico or Arizona, the upper level winds will be from northeast,
and enhance the northeast surface flow. The cold air associated with the upper low forms a dry
front coming from the northeast. As the northeast winds encounter the mountain barriers of
Southern California, a lee side turbulent mountain wave results (imagine a flag waving in a
horizontal orientation). Strong subsidence, associated with the cold air following these fronts,
forces these strong mountain waves downward to the surface.

On rare occasions, there may be precipitation with the system and a “wet Santa Ana” results, but
most of the time a Santa Ana event brings clear skies and warm weather. Clockwise circulation
around this high pressure area and subsidence (sinking motion) forces air down the mountain
slopes from the higher plateau. As the air descends, the higher pressure at lower elevations
compresses the air, like a bicycle pump warms the compressed air. The dry warm air accelerates
as it descends toward the coast. When the temperature gradients or winds aloft do not provide the
upper support to push the winds, the pressure gradient by itself can drive them. These “gradient
driven” winds are often quite localized, narrow corridors or rivers of winds and are channeled
mainly through topographical breaks like canyons and passes. Without the upper support, they
also are not as strong.

Santa Ana winds occur mainly during fall and

winter and are most common during December.
Summer events are rare. A reasonably strong event
can produce sustained wind speeds of 30 to 40 mph
with gusts over 60 mph. During exceptional events
the top gusts can exceed 100 mph. The strongest
winds usually occur during the night and morning
due to the absence of a competing sea breeze.

The impacts of these winds are numerous. There is

always a high fire danger during these events. Trees and
power lines are toppled, leading to property damage
and power outages. High profile vehicles are at risk of
being blown over. Turbulence and low level wind shear
adversely affect aircraft, while strong winds and
associated waves can present great danger to boaters.

Fall events can bring hot weather as well as strong

winds. Most high temperature records in coastal
California have occurred during a hot Santa Ana. Legend and lore have sprung from these
uncomfortable conditions. Some have called it “Devil’s Breath”. Early Mexican residents called
them los vientos del diablo - the devil winds. It is a strange time for residents near the coast
because their mild climate turns into the Sahara for a time. Fires increase, crime seems to go up,
and numerous health conditions worsen, such as allergies. Some claim earthquakes are more
likely during this “earthquake weather.” Like the time during a full moon, it just seems that more
weird things happen.

Hot weather is relative in our region of wide variations. In the lower deserts it is a staple of life.
48
Near the coast it is a rather rare occurrence. Extreme heat most often comes when strong high
pressure aloft is present over the region. This produces an atmosphere that is generally subsiding,
or sinking. As the air subsides, it compresses and warms as the pressure increases near the
surface. When the monsoon flow over the desert southwest sends moisture into our region, this
added humidity compounds the danger of the heat. Years ago, the National Weather Service
developed the Heat Index to properly account for the body’s reaction to the combined effects of
heat and humidity. See appendix H for the Heat Index Table.

Dust devils are products of a heated land surface and do not need extreme heat to develop. On
sunny days, the ground heats up in a non-uniform way producing rising pockets of air called
thermals. In strong thermals, the rising air develops a spin and the result is a dust devil, a narrow
rotating column of air that can sometimes reach several hundred feet into the sky. Dust devils are
usually not dangerous, but some can cause minor property damage. They are not associated with
tornadoes, since tornadoes only develop from strong thunderstorms. They are most common in
the inland valleys and deserts of our region.

Tropical Connections: Hurricanes and Their Remnants

Hurricanes need warm ocean waters to survive and

grow; as a general rule, the sea surface temperature
should be above 80 degrees. Below that temperature, the
hurricane will lose its energy and die. The California
Current is a cool ocean current that parallels the
California coast, maintaining the sea surface
temperatures safely below 80 degrees. This is why
hurricanes normally do not strike the California coast.

However, on October 2, 1858, a category 1 hurricane did indeed strike San Diego. This is
documented by leading hurricane researchers and published by the American Meteorological
Society. You can find the article on their website www.ametsoc.org. On two other occasions in
recorded history has a tropical storm hit Southern California. Since a legitimate hurricane has
struck our coast, that means it can in the future, with a similar likelihood as a major earthquake
or tsunami. It may not happen in our lifetimes, but we should think about hurricane preparedness
in the same way we think about preparedness for major earthquakes and tsunamis.

The eastern Pacific hurricane season runs generally from June through October, officially from
May 15 to November 30. Hurricanes or tropical storms moving into the cooler waters will decay,
but on occasion are strong enough to come very close to California at tropical storm strength and
produce a wild, off-season rainfall event with widespread flash flood damage. Some of Southern
California’s heaviest rainfall events have been the result.

More likely, only the remnants of these storms will provide a source of warm, moist and unstable
air off the coast of Mexico. If the upper level flow is from the south, this unstable air is brought
into the region. There is very little rising motion associated with these moist air masses, but the
great amount of moisture is sufficient to produce showers. Some local effects can enhance the
precipitation. The ocean waters are warmest during late summer, so the stabilizing effect of the
normally cool ocean waters is reduced. As these unstable tropical remnants move into Southern
49
California, the orographic (mountain) effect and surface heating provide additional uplift
necessary to produce the showers and thunderstorms.

Tropical cyclones can generate large swell. If the track and speed of the cyclone are just right,
and it moves through a narrow window of area off the coast of Mexico, the hurricane can send
these large swell to Southern California beaches and the result is large surf, particularly on south-
facing beaches.

El Niño and La Niña

The term El Niño (Spanish for the “Christ child”) was originally used by fishermen along the
coasts of Ecuador and Peru to refer to a warm ocean current that typically appears around the
Christmas season. The term El Niño has come to be used for these exceptionally strong warm
intervals that not only disrupt the fishing industry but also bring heavy rains to the normally dry
region. La Niña (El Niño’s sister) is the opposite of El Niño, where equatorial Pacific Ocean
waters are cooler than normal.

Normally in the tropical Pacific Ocean, the trade winds are

persistent winds that blow westward from a region of higher
pressure over the eastern Pacific toward a region of lower
pressure centered over Indonesia. During El Niño years, this
atmospheric pressure pattern breaks down. Air pressure
rises over the western Pacific and lowers over the eastern
Pacific. This change weakens or even reverses the trade
winds. This fluctuation in pressure across the Pacific Ocean
is called the Southern Oscillation. The normally strong

coastal upwelling of ocean waters along

the west coast of South America is
decreased or stopped by the weakened
trade winds and this allows warmer
surface waters from the western Pacific to
surge eastward toward South America.
Because these pressure reversals and
ocean warming are concurrent, it is
referred to as the El Niño - Southern
Oscillation, or ENSO.

The oceans and the atmosphere greatly

influence each other. During normal years,
the eastern Pacific waters cool the air
above them. Cool dense air does not easily
form clouds and rain, so the coasts of Peru
and northern Chile receive very little rain.
When the ocean warms, the moist warm
50
air above it becomes buoyant enough to produce rain. This shift in major rain zones has a ripple
effect on wind patterns and climatic conditions all over the globe. With the presence of a strong
El Niño, the subtropical jet stream becomes oriented over California, carrying large amounts of
warm moist air into the region. The upper figure on the previous page shows a normal January
jet stream weakening before reaching California. The lower figure shows the strong jet stream
during the strong El Niño of January 1998 actually reaching California.

The impacts of El Niño and La Niña show up most clearly during the northern winter. El Niño
winters are milder over Canada and the northern United States, while cooler and wetter than
normal winters are experienced in the southern U.S. During La Niña years, winters are warmer in
the upper Midwest and cooler in the Southeast and Southwest. It is wetter than normal in the
Northwest and drier than normal in the southern third of the U.S. For more information about El
Niño and La Niña, click on: www.cpc.noaa.gov/products/analysis_monitoring/lanina or
meteora.ucsd.edu/~pierce/elnino/elnino.html.

Global Warming, the Greenhouse Effect, and Climate Change

In recent decades it has been observed that the average temperature of the earth is rising. The
numerous effects of this rise in temperature can greatly impact global climates and human life.
This has produced cause for concern well beyond the scientific community. At the NWS in San
Diego, no direct research or study of global warming is performed. For more information on the
subject, click on: www.epa.gov/globalwarming.

Sun, Earth, Sea, Space, and Optical Phenomena

The sun, earth, sea and sky produce naturally occurring phenomena that generate questions
directed to the NWS for explanation. These may include solar and lunar phenomena, optics,
astronomy, space weather such as aurora borealis or solar flares, ocean behaviors beyond sea
state, earthquakes, volcanoes, and geology.

These phenomena do not fall under the expertise of meteorologists at the NWS. Meteorologists
may have some knowledge about these phenomena and may offer it, but the knowledge or
opinion is not qualified professionally, only possibly from a personal interest or hobby.

51
Appendix A

A History of Significant Weather Events in Southern California

Organized by Weather Type

Compiled January 2007

The following weather events occurred in or near the forecast area of the National Weather
Service in San Diego, which includes Orange and San Diego Counties, southwestern San
Bernardino County, and western Riverside County. Some events from Los Angeles and
surrounding areas are included. Events were included based on infrequency, severity, and
impact. An electronic copy is found at: www.wrh.noaa.gov/sgx/document/weatherhistory.pdf.

Note: This listing is not comprehensive.

52
Heavy Rain: Flooding and Flash Flooding, Mud Slides, Debris
Flows, Landslides

Date(s) Weather Adverse Impacts

1825 A great flood changed the course of

the Santa Ana River.

10.2.1858 Category 1 hurricane hits San Diego, Extensive wind damage to property
the only actual hurricane on record to (F2). Streets swept clean by heavy
strike California. Implied winds of 75 rains.
mph.

1861-1862 Epic floods. It rained 30 days in The Santa Ana River in Anaheim
succession, beginning 12.24.1861 to ran 4’ deep and spread in an
1.23.1862. 35” fell in LA. In San unbroken sheet to Coyote Hills, 3
Diego over 7” fell in January alone. miles beyond (present Fullerton).
The worst flooding in San Diego
County occurred after six weeks of
rain. All of Mission Valley was
underwater, Old Town was
evacuated. The tide backed its
waters into the San Diego River
and cut a new channel into the bay.
20 died in Orange County.

8.11-12.1873 1.95” fell in San Diego from a tropical 1’ of water was reported on the
storm. 1.80” fell on 8.12, the wettest ground at “Cajon Ranch”.
calendar day in August on record.
1.72” fell in Paradise Valley (SE San
Diego). Nearly 3” fell in “Cajon
Ranch”. This was called the greatest
summer rainfall in history. The
previous daily August rainfall record
was 0.31” in 1867.

12.4.1873 2.52” of rain fell in San Diego, the

ninth wettest calendar day on record
and the third wettest December day.

11.9.1879 2.68” of rain fell in San Diego, the

fifth wettest calendar day on record
and the wettest November day.

12.29-30.1879 4.23” fell in San Diego in 48 hours,

the heaviest storm in 30 years.

53
12.18.1880 Heavy rains. San Diego streets flooded.

1.12.1882 2.49” of rain fell in San Diego, the

tenth wettest calendar day on record
and the second wettest January day.
4.75” fell in Poway.

2.14-20.1884 5+” of rain falls in Spring Valley. Flooding and damage to crops,
Fallbrook gets heavy rain (more than livestock and railroads in the area,
15” in the month). Rains continued all including Temecula Canyon. San
during the spring with disastrous Diego River “booming” through
results. The season ended as the Mission Valley on 3.10.1884.
wettest in San Diego history.

7.14.1886 LA records its greatest 24 hr rainfall

amount for July: 0.24”.

8.31.1889 LA records its greatest 24 hr rainfall

amount for August: 0.61”.

10.12.1889 A monsoon-type thunderstorm

brought 7.58” to Encinitas in 8 hrs.
0.44” fell in San Diego.

2.19-23.1891 33” of rain was reported in Descanso Heavy damage and losses to
in a 60 hour period. 2.56” in San homes, land, livestock,
Diego. From 2.16 to 2.25, a total of transportation and power
4.69” fell in San Diego. Reverend throughout the Tijuana and San
Father Ubach of St. Joseph’s had Diego River Basins. The worst was
prayed for rain on 2.2.1891. flooding along the Tijuana River
where all structures were swept
away and a man was killed. Three
prospectors died at Table Mountain
in Baja California.

8.12.1891 Two thunderstorm cells merge. 16.10”

at Campo; 11.50” in 80 minutes, a
record 80 minute rainfall for the state
(and at one time the record 80 minute
rainfall for the nation).

12.9.1898 Heavy rain. Railroad washed out and ½ mile

covered in mud in Rose Canyon,
near Pacific Beach. A trestle in
Chollas was washed out. “Several
hundred dollars” in damage.

54
7.20-21.1902 A dying tropical cyclone brought 2”
of rain to the mountains and deserts of
Southern California during a very
strong El Niño event of 1901-02.

7.25.1902 0.83 inch of rain fell in San Diego, the

wettest calendar day in July on record.

1905-1907 Heavy rainfall in 1905 in the Colorado The Colorado River swells and
River basin. eventually breaches an Imperial
Valley dike. It took nearly two
years to finally control the River’s
flow into the Salton Basin and stop
the flooding. The result of the
sudden influx of water and the lack
of natural drainage from the basin
resulted in the formation of the
Salton Sea.

3.15.1905 0.94” fell in San Diego in 30 minutes,

the greatest 30 minute rainfall on
record.

3.24-25.1906 2.36” of rain fell in San Diego on Widespread flooding in Fallbrook.

3.24, the wettest calendar day in Streets flooded and roads washed
March on record. Almost 1” in three out in the San Diego Metro area.
hours. 5.10” at Cuyamaca, 4” at
Escondido, Oceanside and Ramona,
3” in El Cajon and Lakeside. Storm
totals: 6.41” in Oceanside, 6.30” in
Escondido, and 2.78” in San Diego.

8.18-19.1906 A tropical storm came up into the

Gulf of California and the
southwestern United States, giving the
mountains and deserts heavy rainfall.
Needles received 5.66” of rain, twice
the normal of seasonal rainfall. This
occurred during the El Niño of 1905-
06.

8.26.1915 The remnants of a tropical cyclone

moved northward across northern
Baja California into the deserts of
southern California with rainfall of 1
inch at Riverside. This occurred
during the strong El Niño of 1914-15.

55
1.14-21.1916 Widespread heavy rains in Southern Widespread flooding. At least 22
California. 16.71” in 24 hours at dead. Roofs in Chula Vista, poultry
Squirrel Inn (near Lake Arrowhead) farm in Vista, boats in Coronado
during 1.16 and 1.17, a record 24 hour and Newport damaged. Most cities
rainfall for California until 1943. completely inundated. Pine trees
More than 9” fell in two storms in the from Palomar Mountain floating
Coachella Valley. Previous storms down San Luis Rey River through
had deposited deep snow in the Oceanside. The cities of Indio,
mountains, adding to the runoff. Coachella and Mecca underwater.

1.25-30.1916 Heavy rain exacerbates the flooding Most extensive flooding in

earlier in the month. Monthly rainfall Southern California to date and
totals for 1.1916 ranged from 7.56” at resulted in 28 total deaths in the
San Diego to 57.91” at Dorman’s region, 22 in San Diego County.
Ranch (in San Bernardino Mtns., This is the most destructive and
2,500’ elev.) 5” fell in less than 12 deadly weather event in San Diego
hours in San Diego. County History. The Lower Otay
dam broke sending a 40’ wall of
water downstream, killing 15. A
few others drowned in Mission
Valley and in the San Luis Rey
River. The Sweetwater Dam also
broke. Every large bridge in San
Diego County but one was
seriously damaged or destroyed.
Four drowned in Orange County,
two in a cottage floating down the
Santa Ana River. Two drowned in
San Bernardino County. Total
damage was nearly $8 million
(1916 dollars).

8.20-21.1921 The remnants of a tropical cyclone

tracked northward into western
Arizona from central Baja California
generating rainfall of up to 2” in the
deserts and southern mountains of
southern California. This occurred
during the La Niña of 1920-21.

9.30.1921 4” of rain fell on the deserts of

Southern California as a result of a
dying tropical cyclone that crossed
Baja California and moved into
southwestern Arizona. 1.23” of rain
fell in San Diego, the wettest calendar
day in September on record.
56
12.24-26.1921 Heavy storm. 6.76” in LA. On 12.26 Flooded roads, bridges, railroads.
2.10” fell in Redlands, 1.71” in San
Bernardino.

10.4.1925 2.95” fell at San Diego, the second

wettest calendar day on record and the
wettest in October.

4.5.1926 3.23” at San Diego, the wettest

calendar day on record. 0.65” fell in
one minute at Opid’s Camp in the San
Gabriel Mountains.

2.11-17.1927 Continual rain for 6 days. 21.86” fell Unprecedented flow of the
at Cuyamaca, 13.10” at El Capitan, Whitewater River. Floods washed
10.70” at El Cajon, 9.54” at La Mesa out roads and bridges in Thousand
and 6.33 at San Diego. On 2.17, Palms and Palm Desert. Levees
12.81” at Cuyamaca, 2.65” at El broken, Thermal inundated. Several
Capitan, 2.20” at El Cajon, 1.47 at La San Diego County dams
Mesa. Heavy warm rains melted overtopped, causing widespread
mountain snows. Snow Creek flooding downstream. Bridges and
recorded 7” of rain in one day. roads were washed out in east San
Diego metro area. Large areas of
Long Beach, Fullerton and
Anaheim inundated.

9.18.1929 A tropical cyclone moved north

northwestward just off the west coast
of Baja California, dissipating off the
coast of northern Baja California.
Rainfall of up to 4” occurred in the
southern mountains and deserts of
southern California on 9.18.
Four days of heavy rains from a dying
9.28-10.1.1932 Flooding to parts of the mountains
tropical cyclone brought flooding to and deserts. Floods on Agua
parts of the mountains and deserts of
Caliente and Tehachapi Creeks
southern California. Rainfall of 4.38” around Tehachapi resulted in 15
fell at Tehachapi in 7 hours on 9.30. deaths.
This occurred during the El Niño year
of 1932-33.

57
12.30-1.1.1934 A major storm. 7.36” in 24 hrs at LA 45 die all over Southern California
(8.26” storm total since 12.30.1933). in floods. Walls of water and
Storm totals in southern slopes of debris up to 10’ high were noted in
mountains topped 12” (heaviest: some canyon areas.
16.29” in Azusa). Daily totals on 1.1:
6.21” at Fullerton, 6.90” Placentia,
5.16” Yorba Linda, 4.69” Buena Park,
5.04” Anaheim, 5.38” Orange , 4.81”
Garden Grove, 3.24” Newport Beach,
2.96” Laguna Beach, 3.55” San Juan
Cap., 3” San Clemente, 2.65”
Redlands, 2.68” Oceanside, 1.56”
Carlsbad, 2.44” Escondido, 0.67” San
Diego , 0.48” Victorville.

8.25.1935 A tropical cyclone tracked northward

across southern and central Baja
California. The remnants spread into
Arizona generating rainfall of up to 2”
in the southern valleys, mountains,
and deserts.

8.9.1936 A tropical cyclone tracked north

northwestward across the Gulf of
California with the remnants tracking
northward into western Arizona.
Locally heavy rainfall occurred in the
mountains surrounding LA.

2.6.1937 2.71” of rain fell in San Diego, the Flooding kills several. LA basin
third wettest calendar day and the flooded in many communities.
wettest February day on record. 2.60” Hodges Dam overtopped.
fell in 12 hours. For the storm, 8.20” Mountain snowmelt added to the
fell in Descanso, 5.70” in Escondido. flooding.
4.25” fell in Long Beach, a 24-hr
record.

58
2.27-3.4.1938 Storm of tropical origin. 11.06” at LA. 210 reported dead or missing in
More than 30” at several mountain flooding across Southern
stations of San Gabriel and San California. 45 in Orange County, of
Bernardino Mountains (32.2” at which 43 perished in Mexican-
8,300’ elev.). More than 22” in the American Atwood from an 8 ft.
Santa Ana River headwaters. wall of water. Hundreds injured.
Considerable snow was melted, Santa Ana River floods, inundates
adding to the runoff. This led to nearly all of northern Orange
unprecedented flood control efforts, County. Catastrophic damage to
including a network of dams and more than 1,500 residences. 400
canals and concrete channels. On 3.3 cabins and buildings washed away
2.80” fell at Descanso, 2.47” at in and around San Antonio
Escondido, where the storm total was Canyon. Whitewater River floods,
6.95”. isolates Palm Springs.

9.4-6.1939 The remnants of a hurricane tracked Floods through eastern canyons

northeastward across northern Baja inundate Thermal with 3’ of water.
California into southwest Arizona Extensive damage in Mecca.
generating rainfall of up to 7” on the
mountains and deserts. Blythe
received more rain than would
normally fall in 1 year and Imperial
received more rain than would
normally fall in 2 years. Four tropical
cyclones would impact Southern
California during the month of
September 1939, an unprecedented
occurrence. 1.21” fell in San Diego.

9.11-12.1939 4” of rain fell across the deserts and

mountains as a dying tropical cyclone
moved across Baja California into
southwestern Arizona. This was the
second tropical cyclone to affect
California during the busy month of
September 1939. A strong El Niño
contributed to the activity.

9.19-21.1939 A tropical cyclone moving

northwestward, just off the west coast
of Mexico, moved into southern Baja
California and dissipated. The
moisture from this tropical cyclone
generated rainfall of up to 3” in the
deserts and mountains.

59
9.24-26.1939 “El Cordonazo” or “The Lash of St. 45 killed in floods all over
Francis” a tropical storm hits Southern Southern California, and 48 more
California and causes the greatest at sea. $2 million damage to
September rainfall ever. The storm structures along the coast and to
lost hurricane status shortly before crops. Eastern Coachella Valley
moving onshore at San Pedro at under 2’ of water. Californians
tropical storm strength. Torrential were generally unprepared and
rains: LA 5.42” in 24 hours, Mt. were alerted to their vulnerability
Wilson 11.60” (also records for the to tropical storms. In response, the
month of September). Nearly 7” in weather bureau established a
three hours at Indio from one forecast office for southern
thunderstorm. 9.65” at Raywood Flat, California, which began operations
1.51” Palm Springs. A thunderstorm in February of 1940.
preceding the tropical storm dropped
6.45” in 6 hours at Indio on 9.24.

11.27.1939 0.65” rain fell in San Diego in 15

minutes, the greatest 15 minute
rainfall on record.

12.23-24 .1940 3.62” at San Diego, the greatest 24 Heavy rains loosened soil in Del
hour rainfall on record. Mar that led to a landslide along a
train track, derailing the train and
killing three.

8.10.1941 Thunderstorms in eastern Coachella Buildings damaged. Water 30”

Valley. deep in Mecca.

1.23-24.1943 26.12” fell in 24 hours at Hoegees

Camp in the San Gabriel Mountains,
setting the state 24 hour precipitation
record. 4.56” at Palm Springs.

12.10.1943 2.56” of rain fell at San Diego, the

eighth wettest day on record and the
second wettest December day.

8.18.1945 Thunderstorms in eastern Coachella Extensive damage at Oasis. Water

Valley. 18” deep in Mecca.

9.9-10.1945 A tropical cyclone moving north

northwestward just off the west coast
of Baja California dissipated off the
coast of northern Baja California.
Showers produced rainfall up to 2” in
the mountains.

60
12.22.1945 2.60” of rain fell in San Diego, the
sixth wettest calendar day and the
wettest December day on record.

9.30-10.1.1946 A tropical storm moved northward

into northern Baja California and
dissipated with rainfall of up to 4” in
the mountains on 9.30 and exceeding
4” in the mountains on 10.1. This
occurred during the El Niño of 1946-
47.

7.23.1948 Thunderstorms in Palm Desert and La Homes flooded. Erosion damage to

Quinta. roads and canals.

2.6.1950 Heavy rain. Chino Creek inundates Hwy 71

from Corona to Ontario.

8.27-29.1951 A hurricane moving north

northwestward just off the west coast
of Baja California moved
northeastward into northern Baja
California and dissipated. Moisture
from this tropical cyclone resulted in
rainfall of 2 to 5” in the mountains
and deserts. Many roads were washed
out in the Imperial Valley, but
otherwise no major damage occurred
in southern California. This occurred
during the El Niño of 1951-52.

1.18.1952 3.98” in LA, 3.17” in 24 hours. At least 8 dead in flooding.

9.19-21.1952 A west-northwestward moving

tropical storm southwest of Baja
California dissipated. Moisture from
this storm resulted in rainfall of up to
2” in the mountains and deserts, with
most falling on 9.19. This occurred
during the El Niño of 1951-52.

7.17-19.1954 A northward moving hurricane made

landfall in central Baja California with
the remnants moving into Arizona.
Rainfall of up to 2” occurred in the
mountains and deserts. This occurred
during the El Niño of 1953-54.

61
7.25.1956 Thunderstorms: 1.26” Riverside, Flash flooding in San Bernardino,
1.05” Yucaipa, 1.01” Lytle Creek, Riverside and Ontario.
1.15” Upland. Almost 0.5” in five
minutes at Glendora.

7.28-29.1958 Moisture from a west northwestward

moving tropical storm which
dissipated west of central Baja
California generated up to 2” of
rainfall in the deserts and mountains.
This occurred during the El Niño of
1957-58.

1.4-5.1959 Big winter storm. Roof damage and animals killed at

San Diego. Considerable property
damage from flooding and mud
slides. Rattlesnake Creek in Poway
inundates the city.

2.14-16.1959 Heavy rain. Flooding in San Diego.

4.27-28.1960 Heavy rain. 1 drowning death and 3 traffic

deaths. Flooding and closed
highways.

9.9-10.1960 North northwestward moving

Hurricane Estelle dissipated west of
the central Baja California coast. The
heaviest rains were over the San
Diego County Mountains with 3.40”
recorded at Julian.

11.5.1960 Heavy rain, mainly from Orange 1 drowning death, 2 injuries.

County northward. Flooding, mud slides, and property
damage. Power outages.

8.4.1961 Heavy thunderstorm near El Capitan Los Coches and Quail Creeks flood
Reservoir: 1.75” in 90 minutes. Lakeside.

2.7-26.1962 A very wet period for Southern 20 killed, 15 injured in flooding,

California. 20”+ in wettest mountain mud slides. Property damage, trees
locations. down, boats damaged.

2.9-11.1963 Heavy rain. Flooded highways and homes.

62
9.17-19.1963 Northeastward moving Tropical
Storm Katherine made landfall in
northern Baja California with rainfall
of up to 6.50” in the mountains. 1.90”
fell in San Diego.

11.19-20.1963 Heavy rain. 6 injured in local flooding and

numerous traffic accidents.

12.1964 40 dead from flooding in LA and

Orange Counties.

11.22-25.1965 Heavy storms drawing tropical All of Southern California hit by

moisture in the mountains and desert. road and bridge washouts,
Storm totals: 20” at Mt. San landslides, and floods. Santee was
Gorgonio, 16: at Mt. San Jacinto, inundated. Two drown attempting
9.59” at Cuyamaca, 6-9” at Banning- to cross the Whitewater River. Five
Cabezon, over 4” at Palm Springs, died in Tijuana. Record flood
less than 1” near the Salton Sea. One levels on Tahquitz Creek. Largest
day total over 9” at Snow Creek. flood on Whitewater River since
1938. Spring Valley Creek floods
in southeast San Diego.

12.10.1965 1.36” fell in San Diego in one hour,

the greatest one hour rainfall on
record.

12.2-3.1966 Heavy rain. Local flooding at the coast.

Damage to buildings and highways.
Flooding in Palm Springs.

12.5-6.1966 6.66” at Idyllwild on 12.5, 9.42” at Flooding. Highway damage.

Big Bear Lake on 12.6.

8.16-17.1967 Thunderstorms in the lower desert.

2.5” in 1.5 hours at Cathedral City,
0.75” at Indio.

8.30-31.1967 Hurricane Katrina crossed the La Quinta cut off for several hours.
southern tip of Baja California, then 150 homes damaged by floods in
traversed almost the entire length of Palm Desert and Indian Wells.
the Gulf of California before making Numerous roads washed out in
landfall again and rapidly weakening. Coachella Valley.
2”+ of rain fell on parts of the lower
desert. 2” at La Quinta on 8.30.

63
11.18-21.1967 14”+ in mountains above LA, 7.96” in 2 killed. Flash flooding and mud
LA. Called “worst since 1934.” On slides. 400 stranded in mountains
11.21 0.51” in San Diego in 10 due to closed highways.
minutes, the greatest 10 minute
rainfall on record.

12.12-15.1967 Heavy rain. 2 drowning deaths in San Diego

County.

3.6-8.1968 Heavy rain. 1 drowning death. Local flooding.

Damage to buildings, homes, and
schools. Landslides closed several
highways.

1.18-28.1969 Heavy rains of tropical origin hit in 87 reported dead from flooding and
two waves, one beginning 1.18 and mud slides all over California.
the other 1.23. The totals: as much as Scores dead in traffic accidents.
50” of rain at 7,700’ elev., 37.5” at Hundreds of homes and buildings
Lake Arrowhead, 31” of rain on south destroyed in slides, including 14
slopes of Mt. San Gorgonio, 15.5” at destroyed and 11 damaged homes
San Jacinto Peak, 13.4” in LA, ~10” in Mt. Baldy Village. 50 homes
at Banning, less than 1” from Indio near Forest Home (Forest Falls)
southeast. 11.72” at Forest Falls on were damaged by flooding.
1.25. Highways and railroads washed
out. Power outages. Cucamonga
Creek itself caused $10 million in
damage. The Mojave River took
out numerous bridges and flooded
farmlands in the upper desert.

64
2.16-26.1969 Heavy rain continued. Up to 30” of The death and destruction
rain on south slopes of Mt. San continued from the previous month.
Gorgonio, 13” northwest of Mt. San 21dead from flooding and mud
Jacinto, ~10” at Banning, less than 1” slides all over California. An entire
in eastern Coachella Valley. 5-15” of family was killed in Mt. Baldy
rain in the lowlands from 2.22 to 2.25. Village when a mud slide hit their
9.25” at Forest Falls on 2.24. home. Extensive damage to crops,
farmland and livestock. Creeks
around Yucaipa all left their banks
and substantial flooding occurred
to residences and businesses. In the
upper desert farmlands became
lakes and more than 100 homes
along the Mojave River were
damaged. Roads and bridges
recently repaired from previous
month’s damage either washed out
or were destroyed again.

9.30-10.1.1971 Caribbean Sea Hurricane Irene

crossed Nicaragua and reformed in the
eastern Pacific as Hurricane Olivia.
Olivia recurved to the northeast and
made landfall in central Baja
California with rainfall of up to one
inch in the southern deserts. This
occurred during the La Niña of 1970-
71.

11.16.1971 Poway Creek floods Poway.

8.29-9.6.1972 Hurricane Hyacinth moved as far west

as 125 West before recurving to the
northeast. The remnants made landfall
between Los Angeles and San Diego
on the 9.3 with winds of 25 mph and
rainfall of up to one inch in the
mountains. This tropical cyclone
holds the distinction of traveling the
farthest west before recurving and
making landfall in Southern
California. This occurred during the
El Niño of 1972-73. 0.44” measured
in San Diego.

65
10.6.1972 Hurricane Joanne recurved making
landfall in northern Baja California,
maintaining tropical storm strength
into Arizona and generating rainfall
up to 2” in the southeast deserts. This
occurred during the strong El Niño of
1972-73.

1.16-18.1973 Local amounts up to 3” on 1.16 and Local flooding, mud slides, power
an additional 3” on 1.18. outages.

2.10-11.1973 1-2” at coast, 3-7” coastal valleys, up Flooding and mud slides closed
to 12” at Mts. Wilson and Baldy. 6” in many roads.
6 hours at Mt. Wilson on 2.11.

1.3-5.1974 Heavy rain. 1 drowning death near Temecula.

Many highways closed due to
flooding and mud slides.

12.3-4.1974 Heavy rain. Considerable flooding of low lying

areas of Orange County. Forester
Creek in El Cajon floods.

2.4-10.1976 Heavy rain period. 4.30” at San

Diego.

9.9-12.1976 Record rains, flooding from Tropical 6 buried and killed in sand in
Storm Kathleen (a 160+ year event). Ocotillo. Much of the Imperial
14.76” on south slopes of Mt. San Valley flooded. I-8 and other
Gorgonio, 8” Mt. San Jacinto, 10.13” highways ripped out in several
Mt. Laguna, 4+” in Little San locations in the mountains and
Bernardino Mountains, 1.8”-2.8” in desert. Floods of record attained at
the Coachella Valley. Deep Canyon numerous streams above the
(above La Quinta) recorded 2.96” in 3 Coachella Valley. Widespread
hours on 9.10. Rainfall in the Santa property damage on the eastern
Rosa Mountains above the Coachella slopes of the peninsular range and
Valley called “heaviest in recorded the adjacent deserts.
history.” 1” in San Diego. 2.8” fell in
3 hrs in Borrego Valley on 9.10. This
occurred during the El Niño of 1976-
77.

9.23.1976 A thunderstorm dropped 4” of rain in Damage and erosion to fields,

3 hrs in Borrego Valley. Only 1.2” fell property and the airport.
at the Anza Borrego Desert Park
headquarters.

66
5.8.1977 1.49” of rain fell in San Diego, the
wettest calendar day in May on
record.

8.15-17.1977 Hurricane Doreen tracked north 4 dead and $25 million in damage
northwestward along the west coast of in Southern California. Debris
Baja California, dissipating over the flows and flooding from Henderson
coastal waters. Most areas received at Canyon into Borrego Springs De
least 2” of rainfall with up to 8” in the Anza neighborhood, damaging 100
mountains. This occurred during the homes. Mud flows up to 5’ deep.
El Niño of 1977-78. Heavy rainfall Flooded roads in desert areas.
included 4.9” Mt. Laguna, 4.5” Floods and crop damage at the
Borrego Palm Canyon, 4.0” Palomar Salton Sea.
Mtn. and Lake Henshaw, 3.26”
Borrego Springs (2.53” in 6 hrs on
8.16, a 100 year event), 2”+ Palm
Springs, 4.5” Salton Sea in several
hours. 2.13” at San Diego for the
period, 1.44” on 8.16.

9.10.1977 Heavy rains in Little San Bernardino Floods down Thousand Palms
Mountains (Joshua Tree NP) produced Wash caused extensive damage to
a rainfall of nearly 5” fell in 1 hour Thousand Palms area, nearly
above the Thousand Palms Wash. destroying the oasis in the valley.
The California Aqueduct that runs
just north of the preserve was
clogged with debris, resulting in
the flood of nearly a billion gallons
of water through this area.

10.6-7.1977 Hurricane Heather recurved with the

remnants tracking across northern
Baja California into Arizona. There
was rainfall up to 2” in the southern
mountains and deserts. This occurred
during the El Niño of 1977-78.

12.27.1977 Heavy rain. Mud slide in mountains northeast

of Redlands buries a car killing 1
and injuring 3.

2.8-10.1978 Heavy rain: 16.4” at Lytle Creek, 20 killed all over Southern
13.64” Lake Arrowhead, 11.97” California, 13 of them in Hidden
Wrightwood, 11.15” Devore, 10.4” Springs in the San Gabriel
Santiago Peak, 8.5” Crestline, 5” Mountains. Widespread flooding,
Ontario, 4.79” Big Bear Lake, 3.83” flash flooding, and mud slides.
Santa Ana. Numerous homes washed away.

67
3.4-5.1978 Heavy rain. 20 deaths from flooding and
mudslides in LA area. 3 drowning
deaths and disastrous flooding in
Lakeside. 26 dead and 600 left
homeless in Tijuana and Ensenada.

9.5-6.1978 Hurricane Norman recurved with the

remnants tracking into southern
California from the south southwest.
Rainfall exceeded 3” in the
mountains. This occurred during the
El Niño of 1977-78.

1.30-31.1979 2-4” rainfall in 24 hours over much of Flooding along Silver Strand
coastal Southern California. 2.57” of highway, in Fashion Valley, also in
rain fell in San Diego on 1.31, the Spring Valley, Lemon Grove,
seventh wettest calendar day and the Lakeside and Carlsbad. Lake
wettest January day on record. 4.82” Hodges overflowed.
fell in National City, 4.25” in La
Mesa, 3.30” at SDSU, 3.78” in El
Cajon.

7.20.1979 Big thunderstorm in Palm Desert and Debris flow killed one and caused
Rancho Mirage. $7 million damage. Flash flooding
hit hundreds of homes in Rancho
Mirage, Palm Desert and La
Quinta. Some residents swept out
of their homes at night.

2.13-21.1980 Six storms hit Southern California. 30 killed in widespread floods and
31.69” in Mt. Wilson, 25.56” in mud slides. Post-fire flooding
Palomar Mtn., 24.34” in Cuyamaca, overwhelmed a basin below
20.65” in Julian, 18.27” in Mt. Harrison Canyon in north San
Laguna, 12.88” in Ramona, 12.75” in Bernardino four times. Forty homes
LA, 10.09” in Escondido, 6.80” in La were damaged or destroyed there.
Mesa, 4.47” in San Diego. Roads and hundreds of homes
destroyed or damaged. Mission
Valley completely inundated
between Friars Rd. and I-8.

3.1-3.1981 3” along coast and 5-6” in local Widespread street flooding and
mountains. mud slides. Power outages.

11.27-28.1981 Nearly 2” in LA area. Highway deaths.

3.16-18.1982 2-4” in San Diego County. 2.13” of Local flooding closed many streets.
rain fell in 24 hours in Pt. Loma from
3.17-3.18.
68
9.17-18.1982 The remnants of Hurricane Norman
tracked northeastward across northern
Baja California into Arizona with
scattered rainfall amounts up to 1 inch
in the southern mountains and deserts.
This occurred during the strong El
Niño of 1982-83.

9.24-26.1982 The remnants of Hurricane Olivia

recurved northeastward across
Southern California with rainfall up to
4” in the mountains. This occurred
during the strong El Niño of 1982-83.

12.8-9.1982 Heavy rain in eastern San Diego Flooding; disastrous flooding in

County. Ocotillo.

2.24-28.1983 Heavy rain. Extensive street flooding. Damage

to 30 cars and an apartment
building in Anaheim.

3.1-3.1983 Heavy rain. Up to 18” precipitation

from Santa Barbara to LA. On 3.1
0.33” fell in 5 minutes in San Diego,
the greatest 5 minute rainfall on
record.

4.17-20.1983 Heavy rain. Street flooding and mud slides.

9.20-21.1983 Northward moving Hurricane Manuel

dissipated off the west coast of
northern Baja California with up to 3”
of rainfall in the southern mountains
and deserts. This occurred during the
strong El Niño of 1982-83.

2.18-19.1984 Heavy rain. Mud slides in Orange County up to

2' deep.

2.14-17.1986 Heavy rain. 1 death from flash flooding.

3.15-16.1986 Heavy rain in Orange County. Mud slides along the coast.

69
9.24-25.1986 Unseasonable rainfall hit San Diego
County: 1.04” at San Diego, 5.14” in
Palomar Mountain, 2.07” in Julian,
1.88” in Mt. Laguna, 1.61” in Lemon
Grove, 1.58” in Pt. Loma, 1.57” in
Vista, 1.47” in SDSU.

10.10.1986 Thunderstorms dropped 2.40” at Mt. Rainwater flooded through a leaky

Laguna, 2.10” at Campo, 2.03” at roof at downtown San Diego police
Julian, 1.90” at El Cajon, 1.50” at headquarters.
Alpine, 1.39” at San Diego, 0.41” at
Miramar. Most of these became daily
rainfall records. Hail the size of
marbles was reported in San Diego’s
east county.

11.17-18.1986 Early season storm brought 1.16” to Numerous traffic accidents, a few
San Diego, more rain that falls in than power outages. The San Diego
a normal November. Montgomery River flooded causing many road
Field 1.49”, 1.21” at Mt. Laguna, closures in Mission Valley. Street
1.07” at Miramar, 1.03” in Oceanside flooding occurred in North Park
and 0.41” in Chula Vista. and Midway areas and in Encinitas.
A mudslide blocked Malibu
Canyon road. A traffic accident
claimed two lives in LA.

12.20.1986 Thunderstorm and heavy rain for two Power outages occurred from
hours. 0.70” Oceanside, >0.5” Alpine, lightning strikes and power lines
0.32” in San Diego. blown down.

1.4-5.1987 Heavy rain and snow from powerful Two died on slick roads in San
Pacific storm: 1-2”+ in the northern Diego County. The San Diego
Inland Empire, 2.20” at Chino. 1.68” River flooded Mission Valley,
at San Diego, Cuyamaca Park 2.73”, stranding cars and closing roads,
Julian 2.59”, Lemon Grove 1.52”, including Friars Rd. Lots of street
National City 1.40”, El Cajon 1.34”, flooding in Pacific Beach, Sorrento
Escondido 1.30”, Coronado 0.95” and Valley and Spring Valley near the
Del Mar 0.80”. Sweetwater River. Sewage spilled
into Mission Bay. Road washouts
in the high desert. Scattered power
outages. Mud slides occurred on
the Sunrise Highway. A mud slide
in Pomona blocked traffic on the
60 freeway.

70
5.15.1987 The monsoon made a very early visit.
Thunderstorms arrived in the
mountains and deserts. 0.20 inch fell
in Mt. Laguna.

9.22-23.1987 Thunderstorms developed on this day Very frequent lightning caused

and on 9.23 from San Diego to El numerous power outages and
Cajon from the remnants of Hurricane property damage, and ignited small
Norma. Rainfall was 0.55 inch in two fires. Lots of street flooding. Road
hours at Lemon Grove and 0.97 inch washouts in the high desert.
total. 0.70 inch fell at Lindbergh
Field, a record for the date.
Scattered flooding and power
10.5-12.1987 Heavy rain from Hurricane Ramon:
outages. A Palomar Mountain fire
0.75” at coast, 2” in mountains, 2.14”
was extinguished.
at Camp Pendleton, 2.08” in
Fallbrook, 0.69” at Lindbergh Field.

10.22.1987 Heavy rain with amounts ranging up Flash flooding resulted in 2 deaths,
to 5” at Blue Jay. Heavy rain also in 10 injuries, and more than a million
northern San Diego County: 0.95” in dollars damage in Blue Jay. Flash
Palomar Mountain. flooding and debris/mud flows in
Pauma Valley (exacerbated by a
previous fire on southwest slopes
of Palomar Mountain). A building
destroyed, 4 homes evacuated.

10.31.1987 Heavy rain. Mt. Wilson received Numerous mudslides. 3 die and 25
3.14” of rain in 24 hours. 2.34” in Mt. are injured in weather-related auto
Laguna, 1.1” in El Cajon. accidents. Sewage spills closed an
80-mile stretch of beaches in LA.

11.4-5.1987 Low pressure of the California coast Numerous flooded roadways and
produces heavy rain and intersections around San Diego. A
thunderstorms. 2.02” fell in Palomar roof collapsed in San Diego. Minor
Mountain and 1.16” in San Diego. mud slides on I-8 at SDSU,
Mission Valley and near Temecula.
Flash flooding stranded 8,000 in
Death Valley.

71
12.4-5.1987 A cold front crossing the Pacific Coast Flooding in downtown LA
brought heavy rain. Mt. Wilson was prompted some evacuations.
drenched with 2.17” in 6 hours. 1.02” Flooded intersections, power
fell at LA between 5 and 7 pm and outages, tree damage, numerous
rain rates of 1” per hour were reported traffic accidents. Flooding,
for a time at John Wayne Airport, and including water into some houses,
0.61” fell in 30 minutes in San Diego was reported in Fallbrook. More
all on 12.4. Storm totals: 1.5” in San flooding was reported all across
Diego, 1.05” in Montgomery Field, San Diego County, including
0.89” in La Mesa, 0.82” San Diego downtown San Diego, where
State Univ, Miramar 0.75”, Chula numerous motorists were trapped
Vista 0.32”. in their vehicles. A mudslide closed
Valley Center Road and Lake
Wohlford Road.

12.16-17.1987 A heavy rain storm hit San Diego Minor flooding in Mission Valley.
County. 2.01” in Oceanside, 2” in El
Cajon and La Mesa, 1.97” National
City, 1.85” Poway, 1.73”
Montgomery Field.

2.2.1988 A dying subtropical system drops 4” Standing water 5' deep in some
in the mountains of San Diego intersections. 50 homes in Imperial
County. More than 4” fell in Imperial Beach flooded. Some homes
Beach in 24 hours and 3.71” in 8 hrs. flooded with 3-6' of water. $0.5
1.5” fell in Chula Vista. 1.25” fell in million in damage. 30 families
San Diego and less than an inch fell in displaced by flooded homes. Power
other parts of San Diego County. outages, road closures.

4.15.1988 1.53” of rain in 24 hrs. at Death

Valley.

72
4.19-23.1988 Heavy rain. 4.15” of rain fell in 24 Flooding, mud slides, and
hours at Mt. Wilson. 1.75” fell at numerous traffic accidents. 26
Cuyamaca Rancho State Park on from injured in major collision around
2.22 to 2.23. 0.79” at San Diego. LA. Flooding of intersections and
several road closures occurred all
over San Diego, Orange and LA
Counties. A Mission Valley hotel
was flooded. Los Penasquitos
Creek flooded a portion of Poway.
Street flooding occurred in
southern San Diego County along
with downed trees, power outages,
and overflowed sewer lines. 3
straight Dodgers games rained out
(only 12 rainouts in previous 26
years). Trees fell on power lines
causing power outages.

12.16.1988 Strong Pacific storm. 2” in 6 hours

during the early morning at Mt.
Wilson and a storm total of more than
3.5”.

8.7-11.1989 One of the most severe convective

outbreaks of record in Southern
California climaxed on 8.11.

2.4.1990 Heavy rain in the San Bernardino 1 death from flooding.

area.

6.9-10.1990 Rain and thunderstorms from

Hurricane Boris. 0.37” at San Diego
in 30 minutes, 1.41” Mt. Laguna,
0.98” Escondido, 0.87” Fallbrook.
0.49” fell in San Diego on 6.10, the
wettest calendar day in June on
record.

2.27-3.1.1991 Series of storms produced 3-6” at 2 dead, 6 injured. Urban flooding,

lower elevations, 11-14” in the mud slides, and road washouts.
mountains. 9.58” at Palomar Flood waters 5' deep at Desert Hot
Mountain. Springs.

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3.17-22.1991 A vigorous storm produced 1-8” in Local flooding and mud slides.
lower elevations, up to 14” in the Mud and rock slides along Del
mountains. 4” fell in Santa Barbara. Dios highway on 3.19. On 3.20
On 3.19 1.58” at Lindbergh Field in Hwy. 78 was closed for a long time
24 hours. More than 1” in Poway, due to flooding. Streets in Mission
Alpine, Julian, Campo and Ramona. Valley flooded. On 3.21 mud
On 3.21 1.98” fell in La Mesa, 0.81” slides, road washouts and power
at Lindbergh Field. outages were reported at Rincon
Indian Res.

3.26-27.1991 A strong winter storm produced 1.80” Golf courses and shopping centers
in 24 hours in Escondido, 1.71” in flooded by the San Diego River in
Poway, 1.56” in Fallbrook, 1.55” in Mission Valley. Flooding damaged
La Mesa, 1.52” in Ramona, 1.48” in apartments in North Park. Flooding
El Cajon, 1.09” in San Diego. damaged Highway 78 east of the
San Diego Wild Animal Park.

7.30-31.1991 Monsoon flow spawned Part of a store and a house were

thunderstorms that drenched the flooded and buried in mud and
region. On 7.30, 0.77” fell in La sand. Imperial highway was
Mesa, 0.58” in El Cajon, 0.56” in washed out. On 7.30 Mobile homes
Santee, 0.33” in Balboa Park, 0.23” in were flooded in La Mesa and
San Diego Mission Valley and homes and streets were flooded in
Lindbergh Field. On 7.31 Ocotillo East City Heights and Mission
was hit with 6” rain in two hours. Gorge. Trees downed, power
outages.

12.27-29.1991 Back to back storms dropped 2-7” at Flooding of low lying areas, mud
lower elevations. slides, and closed highways.

1.5-7.1992 1-2” at lower elevations. Flooding and mud slides.

2.5-16.1992 A series of many intense storms 2 killed in avalanche at Mt. Baldy.

brought heavy rain. A total of 20”+ in Flash flooding, mud slides, and
the mountains and 8-16”+ at lower road closures.
elevations.

3.1-7.1992 A series of storms brings 1-4”. Local flooding.

3.20-23.1992 A series of storms brings 1-5”. Local flooding.

4.1.1992 Heavy rain from thunderstorms. 3” in Flash flooding.

less than 1 hour at Escondido.

74
8.13.1992 Massive outbreak of tropical moisture
created thunderstorms with some of
the heaviest rainfall rates in history.
6.5” in 90 minutes at Palomar
Mountain, 4” in 2 hours at Mt.
Laguna.

12.4-7.1992 Big storm produces 0.5-6” from the Local flooding. Mud slides,
coast to the mountains. standing water, and road closures.

1.1993 Subtropical moisture joined a strong Flooding and flash flooding, mud
upper level low in the Pacific. A series slides, etc.
of storms produced 20-50” of
precipitation in the mountains and up
to 12” at lower elevations over a two
week period (1.6-1.18). One of the
longest periods of consecutive days of
rain on record (13) and measurable
rain fell nearly every day from 1.2 to
1.19.

1.5-10.1993 14+” of rain fell in Cuyamaca and The State declared San Diego
Palomar Mountain. 6+” in Escondido. County a disaster area.

1.12-18.1993 A second stormy period in the month Heavy flooding occurred on the
dropped 18+” at Palomar Mountain, Santa Margarita and San Luis Rey
12+” at Cuyamaca and De Luz. Rivers. Hwy. 76 was washed out
11.62” fell at De Luz in 48 hours on near I-15. The airports at Camp
1.16-1.17. Pendleton and Oceanside sustained
flood damage. In Tijuana, homes
and streets were flooded along the
Tijuana River. 5 died and 139
people were caught in floodwaters,
600 were evacuated.

2.7-10.1993 1-5” near the coast, up to 10” in the Widespread flooding.

mountains, 0.5-1.5” in the deserts.

2.18-20.1993 Heavy rain: 9” at Palomar Mountain, Flooding from Oceanside to

6+” at Cuyamaca, 1-3” at the coastal Encinitas. Homes damaged along
areas and valleys of San Diego Mojave River in Hesperia.
County.

3.25-26.1993 Heavy rain. Local flooding, mud, debris, and

road closures in Orange County.

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6.5.1993 A strong, late season spring storm
moved into California. The 0.76” of
rain at LA set a new daily rainfall
record for June. Lake Gregory was
deluged with 3.24” of rain. 1” in
Palomar Mountain.

8.25-26.1993 Rain and thunderstorms from Flash flooding in Yucaipa and

Hurricane Hilary. 3-4” in two hours Morongo Valley.
from heavy thunderstorms in the San
Bernardino Mountains, Morongo
Valley, and Desert Hot Springs.

1.3-4.1995 Heavy rain. Flash flooding in Seal Beach,

Norco, and Oceanside.

1.10-11.1995 Heavy rain. Extensive flooding in Orange

County.

1.14.1995 8-9” in northern Inland Empire. Extensive flooding in Yucaipa.

Many roads closed.

2.14.1995 3” of rain fell in San Diego County. The San Diego River overflowed
onto adjacent streets in Santee,
forcing some residents to evacuate
their homes. In eastern San Diego,
heavy rains flooded some homes.
One woman drowned in her
basement when it became
submerged with 5’ of water.

3.4.1995 The La Conchita mud slide (near

Santa Barbara) destroyed nine
houses within a few seconds.

3.5-6.1995 6” in 24 hours, 10.34” in 48 hours at Floodwaters washed out a stretch

Idyllwild. 8.57” in 24 hours and of I-5, closing it for over a week.
14.58” in 48 hours at Palomar The overall toll from a series of
Mountain. Pacific storms: 27 killed, $3 billion
in damage. 10,000 homes were
damaged.

3.11.1995 3.07” at Banning - Beaumont, 2.75” at Section of I-5 washed out, lots of
Murrieta, 2.10” at Moreno Valley, local flooding.
1.23” at Riverside, 0.84” at Palm
Springs, 7.73” at Wrightwood in 48
hours.

76
2.25-28.1996 0.5-1.5” in coastal areas.

12.21-22.1996 2” in coastal areas, 2-5” in inland

valleys and foothills.

1.12-13.1997 1-3” in coastal areas and valleys.

2.23-24.1997 Heavy rain. Widespread flooding in coastal

cities and Inland Empire. Homes
stranded in De Luz. Cliff erosion in
Del Mar and Solana Beach.

9.2.1997 Thunderstorm at Pine Cove drops 3.7”

in one hour.

9.4.1997 Hurricane Linda became the strongest Disastrous flooding and debris
storm recorded in the eastern Pacific flows at Forest Falls: $3.2 million
with winds estimated at 180 mph and damage, 2 houses destroyed, 77
gusts to 218 mph. For a time it damaged, car-size boulders, wall of
threatened to come ashore in mud 150' wide and 15' tall.
California as a tropical storm, but the Flooding damage also at Oak Glen.
storm turned away, affecting the
region with added moisture for
showers and thunderstorms. This
occurred during the strong El Niño of
1997-98. 2.5” per hour rain rates were
recorded at Forest Falls.

9.24-26.1997 Heavy rain and thunderstorms from Flooding in Palm Springs, Borrego
Hurricane Nora. 5.50” at Mt. San Springs and Spring Valley. Traffic
Jacinto, 4.70” Mt. Laguna, 4.41” Mt. deaths.
San Gorgonio, 3-4” at several
locations in mountains, 3.07”
Twentynine Palms, 1.5-2” at
Coachella and Borrego Valleys, 2.88”
Hemet, 1-2” in many inland areas.

10.7.1997 Heavy rain in Inland Empire. Storm Floods and debris flows. $2.5
was of 100 year intensity. 1.65” in 1 million damage. Large trees, mud
hour and 15 minutes, 0.31” in 3 and boulders swept down canyons.
minutes at Hemet. Homes, apartments flooded at north
San Bernardino and Highland.

77
12.6-8.1997 Heavy rains of 4-8” across Orange Widespread flooding in Orange
County, heaviest in 70 years. 10” at County. Mud slides and coastal
Mission Viejo, over 4” Corona. Heavy erosion. Flooding in Corona and
downpours in Victor Valley. several communities of Victor
Valley. Mud flow through
Adelanto.

1.8-10.1998 Heavy rain of 2”. Floods and mud in Del Dios (near
Escondido).

2.3-4.1998 Heavy rain of 3”. Flooding, mud slides, power

outages.

2.6-9.1998 Heavy rain. Up to 3” rainfall over all Catastrophic and widespread

of Southern California. flooding, especially in Newport
Beach and Irvine. Lots of property
damage in southern Orange
County. Evacuations and swift
water rescues. Landslides, mud
slides, and sink holes. Roads,
bridges, and railroads damaged.

2.14-15.1998 1-2” in coastal areas, 3-5” in valleys Flooding and mud slides.
and foothills.

2.23-24.1998 Heavy rain. 2-5” rainfall over all of 2 dead, 2 injured. $100 million
Southern California. estimated damage. Power outages.
Catastrophic and widespread
flooding. Hundreds of homes
damaged. Numerous evacuations
and swift water rescues.
Landslides, mud slides, and sink
holes. Roads, bridges, and railroads
damaged. Livestock and crop loss.

3.25.1998 3.5” in 4 hours at San Clemente. Flooding.

5.12.1998 Rain in San Diego. First rain-out of a San Diego

Padres game in Mission Valley in
over 15 years.

7.20.1998 Heavy thunderstorms. 1.11” fell at Flooding at Mission Beach and

Cuyamaca. Barton Flats in San Bernardino
Mountains.

8.12-14.1998 Strong thunderstorms in Apple Flash flooding.

Valley.

78
8.29-31.1998 Strong thunderstorms. 0.77” in 45 Flash flooding in Hemet. Homes
minutes at Wrightwood, 1.5” at Apple and roads flooded with 4 to 6” of
Valley, 0.68” in 30 minutes at Forest water in Hesperia and Apple
Falls. Valley. Rock slides in Mill Creek.
Flooding of roads in Sugarloaf and
Forest Falls.

7.8.1999 Heavy thunderstorms. Flooding in San Jacinto, Palm

Springs, Cathedral City, and Palm
Desert.

7.11-13.1999 Heavy thunderstorms in and around 2 dead, dozens injured, 6 homes

the higher mountains. 1.65” in less destroyed, many more damaged,
than 30 minutes at Lake Henshaw, 20' high wall of water moving at 45
1.57” in 20 minutes at Big Bear City, mph moving 70-ton boulders at
1.40” in 30 minutes at Sugarloaf, 1.6” Forest Falls. Buildings washed
in 85 minutes at Forest Falls, 1” in 1 away at Jenks Lake. Disastrous
hour at Pine Cove, 1” in 25 minutes at flooding and mud slides at Oak
Shelter Valley. 1” per hour rain rate at Glen, Big Bear City, and Apple
Phelan. 1.8” in 25 minutes at Forest Valley. Flooding in Yucca Valley
Falls again on 7.13. area, Beaumont area and Palm
Springs. Roadways closed due to
flash flooding.

7.21.1999 Heavy thunderstorms near Borrego Flash flooding damage at Borrego

Springs. Springs and Ocotillo Wells.

2.10.2000 Heavy rain. 3 killed, 8 injured from flooding

and mud slides.

2.21-23.2000 Heavy rain. Lots of flooding, mud slides. Roads

washed out in Hemet.

4.17-18.2000 Up to 2” at lower elevations.

6.21.2000 Heavy rains (about one inch) at La Flooding and mudslides along
Jolla Indian Reservation near Palomar Hwy. 76. 200’ of highway covered
Mountain on a recently burned area. by up to 18” of mud.

8.24.2000 Thunderstorm drops 0.76” at Palomar Mudslide closes Highway 76.

Mountain.

8.29.2000 Desert thunderstorms: 1.5” in 45 Flash flooding, mud in homes,

minutes at Borrego Springs. roads damaged in Borrego Springs
area. Flash floods, mud, and debris
covered roads from Yucca Valley
to Palm Springs and Oasis.

79
9.7.2000 Heavy thunderstorm in Morongo Flash flooding.
Valley.

1.10-11.2001 Heavy winter storm. Two to four” of Flash flooding from Seal Beach to
rain. 1.74” of precipitation (some Garden Grove to Costa Mesa.
snow) at Phelan. Several mud slides in San Diego
County

2.11-13.2001 Heavy winter storm. 2-5” at Orange Extensive urban flooding and mud
County and the western Inland slides. Trees and power lines
Empire. 1-2” over the rest of the knocked down.
lowlands.

7.6.2001 Strong thunderstorms in eastern Roads inundated. Damage and

Coachella Valley. erosion around Oasis.

7.7.2001 Strong thunderstorms in Victor and Roads closed due to flash flooding,
Lucerne Valleys. 0.25” in five mud slides.
minutes at Lucerne Valley.

9.2-3.2001 Thunderstorms generated from Flash floods and mud slides in the
remnants of Hurricane Flossie. 2.1” in San Bernardino Mountains and
1 hour at Lake Cuyamaca. Lake Cuyamaca.

9.30-10.1.2001 Thunderstorms in mountains and Flooding in Beaumont.

inland valleys.

2.11-14.2003 Heavy rain: 10.15” at Forest Falls, Localized flooding.

9.75” Lytle Creek, 8.47” Lake
Arrowhead, 7.60” Santiago Peak,
6.86” Mira Loma, 5.15” Wrightwood,
3.95” Hesperia, 3.87” Lake Elsinore,
3” Lindbergh Field.

8.1.2003 Thunderstorms in Borrego Valley. Flash flooding: 4 ft of water

Estimated 2.5-3” rain in 2 hours. running in San Felipe Wash. 1 car
and family stranded in Borrego
Palm Canyon. Half of Ocotillo
Wells Airport runway inundated,
debris on Hwy. 78.

8.20.2003 Thunderstorms. 3” at Yucca Valley, Flash Flooding. 5 residences

2.63” in 1 hr, 7 min. at San Felipe flooded in Yucca Valley. 3 dead
Valley, 1.92” in 2 hours at Ocotillo and 2 swift water rescues from
Wells. trapped vehicles in 29 Palms.
Numerous washes flooded. Hwy.
S2 near Warner Springs closed to
flooding.
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8.24.2003 Thunderstorms. 2” at Pine Valley in Flash Flooding east of Alpine and
35 min. in Pine Valley.

8.25-27.2003 Thunderstorms in the mountains. Flooding closes Hwy. 38 in Big

Bear City, roads near Guatay,
routes S2 and S22 near Ranchita,
Hwy. 78 east of Julian (rock and
mud slides), streets in Borrego
Springs and Campo.

9.2-3.2003 Thunderstorms in mountains and Flash flooding and roadways

deserts. Rain rates over 1 inch per flooded in Lake Henshaw area,
hour with many of them. Palm Canyon near Palm Springs,
Yucca Valley, Idyllwild, Santa
Ysabel, Mt. Laguna and Borrego
Springs.

12.25.2003 Heavy rain. 8.58” at Lytle Creek, 15 dead in mudslides in areas

5.79” Devore, 5.59” Santiago Peak, burned by wildfires in Oct 2003: 13
5.40” Forest Falls, 3.94” Volcan in a church camp in Waterman
Mountain. 0.35”-2.5” fell at lower Canyon north of San Bernardino, 2
elevations. in a campground in Devore.

8.13-14.2004 Monsoon thunderstorms produced Flash flooding. On 8.13 flash

0.71” in 30 minutes in Phelan, 0.63” floods in Wildomar, Sage, and La
in 8 minutes at Volcan Mountain Quinta. Hwy. 78 near Yaqui Pass
(north of Julian), 0.66” in 11 minutes closed. On 8.14 severe flash
in San Felipe Valley (south of flooding of homes in Spring Valley
Borrego Springs). Lake (Victorville) and Hesperia.
Vehicles trapped in 5’ water. Water
8’ deep inundated a railroad
causing major delays (a 60 train
backup extending to Cajon Pass).

9.10-11.2004 Thunderstorms in Borrego Palm Severe flash flooding. In Borrego

Canyon produced a wall of mud 8-10’ Springs 70-90 homes damaged, a
high and 150 yards wide. Training campground was washed out and
thunderstorms over Johnson Valley. major damage occurred at a golf
course. In Johnson Valley, Hwy.
247 was washed out in numerous
sections. Minor damage to homes.

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10.20,27.2004 Monthly record rainfall received in On 10.20: Widespread flooding.
one day, and in 6 hours in many Bridge washed out near
locations of Orange Co. Totals for last Wrightwood. One killed in
two weeks of Oct: 4-8” in lower floodwaters near Lytle Creek.
elevations, up to 14” at Lake Many mountain roads impassable
Arrowhead. 2.70” fell at Lindbergh with mud and rockslides. Railroad
Field, the fourth most on a calendar tracks washed out, derailing train.
day on record. Horses neck deep in flood waters.
Golf course rescue. 10.27: 7
rescued from vehicles in flooded
intersection in Sun City. 12
vehicles trapped in mud at Scissors
Crossing (east of Julian). Homeless
man rescued in San Diego River.
Several vehicles stuck in San
Jacinto River floodwaters near
Perris.

12.28-29.2004 Heavy rain from a big storm. 1.10 in Flash flooding in Waterman
40 minutes at San Diego Country Canyon and other mountain areas.
Estates (east of Ramona). Debris flow in San Diego Country
Estates. Flooding on Lytle Creek
road and Hesperia.

12.31.2004 Mud slides occurred on Hwy. 138 and Hwy. 138 closed for three days.
on Hwy. 18 in the San Bernardino
Mountains.

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1.7-11.2005 Five consecutive days of heavy Widespread and catastrophic
precipitation all over Southern flooding and damage totaling $100
California. More than 30” of million. A mountain slope failed on
precipitation in the San Bernardino top of La Conchita. Damage to
Mountains. 4-10” at lower elevations. crops, golf courses, and there were
31.75” of precipitation fell at Lake sewage spillages. A state of
Arrowhead, 29.70” at Lytle Creek, emergency was declared for all
19.86” at Devore, and 15.09” at four counties. On 1.10 a woman
Palomar Mountain. This followed and her unborn child were swept
heavy storms in late Dec and early away by City Creek in Highland
Jan. and killed. Debris flows in City
Creek. Lytle Creek grew to 200’
wide and flooded homes. 350
homes were flooded in Placentia.
Numerous rescues needed across
the region. Debris flows across I-
215 in Devore. In Big Bear City,
111 homes, schools and businesses
were flooded. On 1.9 mudslides
destroyed three homes, damaged 7
others in Lake Arrowhead area.
Mudslides in Anaheim caused
damage. I-15 in Temecula damaged
and closed by mudslides and
flooding. Ortega Highway closed.
Homes were flooded in southern
Inland Empire and Valley Center.
San Luis Rey River flooded and
washed out Pacific St. in
Oceanside, cresting above flood
stage twice, peaking at 20.7’ on
1.11. On 1.11 a hotel in Crestline
was destroyed by mudslide. A tree
killed one in San Diego. Felled
trees caused extensive damage in
San Diego County. By 1.11
numerous highways in the San
Bernardino Mountains were closed.
The Mojave River flooded 3 homes
and other structures, and caused
extensive damage in Hesperia and
Oro Grande. On 1.14 a forced
release of water at Prado Dam
flooded the Santa Ana River valley
and damaged the Corona Airport.

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2.18-23.2005 Heavy storm rains dumped 3-6” near Dairy Farm losses in the northern
the coast and valleys, 6-12” in the Inland Empire. Most back roads
mountains, more than 2” in the damaged in the San Bernardino
deserts. 18.79” fell at Lytle Creek, Mountains beyond use. Lake
12.33” at Lake Arrowhead and 6.80” Hodges, which was only 17% of
at Fullerton. capacity in October, began to spill.
San Diego River flooded, killing
one. On 2.21 an earthen dam near
Wrightwood gave way, flooding
and causing extensive damage
downstream. Numerous mudslides
across the region damaged many
homes. A landslide sent boulders
into a home in Silverado Canyon
and killed one.

6.1.2005 An enormous landslide occurred in 15 homes were destroyed or

Laguna Beach. Caused by saturated severely damaged. Minor injuries.
soils from the previous winter’s epic $27 million estimated damage.
rains.

7.23.2005 Thunderstorms produced rain rates in Flash flooding in Hemet area.

Hemet of 1.5” in 30 minutes, and 1 Residences and businesses were
inch in 15 minutes. flooded.

7.24.2005 Heavy thunderstorms hit the Flash floods hit Lucerne Valley and
mountains and deserts. 2.30” fell in highway 247. Vehicles swept off
Mt. Laguna in 40 minutes. 0.72” fell roads and rescues needed. Roads
in Cuyamaca in 36 minutes. 5.58” fell washed out in Apple Valley. Three
in 12 hours in Victorville. major mud slides hit Forest Falls.
Flash flooding also in Phelan,
Hemet, and east of Julian.

7.29.2005 Intense rain from thunderstorms hit Flash flooding was reported in the
the mountains and deserts. 0.91” hit Mt. San Jacinto Wilderness, also in
Mt. Laguna in 28 minutes, 0.63 in 14 Ranchita and Warner Springs.
minutes. 0.5” hit San Felipe Wash in
10 minutes.

7.30.2005 Intense thunderstorms hit the Flash flooding in the wilderness

mountains and deserts. area of Mt. San Gorgonio, Barton
Flats, Lucerne Valley and
Idyllwild. The Banning airport was
flooded.

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7.31.2005 Thunderstorms produced 0.52” in 13 Flash flooding occurred in Big
minutes fell at Lake Morena. 0.75” Bear City, Anza, and south of
fell in 22 minutes at Yucaipa Ridge. Warner Springs.

6.28.2006 A heavy thunderstorm produced 1.25” Visibility was reduced to near zero
in 15 minutes at Loma Tova, just in the heavy rain along Interstate 8.
south of the border east of Tecate.

7.7.2006 Thunderstorms dropped 0.75” in 15 Flooding occurred along some Mill

minutes and 1.22” in 40 minutes at Creek tributaries. Mud and rock
Yucaipa Ridge. debris covered parts of Valley of
the Falls Drive.

9.2.2006 A thunderstorm near Pinyon Pines Flash flooding occurred in Pinyon

dropped 1.14” in 30 minutes. Flats, eroding roads. Mudslides
trapped several vehicles on Hwy.
74.

9.3.2006 A microburst hit northeast of Sun Power lines and poles were
City. knocked down. Power outages
resulted.

9.4.2006 A thunderstorm dropped heavy rain Significant mudslides (debris

along the Elsinore Convergence Zone. flows) occurred in north San
Jacinto, trapping 19 vehicles. A
few homes and businesses were
damaged.

9.6.2006 Heavy thunderstorms occurred along Flash floods closed roads in Hemet,
the Elsinore Convergence Zone near cars were stalled, a mudslide along
Hemet. Hwy. 74.

10.13.2006 A thunderstorm dropped 0.51” in 5 18 homes and businesses and two

minutes and 1.81” in 30 minutes in vehicles were damaged by
San Bernardino. flooding. Big sinkholes were left in
a road. One swift water rescue.
Mud and debris were left on roads.

85
Heavy Snow, Rare Snow at Low Elevations

Date(s) Weather Adverse Impacts

12.1847 Light snow in hills above Old Town

San Diego. Greater amounts to the
east.

1.12-14.1882 15” at San Bernardino. 3' in Campo Birds and livestock killed,
over four days producing 8’ drifts. 2- telegraph lines down. Citrus
5” in outlying San Diego, including: damage.
4” along Poway Grade, 3” at El
Cajon, 1” Poway (disappearing in a
few hours). The foothills above
Poway stayed white for 2 or 3 days.
Light snow in Del Mar. 5” in
Riverside. 20” in Campo on 1.13.
Snow flakes, but not sticking at San
Diego.

4.21-22.1908 0.6” fell in Santa Ana, the greatest

snowfall on record.

11.27.1919 Snow brought a white mantle to area

hills and valleys around San Diego. 8”
in Morena 8”, 5” at Carrizo Gorge,
and 4” at Warner Springs.

1.11.1930 2” at Palm Springs.

1.15.1932 Up to 2” snow all over the LA Basin

(called the heaviest on record). 1” at
LA Civic Center and beaches at Santa
Monica whitened. 18” in Julian, 17” at
Mt. Laguna, 14” at Cuyamaca, and 6”
at Descanso.

1.21.1937 Snow flurries at San Diego. Trace

amounts stuck to northern and eastern
parts of the city.

2.11.1946 Snow flurries in many parts of San

Diego.

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1.9-11.1949 Snow in lowlands: 14” Woodland Snarled all kinds of transportation.
Hills, 8” La Canada and Catalina Power outages and emergencies.
Island (2,100'), 6” Altadena, 5” Plane crash kills 5 and injures 1
Burbank, 4” Pasadena, 1” Laguna near Julian. Camping group
Beach and Long Beach.. A trace in stranded at Cuyamaca.
San Diego, the only time since 1882.
3' Mt. Laguna, 18” Cuyamaca, 1'
Julian, 4-8” as low as 1000' elevation.
A light covering in La Jolla, Point
Loma, Miramar, Escondido, Spring
Valley, and other outlying San Diego
areas.

4.13.1956 A cold snowstorm brought 1’ to Mt.

Laguna, at least 6” at Palomar
Mountain, 1.5” at Julian.

1.29.1957 24” at Mt. Laguna, 21” at Palomar The snowstorm stranded 200
Mtn., 20” at Lake Cuyamaca, 12” at people north of LA.
Julian, 10” at Mesa Grande, 6” at
Lake Henshaw.

1.20-21.1962 Snow to lower elevations. Highways closed.

12.9.1963 Heavy snow in the mountains. 5 killed, 6 injured. Highways

blocked.

3.22-24.1964 Big snow storm. Totals: 29” in

Idyllwild (22” on 3.24), 26” at Lake
Arrowhead, 23” at Palomar Mtn., 18”
at Big Bear Lake.

3.12-13.1967 Heavy snow in the mountains. Highways closed.

12.13-19.1967 50” at Mt. Laguna in 24 hours on 1 freezing death. Numerous schools

12.18 and 12.19, 38” Idyllwild, 2' and highways closed.
Palomar Mountain, 12-18” in higher Transportation disrupted and chains
elevations. 6” Temecula, 5” were required on Hwy. 395 just
Fallbrook, 4.5” Anza Borrego State north of Mission Valley. Power
Park, 3” Borrego Springs, 2” Carlsbad outages.
on 12.13. Light covering over many
San Diego mesas. Mt. Laguna
recorded an 8 day total of 96.5”.

2.20-25.1969 Heavy snow in mountains approach

greatest depths on record.

87
3.11.1973 8” fell at Mt. Laguna and 4” at
Palomar Mountain.

1.3-5.1974 Over 18” in San Bernardino Structures and a few roofs collapse
Mountains. 17” fell in Victorville on due to weight of snow. Power lines
1.5, the greatest daily amount on and trees snapped.
record. On 1.4, flurries were reported
in Palm Springs.

11.28-29.1975 First winter storm of season was 20 stranded campers rescued after a
heavy. Up to 2' in San Bernardino few days.
Mountains, 16” at Big Bear Lake.

3.2-4.1976 20” at Running Springs.

1.30-2.2.1979 Widespread snow. 2” at Palm Springs. On 1.31, all major interstates into
56” fell in Big Bear Lake, the greatest LA (I-5, I-15, and I-10) were
snowfall on record. On 1.31, snow fell closed. Snow drifts shut down
heavily in Palm Springs and 8” fell at Interstate 10 on both sides of Palm
Lancaster. Snow and rain mix at Springs, isolating the city. Schools
Borrego Springs. Mt. Laguna 2’ and were closed and hundreds of cars
Julian 1’. were abandoned.

11.27-28.1981 3' at Big Bear Lake.

3.18.1982 25” at Palomar Mountain.

2.18-19.1984 Up to 16” in the mountains.

12.18-19.1984 A major snowstorm brings up to 16” Edwards AFB and Interstate 5

to the mountains and upper deserts, (from Castaic to the San Joaquin
including 13” to Lancaster. Valley) were both closed.

12.28.1984 A rain and snow mix fell in Borrego

Springs.

2.2.1985 Up to 2” snow in Palm Springs.

3.2.1985 Snow fell briefly in Escondido. Ice

pellets fell in Poway, Coronado, La
Mesa, and Escondido, with hail in
Linda Vista and downtown San
Diego.

3.15-16.1986 3' in the San Bernardino Mountains.

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10.3.1986 Rain and thunderstorms hit LA area. Classes were cancelled at CSU-
1.50” in Pasadena, 1.02” in LA. 3” of Northridge because of hail. Several
hail piled up in Pasadena. serious traffic accidents in
Pasadena.

1.4.1987 A ski resort in Big Bear received up to

2’ of snow at the higher lifts. Up to
15” occurred elsewhere in the San
Bernardino Mountains. 9” in Mt.
Laguna, 4” in Cuyamaca Park and a
few inches in Julian.

2.22-25.1987 24” at Mt. Laguna, 22” at Cuyamaca, Roads and schools were closed in
12-17” in the San Bernardino mountain areas. An aircraft
Mountains (17” at Big Bear Lake), 6” accident in a snow squall near
Pine Valley, 3” Lake Morena. 4” fell Anza killed four.
in one hour at Lake Hughes. Snow
pellets to coastal areas: 2-3” at
Huntington Beach, measurable sleet
and hail at San Diego Bay front. On
2.25 light snow was recorded in
Tarzana, Northridge, Torrance,
Fontana and Redlands.

12.16-17.1987 Snow fell for two minutes at Malibu Disneyland was closed due to the
Beach on 12.16. A foot of snow fell in weather for only the second time in
the mountains north and east of LA. 24 years. Other theme parks and I-5
24” of snow fell in Julian. 9” of snow and I-15 were closed on stretches
fell at Mt. Laguna on 12.17. through the mountains stranding
motorists in the Southland.
Numerous accidents killed some
motorists. Snow cancelled all
schools in the mountains of San
Diego County and sent 16,000
students home in the Santa Clarita
Valley.

12.24.1987 Snow flurries over the entire San

Diego metro area, but not a flake
officially at San Diego. Heavy snow
in the Laguna Mountains.

1.17-18.1988 14” at Mt. Laguna.

2.7-9.1989 Snow at the beaches in LA to the Major road closures. Numerous

desert in Palm Springs. 15” in the traffic accidents.
mountains. 3” at Palmdale.

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1.16-17.1990 Snow flurries within San Diego city
limits. None officially at San Diego.
14” at Mt. Laguna. 10-16” in
mountains.

2.4.1990 10-13” in the mountains.

2.14.1990 Snow flakes reported all over the San

Diego metro area.

2.16-18.1990 3-4' in the mountains. 48” at Green Avalanche at Wrightwood buries

Valley and 46” at Big Bear Lake. 10 hikers, injuring 1.

2.27-3.1.1991 Back to back storms dump 2-3' in the Highways closed.

Big Bear area, up to 2' elsewhere in
the mountains.

3.17-20.1991 2-5' in the mountains. On 3.19 1’ of Schools and roads closed in the
snow fell at Mt. Laguna, 6” at mountains, including I-8 from
Palomar Mountain and Cuyamaca. Alpine to Imperial County.
Downed trees and power outages.

3.26-27.1991 36” at Lake Arrowhead, 27” Big Bear An avalanche of snow isolated 100
Lake, and 18.5” Idyllwild. 18” fell at people in Big Bear Lake by
Mt. Laguna. blocking Highway 18.

1.5-7.1992 6-20” in the mountains, 2-8” in

foothills and high desert floors.

12.4-7.1992 6” to 2' in the mountains.

2.7-10.1993 8-18” in the mountains.

1.3-4.1995 6-12” in the mountains. Snow in the

high desert: 2” of heavy, wet snow at
2300'.

3.11.1995 Over 20” at Bear Mountain.

12.23.1995 12” in the San Bernardino Mountains,

8” on the high desert floors.

1.22-23.1996 12” above 4000'.

2.25-28.1996 10” at Idyllwild, 2” Yucaipa, a dusting

at Hemet and Corona. 1-2' in
mountains, up to 6” in high desert.

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3.12-13.1996 8-12” in the San Bernardino
Mountains.

1.12-15.1997 18” at Mt. Laguna. 18”-3' snow above 13 illegal immigrants die near Pine
2500'. Ski resort at Snow Valley open Valley.
until 5.18, the latest in 78 year history.

2.23-24.1998 1-2' above 6000', 3-4' above 7000'. Trees and power lines down.

3.28-29.1998 Coldest storm of the year. 1-3' above Considerable damage to crops.
5000', 4-8” above 3000'. Ice pellets Serious traffic accidents.
and hail 1” deep in some coastal and
foothill areas.

4.1.1998 Up to 3' of powder at ski resorts. 18”

at Pine Cove.

1.26.1999 22” over a large area around Running Road closures.

Springs, 18” at Angelus Oaks.

4.1-2.1999 18” in 12 hours at Mt. Laguna. 7-9” at 8 illegal immigrants found dead
Pine Valley and Descanso, 2” at near Descanso, 2 just over the
Boulevard, “heavy snow” reported at border. 50 survived wearing only
Cherry Valley (3000'), 1” at light clothing and tennis shoes and
Homeland (1,700'). had never experienced snow; they
had been on foot for 3 days.

6.2-3.1999 Latest measurable snow on record for

area mountains. 3” at Mt. Laguna, 1”
Wrightwood.

2.21-23.2000 18” at Forest Falls.

3.4-6.2000 Up to 17” in 24 hours in the 3 illegal immigrants dead south of

mountains. 14” at Forest Falls. Mt. Laguna.

4.17-18.2000 Late winter storm: 18” at

Wrightwood.

1.10-11.2001 13-18” in Idyllwild area. 3” in Phelan.

2.6-14.2001 Over a week of heavy snow called Roof of ice rink caves in at Blue
“most in a decade”: 5' at Blue Jay and Jay.
Mountain High, 2' Snow Summit, 5-
12” at Apple Valley. Mountain High
reports 12” on 2.6, 10” on 2.11, 36”
on 2.12, 30” on 2.13, 8” on 2.14.

2.28.2001 32” at Mountain High.

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1.28-29.2002 Light snow in southern Inland Empire.

3.18.2002 3” in Apple Valley, the greatest daily

snow amount for March. 1” in
Hesperia.

10.27.2004 2’ in Big Bear, most of which fell in A few local ski resorts opened on
12 hour period. the earliest date in their history.

11.20-22.2004 Thundersnow started in the upper Tree damage in lower elevations

desert late on 11.20 and snow caused house damage and power
continued at times for two days. outages. Snow lined I-10 near
Widespread reports of 2’ with drifts to Calimesa for a few days.
3’ at Wrightwood, Lake Arrowhead,
Big Bear and Palm Springs Tramway.
Snow level as low as 1,000’. 18-20”
in foothills south of Yucca Valley,
14” in Phelan, 9-12” in Hesperia and
Apple Valley, 9” in Yucaipa and
Calimesa, up to 3” throughout
southern Inland Empire.

1.3-4.2005 Heavy snow fell as low as 2500’. Up

to 1’ at higher elevations, up to 10” in
the San Diego County mountains. Big
Bear Lake completely froze over by
1.5.

1.7-8.2005 Heavy snow up to several feet fell in 200 motorists were rescued on
the mountains. Hwy. 18 west of Big Bear Lake.

2.19-23.2005 A strong winter storm brought 4-8’ to Lift chairs and shacks had to be
Mt. Baldy and Mountain High ski dug out of the snow at Mountain
resorts. Reports of 10’ on the highest High.
peaks. Only 1-2’ of new snow at Big
Bear ski resorts. Big Bear Lake only
measured 9”.

3.10-11.2006 Snow fell as low as 1500’. 36” fell at All the mountain highways were
Big Bear Lake, Lake Arrowhead and closed. Roof damage in Guatay.
the Palm Springs Tram. 27” at Pine One immigrant was killed and
Cove and Idyllwild, 25” at Cuyamaca, seven injured near Pine Valley.
13” in Warner Springs, 12” in Pine
Valley.

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Severe Thunderstorms: Large Hail, Strong Thunderstorm Winds,
and Killer Lightning (See flash flooding in heavy rain section)

Date(s) Weather Adverse Impacts

2.28-3.3.1938 Thunderstorms. 1 killed by lightning in Corona.

9.20.1939 Lightning struck two street cars and Several small fires started in the
other structures. city. Damage to structures.

10.20-21.1957 Widespread thunderstorms. Hail

drifted to 18” in East LA.

9.2.1960 Golf ball size and baseball size hail at Considerable damage to houses.
Boulevard area. 2-3” precipitation.
Hail diameter measured at 2.75” and
weighed over 1 lb., some stones
estimated larger. 2.75” hail also in
Riverside County. This is the largest
known hail to hit Southern California.

10.8.1961 Hail up to 2” deep covered Mt. Helix

area.

12.13.1967 Marble size hail hit Palomar Mountain

from thunderstorms preceding a major
snow storm.

1.30-31.1979 Golf ball size hail.

4.1.1982 Strong storm winds hit Encinitas – Trees were downed, greenhouses
Leucadia. destroyed.

10.3.1986 Rain and thunderstorms hit LA area. Classes were cancelled at CSU-
1.50” in Pasadena (in a little more Northridge from power outages and
than 1 hour), 1.02” in LA (in less than several serious traffic accidents
1 hour) and 0.77” in Monrovia. 3” of resulted in Pasadena because of
hail piled up in Pasadena. Wind gusts hail. Minor flooding.
to 35 mph. Hail nearly ½” in diameter
in Westwood. In Blythe, winds gusted
over 50 mph and 0.79” fell in 30
minutes.

10.10.1986 Hail the size of marbles was reported

during a Pacific storm with
thunderstorms embedded in San
Diego’s east county.

93
2.23.1987 Thunderstorms with hail and lightning 2” of sleet and hail piled up in
hit San Diego, Coronado and downtown San Diego (a snowman
Encinitas. was built at Seaport Village).
Lightning struck a transformer in
Logan Heights, knocking out
power.

6.6.1987 Rare June thunderstorms hit the LA Power was knocked out. Lightning
region and Mojave Desert. A severe sparked small fires. In Lancaster,
thunderstorm hit Palmdale and mobile homes were damaged by
Lancaster. 1” diameter hail at Mt. strong winds (possible tornado?)
Pinos in northern LA County, ¾” hail and lightning. Two-by-fours were
at Palmdale, 1/2” hail hit Pine driven into the roofs of mobile
Mountain near the LA-Kern county homes. Utility poles were uprooted
line. Lightning struck the Santa and broken in half.
Monica Bay.

9.1-2.1987 Remnants of tropical storm Lidia On 9.1 lightning struck a power

brought thunderstorms to the San pole in El Cajon, which ruptured
Diego Valleys with lightning and gas lines. Another bolt started a
strong damaging winds (possibly a house fire. Lightning caused
tornado). 35 mph winds were reported several small fires. What was
at Pt. Loma. reported as a dust devil was
probably a microburst or a tornado
damaged awnings and other items
to mobile homes near Lake
Jennings. In El Cajon a tree with an
8-inch trunk was snapped in half.
On 9.2 a woman was struck by
lightning near Lake Henshaw. Ten
fires were started by lightning in
the mountains of San Diego
County.

9.22-23.1987 Frequent lightning and thunderstorms Numerous power outages, property

from Hurricane Norma in the San damage from lightning strikes, and
Diego area. Numerous lightning small fires ignited.
strikes in Escondido. 0.55” in two
hours at Lemon Grove, 0.97” total.
0.68” at Lindbergh Field.

94
12.4.1987 Thunderstorm winds gusted to 60 mph In Westminster winds damaged 40
in Westminster and 55 mph at mobile homes, 9 of which were
Newport Beach. ripped out of the ground, leaving
24 people homeless. Winds
knocked down power lines in
Newport Beach. Lightning struck a
radio tower in Newport Beach,
knocking the station off the air, and
knocked out power to the area.

4.23.1988 An intense winter-like storm brought 9 girls at Tustin were injured

thunderstorms. (burned and thrown to the ground)
when lightning struck the tree
under which their softball team had
taken shelter from the rain.

3.20.1991 Lightning struck North Park – San Power knocked out by lightning
Diego. Hail reported in El Cajon, struck transformer. A house fire
Miramar and University City. was started.

7.30.1991 Lightning struck San Diego in City Several grass fires were started. A
Heights. big power outage occurred.

4.26.1994 Large hail up to 0.75” from San Section of I-215 closed.

Dimas to Ontario.

5.24.1996 A cold storm system came from the Crop damage around Fallbrook
north and produced thunderstorms. from the hail. Lightning struck two
Streets were buried in pea-size hail in palm trees in Oceanside and burned
Fallbrook. “Ping pong size” hail also like torches. Power was knocked
fell there. Lightning strikes were out.
common.

7.10.1996 Lightning hit the San Diego region. Power was knocked out in central
San Diego, the zoo and other metro
areas.

1.12-13.1997 Dime size hail up to 1' deep over a

small area in Buena Park and Cypress.

2.17.1997 Marble size hail at Yucaipa.

5.18.1997 Wet microburst in Apple Valley (in Building and structure damage.
addition to two tornadoes). Power lines arcing down and
producing fires.

8.3.1997 Dime size hail at Campo.

95
9.1-2.1997 Strong thunderstorm winds: three Large tree blown down in Apple
gusts to 104 mph at Twentynine Valley.
Palms. Apple Valley gust 62 mph.

9.4.1997 Thunderstorms from Hurricane Linda:

golf ball size hail in Forest Falls area.

3.28.1998 Microburst in Lake Elsinore. Tree uprooted, extensive roof

damage.

4.1.1998 Grape size hail piled up 2” deep at

Laguna Niguel.

7.20.1998 Thunderstorms erupted near the coast Lightning sparked at least five fires
and in the mountains. in San Diego County. Strikes also
hit a Clairemont home, and two
trees in Pacific Beach. Lightning
also caused a few power outages.

8.12-14.1998 Downburst in Hemet with winds 70 Buildings damaged, trees and

mph and 0.75” hail. Strong winds in power lines down in Hemet.
Apple Valley. Golf ball size hail at
Cajon Pass. 1.6” rain in 30 minutes at
Boulevard.

8.29-31.1998 Severe thunderstorms. Wind gust of Downed trees and power lines.
86 mph at Sage (south of Hemet), gust Fires started by lightning near
50 Rialto, 45 San Marcos. Barona Ranch.

9.2.1998 Severe thunderstorms at Hemet and Large fires in Orange County.

San Marcos from Hurricane Isis.
Strong winds from thunderstorms in
Orange County with gusts to 40 mph.

12.6.1998 Thunderstorm in Los Alamitos and

Garden Grove: gusts 50-60 mph
called “almost a tornado.”

7.13.1999 0.75” hail at Forest Falls.

3.5-6.2000 Golf ball size hail at Garden Grove, Property damage and trees downed
Santa Ana, and Running Springs. along the coast from Huntington
Strong thunderstorm winds at the Beach to Sunset Cliffs.
coast: gust 60 mph at Huntington
Beach.

96
4.18.2000 A severe thunderstorm brought Severe damage to factories and
downburst winds estimated at 80 to mobile home parks in Paramount
100 mph from Bellflower to Diamond (one mobile home was blown
Bar. ¾” hail was reported in Downey. over). Wind damage was done to
trees, power lines and numerous
buildings along the entire path. In
Norwalk, a large Eucalyptus fell
onto I-5, closing the freeway for 3
hours.

8.1.2000 0.5” hail at Lake Arrowhead.

8.29.2000 Thunderstorm wind gust to 61 mph at

Borrego Springs.

9.7.2000 “Big” hail strikes Forest Falls.

Lightning strikes Oceanside High
School.

2.13.2001 Thunderstorm gust to 89 mph in east

Orange.

2.27.2001 Dime size hail in Mira Mesa, and 8” Traffic delays.

of graupel (soft hail) pile up on I-15.

7.3.2001 A microburst hit Hesperia creating a A radio tower was toppled and
wall of sand and dust and a moaning other property was damaged.
sound.

8.8.2001 Strong thunderstorm in Twentynine Damages.

Palms.

9.2-3.2001 Strong thunderstorms from Hurricane 1 boy killed by lightning in Apple

Flossie. Hail up to 0.5” in Pine Valley. Valley. 1 man killed and 1 boy
injured by lightning at Cuyamaca
Rancho State Park. Trees fell on a
house in Beaumont.

9.30-10.1.2001 Thunderstorms in mountains and 1 killed by lightning at Cuyamaca

inland valleys. Rancho State Park.

8.24.2003 Thunderstorms produce nickel size Major tree damage at Lake

hail in Pine Valley, strong winds at Henshaw.
Lake Henshaw.

8.25.2003 0.75” hail at Big Bear City.

9.2.2003 1.25” hail at Descanso.

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 1.75” hail in Joshua Tree and 29
9.4.2003
Palms. 0.75” hail in Julian area.

8.13-14.2004 Monsoon thunderstorms in the Lightning in Murrieta ignited house

valleys, mountains and deserts. fire. Hail dented cars in Yucca
Lightning struck a house in Murrieta. Valley. Lightning in Victorville
Lightning struck a tree in Victorville. struck a tree and it fell over onto a
Golf ball size (1.75”) hail in Yucca limousine, trapping 15 occupants.
Valley. Nickel size (0.88”) hail in
Phelan.

9.11.2004 1” hail in Borrego Springs, Window broken by hail. Strong

accompanied by 60 mph gust in winds knocked down six power
Borrego Springs. This could have poles. In La Quinta: 138 trees
been stronger, but the anemometer knocked down at one golf course
was destroyed. Strong winds in La with building damage, more trees
Quinta. down at other golf courses. Roof
tiles blown off. Damage to power
poles and transformers.

1.3.2004 Numerous lightning strikes from 1 injured in Fontana from flying

Norco to Devore. glass when a 100’ tree was struck
and fell on a house.

2.19.2005 ¾” hail reported in Anaheim. In Winds blew down fences and trees
Laguna Hills thunderstorm winds had and damaged a mobile home in
estimated gusts of 81 mph. Laguna Hills.

2.22.2005 Thunderstorm wind gusts to 68 mph

in Newport Beach. 1” hail hit Costa
Mesa.

2.24.2005 Numerous thunderstorms in the Inland Lightning struck a girl in Moreno

Empire. Valley.

4.28.2005 A squall line raced ashore in Orange Homes and businesses damaged in
County with 70 mph winds. Dana Point, San Clemente and San
Juan Capistrano. Numerous trees
felled.

7.22-23.2005 Lightning strikes. Thunderstorms Lightning sparked fires near Big

reaching the coast in San Diego Bear Lake on 7.22 and 15 fires in
County. Hail to the size of nickels San Diego County, including Vista
(0.88”) fell in Hemet. 60-70 mph on 7.23, burning 150 acres and
winds hit the Hemet and Menifee causing power outages. The winds
region. in Hemet and Menifee downed
trees and flung lawn furniture.

98
7.24.2005 Thunderstorm winds were estimated A fence was blown over.
to 60 mph at Canyon Lake.

7.29.2005 Nickel size (0.88”) hail hit Buckman

Springs, ¾” hail hit Big Bear Lake,
Ranchita, and the Boulevard-Jacumba
area along I-8. Multiple reports of 60
mph wind gusts in Ranchita.

7.30.2005 1.5” hail hit Forest Falls and ¾” hail

hit Big Bear City.

9.20.2005 Numerous thunderstorms hit northern Lightning was the big problem,
San Diego County. knocking out power, starting a
number of tree fires from Carlsbad
to Escondido, and producing
damage to a school in Valley
Center.

3.10-11.2006 Large hail fell with a big winter storm.

On 1.10 1” hail fell in Escondido. Hail
was widespread throughout San Diego
county and even accumulated. On
1.11 a supercell thunderstorm went
through northern San Diego County
leaving 1” hail again in Escondido,
and 0.5” hail accumulated to 1” deep
from Carlsbad to Escondido.

4.5.2006 ¾” hail fell in Corona. Lightning caused damage to two

homes in Rialto. Thunderstorm
winds blew down trees in Mira
Loma.

7.9.2006 Lightning sparked the Sawtooth and The Sawtooth burned 62,000 acres,
Millard Wildfires near Morongo caused considerable damage in
Valley and Banning. Pioneertown and killed a man. The
Millard Fire burned 24,000 acres.

7.5.2006 A thunderstorm produced one inch

hail and 40-50 mph winds near
Boulevard and Tierra del Sol.

7.22.2006 Strong thunderstorm winds hit Lake A 40’ tree was blown over.
Elsinore.

99
7.23.2006 Strong thunderstorm winds hit Numerous trees were blown down,
Menifee. Lightning sparked the some of which fell on homes. The
Coyote Fire southeast of Anza. Coyote Fire burned 460 acres.

7.26.2006 A thunderstorm produced one inch

hail southeast of Julian.

9.2.2006 Thunderstorm winds were estimated In the Coachella Valley damage

at 58 mph in the Coachella Valley. was done to trees, power lines and
Nickel size hail fell near Campo. street signs.
Lightning sparked two fires near
Warner Springs.

9.6.2006 Strong thunderstorms produced strong Damage to trees, buildings, power

winds estimated at 70 mph. lines occurred from San Jacinto to
Temecula. Extensive damage to
wineries.

100
Tornadoes, Funnel Clouds, Waterspouts, and Damaging Dust Devils

Date(s) Weather Adverse Impacts

12.9.1898 A waterspout was observed off Mt. Vegetation was washed out,
Soledad – La Jolla and Pt. Loma for leaving bare rock exposed in
10 minutes. This was considered the considerable areas on the south
first such thing in history on this slope of Mt. Soledad.
stretch of coast. It was reported to
move ashore a few thousand yards.

3.11.1909 Two waterspouts observed several

miles off Pt. Loma for 20 minutes.

4.5.1926 A tornado hit San Diego. Waterspout 8 injured. Roofs torn off homes.
comes ashore in National City
resulting in the most damaging
tornado on record in San Diego
County.

4.27.1931 A waterspout and two funnel clouds

were sited off the coast of San Diego
during the morning.

9.20.1939 Two tornadoes reported in San Diego. Damage to garage. Debris.

3.16.1952 Tornado in Santa Monica. 3 dead in storm; damage.

6.25.1954 Tornado northeast of Victorville.

4.6.1955 Tornado north of Moreno Valley.

4.13.1956 Strong storm winds hit Chula Vista. Roof damage done to 60 homes
Counted officially as a tornado (one and extensively to a school. Two
witness, a Texas native, claimed it injured by flying glass. Trees
was). uprooted, TV antennas toppled and
windows shattered. 10 fish were
sucked out of San Diego Bay and
deposited on the ground.

1.29.1957 Waterspout off Ocean Beach. Two

funnel clouds observed over North
Island (possibly the waterspout) and
Mt. Soledad – La Jolla.

10.20-21.1957 Waterspouts were sighted off Point

Mugu and Oceanside.

101
4.1.1958 Tornado in Laguna Beach.

5.3.1959 A tornado hit North Island Naval Air Metal shelter was picked up. Power
Station. lines and trees down, debris
scattered.

10.8.1961 At least 10 waterspouts were observed Roof ripped off, trees felled, fences
between Del Mar and Oceanside. A downed in Carlsbad and Oceanside.
waterspout moved ashore to become a Three injured from flying objects.
tornado in Carlsbad. Three of the Boats torn from moorings in
waterspouts were observed off Del Oceanside. Damage to Carlsbad
Mar. SDG&E electric generator plant.

2.19.1962 Tornado in Irvine.

3.7.1964 Two waterspouts observed, one off

Oceanside and one off La Jolla.

12.13.1965 Waterspout observed around 1 pm.

Location unknown.

4.8.1965 Tornado in Costa Mesa.

11.7.1966 Tornadoes in Newport Beach and Property Damage.

Costa Mesa.

7.22.1966 Tornado in Victorville.

11.30.1970 A waterspout and three small funnel

clouds reported six miles west of San
Diego.

2.23.1971 A tornado 10 miles east of Brown No damage reported.

Field, Otay Mesa, near Mt. San
Miguel. At least six funnel clouds in
Chula Vista, Brown Field, and San
Ysidro. A waterspout off Imperial
Beach.

10.17.1971 Waterspout observed for 10 minutes

just west of Pt. Loma.

2.23.1973 Tornado near San Diego.

7.20.1974 Tornado in Hemet. Property damage.

10.22.1974 Tornado in Yucca Valley. Property damage.

10.29.1974 Tornado in Encinitas.

102
9.4-6.1976 Six tornadoes. 5 around El Mirage, Property damage.
west of Adelanto, one near Mt. Baldy.

3.16.1977 Tornado skipped from Fullerton to 4 injured. Damage to 80 homes.

Brea.

1.5.1978 Tornado in Costa Mesa at 9 pm. Trees fell and caused roof damage.
Roof damage, power lines down.

1.11.1978 Two waterspouts and several

waterspouts were reported off the
coast of La Jolla.

2.9.1978 Tornado in Irvine.

2.10.1978 Tornadoes in El Segundo and in In El Segundo, trees were hurled

Huntington Beach. onto parked cars. Power poles were
knocked down along a one mile
path. In Huntington Beach 6
injured; $3 million property
damage.

3.5.1978 A funnel cloud was reported from the

El Toro Marine Base.

12.19.1978 Tornado in Oceanside. 3 injured. $15,000 damage to

vehicles and structures.

1.5.1979 A waterspout came ashore and Several boats were tossed and
became a tornado at Mission Beach. damaged. A catamaran was tossed
50’ on to the boardwalk, damaging
it.

1.18.1979 Tornadoes in Tierrasanta and Midway Ripped up signs, sidings, street

- San Diego. The same tornado or lights, etc., and dropping debris in
other tornadoes may have hit Mission traffic in Midway. Lots of property
Hills and Encanto. damage in Midway, Encanto and
Mission Hills. Property damage in
Tierrasanta.

1.31.1979 Tornado in Santa Ana, possibly Numerous power outages.

elsewhere.

2.20.1980 Tornado in Clairemont - San Diego. Considerable property damage.

1.20.1982 Tornado in Riverside.

3.17-18.1982 Tornado at Lindbergh Field - San

Diego and at Loma Portal – Pt. Loma.
103
9.7.1982 Tornado in Landers. Property damage.

11.9.1982 Seven tornadoes touched down in the Property damage, especially with
LA Basin. Three of the tornadoes the Long Beach
began as waterspouts at Pt. Mugu, waterspout/tornado.
Malibu and Long Beach. The Long
Beach waterspout moved ten miles
inland, becoming an F2 tornado.
Another tornado reached F2 strength
in Van Nuys. Two other tornadoes
were in Garden Grove and Mission
Viejo.

3.1.1983 Two tornadoes around LA, an F2 and In all, 30 people were injured and
an F0. 100 homes were damaged. At 8 pm
one F2 tornado damaged seven
businesses and 50 homes in South
Central LA, caused 30 injuries and
lifted about one mile before
reaching the civic center. The F0
tornado injured a motorist when his
Cadillac was lifted 15’ and carried
across a highway in San Marino.

8.1.1983 Tornado in Landers. Property damage.

9.28.1983 Six funnel clouds sited off the coast of

San Diego.

1.13.1984 Tornado in Huntington Beach. Property damage.

1.27.1985 Funnel cloud west of Lindbergh Field.

2.3-4.1985 Tornado in Tierrasanta and Allied Eight mobile homes damaged.

Gardens - San Diego. Funnel clouds at Roofs torn off. Other property
Brown Field. damage.

9.18.1985 Tornado around the north shore of the

Salton Sea.

11.12.1985 Waterspout came ashore in Encinitas, $100,000s in damage. Forty

becoming a tornado. greenhouses damaged or destroyed,
roof flung on car, destroying it.
Trees down. Other property
damage.

11.25.1985 Funnel cloud sited at Imperial Beach.

104
2.25.1986 Waterspout reported 5 miles west of
Lindbergh Field – San Diego and
reported from Silver Strand. 2 funnel
clouds were reported near Pacific
Beach.

3.16.1986 Tornado in Anaheim near Disneyland. Property damage.

2.22-24.1987 Tornadoes and waterspouts in the

Huntington Beach area.

2.25.1987 Several funnel clouds and waterspouts Waterspouts damaged many boats
around San Diego County. One in Coronado harbors. A waterspout
waterspout was 7 miles west of picked up a dropped a 30’, 5-ton
Crystal Pier in Pacific Beach, another cabin cruiser. A dinghy was also
7 miles west of the San Diego River tossed and reported to have been in
channel. A funnel cloud was observed the air for 15-20 seconds.
off Imperial Beach.

7.27.1987 Tornado in Twentynine Palms.

9.1.1987 Thunderstorms hit San Diego Valleys What was reported as a dust devil
with lightning and strong damaging was probably a microburst or a
winds (possibly a tornado). tornado damaged awnings and
other items to mobile homes near
Lake Jennings. In El Cajon a tree
with an 8-inch trunk was snapped
in half.

9.24.1987 Two funnel clouds were reported

around Earp (on Colorado River).

1.18.1988 Tornadoes in Mission Viejo and San Property damage. A baseball

Clemente. dugout was blown 150 yards into
the middle of a city street.

1.14.1990 Tornado in East City Heights - San Property damage. Boats tossed in
Diego. A waterspout turned tornado Shelter Island.
hit Shelter Island – San Diego.

2.28.1991 Tornado in Tustin.

105
3.19-20.1991 Tornadoes in East City Heights and Property damage in San Diego. In
San Carlos areas of San Diego on San Carlos pines were ripped out
3.19. Tornadoes in Riverside and by roots, palm and cottonwood
Muscoy (near San Bernardino) on trees snapped in half. Cars were
3.20. Also on 3.20 a waterspout came smashed by falling objects, debris
ashore to become a tornado at Camp and patio furniture was strewn
Pendleton. Two other waterspouts throughout the neighborhood,
were seen off the coast there. including a refrigerator. A car was
moved 60’ by a falling palm.

3.26-27.1991 On 3.26 tornado at Vandenberg AFB. In Huntington Beach the roofs were
On 3.27 Tornadoes in Huntington taken off of six homes. Dozens of
Beach and rural San Marcos. The other homes were damaged and 50
tornado in Huntington Beach cut a mobile homes were severely
five-mile swath. damaged.

2.15.1992 Tornado in Camp Pendleton. Property damage.

12.7.1992 Tornadoes in Anaheim, Westminster, Property damage. Three carports

and Carlsbad. Waterspout 8 miles off and two mobile homes damaged in
San Diego coast. Another one 11.5 Carlsbad.
miles off Mission Beach.

12.29.1992 Tornado in San Clemente. Property damage.

1.18.1993 Tornado in Orange County. Funnel Property damage.

cloud in Hemet.

2.8.1993 Tornado in Brea. Property damage.

3.26-28.1993 Funnel clouds near Temecula and a

funnel cloud in Moreno Valley.

11.11.1993 Tornado in Portola Hills (near Tustin). 2 injuries; property damage.

2.7.1994 Tornado from Newport Beach to Roof and window damage. Trees
Tustin. blown down.

4.26.1994 Waterspout 11 miles southwest of

Camp Pendleton.

8.12.1994 Tornado in Valle Vista (east of Trees uprooted. Power poles blown
Hemet) and several funnel clouds in over. A home damaged and a trailer
Hemet. destroyed.

12.13.1994 Two waterspouts about 0.5 mile off

Newport Beach.

12.13.1995 Funnel cloud near Fullerton airport.

106
3.13.1996 Funnel cloud in Irvine, two southwest
of Moreno Valley, and one northwest
of Hemet.

5.25.1996 Funnel cloud 10 miles west of

Lindbergh Field - San Diego.

12.22.1996 Tornado in Cabazon. Threw a 5 ton mobile home 30’.

Minor damage to six other mobile
homes.

1.12.1997 A waterspout 2 miles southwest of Damage to resort.

Lindbergh Field - San Diego came
ashore at Shelter Island.

2.28.1997 Funnel cloud in Kearny Mesa - San

Diego.

4.2.1997 Funnel cloud 5 miles west of

Lindbergh Field - San Diego.

5.11.1997 Tornado in Apple Valley. Catastrophic damage to buildings,

structures, trees, power lines.

5.18.1997 Two tornadoes in Apple Valley and a Building and structure damage.
wet microburst. Estimated 130-140 Power lines arcing down and
mph winds. producing fires.

5.20.1997 Tornado 7 miles east of Borrego

Springs.

6.6.1997 Tornado in Hesperia. Destroyed a large fountain.

6.13.1997 Funnel cloud 2 miles northwest of

Lindbergh Field - San Diego.

8.6.1997 Funnel cloud in Pine Valley.

11.10-11.1997 A waterspout came ashore at Newport Minor power outages. Little

Pier 11.10 and quickly dissipated over damage. A fisherman was blown
western Costa Mesa. Winds were from one end of the Newport pier
estimated at 60 to 70 mph. to another. Property and vehicle
Tornado in Irvine 11.11, and another damage in Irvine from flying
funnel developed. debris. Ten cars were thrown a few
feet.

11.30.1997 Waterspout 6 miles south of Newport

Beach.

107
12.8.1997 Funnel cloud in Del Mar.

12.21.1997 Waterspout and tornado in Huntington Considerable damage to boats,

Beach developed from a supercell houses, and city property.
thunderstorm.

1.2.1998 Funnel cloud southwest of Chula

Vista.

1.9.1998 Waterspout 3 miles off Laguna Beach. Property damage in Long Beach.
Tornado at Long Beach

1.29.1998 Waterspout moves ashore on Property damage.

Moonlight Beach and becomes a
tornado at Encinitas

2.9.1998 Tornado in Cardiff - Encinitas and Minor damage.

Rancho Santa Fe.

2.17.1998 Waterspout off Point Loma.

2.24.1998 Tornado in Huntington Beach. Property damage, power outage.

Waterspout off Mission Beach. Roof travels 1/4 mile.

3.13-14.1998 Numerous waterspouts between Long

Beach, Huntington Beach and
Catalina. Funnel clouds in Phelan and
Hesperia.

3.28.1998 Funnel cloud in Dulzura.

3.31-4.1.1998 Numerous funnel clouds reported near

Orange and San Diego County coasts,
two of which became waterspouts off
Orange County. One waterspout
briefly hit the coast south of the
Huntington Beach Pier.

5.5.1998 “Apparent” tornado in San Bernardino Shredded metal siding in Rialto.

and Rialto

5.6.1998 Waterspout 1 mile west of North

Island.

5.13.1998 Tornado in Homeland. Funnel clouds Damage to mobile homes in

in Homeland and Moreno Valley. Homeland.

6.6.1998 Two funnel clouds off Dana Point.

108
9.2.1998 Funnel cloud in Pomona.

9.27.1998 Funnel cloud over Mission Beach.

12.5.1998 Funnel cloud 2 miles southwest of

Imperial Beach.

1.25.1999 Funnel cloud 1 mile off Costa Mesa

coast.

4.1-3.1999 Waterspout 6 miles off Newport

Beach on 4.1. Funnel cloud 3 miles
west of La Jolla on 4.2. Waterspout 3
miles southwest of Oceanside on 4.3.

4.7.1999 Funnel cloud 2 miles west of La Jolla.

4.12.1999 Funnel cloud northeast of Temecula.

6.3-4.1999 Funnel cloud 1 mile off San

Clemente. Waterspout off Laguna
Beach.

7.10.1999 Funnel cloud in Hesperia.

7.12.1999 Tornado 6 miles east of Julian. Building and structure damage.

Recorded wind speeds 43 mph. Trees uprooted and knocked over.

7.21.1999 Tornado in Shelter Valley. Property damage.

12.31.1999 Funnel clouds in Santa Ana and

Oceanside. Waterspout off Costa
Mesa coast.

2.21.2000 Tornado at Anaheim Hills. Property damage.

3.3.2000 Waterspout 3 miles west of La Jolla.

3.7.2000 Waterspout 10 Miles West of San

Clemente. Funnel cloud 2 miles west
of La Jolla.

6.14.2000 Funnel cloud in Phelan.

6.23.2000 Two funnel clouds around Hesperia.

6.25.2000 Funnel cloud 12 miles west of Ocean

Beach.

109
8.25.2000 Funnel cloud came within 200’ of the
ground in Jacumba.

9.7.2000 Funnel cloud over Carlsbad.

10.28.2000 Funnel clouds around Newport Beach

and Costa Mesa.

11.10.2000 Tornado in southeast Poway. Damage to 8 houses, trees uprooted

and knocked down, vehicles
moved.

1.10-12.2001 Funnel cloud at Orange County

Airport, Newport Beach on 1.10, and
Kearny Mesa - San Diego on 1.11.
Waterspout 3 miles west of Chula
Vista on 1.11 and 12 miles west of
Mission Beach on 1.12.

2.10-11.2001 Waterspout 2 miles west of La Jolla

and a funnel cloud 3 miles northwest
of La Jolla on 2.10.Waterspout 3
miles off Laguna Beach and two
waterspouts 1 mile west of Ocean
Beach on 2.11.

2.13-14.2001 Funnel clouds in Palm Desert on 2.13

and 9 miles west of Oceanside on
2.14.

2.24.2001 Tornado in Orange. Damage to a warehouse, 6

structures, fences, and telephone
wires.

2.27.2001 Several funnel clouds in Escondido. A

waterspout 10 miles west of San
Diego - Lindbergh Field.

3.6.2001 Funnel cloud in Yorba Linda.

4.9.2001 Two funnel clouds 4 miles southwest

of San Diego - Lindbergh Field.

5.28.2001 Two brief waterspouts 5 miles west of

Laguna Beach.

7.3.2001 Dust devil in Hesperia (may be a Blows off roof.

microburst or other thunderstorm
wind).
110
7.7.2001 Tornado at Twentynine Palms and Minor damage to homes and
Joshua Tree. businesses in Joshua Tree.

8.15.2001 Dust devil in Menifee. Damage to shed.

8.17.2001 Funnel cloud in Dulzura.

2.17.2002 Two funnel clouds around Carlsbad.

3.24.2002 Two funnel clouds around Carlsbad.

5.20.2002 Three funnel clouds and one

waterspout off the coast near Dana
Point.

10.26.2002 Funnel cloud 5 miles northeast of

Borrego Springs.

5.27.2003 Dust devil in Sugarloaf. Damage to three vehicles.

9.4.2003 Tornado in Joshua Tree - Yucca Extensive damage ($25K) to one

Valley. residence. Minor damage to 11
other residences. No injuries.

11.1.2003 Large waterspout between Laguna

Beach and Catalina Island.

8.14.2004 Tornadoes hit Yucca Valley and

Phelan.

9.5.2004 A strong dust devil hit Vista. Ripped a sign off a fence and threw
it 40’ away over a house.

10.17.2004 A tornado hit Oceanside. It was a Damage to structures, trees,

waterspout that came ashore. Funnel windows, etc.
cloud occurred near Carlsbad at Moon
Beach.

10.20.2004 Several funnel clouds offshore from

San Clemente.

10.21.2004 A waterspout was 2 miles southwest

of North Island.

12.28.2004 Tornadoes in Long Beach, Inglewood The tornadoes caused minor

and Whittier. A funnel cloud was damage to trees and roofs.
reported in Fullerton. A waterspout
was reported 10 miles west of
Oceanside Harbor.

111
1.2-4.2005 On 1.2: Funnel clouds were reported
10 miles west of Huntington Beach
pier, off Dana Point and northwest of
San Diego Bay. On 1.3: Funnel clouds
were reported in Fullerton and
Huntington Beach. On 1.4: A funnel
cloud was reported in Costa Mesa.

1.9.2005 A tornado hit Hemet. A funnel cloud The tornado picked up a storage
was reported in Mira Loma. shed in Diamond Valley and threw
it into a power pole.

2.19.2005 A waterspout moved ashore (within The tornado in Huntington Beach

100 yards of the pier) and became a damaged and downed trees and
tornado in Huntington Beach. power poles. Extensive damage to
Multiple waterspouts were reported. A cars, trees, roofs, fences, etc. in
super cell thunderstorm moved ashore Fallbrook, Rainbow and Temecula.
in Oceanside and spawned an F1
tornado that moved through
Fallbrook, Rainbow and Temecula.

2.22-23.2005 On 2.23 A tornado hit Chula Vista. The tornado stopped traffic on the
On 2.22 funnel clouds were reported 805 freeway.
in San Diego – Clairemont, Dana
Point, north of Victorville, and Mira
Loma. On 2.23 funnel clouds were
reported in La Jolla and Spring
Valley.

2.26.2005 A landspout-tornado hit Lake

Elsinore, lasting about 5 minutes.

3.4.2005 A tornado hit Fontana. A funnel cloud The tornado felled several trees and
was reported in Carmel Valley – Del power lines. Roof damage to three
Mar. homes. Roof taken off of building.

4.28.2005 Funnel clouds were reported in Hemet

and in Carlsbad.

5.6.2005 A waterspout was spotted off Imperial

Beach. A funnel cloud was reported
near Tustin.

7.23.2005 A tornado struck Hemet. Trees downed.

7.29-30.2005 Thunderstorms produced funnel

clouds in Mt. Laguna on 7.29 and in
the San Gorgonio Wilderness on 7.30.
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2.18.2006 A waterspout was observed 6 nautical
miles off Dana Point.

3.10-11.2006 On 3.10 a waterspout came ashore in In Encinitas a tree fell over a

Encinitas (becoming a tornado). On railroad track and halted traffic. In
3.11 a supercell thunderstorm Ramona trees were downed and
produced a waterspout off south some property damage was
Carlsbad. A tornado was later reported incurred.
in north Ramona from this storm.

4.5.2006 A funnel cloud was spotted in

Riverside near Highway 60 and I-215.

4.14.2006 A funnel cloud was observed over Del

Mar.

113
Strong winds (for thunderstorm related winds, see severe thunderstorms)

Date(s) Weather Adverse Impacts

10.2.1858 Category 1 hurricane hits San Extensive wind damage to property

Diego. Implied winds of 75 mph. (F2).

8.11-12.1873 A tropical storm hit San Diego with Damage to roof tops and felled
winds that “stiffened up to quite a trees.
gale”.

11.13.1880 Severe Santa Ana winds and Extensive damage.

sandstorms in Southern California.

2.24.1891 Strong and continuous storm winds Boats were smashed on shore. A
blew at 40 mph. roof was taken off a warehouse.

1.27.1916 All wind velocity records were

broken in San Diego. Peak wind 54
mph, with a max gust to 62 mph.
Average speed for the day was 26.2
mph.

1.10.1918 Strong offshore winds. Peak wind at Skies were full of dust with 300
San Diego was north at 31 mph at yards visibility. At noon visibility
6:38 am. was only a few miles.

11.25.1918 Strong windstorm produced a wind

gust of 96 mph at Mt. Wilson.

5.23.1932 Strong winds and low humidity. 12 serious brush fires resulted,
blackening nearly 2000 acres in
San Diego County. The biggest fire
was in Spring Valley.

3.5.1933 Strong east winds. A fire in De Luz area spread

rapidly westward and scorched
more than 800 acres.

9.24-25.1939 Tropical storm lost hurricane status 48 dead from sinking boats.
shortly before moving onshore at
San Pedro. Sustained winds of 50
mph.

2.11.1946 Icy cold winds in mountains of San

Diego County with gust 72 mph.

114
1.10.1949 Cold winter storm. Gust to 75 mph Plane crash kills 5 and injures 1
in the mountains of San Diego near Julian.
County, gust to 40 mph in San
Diego.

4.13.1956 Strong storm winds hit Chula Vista. Roof damage done to 60 homes
Possible tornado (one witness, a and extensively to a school. Two
Texas native, claimed it was). injured by flying glass. Trees
uprooted, TV antennas toppled and
windows shattered. 10 fish were
sucked out of San Diego Bay and
deposited on the ground.

11.21-22.1957 Extremely destructive Santa Ana Winds produced a 28,000 acre

winds. brush fire on a 40-mile front west
of Crystal Lake. People were
ordered off streets in some areas
due to flying debris.

11.5-6.1961 Strong Santa Ana winds fanned fires Fire in Topanga Canyon. 103
in Bel Air and Brentwood. 74° at 10 injured firemen, $100 million
pm at LA, 5° dew point. 3% relative economic losses including 484
humidity in Burbank on 11.6. buildings (mostly residential) and
6,090 acres destroyed.

9.26.1963 Santa Ana winds. Gusts over 50 Hottest heat wave west of
mph in the mountains of San Diego mountains in the county on record.
County.

11.19-20.1963 Strong storm winds. Hundreds of trees downed. Power

lines downed.

12.2-3.1966 Strong storm winds. Power outages.

1.18-28.1969 Strong storm winds. 4 dead from falling trees. Power

outages.

2.20-25.1969 Strong storm winds. Telephone, power, and gas outages.

9.26-29.1970 Gusts to 60 mph at Cuyamaca The Laguna Fire. 8 killed, 400

Rancho State Park. homes destroyed, 185,000 acres
burned as of 9.28 from Cuyamaca
to Alpine.

2.10-11.1973 Strong storm winds. 57 mph at Some 200 trees uprooted in Pacific
Riverside, 46 Newport Beach. Beach alone.

115
3.25.1975 Wind gust of 101 mph at Sandberg,
a California record.

2.4-10.1976 Strong storm winds: 64 mph at

Palmdale.

9.10.1976 Hurricane Kathleen brought the

southwest the highest sustained
winds ever associated with an
eastern Pacific tropical cyclone with
sustained winds of 57 mph at Yuma.

11.30-12.1.1982 Widespread strong wind with a big Power out to 1.6 million homes.
storm.

3.1.1985 Strong storm winds struck San Trees and antennas were toppled,
Diego County. causing numerous power outages.

3.26.1984 Ferocious winds strafed the Mojave Power outages, road closures. A
Desert with winds of 60-90 mph. CHP officer reported a car door
Peak wind at Mojave 103 mph, ripped off and hit by a sizable rock
Daggett 66 mph. near Indio and another car had its
windows blown out.

11.23.1986 Strong Santa Ana winds hit LA and An unfinished house in Glendale
mountain foothills. Gusts to 54 mph was blown to bits. Numerous beach
were recorded, but estimated gusts rescues were needed for sailors and
were 70 mph. Only 30-40 mph gusts windsurfers. Two sailboat masts
were estimated at Mt. Laguna. were snapped in a boat race at
Channel Islands.

1.20.1987 Wind gusts to 80 mph below Cajon Thick dust clouds. Trucks blown
Pass, 70 mph in San Bernardino, 60 over. Trees down. A hundred
mph at Mt. Laguna and 40 mph in power poles were down in the
El Toro. Inland Empire. Numerous power
outages. Schools closed in Fontana
as a result of power outages. A
mobile classroom was knocked
over. Brush fires were started.

2.6-7.1987 Santa Ana winds: Gusts up to 75 Plane flipped over at Brown Field.
mph Cuyamaca and Palomar Winds forced a sailboat into the
Mountain areas. Gusts to 60 mph hit rocks at Pt. Loma. I-8 was closed
Brown Field and Warner Springs, for two hours in eastern San Diego
40 mph in Julian and Valley Center. County. Trees, power lines and
35 mph at San Diego. fences were downed, causing
damage and power outages. A
highway sign fell on cars.
116
2.23-24.1987 Storm winds were clocked at 50
mph in Mt. Laguna. Gusts reached
34 mph at San Diego.

3.15.1987 Widespread strong storm winds. Power outages all over San Diego
Gusts to 40 mph at San Diego with metro area. Motor homes toppled
sustained winds 25-35 mph all day. in the desert. A light standard fell
over onto cars in Coronado. Boats
flipped over in harbors. A 22’ boat
turned over at Mission Beach jetty.
Catalina cruise ships were delayed,
stranding 1,200 tourists there.

11.18.1987 Santa Ana winds buffeted the

mountains and valleys.

12.4-5.1987 Strong Pacific storm brought gale Trees down, power outages.
force winds along the coast
exceeding 40 mph.

12.12-13.1987 Strong Santa Ana winds in San 80 power poles were blown down
Bernardino, with gusts to 60 mph. within a ½ mile stretch in Fontana
Gusts up to 80 mph around San and Rancho Cucamonga. One was
Bernardino. Strong damaging winds injured when a tree fell on a truck.
in San Diego County. 38 mph Downed tree limbs damaged cars,
recorded at San Diego. homes and gardens. Power poles
and freeway signs were damaged.
A parked helicopter was blown
down a hillside in Altadena. Trees
blown down and power outages in
San Diego County. One was killed
by a Eucalyptus tree falling on a
truck in Spring Valley.

12.15.1987 Strong storm winds of 100 mph at One truck overturned.

Wheeler Ridge in the Tehachapi
Mountains. 80 mph in San
Bernardino Co. Up to 70 mph gusts
at Pt. Arguello and gusts up to 60
mph gusts were clocked in Orange
Co. and the San Gabriel Mountains.

12.17.1987 A strong Alaskan storm brought Boats broke free of moorings at

strong winds. Shelter Island, San Diego.

117
1.17.1988 Major Pacific storm produced a gust Trees uprooted in the San Diego
to 64 mph from the west at San area. Boats in San Diego harbor
Diego - Lindbergh Field, highest damaged intensively. Apartment
wind on record. windows were ripped out in
Imperial Beach, where damage
estimated $1 million. Trees were
knocked down and debris was
strewn all around San Diego and
the zoo. Zoo was closed for the
first time in 72 years to remove
damage. Kelp beds were damaged.

1.21-22.1988 Strong offshore winds following a Power poles, road signs big rigs
major Pacific storm. Gusts to 80 knocked down in the Inland
mph at the Grapevine and gusts to Empire. In San Diego County, 6
60 mph at Ontario on the night of were injured, roofs were blown off
1.21. Gusts were reported up to 80 houses, trees were toppled and
mph in San Diego County on 1.22. crops destroyed. A barn was
demolished and a garage crushed
by a giant tree in Pine Valley. 20
buildings were destroyed or
damaged at Viejas. Avocado and
flower crops were destroyed in
Fallbrook and Encinitas,
respectively. Five greenhouses
were destroyed in Encinitas.

118
2.16-19.1988 Very strong Santa Ana winds: Gusts Numerous trees and power lines
of 90 mph at Newport Beach, 70+ downed and power outages all near
mph in the San Gabriel Mountain the foothills of the San Gabriel and
foothills on 2.17. Gusts to 76 mph at San Bernardino Mountains. On
Monument Peak - Mt. Laguna on 2.19 in Pauma Valley a mobile
2.18. Gust 63 at Ontario on 2.17, home was overturned and shingles
gust 50 at Rancho Cucamonga on were torn off roofs. Fontana
2.16. schools were closed due to wind
damage at schools. Three were
killed when a big rig truck
overturned and burned, one was
killed having stepped on a downed
power line). Power outages hit
200,000 customers in LA and
Orange counties. Minor structural
damage occurred to signs, etc.
Grass fires resulted. Roof damage
was widespread in communities
around Glendale and Pasadena.
Planes flipped in Burbank and at
John Wayne airports. Boats were
torn from moorings in Newport
Harbor.
5.29.1988 Gale force winds hit the coast. Gusts Hang glider crashed and died.
to 60 mph in the mountains, 45 mph Power went out. Brush fires started.
at LAX. Gusts to 40 mph at San
Diego.

11.30.1988 Santa An winds gusted to 75 mph at

Laguna Peak (Ventura Co.).

12.8.1988 Strong Santa Ana winds across Winds fanned several major fires.
Southern California. Gust 92 mph at Buildings unroofed, trees and
Laguna Peak (Ventura Co.). power lines brought down.
Estimated damage $20 million.

11.28.1989 Strong Santa Ana winds. Gusts to 70 Several tractor- trailer trucks were
mph at the Rialto Airport. overturned east of Los Angeles.

12.11.1989 Strong Santa Ana winds. Gusts to Winds reduced visibilities to near
100 mph near the Grapevine. zero in the desert areas, and closed
major interstate highways east of
Ontario.

119
3.18-19.1991 Storm winds gusted to 125 mph on Extensive damage in San Carlos
Laguna Peak (Ventura Co.). Winds area of San Diego.
of 60 mph in San Carlos area of San
Diego, probably a tornado.

10.26-27.1993 Santa Ana winds: gust 62 mph at Twenty fires ravaged Southern
Ontario. California including in Laguna Hills. 4
dead, 162 injured, $1 billion
economic losses in property alone
and 194,000 acres were destroyed.

12.24.1993 Santa Ana winds: gust 75 mph at

Ontario.

12.14.1996 Santa Ana winds: gust 111 mph at 2 killed from flying debris.
Fremont Canyon, gust 92 Rialto.

12.21-22.1996 Storm winds 40-50 mph.

1.5-6.1997 Storm winds: gust 99 mph at

Fremont Canyon, 58 mph
elsewhere.

1.29.1997 Santa Ana winds: gust 100 mph at Big rigs blown over.
Fremont Canyon, 87 Rialto.

8.20.1997 The remnants of Tropical Storm

Ignacio tracked northward moving
inland in central California with gale
force winds over portions of the
Southern California coastal waters.
This occurred during the strong El
Niño of 1997-98.

10.14.1997 Santa Ana winds: gusts 87 mph in Large fire in Orange County.
central Orange County.

12.10-12 .1997 Santa Ana winds: gust 96 mph at 2 killed from flying debris.
Pine Valley, 87 Upland. Property damage in Sun City. Crop
damage. Boats damaged and sunk
at Coronado and Avalon.

12.18-22 .1997 Gusts 60 mph at Rialto. Gusts 67 1 killed. Fire, trees down, and
mph at Idyllwild and below Cajon widespread wind damage.
Pass.

12.29 .1997 Gusts 60+ mph at Santa Ana.

120
2.3-4.1998 Strong storm winds: gust 60 mph at
Newport Harbor, 51 San Clemente.

2.23-24.1998 Strong widespread storm winds 40- Trees and power lines knocked
60 mph. down. Damage.

3.28-29.1998 Strong storm winds in Orange Trees down, power out, and
County: sustained 30-40 mph. Gust damage across Orange and San
70 mph at Newport Beach, gust 60 Diego Counties. 1 illegal
Huntington Beach. Gusts to 60 mph immigrant dead in Jamul.
in the mountains.

12.9-10.1998 Santa Ana winds: gust 101 mph at Trees and power lines down.
Modjeska Canyon, gust 93 Fremont Overturned vehicles. Property
Canyon, 52 Santa Ana, 83 Ontario. damage.

1.21.1999 Gust 80 mph in the Salton Sea area.

Gusts up to 70 mph in the Coachella
Valley, 47 Palm Springs, 36
Thermal.

2.10-12.1999 Santa Ana winds: gust 85 mph at I-8 closed.

Rialto, gusts to 80 mph reported
from I-8.

5.13.1999 Strong winds: sustained 61 mph at Roof and tree damage.

Borrego Springs.

11.22.1999 Gust 80 mph at Highland.

12.3.1999 Santa Ana winds: gust 90 mph at

San Bernardino, 68 Fontana.

12.10-11.1999 Gust 60 mph at Palm Springs.

12.21-22.1999 Santa Ana winds: gust 68 mph at House and tree damage in Hemet.
Campo, 53 Huntington Beach, 44
Orange.

1.5-6.2000 Santa Ana winds: gust 93 mph at I-15 closed.

Fremont Canyon, 60 Ontario, 58
Devore.

2.19.2000 Santa Ana winds: gust 92 mph at

Fremont Canyon.

2.21-23.2000 Winter storm winds: gust 75 mph Trees down at Lake Arrowhead.
along Highway 91.

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4.1.2000 Santa Ana winds: gust 93 mph at
Mission Viejo, 67 Anaheim Hills.

4.17-18.2000 Late winter storm: gust 68 mph in

the mountains of San Diego County.

11.7.2000 Santa Ana winds: gust 82 mph at

Fremont Canyon.

12.25-26.2000 Santa Ana winds: gust 87 mph at Damage and injuries in Mira Loma,
Fremont Canyon. and Orange and Riverside
Counties.

1.2-3.2001 Santa Ana winds: gust 52 mph at Viejas Fire. 5,500 acres burned.
Ontario, 60 Rialto. Trees and power lines down.

1.10-11.2001 Winter storm: gust 71 mph at

Phelan.

2.7.2001 Winter storm: gusts 50 mph at Palm

Springs and Thermal, 54 Fish Creek.

11.27.2001 Strong Santa Ana winds extend Damage. A boat accident off
offshore from the coast. Newport Beach.

12.7-8.2001 Santa Ana winds: gust 87 mph at Potrero Fire.

Fremont Canyon.

1.24.2002 Santa Ana winds.

2.8-10.2002 Santa Ana winds: gust 80 mph at Fire in Fallbrook area.

Descanso, 78 Fremont Canyon, 76
San Bernardino.

1.6-7.2003 Very widespread Santa Ana winds: 2 dead, 11 injured. Widespread

gust 100 mph at Fremont Canyon, property damage, road closures,
90 Ontario, 80 Upland, 72 Trabuco power outages, trees down,
Canyon, 70 Riverside, 58 Miramar. wildfires, crop damage.

10.25-27.2003 Santa Ana Winds: gust 56 mph at Unprecedented wildfires consumed

Descanso, 46 Anza, 45 Ontario, 43 hundreds of thousands of acres,
Fremont Canyon, 41 Beaumont, 40 killed over 20 people, caused over
Campo. one billion dollars in damage.

10.20.2004 A storm wind of 39 mph was

measured at Lindbergh Field from
the south, the strongest October
wind on record.

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11.21.2004 A cold storm brought wind gusts to
84 mph to Fremont Canyon.

12.16.2004 Santa Ana winds sustained 51 mph Big rigs blown over, closing a
with gusts to 78 mph at Fremont freeway for a short time. Other
Canyon. Gusts to 69 mph northwest damage.
of San Bernardino and 66 mph near
Pine Valley.

12.29.2004 A storm wind of 58 mph was Widespread wind damage across

measured at Lindbergh Field on the coasts and valleys.
12.29 from the south, the strongest
December wind on record. Wind
gusts to 69 mph at Julian, 60-65
mph gusts in the Inland Empire and
60 mph at Alpine.

2.3.2005 Strong storm winds of 70 mph hit Homes in Idyllwild were damaged
the region. by felled trees. Downed power
lines in the Inland Empire. Big rig
overturned on I-8.

4.7.2005 Strong winds in the Coachella Reduced visibility in La Quinta led

Valley. Gust of 52 mph at Thermal, to a 12 car pileup accident.
but likely stronger in the region.

1.2.2006 Post frontal winds more than 50 The “M” above Moreno Valley was
mph widespread across the region. demolished. Trees were downed,
power lines, power poles, on to
houses and cars. In Crestline there
were 20 homes left uninhabitable.
In San Diego Bay boats broke
loose from their moorings.

1.22-24.2006 Santa Ana wind event. Peak winds 7 big rigs overturned in Fontana.
occurred on 1.24 at Fremont Canyon Downed power lines and trees
at 71 mph. During these days, wind caused power outages and property
gusts exceeded 60 mph on 19 hourly damage. Roof of a car port torn off
observations. in Hemet. Dust storm closed
Ramona Expressway.

2.6-7.2006 Santa Ana winds blew. The Sierra Fire east of Orange
burned nearly 11,000 acres. Eight
minor injuries.

123
10.26.2006 Offshore winds blew to 40 mph in The Esperanza Fire was started by
the Banning Pass. an arsonist. It burned 40,200 acres
from Cabazon to San Jacinto. It
destroyed 34 homes and killed 5
firefighters.

11.29.2006 Offshore winds gusted to 73 mph at Widespread property damage and

Fremont Canyon (sustained 54 power outages as a result of
mph), 58 mph at Ontario. downed power lines, poles and
trees.

12.3.2006 Offshore winds gusted to 92 mph Downed power lines sparked a

with seven gusts over 75 mph in small fire in the Inland Empire. 16
northwest San Bernardino. Gusts to power poles were downed in
75 mph at Fremont Canyon. Valley Center.

12.27.2006 Strong storm winds hit the coast. Numerous trees were downed,
Gusts hit 54 mph at La Jolla, 52 damaging several vehicles.
mph at Torrey Pines and San
Clemente Island, 51 mph at Pt.
Loma, 49 mph at Huntington Beach,
46 mph at North Island and 40 mph
at San Diego Lindbergh Field.

124
Extreme Heat

Date(s) Weather Adverse Impacts

6.17.1859 133° in Santa Barbara from hot Roasted fruit on one side.
offshore (sundowner) winds.
Accuracy discredited as temperature
sensor was in full sun.

6.11.1877 112° observed in LA. It would be the

all-time record, but official records
didn’t begin until 20 days later.

3.28-29.1879 95° on 3.28 and 99° on 3.29 at San

Diego. 99° in LA on 3.29.

7.25.1891 109° in LA.

5.27.1896 124° at Salton (City), the national

maximum temperature for May.

4.25.1898 118° at Volcano Springs (east side of

Salton Sea, before the sea), the
national maximum temperature for
April. It was 117° at Salton (on the
west side of the “sea”).

6.23.1902 129° at Volcano Springs (east side of

Salton Sea, before the sea), the
national maximum temperature for
June. It was 127° at Salton (on the
west side of the “sea”).

11.12.1906 105° at Craftonville (now Crafton

Hills, near Redlands), the national
maximum temperature for November.

4.23.1910 100° in LA, a record for April.

7.10.1913 134° at Death Valley, the hottest

reading on record for the Western
Hemisphere. And the nation’s highest
temperature on record for July.
Sandstorm conditions accompanied
the heat.

9.17.1913 110° at San Diego.

125
6.16.1917 124° at Mecca climaxes the most
destructive heat wave of record in
California history.

2.25.1921 92° in LA, the hottest ever in

February.

9.16-17.1929 A hot spell hits San Diego. 111° in the

coastal valleys. A reading of 94° was
at San Diego at 4 am on 9.17.

12.8.1938 100° at La Mesa, the national

maximum temperature for December.

9.18-22.1939 95+° records at San Diego each day, Eight heat-related deaths in LA.
highest of 106° on 9.21. LA reaches
100° for seven consecutive days,
peaking at 107° on 9.20. On 9.20 it
was 107° in Escondido and 104° in
the San Diego - College area.

7.10.1940 97° at Santa Ana, 96° Laguna Beach.

9.2.1950 126° at Mecca, the national maximum

temperature for September.

8.31-9.7.1955 Heat wave. 110° in LA on 9.1, an all

time record.

7.17.1960 101° at Idyllwild.

9.26.1963 113° at El Toro, the hot spot in the Crop damage and animals killed.
nation for the date. 111° at Lindbergh Schools dismissed, workers sent
Field, highest temperature on record home, etc.
(95° at 8 am). 112° at El Cajon, 109° Surf temperature dropped from 70°
at Imperial Beach, 108° at Carlsbad, to 64° in one day due to the
Oceanside, Santee and Chula Vista, increased upwelling caused by
107° at SDSU, Lemon Grove, La offshore winds.
Mesa and Escondido, (only) 96° at
Coronado.

10.20-29.1965 A very long heat wave. A peak of

104° at San Diego on 10.22. LA had
10 consecutive days with afternoon
highs reaching 100 degrees.

126
11.1.1966 101° at LA airport, 100° at LA, the all Santa Ana winds fan fires, which
time November high, 97° at San killed 16 fire fighters.
Diego.

8.22.1969 110° at Cuyamaca.

9.25-30.1970 Drought in southern California came The Laguna Fire consumed whole
to a climax. Hot Santa Ana winds sent communities of interior San Diego
the temperature soaring to 105° at LA County were. Half a million acres
and 97° at San Diego on 9.25. were burned, and the fires caused
fifty million dollars damage.

8.11-13.1971 100° at Palomar Mountain.

9.12.1971 103° in LA.

7.28-30.1972 100° at Palomar Mountain.

6.9-13.1979 Five consecutive days of 90+° at San

Diego, peaking with 101° on 6.10.
Minima between 69° and 72°.

7.10.1979 123° at Palm Springs.

9.4-19.1984 Record minima set each day except

one at San Diego, ranging from 73° to
the highest minimum of all time of
78° on 9.9. 100° maximum on 9.8.

6.30.1985 100+° in parts of the city of San Fire in Normal Heights - San
Diego. Diego.

2.6.1987 A Santa Ana event brought warm

weather to the coast: 82° at San
Diego, 84° at Oceanside.

4.21-22.1987 A rare springtime weak Santa Ana Numerous small brush fires erupted
event brought 90°+ temperatures. 97° in the San Diego valleys.
in El Cajon, 95° in Spring Valley, 94°
in Santee, 93° at SDSU, Miramar, La
Mesa, LA and Borrego Springs. It was
91° in Poway, Escondido and
Fallbrook, and 87° in San Diego.

127
9.1.1987 A tropical air mass (remnants of
tropical storm Lidia) brought heat to
the region: 109° at the Wild Animal
Park, 106° in El Cajon, 105° in
Escondido and Santee, 99° at SDSU,
89° in National City and 83° at San
Diego.

10.3-4.1987 108° in LA on both days, a record for Dry weather and winds fuel the
October. It was 109° in El Cajon, 106° Palomar Mountain fire.
in Chula Vista, Fallbrook and Santee,
and 104° in San Diego on 10.3.

2.10-11.1988 Record heat from Santa Ana

conditions: On 2.10: 92° at San Juan
Capistrano, the nation’s high, 90° at
Lemon Grove, 88° at Los Angeles and
Escondido. On 2.11: 83° in San
Diego, 87° in many locations around
San Diego.
Santa Ana conditions brought temps
3.25-26.1988 Several brush fires resulted.
in the 90s all over the region and
record heat: 102° in Santee on 3.25,
97° throughout the San Diego
Valleys, 95° in LA and Santa Maria,
90° in San Diego.

4.6-7.1989 Daily high temperature records broken

at ALL recording stations in Southern
California. Many monthly record high
temperatures set for April: Some
highlights: 112° Palm Springs, 106°
LA, 104° Riverside, 103° Escondido,
101° Tustin, 98° San Diego, 95°
Victorville, 76° Big Bear Lake. Part
of major heat wave from late March
into mid April.

7.4.1989 115° at Dulzura.

5.5.1990 The high of 101° in downtown LA

was 8 degrees higher than their
previous record for the date.

7.28.1991 120° in Borrego Springs, 100° in

Campo.

128
8.12.1991 Tropical storm Hilda sent hot humid
air into the region. 94° at San Diego.

8.1.1993 123° at Palm Springs.

2.20.1995 95° in LA, the highest temperature on

record for February.

7.27-29.1995 Heat wave: 123° at Palm Springs on

7.28-29. 120° at Coachella, 113° San
Jacinto, 112° Riverside, 111°
Banning, Moreno Valley, and Sun
City. 110° at Yucaipa on 7.27.

8.2-7.1997 Heat wave: 121° at Thermal, 113° 5 deaths.

Brea, 110° Riverside and Ontario,
101° Julian. Low of 93° at Palm
Springs on 8.5.

7.16.1998 120° at Palm Springs, 118° Borrego

Springs (127° Death Valley).

7.27.1998 123° at Thermal, 119° at Borrego

Springs, 118° Palm Springs.

8.29-31.1998 Record heat near coast. 112° at Yorba Firefighters were slowed while
Linda and the Wild Animal Park, 110° battling blazes at Lake Jennings
at El Cajon, Hemet and Riverside, and Camp Pendleton.
108° at Ramona, 106° in Vista and
Escondido, over 100° in most of
Orange County. 114° at Dulzura on
8.29.

5.7-9.2001 Heat wave. 109° at Palm Springs,

Thermal, and Borrego Springs, 103°
at Hemet, 102° San Bernardino.

9.1.2002 Tropical heat wave: 118° at Dulzura,

113° Temecula, 112° Riverside and
Menifee. Sharp temperature gradients:
77° at Newport Beach to 107° Santa
Ana (10 miles), 72° Oceanside Harbor
to 87° Oceanside Airport (2 miles),
81° Sea World to 91° San Diego -
Lindbergh Field (3 miles).

129
7.10-20.2005 Strong high pressure brought a One death in the Anza Borrego
lengthy heat wave to the region. 121° Desert. Near record power
in Thermal, 120° in Palm Springs and consumption.
Borrego Springs, 116° in Hesperia.
Big Bear Lake tied their all-time
record at 94° on 7.18. 98° at Idyllwild.
Low temperature at Indio was 90° on
7.13.

7.22.2006 A major heat wave with humidity, in 16 were killed from the heat, and
some ways unprecedented, hit many more were treated. Some
Southern California. 121° in Palm power outages occurred.
Springs, 120° at Indio and Thermal,
114° at Ontario and the Wild Animal
Park, 113° at El Cajon. It was 112° at
Escondido and 109° in La Mesa (both
highest all time). Record minimum
temperatures were recorded in most
places. Desert locations reported the
all-time warmest month on record.
Sea temperatures hit 80°.

130
Extreme Cold

Date(s) Weather Adverse Impacts

1.9.1888 Cold wave. Freezing temperatures in Loss of citrus crop.

citrus growing areas.

12.23-30.1891 Cold wave. 0.5” thick ice in San Diego pools,

1” thick ice on oranges on trees in
Mission Valley.

12.17.1897 26° at Riverside.

1.6-7.1913 25° at San Diego on 1.7, the lowest Killing freeze all over San Diego
temperature on record. 28° on 1.6 County and many crops and fruit
with a high temperature of only 45°, lost. Water pipes frozen, trolley
the lowest maximum temperature on lines disrupted, fishing nets
record. Also on 1.7: 4° at Campo, 9° unusable. Ice skating in a San
Cuyamaca, 13° Alpine , 15° Julian Diego fountain on ice 0.75” thick.
and Lakeside, 20° El Cajon, 22° Extreme damage to citrus crop all
Lemon Grove, 24° La Mesa, and 26° over California. This directly led to
Chula Vista. the establishment of the U.S.
Weather Bureau’s Fruit Frost
forecast program.

12.14.1920 Frost was observed at the bay side in

San Diego.

1.22.1937 19° at Palm Springs.

1.4.1949 8° at Palomar Mountain.

1.25.1949 -4° at Cuyamaca. The lowest temperature ever

recorded in San Diego County.

1.5.1971 1° at Idyllwild.

1.29.1979 -25° in Big Bear Lake. The lowest temperature ever

recorded in Southern California.

1.16-18.1987 A very cold air mass remained over Substantial avocado crop loss in the
the region. It was 10° at Mt. Laguna, millions of dollars. Two homeless
17° at Bonsall, 22° at Valley Center, died of hypothermia on 1.17.
24° in Poway, 26° in El Cajon, 31° in
Chula Vista and 36° at San Diego. On
1.17 it was 24° in Fallbrook, 28° in
Del Mar

131
2.22-25.1987 Lows below 40° at Lindbergh for
three consecutive days (coldest stretch
since 1978).

12.14-15.1987 13° in Mt. Laguna, 18° in Campo, 23° Minor damage to crops.
in Valley Center, 24° in Escondido,
28° in El Cajon, 31° in Del Mar, 32°
in Imperial Beach, 33° in Chula Vista.

12.25-26.1987 9° at Mt. Laguna and 22° in Valley Extensive damage to avocado and
Center on 12.25. On 12.26: 15° in citrus crop.
Julian and Mt. Laguna, 16° in Campo,
22° in Poway, 26° in El Cajon, 30° in
Del Mar, 37° at San Diego.

12.24-30.1988 A week of subfreezing temperatures 5 people died as a result of the

in Southern California. cold.

2.14.1990 A wind chill of -25° was reported at

Mt. Laguna. High temperature was
52° at San Diego – Lindbergh Field.

6.3.1999 The high temperature of 38° at Mt.

Wilson became the lowest high
temperature on record for June.

12.26.1997 0° at Big Bear Lake, 4° Big Bear

Airport.

12.7.1998 30° at Capistrano Beach and Dana

Point, 29° at Mission Viejo and San
Clemente.

6.3.1999 Unseasonably cold air mass brings

record cold so late in the season.
Highs of 42° at Palomar Mountain
and Mt. Laguna.

2.14.2001 0° at Wrightwood.

1.30-31.2002 13° at Shelter Valley, 17° Campo, 22° Crops damaged in northern San
Ramona, 28° Escondido. Diego County.

12.1-3.2004 30s at the coast, 20s in inland valleys Crops were damaged.
and deserts, teens and single digits in
the mountains. 8° on all three
mornings at Big Bear. Wrightwood
dipped to 9°.

132
High Surf, Stormy Seas, Tsunamis, Coastal Flooding and Erosion

Date(s) Weather Adverse Impacts

7.10.1855 An earthquake in LA causes two large

swell to hit Dana Point.

8.23.1856 A 7.8 magnitude earthquake in Japan.

San Diego Bay rises 12' over the high
water mark.

5.27.1862 A 5.9 magnitude earthquake causes

landslides into San Diego Bay and 3-4'
wave runup.

8.13.1868 Two earthquakes near 8.5 magnitude

off Chile produce 2.64' wave height in
San Diego.

8.7.1906 Tsunami in San Diego from local sea

quake.

1927 A tsunami hit Southern California,

raising the ocean by 6’.

8.21.1934 Tsunami in San Diego with 20'

maximum amplitude from local sea
quake.

12.12.1937 High surf. Three piers ripped out from LA to

Santa Barbara.

9.24.1939 Tropical storm. 50 mph winds. 48 dead from sinking boats.

Extremely large waves. Harbors damaged.

4.1.1946 An 7.8 magnitude earthquake hits the

Aleutian Islands. Newport Harbor
shows a 5' drop in tide. San Pedro
shows a 2.5' jump in tide.

1.4-5.1959 High surf from a big storm. Coastal damage in San Diego and
Orange Counties. Boats and
harbors damaged.

133
5.22-24.1960 An 8.5 magnitude earthquake hits Docks near Pt. Loma were
Chile. Waves 8' above normal hit San destroyed. A barge broke in half.
Diego. Tide currents estimated at 20- Extensive damage to docks
25 kts. throughout the harbor. In LA:
scuba diver drowned, major
damage to small craft, $1 million
damage.

2.9-11.1963 High surf from a big storm. Damage to coastal homes and
structures.

3.28.1964 An 8.4 magnitude earthquake hits Damage.

Alaska. Tsunami reaches all of
California. 2' maximum amplitude in
San Diego, 6.4' rise in 10 minutes.

11.29.1975 A 7.2 magnitude earthquake hits Damage.

Hawaii. Tsunami hits Catalina. 2.4'
maximum amplitude in San Diego.

2.13-21.1980 Large waves hit coast. Coastal flooding

at Mission Beach; water over
boardwalk and into houses.

1.22-29.1983 A series of storms produces surf up to On 1.26 several piers were heavily
20’ high. High tides and surf produce damaged in Santa Monica, Seal
the peak of the damage on 1.26. Beach and Crystal Pier in Pacific
Beach. Flooding damage to
numerous businesses and homes in
Malibu, Venice, Redondo Beach.
Residents were evacuated from
Seal Beach and Sunset Beach.
Several injuries to people swept off
rocks.

3.2-3.1983 Waves 15-20’ hit the coast around LA.

2.14-17.1986 High surf from a big storm. 2 drowning deaths.

12.1-2.1986 High tides of 7.7’ at San Diego. Minor flooding at La Jolla Shores’
parking lot. A few beach closures.
On 12.1 minor flooding (4” of sea
water) along Pacific Coast Hwy. in
Huntington Beach from rising tides
prompted lane closures.

134
12.31.1986 High tide in San Diego 7.8’. In Eureka Luckily the weather was fine and
the tide was 9.1’, thought to be the surf was small. Minor flooding at
highest in a century. coastal low spots on Mission Beach
and Ocean Beach. Water lapping at
the curbs of streets in Balboa
Island, Newport Beach.

1.12.1987 Waves of 6-9’ with sets up to 12’ hit One suspected drowning. 11’ boat
the coast. swamped.

2.2-4.1987 On 2.2 5-6’ waves hit the coast. Large surf inundated Seacoast Dr.
in Imperial Beach. A man and his
son were swept off Sunset Cliffs
and died.

2.6.1987 A 20’ rogue wave capsized a 10 of 12 boaters died.

sportfishing boat off San Quintin, Baja.

12.16.1987 Stormy seas resulted from a strong 6 were rescued and 3 feared dead in
Alaskan storm. a sinking of a fishing boat near
Santa Barbara Island. A barge and
fishing boat uprooted moorings and
smashed into a wharf, and three
sailboats were thrown onto the
beach in Santa Barbara.

1.18-19.1988 Surf rose to 20’ along beaches, some 8 killed, 3 reported missing all over
breakers to 25’. Southern California. More than $68
million damage caused by surf.
Boulders protecting Mission Bay
were washed away. Asphalt and
dunes were washed out in
Coronado. Mission Beach condos
flooded by ocean water and kelp;
3’ of kelp landed in a front yard
and more kelp went through a
garage window! A boat was
capsized. 7 beach swimmers were
missing and 4 presumed drowned
on 1.21.

2.17.1988 Santa Ana winds reach 60 mph in LA 3 killed when truck overturned and
and Orange Counties. burned. 1 killed having stepped on
a downed power line. Power
outages (200,000 customers in LA
and Orange Co.). Minor structural
damage to signs, etc. Grass fires.

135
4.30.1988 An earthquake 46 miles west of San
Diego generates large surf of 14' with
sets to 20'.

5.29.1988 Gale force winds cause stormy seas. Avalon Harbor was closed after
several boats were driven ashore or
scattered. One boater presumed
dead. In Mission Bay one was
injured when a catamaran was
capsized. Piers were closed and
surf claimed part of a restaurant in
Redondo Beach. Boats were
capsized around San Pedro. Two
boaters died. Several boats were
smashed against the rocks in
Avalon Harbor.

3.19.1991 Strong storm winds created large A 33’ sailboat was blown aground
waves and surf. and destroyed at Pt. Loma.

7.24-26.1996 7-10’ surf with sets to 12’ generated by 500+ rescues made at Southern CA
an intense South Pacific storm south of beaches.
Tahiti.

8.17-19.1997 Tropical storm Ignacio produces 18'

waves in Orange County.

9.4.1997 Hurricane Linda became the strongest

storm recorded in the eastern Pacific
with winds estimated at 180 mph and
gusts to 218 mph. For a time it
threatened to come ashore in California
as a tropical storm, but the storm
turned away, affecting the state with
high surf: 15-18' waves at the Wedge at
Newport Beach.

9.25-26.1997 Hurricane Nora produces waves 20'+ at Tidal flooding over a 14 block
Seal Beach. stretch in Seal Beach.

12.7-8.1997 Coastal erosion in Laguna Beach.

1.30.1998 High surf. Coastal damage.

136
2.23-28.1998 High surf from a big storm combined Coastal damage and flooding
with high tides. (damage to Ocean Beach Pier).
Several homes destroyed in San
Diego County. Rocks were on
highway 101 in Cardiff. Parking
lots of restaurant row were littered
with rocks and debris up to 1’ deep.
Restaurants forced to cover
windows with plywood.

10.27.2000 Heavy rain and very high tides. Coastal inundation and flooding at
Sunset Beach (Seal Beach).

1.9.2001 Very high tide, but only 4' surf. Surfside in Seal Beach flooded.

11.27.2001 Strong winds off the coast. Boat accident off Newport Beach.

9.5-6.2004 Large surf from Hurricane Howard. More than 1,000 rescues during the
Waves 6-12’ throughout Orange hottest day of the year at the beach.
County. Water temperature 72°. Estimated 575,000 beach visitors.

1.8.2005 Large waves on top of very high tides Coastal flooding of PCH and
greater than 7’. boardwalk at Seal Beach.

12.21.2005 A powerful storm in the east Pacific Broken surfboards, rescues, beach
generated large surf with sets of 20’. erosion. All piers were shut down.
Surf flooded a parking lot in
Carlsbad and floated several cars.
Boardwalk damage in Dana Point.
Tow-in surfing occurred 1.5 miles
off Seal Beach.

12.27.2006 Strong storm winds generated large

surf. Highest sets were 10-16’. Surf
was reported at 10-12’ with a 3 second
period at Newport Beach.

137
Miscellaneous: Dense fog, barometric pressure, dry spells, etc.

Date(s) Weather Adverse Impacts

2.17.1883 Highest barometric pressure at San

Diego: 30.53”.

8.16.1909 A dry spell began in Bagdad, central

San Bernardino County, lasted until
5.6.1912, a stretch of 994 days!
(Southern Pacific RR employees kept
this debated record).

5.6.1912 It rained in Bagdad, ending a national

record dry stretch of 994 consecutive
days that began on 8.16.1909.
(Southern Pacific RR employees kept
this debated record).

10.3.1912 A dry spell began in Bagdad, CA,

lasting 767 days and ended on
11.9.1914. (Southern Pacific RR
employees kept this debated record).

11.9.1914 In Bagdad, rain finally fell ending an

incredible dry spell at 767 days that
started on 10.3.1912. (Southern Pacific
RR employees kept this debated
record).

12.31.1929 Greenland Ranch, in Death Valley,

California, went the entire year without
measurable precipitation.

3.3.1983 Lowest barometric pressure at San

Diego: 29.37”.

12.15.1969 Dense fog in Orange County. 100+ vehicle pile up on I-5.

11.10.1980 Dense fog in San Bernardino. 24 vehicle pile up on I-15. 7 dead,

17 injured.

2.21.1985 A sticky white rain fell across Southern Everything was covered with fine
California. Apparently, strong winds white grit, slightly alkaline, but
blew dust from the dry Owens and non-toxic.
China Lakes and mixed with rain
clouds.

138
1.17.1988 Lowest barometric pressure at Los
Angeles: 29.25”.

12.31.1989 Santa Maria reported their driest year

of record with just 3.3”of precipitation.

2.14.2000 Dense fog at Cajon Pass. 71 vehicle pile up on I-15. 22

injured. I-15 closed for 4 hours.

10.24.2001 Dense fog in Inland Empire. 39 vehicles pile up in 13 separate

accidents on I-215 in Perris. 8
injured.

11.3.2002 Dense fog in south LA. 194 vehicles were involved on two
pileups on the 710 freeway. 0
deaths and 41 injuries.

139
Appendix B - Weather Glossary
Acid Rain: Cloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen, to
make them acidic (eg. pH <7.0). < 7.0)

ACCAS: An acronym for Altocumulus Castellanus.

Adiabatic Process: The change of temperature of air without transferring heat. In an adiabatic
process compression results in warming, and expansion results in cooling.

Advanced Weather Information Processing System (AWIPS): NWS computer workstations

that integrate graphics, including computer models, satellite and radar imagery.

Advection: The horizontal transport of air or atmospheric properties. Commonly used with
temperatures, i.e., “warm air advection”.

Advection Fog: Fog that forms as warmer, moist air moves over a cold surface. The air is cooled
to saturation by the loss of heat to the cold surface.

Advisory: Advisories are issued for weather situations that cause significant inconveniences but
do not meet warning criteria and, if caution is not exercised, could lead to life-threatening
situations. Advisories are issued for significant events that are occurring, are imminent, or have a
very high probability of occurrence.

Air Mass: A large body of air having similar horizontal temperature and moisture
characteristics.

Air Mass Thunderstorm: Generally, a thunderstorm not associated with a front or other type of
synoptic-scale forcing mechanism. Air mass thunderstorms typically are associated with warm,
humid air in the summer months; they develop during the afternoon in response to insolation,
and dissipate rather quickly after sunset. They generally are less likely to be severe than other
types of thunderstorms, but they still are capable of producing downbursts, brief heavy rain, and
(in extreme cases) hail over 0.75” in diameter. Also, see Pulse Thunderstorm, Popcorn
Convection and Single Cell Thunderstorm.

AIRMET (AIRman's METeorological Information): This NWS aviation product advises of

weather that maybe hazardous, other than convective activity, to single engine, other light
aircraft, and Visual Flight Rule (VFR) pilots. However, operators of large aircraft may also be
concerned with these phenomena.

Air Parcel: An imaginary small body of air that is used to explain the behavior of air. A parcel is
large enough to contain a very great number of molecules, but small enough so that the
properties assigned to it are approximately uniform throughout.

Air Pressure: The force exerted on a surface by the weight of the air above it. The
internationally recognized unit for measuring this pressure is the kilopascal.
140
Air Stagnation: A meteorological situation in which there is a major buildup of air pollution in
the atmosphere. This usually occurs when the same air mass is parked over the same area for
several days. During this time, the light winds cannot “cleanse” the buildup of smoke, dust,
gases, and other industrial air pollution.

Air Transportatable Mobile Unit (ATMU): A modularized transportable unit containing

communications and observational equipment necessary to support a meteorologist preparing on-
site forecasts at a wildfire or other incident.

Albedo: The percentage of incoming radiation reflected by a surface.

ALERT Flood Warning System: A cooperative, community-operated flood warning system;

the acronym stands for Automated Local Evaluation (in) Real Time. See also Automated Local
Evaluation in Real Time (ALERT).

Aleutian Low: A semi-permanent, subpolar area of low pressure located in the Gulf of Alaska
near the Aleutian Islands. It is a generating area for storms and migratory lows often reach
maximum intensity in this area. It is most active during the late fall to late spring. During the
summer, it is weaker, retreating towards the North Pole and becoming almost nonexistent.
During this time, the North Pacific High pressure system dominates.

Algorithm: A computer program (or set of programs) which is designed to systematically solve
a certain kind of problem. Numerical Prediction models have algorithms programmed into them
to determine derived fields, such as precipitation or rising motion. WSR-88D radars (NEXRAD)
employ algorithms to analyze radar data and automatically determine storm motion, probability
of hail, VIL, accumulated rainfall, and several other parameters.

Altimeter: An instrument that indicates the altitude of an object above a fixed level. Pressure
altimeters use an aneroid barometer with a scale graduated in altitude instead of pressure.

Altimeter Setting: That pressure value to which an aircraft altimeter scale is set so that it will
indicate the altitude above mean sea-level of an aircraft on the ground at the location for which
the value was determined.

Altitude: Height expressed as the distance above a reference point, which is normally sea level
or ground level.

Altocumulus (Ac): These clouds are composed of mainly water. They appear as white or gray
colored roll like elements or bands. The individual elements are large and darker than in
cirrocumulus clouds. These clouds form between 6,500 and 23,000 feet.

Altocumulus Castellanus (ACCAS): They are middle level convective clouds and possibly they
should be classified as clouds with extensive vertical development. They are composed of mainly
water vapor. They are characterized by their billowing tops and comparatively high bases. These
clouds form between 6,500 and 23,000 feet. These clouds are a sign of instability aloft, and may
precede the rapid development of thunderstorms.
141
Altocumulus Standing Lenticular (ACSL): These clouds are formed on the crests of waves
crested by barriers in the wind flow, such as mountains. The clouds show little movement and
have the shape of a lens, hence the name standing lenticular. Wind, however, can be quite strong
blowing through the cloud. They are characterized by their smooth, polished edges and may look
like a stack of pancakes or a UFO. These may also form on wave crests. They are composed of
mainly water vapor and form between 6,500 and 23,000 feet.

Altostratus (As): It is a bluish veil or layer of clouds having a fibrous appearance. The outline of
the sun may show dimly as through frosted glass. It often merges gradually into cirrostratus. As
with cirrostratus, it often is part of a cloud shield associated with a front. This type of cloud is
composed of mainly water vapor and result from lifting a layer. These clouds form between
6,500 and 23,000 feet.

Anabatic Wind: A wind which blows up a steep slope or mountain side. It is also known as an
upslope flow. These winds typically occur during the daytime in calm sunny weather. A hill or
mountain top will be radiatively warmed by the sun which in turn heats the air just above it. See
Katabatic Wind.

Anemometer: An instrument that measures wind speed.

Aneroid Barometer: An instrument designed to measure atmospheric pressure. It contains no

mercury (Hg).

Anticyclone: An area of high pressure around which the wind blows clockwise in the Northern
Hemisphere and counterclockwise in the Southern Hemisphere. At the center of the circulation,
there is sinking air. Generally, this sinking air provides clear skies.

Anvil: The flat, spreading top of a Cumulonimbus Cloud (Cb). Thunderstorm anvils may spread
hundreds of miles downwind from the thunderstorm itself, and sometimes may spread upwind.

Apparent Temperature: A measure of human discomfort due to combined heat and humidity. It
measures the increased physiological heat stress and discomfort associated with higher than
comfortable humidity. The apparent temperature is less than the actual air temperature when the
humidity is relatively low and that the apparent temperature indicates the reduced stress and
increased comfort associated with the higher rate of evaporative cooling of the skin.
.
Arctic Air: A mass of very cold, dry air that usually originates over the Arctic Ocean north of
Canada and Alaska.

Arctic High: A very cold high pressure that originates over the Arctic Ocean.

Area Forecast Discussion (AFD): This NWS product is intended to provide a well-reasoned
discussion of the meteorological thinking which went into the preparation of the Zone Forecast
Product. The forecaster will try to focus on the most particular challenges of the forecast. At the
end of the discussion, there will be a list of all advisories, watches and warnings that are not
short-fused (lasting less than 6 hours).
142
Arid: An adjunctive applied to regions where precipitation is so deficient in quantity, or occurs
at such times, that agriculture is impracticable without irrigation.

Arroyo: A water-carved channel or gully in arid country, usually rather small with steep banks,
dry most of the time, due to infrequent rainfall and the shallowness of the cut which does not
penetrate below the level of permanent ground water.

ASOS: An acronym for Automated Surface Observing System.

Atmosphere: The gaseous envelope surrounding the earth, composed primarily of nitrogen and
oxygen.

Atmospheric Pressure: The pressure asserted by the mass of the column of air directly above
any specific point (also called air pressure or barometric pressure).

Atmospheric Stability: An indication of how easily a parcel of air is lifted. If the air is very
stable it is difficult to make the parcel rise. If the air is very unstable the parcel may rise on its
own once started.

Aurora: A glowing light display in the nighttime sky cause by excited gases in the upper
atmosphere giving off light. In the Northern Hemisphere, it is called the aurora borealis (northern
lights). In the Southern Hemisphere, it is called aurora australis (southern lights).

Automated Local Evaluation in Real Time (ALERT): A local flood warning system where
river and rainfall data area collected via radio signals in real-time at an ALERT base station.

Automated Surface Observing System: ASOS serves as the nation's primary surface weather
observing network. It is designed to support weather forecast activities and aviation operations
and, at the same time, support the needs of the meteorological, hydrological, and climatological
research communities.

Avalanche: A mass of snow, rock, and/or ice falling down a mountain or incline. In practice, it
usually refers to the snow avalanche. In the United States, the term snow slide is commonly used
to mean a snow avalanche.

Aviation Area Forecast (FA): This NWS aviation product is a forecast of clouds and weather
conditions over an area as large as the size of several states. It must be used in conjunction with
Airmet bulletins for the same area in order to get a complete picture of the weather. The area
forecast together with the Airmet Sierra bulletin are used to determine forecast enroute weather
and to interpolate conditions at airports which do not have terminal forecasts (FT's) issued.

Aviation Weather Center (AWC): One of the National Centers for Environmental Prediction.
The Aviation Weather Center (AWC), located in Kansas City, Mo., enhances aviation safety by
issuing accurate warnings, forecasts and analyses of hazardous weather for aviation interests.
The Center identifies existing or imminent weather hazards to aircraft in flight and creates
warnings for transmission to the aviation community. The Center also originates operational
143
forecasts of weather conditions that will affect domestic and international aviation interests.

AWIPS: Advanced Weather Information Processing System. NWS computer workstations that
integrate graphics, including computer models, satellite and radar imagery.

Back-Building Thunderstorm: A thunderstorm in which new development takes place on the

upwind side (usually the west or southwest side), such that the storm seems to remain stationary
or propagate in a backward direction.

Back Door Cold Front: A cold front moving south or southwest, the opposite of typical cold
fronts which move eastward.

Backing: A counterclockwise change in wind direction with increasing height in the atmosphere.
For example, the wind direction would change from the north at the ground to the northwest
aloft. This is indicative of the airmass cooling or cold air advection (CAA).

Bar: An obstacle formed at the shallow entrance to the mouth of a river or bay.

Baroclinic Zone: A region in which a temperature gradient exists on a constant pressure surface.
Baroclinic zones are favored areas for strengthening and weakening systems; barotropic systems,
on the other hand, do not exhibit significant changes in intensity. Also, wind shear is
characteristic of a baroclinic zone. See Barotropic System.

Barometer: An instrument for measuring atmospheric pressure. The two most common types
are the mercury barometer and the aneroid barometer.

Barometric Pressure: The actual pressure value indicated by a pressure sensor.

Barotropic System: A weather system in which temperature and pressure surfaces are
coincident, i.e., temperature is uniform (no temperature gradient) on a constant pressure surface.
Barotropic systems are characterized by a lack of wind shear. See Baroclinic Zone.

Base Reflectivity (R): This WSR-88D radar product depicts a full 360° sweep of echo intensity
data. It is available for every elevation angle that is sampled in a volume scan. It is used to
observe precipitation intensity and movement; determine storm structure; estimate hail potential;
locate boundaries (cold front, outflow, sea breeze, etc.); identify cloud layers; and detect light
snow, drizzle, birds, insects, and smoke plumes.

Base Velocity (V): This WSR-88D radar product depicts a full 360° sweep of radial velocity
data. It is available for every elevation angle that is sampled in a volume scan. It is used to
estimate wind speed and direction; determine regions of significant shear (convergence, etc.);
locate boundaries (cold front, outflow, sea breeze, etc.); identify areas of circulation; and
determine storm structure.

Beach Erosion: The carrying away of beach materials by wave action, currents, tides, or wind.

144
Bermuda High: A semi-permanent, subtropical area of high pressure in the North Atlantic
Ocean off the East Coast of North America that migrates east and west with varying central
pressure. Depending on the season, it has different names. When it is displaced westward, during
the Northern Hemispheric summer and fall, the center is located in the western North Atlantic,
near Bermuda. In the winter and early spring, it is primarily centered near the Azores in the
eastern part of the North Atlantic. Then it may be referred to as the Azores High.

Best Track: A subjectively smoothed path, versus a precise and very erratic fix-to-fix path, used
to represent tropical cyclone movement. It is based on an assessment of all available data.

Black Ice: Thin, new ice on fresh or saltwater, appearing dark in color because of its
transparency; also popularly applied to thin hazardous ice coverings on roads.

Blizzard: A winter storm which produces the following conditions for at least 3 hours:
* Sustained winds or frequent gusts to 35 miles per hour or greater, and
* Considerable falling and/or blowing snow reducing visibility to less than 1/4 mile.

Blizzard Warning: This product is issued by the NWS when blizzard conditions are life
threatening. The criteria for this warning varies from state to state.

Blocking High: The development of a warm ridge or cutoff high aloft at high latitudes which
becomes associated with a cold high at the surface, causing a split in the westerly winds. Such a
high will move very slowly, tending to move west during intensification and east during
dissipation. It prevents the movement of migratory cyclones across its latitudes. Two examples
are a cut-off high and an Omega block.

Blowing: A descriptor used to amplify observed weather phenomena (dust, sand, snow, and
spray) whenever the phenomena are raised to a height of 6 feet or more above the ground and
reduces horizontal visibility to less than 7 statue miles.

Blowing Dust (BLDU): Wind-driven dust that significantly reduces surface visibility to less than
7 miles.

Blowing Snow (BLSA): Wind-driven sand that significantly reduces surface visibility to less
than 7 miles.

Blowing Snow (BLSN): Wind-driven snow that significantly reduces surface visibility to less
than 7 miles. BLIZZARD: Snow with winds in excess of 35 mph and visibilities of 1/4 mile or
less, for an extended period of time (e.g. > 3 hours).

Boundary Layer: In general, a layer of air adjacent to a bounding surface. Specifically, the term
most often refers to the planetary boundary layer, which is the layer within which the effects of
friction are significant. For the earth, this layer is considered to be roughly the lowest one or two
kilometers of the atmosphere. It is within this layer that temperatures are most strongly affected
by daytime insolation and nighttime radiational cooling, and winds are affected by friction with
the earth's surface. The effects of friction die out gradually with height, so the “top” of this layer
cannot be defined exactly.
145
Broken (BKN): An official sky cover classification for aviation weather observations,
descriptive of a sky cover of 5/8 to 7/8.

CAA: An acronym for Cold air advection.

Cap or Cap Strength: It measures the ability of stable air aloft (a layer of relatively warm air) to
inhibit low-level parcel ascent. Empirical studies show that a cap greater than 2°C often
precludes thunderstorms in the absence of a strong dynamical or forced lift. This occurs even
when the instability is excessive. A strong cap prevents widespread convection from occurring.
Also called a lid.

Calm: A condition when no air motion is detected.

CAPE: An acronym for Convective Available Potential Energy.

Categorical: An NWS precipitation descriptor for a 80%, 90%, or 100% chance of measurable
precipitation (0.01”). See Precipitation Probability (PoP).

Cb: An acronym for cumulonimbus.

Ceiling: The height of the lowest layer of clouds, when the sky is broken or overcast.

Ceilometer: A device used to evaluate the height of clouds or the vertical visibility into a
surface-based obscuration.

Cell: Convection in the form of a single updraft, downdraft, or updraft/downdraft couplet,

typically seen as a vertical dome or tower as in a cumulus or towering cumulus cloud. Some
thunderstorms consist of several cells (see multi-cellular thunderstorm).

Celsius: A temperature scale in which 0° is the freezing point of water and 100° is the boiling
point.

Chaff: Small strips of metal foil usually dropped in large quantities from aircraft or balloons.
Chaff typically produces a radar echo which closely resembles precipitation. Chaff drops once
were conducted by the military in order to confuse enemy radar, but now are conducted mainly
for radar testing and calibration purposes.

Chance: An NWS precipitation descriptor for 30%, 40%, or 50% chance of measurable
precipitation (0.01”). When the precipitation is convective in nature, the term scattered is used.
See Precipitation Probability (PoP).

Chinook Wind: A warm, dry foehn wind that descends the eastern slope of the Rocky
Mountains. The warmth and dryness of this wind can quickly melt and evaporate snowcover.
Another kind of foehn wind is the Santa Ana.

Cirriform: High altitude ice clouds with a very thin wispy appearance.
146
Cirrocumulus(Cc): They are thin clouds, the individual elements which appear as small white
flakes or patches of cotton, usually showing brilliant and glittering quality suggestive of ice
crystals. They form at altitudes between 16,500 to 45,000 feet above ground.

Cirrocumulus Standing Leticular (CCSL): These clouds are formed on the crests of waves
crested by barriers in the wind flow. The clouds show little movement hence the name standing.
Wind, however, can be quite strong blowing through the cloud. They are characterized by their
smooth, polished edges. They may also form on wave crests. They are ice crystal clouds and
generally are whiter than ACSL. These clouds from between 16,500 and 45,000 feet.

Cirrostratus (Cs): They are thin, whitish cloud layers appearing like a sheet or veil. They are
diffuse, sometimes partially striated or fibrous. Due to their ice crystal makeup, these clouds are
associated with halos - large, luminous circles or arcs of circles surrounding the sun or moon.
The layer frequently is the edge of a frontal shield. They form at altitudes between 16,500 to
45,000 feet above ground.

Cirrus (Ci): They are thin, feather like clouds composed entirely of ice crystals. They form at
altitudes between 16,500 to 45,000 feet above ground. Thunderstorm anvils are a form of cirrus
cloud, but most cirrus clouds are not associated with thunderstorms.

Civil Emergency Message (CEM): These NWS statements are issued when a local or state
official wants a warning disseminated regarding nuclear accidents, spills of toxic material, and
other similar situations.

Clear: Sky condition of less than 1/10 cloud coverage.

Climate: The historical record of average daily and seasonal weather events.

Climatological Data (CD): This National Climatic Data Center (NCDC) publication, also
produced monthly and annually, contains daily temperature and precipitation data for over 8,000
locations.

Climate Diagnostics Center (CDC): The CDC is part of the National Oceanic & Atmospheric
Administration (NOAA). Their mission is to identify the nature and causes of climate variations
on time scales ranging from a month to centuries. The goal of this work is to develop the ability
to predict important climate variations on these time scales.

Climate Prediction Center (CPC): The CPC is one of nine national centers that comprises the
National Centers for Environmental Prediction (NCEP). Their mission is to maintain a
continuous watch on short-term climate fluctuations and to diagnose and predict them. These
efforts are designed to assist agencies both inside and outside the federal government in coping
with such climate related problems as food supply, energy allocation, and water resources.

Closed Low: A low pressure area with a distinct center of cyclonic circulation which can be
completely encircled by one or more isobars or height contour lines. The term usually is used to
distinguish a low pressure area aloft from a low-pressure trough. Closed lows aloft typically are
147
partially or completely detached from the main westerly current or jet stream, and thus move
relatively slowly and erratically. See Cutoff Low.

Cloud: A visible aggregate of minute water droplets or ice particles in the atmosphere above the
Earth's surface.

Cloud Height: The height of the base of a cloud or cloud layer above the surface of the earth.

Cloud Layer: An array of clouds whose bases are at approximately the same level.

Cloud Seeding: An experimental process used to weaken hurricanes or enhance rainfall in dry
areas.

Cloud Streets: Rows of cumulus or cumulus-type clouds aligned parallel to the low-level flow.
Cloud streets sometimes can be seen from the ground, but are seen best on satellite photographs.

Cloudy: When the predominant/average sky condition is covered completely by opaque (not
transparent) clouds.

Clutter: Radar echoes that interfere with observation of desired signals on the radar display.

Coalescence: The process by which water droplets in a cloud collide and come together to form
raindrops.

Coastal Convergence: The convergence or running together of land and sea winds, creating a
stronger band of wind near the shore. Factors such as the shape of the shoreline and the angle
between the wind and the shore determine the severity of this effect. See also Island Effect and
Convergence Zone.

Coastal Flood Statement: This NWS product keeps the public and cooperating agencies
informed of the status of existing coastal flood watches and warnings as well as provides an
update on local conditions. It is also used to cancel a Coastal Flood Watch or a Coastal Flood
Warning.

Coastal Flood Warning: This NWS product alerts residents along the Atlantic, Pacific, and
Gulf Coasts that coastal flooding is either imminent or occurring.

Coastal Flood Watch: This NWS product alerts residents along the Atlantic, Pacific, and Gulf
Coasts to the possibility of coastal flooding.

Coastal Flooding: Flooding that occurs where water is driven onto land from an adjacent body
of water, usually caused by a combination of high surf and high tides. The high surf can come
from strong winter storms or tropical cyclones.

Coastal Waters Forecast (CWF): A forecast of wind, wave and weather conditions between the
coastline and 60 miles offshore.

148
Cold Air Advection: Transport of cold air into a region by horizontal winds.

Cold Core Low: A low pressure area which is colder at its center than at its periphery. Mid-
latitude cyclones exhibit this temperature pattern. They usually produce much of their cloud
cover and precipitation during the daytime when the instability is the greatest. At night, the
clouds and precipitation usually diminishes significantly.

Cold Front: The leading edge of a relatively colder airmass which separates two air masses in
which the gradients of temperature and moisture are maximized. In the northern hemisphere
winds ahead of the front will be typically southwest and shift into the northwest with frontal
passage.

Cold Pool: A region of relatively cold air, represented on a weather map analysis as a relative
minimum in temperature surrounded by closed isotherms. Cold pools aloft represent regions of
relatively low stability, while surface-based cold pools are regions of relatively stable air.

Combined Seas: Generally referred to as “Seas”. It is used to describe the combination or

interaction of wind waves and swells. In some prediction techniques, its height is the square root
of the sum of the squares of the wind wave and swell heights. It is generally equal to the height
of the swell plus 1/3 the height of the wind waves.

Comma Cloud: A synoptic scale cloud pattern with a characteristic comma-like shape, often
seen on satellite photographs associated with large and intense low-pressure systems.

Composite Reflectivity(CR): This WSR-88D radar product displays the maximum reflectivities
for each resolution grid box for all elevation angles in a volume scan. Available with combined
attribute table which provides valuable information concerning storm characteristics, such as
storm tops, maximum radial velocity and reflectivity, and possible existence of hail and
mesocyclones. It is used to observe the highest reflectivities in a storm from any scanned
elevation angle; determine intensity trends; and generate cross section through maximum
reflectivity.

Condensation: The process of gas or vapor changing to liquid.

Condensation Funnel: A funnel-shaped cloud associated with rotation and consisting of

condensed water droplets (as opposed to smoke, dust, debris, etc.). Compare with debris cloud.

Continental Air Mass: A dry air mass originating over a large land area.

CONUS: An acroynm for Continental United States.

Convection: Generally, transport of heat and moisture by the movement of a fluid. In

meteorology, the term is used specifically to describe vertical transport of heat and moisture,
especially by updrafts and downdrafts in an unstable atmosphere. The terms “convection” and
“thunderstorms” often are used interchangeably, although thunderstorms are only one form of
convection. Cumulonibus (Cb), towering cumulus clouds, and Altocumulus Castellanus
(ACCAS) clouds all are visible forms of convection. However, convection is not always made
149
visible by clouds. Convection which occurs without cloud formation is called dry convection,
while the visible convection processes referred to above are forms of moist convection.

Convective Available Potential Energy (CAPE): It defines the vertically integrated positive
buoyancy of an adiabatically rising air parcel on a sounding. This is proportional to the amount
kinetic energy that the air parcel gains while it is warmer that the surrounding environment. As a
result, CAPE provides the best measure of the potential instability available in the atmosphere.
Increasing values of CAPE generally lead to progressively vigorous convection. However,
severe thunderstorms can form in environments showing weak to moderate CAPE, especially if
the Storm Relative Helicity values are high.

Convective Clouds: The vertically developed family of cumulus and cumulonimbus clouds. The
height of their bases range from as low as 1,000 feet to a bit more than 10,000 feet. Clouds with
extensive vertical development are positive indications of unstable air. Strong upward currents in
vertically developed clouds can carry high concentrations of supercooled water to high levels
where temperatures are quite cold. Upper portions of these clouds may be composed of water
and ice.

Convective Outlook (SWO): A forecast containing the area(s) of expected thunderstorm

occurrence and expected severity over the contiguous United States, issued several times daily
by the SPC in Norman, Oklahoma. They are sent out as both a narrative and a graphic covering a
period of up to 52 hours in advance. This product serves as guidance to the local NWS Office for
use in the preparation of forecast products issued; to advise the public, media, and other interests
of the possibility of severe weather; and to assist with preliminary staffing should severe weather
be anticipated. The terms approaching, slight risk, moderate risk, and high risk are used to
describe severe thunderstorm potential.

Convective Rain: Rain associated with convective or cumuliform clouds characterized by

vertical development in the form of rising mounds, domes, or towers.

Convective SIGMETs: These NWS aviation products are issued in the conterminous U.S. for
any of the following. Severe thunderstorm due to: surface winds greater than or equal to 50
knots, hail at the surface greater than or equal to 0.75” in diameter, tornadoes, embedded
thunderstorms, line of thunderstorms, or thunderstorms greater than or equal to VIP level 4
affecting 40% or more of an area at least 3000 square miles. Any Convective SIGMET implies
severe or greater turbulence, severe icing, and low level wind shear.

Convergence: A contraction of a vector field; the opposite of divergence. Convergence in a

horizontal wind field indicates that more air is entering a given area than is leaving at that level.
To compensate for the resulting “excess,” vertical motion may result: upward forcing if
convergence is at low levels, or downward forcing (subsidence) if convergence is at high levels.
Upward forcing from low-level convergence increases the potential for thunderstorm
development (when other factors, such as instability, are favorable).

Convergence Line or Zone: A horizontal line or zone along which horizontal convergence of
the airflow is occurring. Common forms of convergence lines are sea-breeze fronts, cold-air
outflow from thunderstorms, and synoptic fronts. In areas of complex terrain, these are often
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produced by air moving around terrain features. The effect is rising air motion along a line of
convergence in the lee of the features, causing convective showers, thunderstorms, waterspouts
or funnel clouds. See also Island Effect.

Cooling Degree Day: see Degree Day.

Cooperative Observer: An individual (or institution) who takes precipitation and temperature
observations-and in some cases other observations such as river stage, soil temperature, and
evaporation-at or near their home, or place of business. Many observers transmit their reports by
touch-tone telephone to an NWS computer, and nearly all observers mail monthly reports to the
National Climatic Data Center to be archived and published.

Coriolis Effect: The effect caused by the Earth's rotation which deflects air moving between two
places. It causes an object to move to the right in the Northern Hemisphere and to the left in the
Southern Hemisphere.

County Warning Area (CWA): The area assigned to a specific NWS Forecast Office for the
purpose of warnings issuance and hazard awareness responsibility.

Creek: A small stream of water which serves as the natural drainage course for a small drainage
basin.

CU: An acronym for cumulus.

Cumuliform: Descriptive of all clouds with vertical development in the form of rising mounds,
domes, or towers.

Cumulonimbus Cloud (Cb): They are the ultimate manifestation of instability. They are
vertically developed clouds of large dimensions with dense “boiling” tops often crowned with
thick veils of dense cirrus (anvil). This is also called a “thunderstorm cloud”. It can produce very
heavy precipitation, lightning, large hail (greater than 0.75”), damaging winds, and tornadoes.

Cumulonimbus Mammatus Cloud (CBMAM): It is associated with a cumulonimbus cloud. It

indicates extreme instability. This cloud is characterized by hanging festoons or protuberances
underneath the anvil of the Cumulonimbus Cloud (Cb). The festoons may be at any level of the
cloud from the underside of the anvil to the base of the cloud.

Cumulus Cloud (Cu): These clouds form in convective currents and are characterized by
relatively flat bases and dome-shaped tops. Fair weather cumulus do not show extensive
“towers” or vertical development and do not produce precipitation. A cumulus may, however, be
an early stage in the development of towering cumulus or cumulonimbus. More often fair
weather cumulus indicate a relatively shallow layer of instability.
Cumulus Congestus: Same as towering cumulus. Sometimes referred to just as congestus.

Cutoff Low: A closed low which has become completely displaced (cut off) from basic westerly
current (such as the jet stream), and moves independently of that current. Cutoff lows may
remain nearly stationary for days, or on occasion may move westward opposite to the prevailing
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flow aloft (i.e., retrogression), or erratically. “Cutoff low” and “closed low” often are used
interchangeably to describe low pressure centers aloft. However, not all closed lows are
completely removed from the influence of the basic westerlies. Therefore, the recommended
usage of the terms is to reserve the use of “cutoff low” only to those closed lows which clearly
are detached completely from the westerlies. See also Closed Low.

Cyclone: An area of low atmospheric pressure that has a closed circulation. Cyclones (or more
commonly called “low pressure areas”) rotate counter-clockwise in the Northern Hemisphere
and clockwise in the Southern Hemisphere. They often bring about clouds and precipitation.
Also the term used for a hurricane in Australia and the Indian Ocean.

Cyclonic Circulation (or Cyclonic Rotation): Circulation (or rotation) which is in the same
sense as the Earth's rotation, i.e., counterclockwise (in the Northern Hemisphere) as would be
seen from above. Nearly all mesocyclones and strong or violent tornadoes exhibit cyclonic
rotation, but some smaller vortices, such as gustnadoes, occasionally rotate anticyclonically
(clockwise). Compare with anticyclonic rotation.

Daily Climate Report: As the name indicates, this tabular climatological product is issued daily
by each NWS office. It is organized so that similar items are grouped together (i.e., temperature,
precipitation, wind, sunrise and sunset times, etc.).

dBZ: A logarithmic expression for reflectivity factor, referenced to (1 mm6 / 1 m3). dBZ = 10 log
( z / 1 mm6 m3). See decibel.

Dead Fuel Moisture: Dead fuel moisture responds solely to ambient environmental conditions
and is critical in determining fire potential. Dead fuel moistures are classed by time lag. Dead
fuels in NFDRS have four classes. 1-hr fuels are fine flashy fuels, less than 0.25” diameter, that
respond quickly to weather changes and are computed from observation time temperature,
humidity and cloudiness. 10-hr fuels are 0.25” to 1” in diameters and are computed from
observation time temperature, humidity, and cloudiness, or may be a standard set of “10-Hr Fuel
Sticks” that are weighed as part of the fire weather observation. 100-hr fuels are 1” to 3” in
diameter and computed from 24 hour average boundary condition composed of day length, hours
of rain, and daily temperature/humidity ranges. 1000-hr fuels are 3” to 6” in diameter and
computed from a 7-day average boundary condition composed of day length, hours of rain, and
daily temperature/humidity ranges.

Debris Cloud: A rotating “cloud” of dust or debris, near or on the ground, often appearing
beneath a condensation funnel and surrounding the base of a tornado. Note that a debris cloud
appearing beneath a thunderstorm will confirm the presence of a tornado, even in the absence of
a condensation funnel.

Decibel (dB): This is a logarithmic expression comparing the energy that the radar emits (Z1) to
the energy that radar receives back from a radar target (Z2). It is expressed mathematically as
Z (dBZ) = 10 log (Z1/Z2) The solution to this equation lets the radar operator know the strength
of a target. The value of Z is a function of the amount of radar beam energy that is back scattered
by a target and detected as a signal (or echo). Higher values of Z (and dBZ) thus indicate more
energy being back scattered by a target. See also dBZ.
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Decouple: The tendency for the surface wind to become much lighter than wind above it at night
when the surface temperature cools.

Degree Day: It gauges the amount of heating or cooling needed for a building using 65°F as a
baseline. To compute heating/cooling degree-days, take the average temperature for a day and
subtract the reference temperature of 65°F. If the difference is positive, it is called a Cooling
Degree Days. If the difference is negative, it is called a Heating Degree Days. The magnitude of
the difference is the number of days. For example, if your average temperature is 50°F for a day
in December, the difference of the average temperature for that day and the reference
temperature of 65°F would yield a minus 15°. Therefore, you know that you are going to have 15
Heating Degree Days that day. Electrical, natural gas, power, and heating, and air conditioning
industries utilize heating and cooling degree information to calculate their needs.

Dense Fog: A fog in which the visibility is <¼ mile.

Dense Fog Advisory: This product is issued by the NWS when widespread fog reduces visibility
to less than or equal to ¼ mile.

Dew: Water droplets that form upon surfaces on or near the ground when air is cooled toward its
dew point.

Dew Point (Dew-Point Temperature): A measure of atmospheric moisture. The temperature to

which air must be cooled, at constant pressure and moisture content, in order for saturation to
occur. The higher the dew point, the greater amount of water vapor in the air mass.

Directional Shear: The component of wind shear which is due to a change in wind direction
with height, e.g., southeasterly winds at the surface and southwesterly winds aloft. A veering
wind with height in the lower part of the atmosphere is a type of directional shear often
considered important for tornado development.

Dirty Ridge: Most of the time, upper-level ridges bring fairly clear weather as the storms are
steered around the ridge. Sometimes, however, strong storms undercut the ridge and create
precipitation. Ridges that experience this undercutting by storms are known as dirty ridges
because of the unusual occurrence of precipitation.

Diurnal: Daily; related to actions which are completed in the course of a calendar day, and
which typically recur every calendar day (e.g., diurnal temperature rises during the day, and
diurnal falls at night).

Divergence: A measure of the expansion or spreading out of a vector field; usually said of
horizontal winds. It is the opposite of convergence. Divergence at upper levels of the atmosphere
enhances upward motion, and hence the potential for thunderstorm development (if other factors
also are favorable).

Doppler Radar: A Weather Surveillance Radar (WSR-88D) system developed in 1988. About
120 systems were installed at Weather Forecast Offices. An additional 24 systems were installed
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at Department of Defense (Air Force Bases) sites. This powerful and sensitive Doppler system
generates many useful products for meteorologists, among them: standard reflectivity echoes,
wind velocity or atmospheric air motion pictures, and areal 1-hour, 3-hour, or storm-total
precipitation images. This radar can also measure radial velocity, the instantaneous component of
motion parallel to the radar beam (i.e., toward or away from the radar antenna).

Doppler Shift: The change in observed frequency of wave energy due to the relative motion of
the observer and wave source. For example, as a train approaches your location, you hear a
higher pitch sound. After the train has passed your location, you will hear a lower pitch sound.
The Doppler radar uses this change in frequency to determine the velocity and direction of the
wind.

Downburst: A strong down draft, initiated by a thunderstorm, that induces an outburst of

damaging straight line winds on or near the ground. Downburst winds can produce damage
similar to a strong tornado. The damage from aloft often looks like a star with debris spreading
out from the center in straight lines. Although usually associated with thunderstorms, downbursts
can occur with showers too weak to produce thunder. Downbursts come in the following to 2
categories: microburst and macroburst.

Downdraft: A small-scale column of air that rapidly sinks toward the ground as in a shower or
thunderstorm. A downburst is the result of a strong downdraft.

Downslope Flow: Air that descends down a mountain chain or over sloping terrain (pressurized
air moving from high pressure to low pressure), resulting in subsequent drying, and in some
cases, dramatic warming of air that can quickly melt a snowcover. Local names for downslope
winds or “foehn winds” in the western United States are Chinook Winds, East Winds, North
Winds, Mono Winds and Santa Ana Winds. Usually associated with little or no clouds.

Drainage Basin or Area: A part of the surface of the earth that is occupied by a drainage
system, which consists of a surface stream or a body of impounded surface water together with
all tributary surface streams and bodies of impounded surface water.

Drizzle (DZ): Fairly uniform precipitation composed exclusively of fine drops with diameters
less than 0.02” (0.5 mm) which are very close together. Drizzle appears to float while following
air currents, although unlike fog droplets, it falls to the ground. The intensity of drizzle is based
solely on visibility.

Drought: A period of abnormally dry weather sufficiently prolonged from the lack of
precipitation to cause a serious hydrologic imbalance.

Drought Index: Computed value which is related to some of the cumulative effects of a
prolonged and abnormal moisture deficiency. (An index of hydrological drought corresponding
to levels below the mean in streams, lakes, and reservoirs.).

Dryline: A boundary separating moist and dry air masses and an important factor in severe
weather frequency in the Great Plains. It typically lies north-south across the central and

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southern high Plains states during the spring and early summer, where it separates moist air from
the Gulf of Mexico (to the east) and dry desert air from the southwestern states (to the west).

Dry Microburst: A microburst with little or no precipitation reaching the ground, most common
in semi-arid regions. They may or may not produce lightning. Dry microbursts may develop in
an otherwise fair-weather pattern; visible signs may include a cumulus cloud or small Cb with a
high base and high-level virga, or perhaps only an orphan anvil from a dying rain shower. At the
ground, the only visible sign might be a dust plume or a ring of blowing dust beneath a local area
of virga. Compare with wet microburst.

Dry Slot: A zone of dry (and relatively cloud-free) air which wraps east or northeast into the
southern and eastern parts of a large or small scale low pressure system. A dry slot generally is
seen best on satellite photographs.

Dust Devil: A small, vigorous whirlwind, usually of short duration, rendered visible by dust,
sand, and debris picked up from the ground. They range from 10 feet to greater than 100 feet in
diameter, and can extend up to 1000 feet above the ground. They are caused by intense surface
heating. This heating causes the air to rapidly rise and thus, a mini low pressure system is
formed. They are usually found in desert or dry climatic regions where dust and dirt can be easily
lifted. Only rarely do they cause any damage. Wind speeds can reach 30 to 60 mph.

Dynamics: Generally, any forces that produce motion or effect change. In operational
meteorology, dynamics usually refer specifically to those forces that produce vertical motion in
the atmosphere.

Easterly Wave: A wavelike disturbance in the tropical easterly winds that usually moves from
east to west. Such waves can grow into tropical depressions.

Ebb Current: A receding tidal current that moves water away from shore or down a tidal river
or estuary.

Echo: Energy back scattered from a target (precipitation, clouds, etc.) and received by and
displayed on a radar screen.

ECMWF: An acronym for European Centre for Medium-Range Weather Forecasting model.
See European Model.

Eddy: A small rotating area of water.

EF Scale: See Enhanced Fujita Scale (EF-scale).

El Niño: The warm phase of the Southern Oscillation (SO). Characterized by the warming of the
sea surface temperatures (SST) in the central and eastern equatorial Pacific Ocean, beginning at
about Christmas time (hence the name “El Niño”, which is Spanish for “Christ child”). This
causes the sardine population to die off the Peru coast. The anomalously warm water also causes
the deep convection to shift from its normal position near Indonesia to the east. This is also
preceded and accompanied by anomalous westerly wind at low levels. During the warm phase of
155
the SO severe drought occurs over Indonesia and Australia. The warming of the ocean in the
tropical Pacific increases the strength of the Hadley circulation (a global wind pattern) and
causes the entire tropics to warm. The strengthened hemispheric north-south temperature
gradient adds energy to the atmosphere. In particular, the subtropical jet is stronger and its
maximum wind extends farther to the east than is normal. This is often related to the deeper than
normal Aleutian low, a split jet-level flow over the western U.S. and a trough in the southeastern
U.S.. This pattern is called the “Pacific North American Teleconnection pattern”. When
established, it leads to warm, dry conditions over the northern U.S., particularly the Northwest,
and to unusually wet conditions over the southern U.S.. The El Niño typically lasts from 12 to 18
months. See Southern Oscillation, ENSO, and La Niña.

El Niño Southern Oscillation (ENSO): An acronym designed to stress the special importance
of the warm phase (El Niño) of the Southern Oscillation. See El Niño and Southern Oscillation.

Emergency Managers Weather Information Network (EMWIN): A means of providing the

emergency management community with access to a set of NWS warnings, watches, forecasts,
and other products at no recurring cost. EMWIN is a suite of data access methods which make
available a live stream of weather and other critical emergency information, including: 1. Radio -
Digital weather information is transmitted using inexpensive radio broadcast and personal
computer (PC) technologies. 2. Internet - The Interactive Weather Information Network (IWIN)
page uses HTML formatting and additional hyperlinks to an EMWIN server that ingests the data.
3. Satellite - Satellite broadcast makes the datastream available nationwide, but not to provide
detailed support (i.e. funding, manpower, or equipment) for state and local efforts to redistribute
the datastream after downlink. The NWS broadcasts EMWIN on GOES 10 and GOES 12
satellites. Note: The above methods are intended to provide data to users at little or no cost.
There are other methods available, at higher cost to the end-user, including various commercial
weather distribution systems. EMWIN is a supplement to other NWS dissemination services,
which include: NOAA Weather Radio (NWR), NOAA Weather Wire System (NWWS), Family
of Services (FOS), NOAAPORT, and NEXRAD Information Dissemination Service (NIDS).

Enhanced Fujita Scale (EF-scale): A system originally developed as the Fujita Scale by Dr.
Theodore Fujita of the University of Chicago to classify tornadoes based on wind damage. The
Enhanced Fujita Scale is an adaptation implemented by the NWS in 2007 to more accurately rate
tornadoes from EF0 for weakest to EF5 for strongest tornadoes. See also Fujita F Scale.

Environmental Modeling Center (EMC): This is one of 9 centers that comprises the National
Centers for Environmental Prediction (NCEP). This center improves numerical weather, marine
and climate predictions, through a broad program of research in data assimilation and modeling.
In support of the NCEP operational forecasting mission, the EMC develops, improves and
monitors data assimilation systems and models of the atmosphere, ocean and coupled system,
using advanced methods developed internally as well as cooperatively with scientists from
Universities, NOAA Laboratories and other government agencies, and the international scientific
community.

European Model: One of medium-range (3 to 7 days) forecast models that forecasters use to
write their extended forecasts. It has a resolution of 75 kilometers and covers the entire northern
hemisphere. This model comes from European Centre for Medium-Range Weather Forecasts
156
(ECMWF) which is an international organization supported by 18 European Member States. See
GFS and UKMET.

Evaporation: A process by which liquid changes into a gas or vapor.

Evapotranspiration: Combination of evaporation from free water surfaces and transpiration of

water from plant surfaces to the atmosphere.

Excessive Heat Warning: This product is issued by the NWS when excessive heat is life
threatening. The criteria for this warning varies from state to state.

Extratropical: A term used in advisories and tropical summaries to indicate that a tropical
cyclone has lost its “tropical” characteristics. The term implies both poleward displacement of
the cyclone and the conversion of the cyclone's primary energy source from the release of latent
heat of condensation to baroclinic (the temperature contrast between warm and cold air masses)
processes. It is important to note that cyclones can become extratropical and still retain winds of
hurricane or tropical storm force.

Eye: The relatively calm center in a hurricane that is more than one half surrounded by wall
cloud. The winds are light, the skies are partly cloudy or even clear (the skies are usually free of
rain) and radar depicts it as an echo-free area within the eye wall. The hurricane eye typically
forms when the maximum sustained tangential wind speeds exceeds about 78 miles an hour. The
eye diameter, as depicted by radar, ranges typically from as small as 5 to 10 miles upwards to
about 100 miles. The average hurricane eye diameter is a little over 20 miles. When the eye is
shrinking in size, the hurricane is intensifying.

F Scale: See Fujita Scale.

Fahrenheit (F): The standard scale used to measure temperature in the United States, in which
the freezing point of water is 32° and the boiling point is 212°.

Fair: It is usually used at night to describe less than 3/8 opaque clouds, no precipitation, no
extremes of visibility, temperature or winds. It describes generally pleasant weather conditions.

Fetch: The area in which ocean waves are generated by the wind. Also refers to the length of the
fetch area, measured in the direction of the wind.

Few (FEW): An official sky cover classification for aviation weather observations, descriptive
of a sky cover of 1/8 to 2/8. This is applied only when obscuring phenomenon aloft are present--
that is, not when obscuring phenomenon are surface-based, such as fog. Also, an NWS
convective precipitation descriptor for a 10% chance of measurable precipitation (0.01”). Few is
used interchangeably with isolated. See Precipitation Probability (PoP).

Fire Behavior: A complex chain-reaction process that describes the ignition, buildup,
propagation, and decline of any fire in wildland fuels.

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Fire Danger: The result of both constant factors (fuels) and variable factors (primarily weather),
which affects the ignition, spread, and difficulty of control of fires and the damage they cause.

Fire Danger Rating: A fire control management system that integrates the effects of selected
fire danger factors into one or more qualitative or numerical indices from which ease of ignition
and probable fire behavior may be estimated.

Fire Weather Services: Routine daily forecasts; spot forecasts; prescribed burn forecasts; smoke
management forecasts and information, advisories, observations, summaries, and briefings
produced in and by an NWS office during normal working hours, plus warnings of critical
weather conditions. Generally, these basic services are tailored to meet the specific needs of user
agencies.

Fire Weather Watch: A product issued by the NWS when fuel conditions and weather portray a
high or extreme fire danger, usually when very low humidity and strong winds are forecast. This
is usually followed by a Red Flag Warning.

Flash Flood: A flood which follows within a few hours (usually less than 6 hours) of heavy or
excessive rainfall, or dam or levee failure. This is a dangerous situation that threatens lives and
property.

Flash Flood Statement (FFS): This product is issued after either a Flash Flood Watch or a Flash
Flood Warning has been issued by a local NWS Forecast Office. It will provide the latest
information on the flash flooding situation or event. It will also be used to remove parts of the
geographical area covered by the original watch or warning when the flash flooding event is no
longer a threat or has ended in a certain area. Finally, this statement can be used to terminate the
original watch or warning when it is no longer valid.

Flash Flood Warning (FFW): This warning signifies a short duration of intense flooding of
communities, streams, or urban areas with high peak rate of flow. Flash floods may result from
such things as torrential downpours or dam and levee breaks. They are issued by the local NWS
Office for 4 hours or less. \

Flash Flood Watch (FFA): This product is issued by the local NWS office for events that have
the potential for short duration (usually less than 6 hours) intense flooding of communities,
streams or areas for which the occurrence is neither certain nor imminent. This watch indicates
that flash flooding is a possibility in or close to the watch area. Those in the affected area are
urged to be ready to take action if a Flash Flood Warning is issued or flooding is observed. A
Flash Flood Watch may be issued for potential flooding from eitherdam breaks, or torrential
downpours.

Flood: The inundation of a normally dry area caused by high flow, or overflow of water in an
established watercourse, such as a river or stream. This is a duration type event with a slower
onset than flash flooding, normally greater than 6 hours.

Flood Stage: A gage height at which a watercouse overtops its banks and begins to cause
damage to any portion of the defined reach.
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Flood Statement (FLS): This product is issued after either a Flash Flood Watch or a Flash Flood
Warning has been issued by a local NWS Forecast Office. It will provide the latest information
on the flash flooding situation or event. It will also be used to remove parts of the geographical
area covered by the original watch or warning when the flash flooding event is no longer a threat
or has ended in a certain area. Finally, this statement can be used to terminate the original watch
or warning when it is no longer valid.

Flood Warning (FLW): This warning signifies a longer duration and more gradual flooding of
communities, streams, or urban areas. Floods usually begin after 6 hours of excessive rainfall.

Flood Watch (FLA): This watch is issued by a local NWS Office to indicate that there is a
potential of flooding in or close to the watch area. Those in the affected area are urged to be
ready to take action if a flood warning is issued or flooding is observed. In flooding, the onset of
flooding take place much slower (usually greater than 6 hours) than a flash flood.

Flow: 1. The general movement of air, either in the upper or lower atmosphere, e.g. “onshore
flow” is air moving from the ocean to land. 2. Volume of water in a river or stream, passing a
specific observation site, during a specific time period. It is typically expressed in units of cubic
feet per second.

Flurries: Light snowfall that generally does not produce a measurable accumulation.

Fog (FG): A visible aggregate of minute water particle (droplets) which are based at the Earth's
surface and reduces horizontal visibility to less than 5/8 statue mile, and unlike drizzle, it does
not fall to the ground. It occurs most frequently in coastal regions because of the great water
vapor content of the air. However, it can occur anywhere. The rapidity with which fog can form
makes it especially hazardous. It forms by any atmospheric process that does one of the
following: Cools the air to its dew point, or raises the dew point to the air temperature. Names
given to fog types identify their methods of formation. The principle types are radiation fog, ice
fog, advection fog, upslope fog, rain induced fog, and steam fog. These types of fog are called
“dense” when the surface visibility is equal to or less than 1/4 mile. A Dense Fog Advisory will
be issued when the dense fog becomes widespread.

Foëhn: A warm dry wind on the lee side of a mountain range. The heating and drying are due to
adiabatic compression as the winds descend downslope. Foëhn winds are Mistrals in France,
Sciroccos in North Africa, Chinooks in the northern plains of the U.S., Mono Winds in Northern
California, Diablo Winds in the San Francisco Bay Area, and Santa Ana Winds in Southern
California.

Forecast Models: Forecasters use numerical weather models to make their forecasts. These
numerical models are classified into four main classes. The first is global models, which focus on
the entire northern hemisphere. The second is national models, which focus on the USA. The
third is regional models. These regional models have a finer grid than national models and are
run out for smaller periods of time. The final class of models is relocatable models, which do not
focus on any permanent geographical location. Relocatable models are very limited on the size
of the geographical area for which they can forecast, but these models have very high
159
resolutions, or very small forecast grid boxes.

Freeze: It is when the surface air temperature is expected to be 32°F or below over a widespread
area for a climatologically significant period of time. Use of the term is usually restricted to
advective situations or to occasions when wind or other conditions prevent frost. Adjectives such
as “killing”, “severe”, or “hard” will be used when appropriate. “Killing” may be used during the
growing season when the temperature is expected to be low enough for a sufficient duration to
kill all but the hardiest herbaceous crops or plants.

Freezing Level: The lowest altitude in the atmosphere, or a given location, at which the air
temperature is 32°F.

Freezing Rain or Drizzle: This occurs when rain or drizzle freezes on surfaces (such as the
ground, trees, power lines, motor vehicles, streets, highways, etc.) that have a temperature of
32°F or below. Small accumulations of ice can cause driving and walking difficulties.
Meanwhile, heavy accumulations of ice can pull down trees and utility lines. In this situation, it
would be called an Ice Storm.

Front: A boundary or transition zone between two air masses of different density, and thus
(usually) of different temperature. A moving front is named according to the advancing air mass,
e.g., cold front if colder air is advancing. See cold front, occluded front, stationary front, and
warm front.

Frost: The formation of ice crystals on the ground or other surfaces in the form of scales,
needles, feathers, or fans. Frost develops under conditions similar to dew, except the
temperatures of the Earth's surface and earthbound objects fall below 32°F. As with the term
“freeze”, this condition is primarily significant during the growing season. If a frost period is
sufficiently severe to end the growing season or delay its beginning, it is commonly referred to
as a “killing frost”. Some objects cool more efficiently than the air, and can cause frost to form
on objects, even when air temperatures are well above freezing.

Frost/Freeze Advisory: This product is issued by the NWS when freezing temperatures or
conditions conducive to the formation of frost occur during the growing season.

Frost Point: Dew point below freezing.

Fractus: Ragged, detached cloud fragments; same as scud.

Fuel Moisture: The water content of fuel particle expressed as a percent of the oven dried
weight of the fuel particle. Fuel moisture observations are generally for the 10-hour time lag
fuels (medium-sized roundwood 0.25” to 1” in diameter).

Fujita Scale (F-scale): A scale used to classify the strength of a tornado. It was devised by Dr.
Theodore Fujita from the University of Chicago. The F-scale gives tornadoes a numerical rating
from F0 to F5 based on wind damage. This system was adjusted by the NWS as the Enhanced
Fujita Scale and implemented in 2007.

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Funnel Cloud (FC): A condensation funnel extending from the base of a towering cumulus or
Cb, associated with a rotating column of air that is not in contact with the ground (and hence
different from a tornado). A condensation funnel is a tornado, not a funnel cloud, if either it is in
contact with the ground, or a debris cloud or dust whirl is visible beneath it.

Gale: Wind speeds from 39 to 54 mph (34 to 47 knots).

Gale Warning: The NWS will issue marine warnings for 1-minute sustained winds between 34
(39 mph) and 47 knots (54 mph) are expected in coastal waters.

Geostationary Satellite: Satellites orbiting at 22,370 miles above the Earth's surface with the
same rotational velocity as the Earth; therefore, the satellite remains over the same location on
the Earth 24 hours a day.

GFS: An acronym for Global Forecast System.

Glaze: Ice formed by freezing precipitation covering the ground or exposed objects.

Global Forecast System (GFS): The MRF and AVN forecast models from NCEP were
combined into a single system and renamed the Global Forecast System (GFS). The GFS
produces forecasts out to 16 days, four times per day.

Global Warming: An overall increase in world temperatures which may be caused by additional
heat being trapped by greenhouse gases.

GOES: Geostationary Operational Environmental Satellite.

Gradient: The time rate or spatial rate of change of an atmospheric property.

Graupel: Small pellets of ice created when supercooled water droplets coat, or rime, a
snowflake. The pellets are cloudy or white, not clear like sleet, and often are mistaken for hail.
Also called soft hail, snow pellets, or tapioca snow.

Gravity Wave: A wave disturbance in which buoyancy acts as the restoring force on parcels
displaced from hydrostatic equilibrium. Waves on the ocean are examples of gravity waves.

Greenhouse Effect: The heating effect caused by gases in the atmosphere absorbing heat (solar
radiation) instead of letting it escape back into space. There are 2 types: Natural - It is what
keeps the Earth's average temperature at 59°F instead of 0°F. In this case, the most abundant
greenhouse gas is water vapor. Anthropogenic - Additional warming caused by having too
much carbon dioxide (CO2).

Ground Clutter: A pattern of radar echoes from fixed ground targets (buildings, hills, etc.) near
the radar. Ground clutter may hide or confuse precipitation echoes near the radar antenna. It is
usually more noticeable at night when the radar beam is encountering superrefractive conditions.

Ground Fog: Fog produced over the land by the cooling of the lower atmosphere as it comes in
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contact with the ground. Also known as radiation fog, and in Central California as tule fog.
Groung fog has little vertical extent (usually 20 feet or less).

Gust: A brief sudden increase in wind speed. Generally the duration is less than 20 seconds and
the fluctuation greater than 10 mph.

Gust Front: Formed when the down draft and rain-cooled air of a thunderstorm reach the
ground, and then spread out along the ground. Usually marked by a sudden wind shift, sharply
falling temperatures, and possibly heavy downpours and/or hail. If two or more of these gust
fronts intersect each other, a new thunderstorm could possibly develop. Sometimes it is
associated with a shelf cloud or roll cloud. Also, see downburst, gustnado, and outflow
boundary. .

Gustnado: Slang for a gust front tornado. A small tornado, usually weak and short-lived, that
occurs along the gust front of a thunderstorm. Often it is visible only as a debris cloud or dust
whirl near the ground. Gustnadoes are not associated with storm-scale rotation (i.e.
mesocyclones).

Gyre: A circular or spiral motion, primarily referring to water currents.

Hail (GR): Precipitation in the form of balls or lumps usually consisting of concentric layers of
ice. A thunderstorm is classified as severe when it produces hail 0.75” or larger in diameter.

Haines Index: This is also called the Lower Atmosphere Stability Index. It is computed from the
morning (12Z) soundings from RAOB stations across North America. The index is composed of
a stability term and a moisture term. The stability term is derived from the temperature difference
at two atmosphere levels. The moisture term is derived from the dew point depression at a single
atmosphere level. This index has been shown to be correlated with large fire growth on initiating
and existing fires where surface winds do not dominate fire behavior. The Haines Indexes range
from 2 to 6 for indicating potential for large fire growth: 2 – Very Low Potential (Moist Stable
Lower Atmosphere), 3 – Very Low Potential, 4 – Low Potential, 5 – Moderate Potential, 6 –
High Potential (Dry unstable lower atmosphere.

Halos: Rings or arcs that seem to encircle the sun or moon. They are caused by the refraction of
light through the ice crystals in cirrus clouds.

Haze (HZ): A concentration of salt particles or other dry particles not readily classified as dust
or other phenomenon. Occurs in stable air usually only a few thousand feet thick, but may extend
as high as 15,000 feet. Haze layers often have definite tops above which the visibilities are good.
However, the visibility in the haze layer can be very poor.

Heat Advisory: This product is issued by the NWS when excessive heat may pose a hazard or is
life threatening if action is not taken. The criteria for this advisory varies from state to state.

Heating Degree Day: see Degree Day.

Heat Index: The Heat Index (HI) or the “Apparent Temperature” is an accurate measure of how
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hot it really feels when the Relative Humidity (RH) is added to the actual air temperature. As an
example, if the air temperature is 90°F and the Relative Humidity (RH) is 70%, the Heat Index
(HI)--or how hot it actually feels--is 106°F. This index was devised for shady, light wind
conditions. Exposure to full sunshine can increase Heat Index (HI) values by up to 15°F. Also
strong winds, particularly with very hot, dry air, can be extremely dangerous. Any value Heat
Index (HI) greater than 105°F is in the Danger Category. When the Heat Index is between 105-
115°F for 3 hours or more, a Heat Advisory will be issued by the local NWS Forecast Office.
See also Apparent Temperature.

Heat Island: A dome of elevated temperatures over an urban area caused by the heat absorbed
by structures and pavement.

Heat Lightning: Lightning that occurs at a distance such that thunder is no longer audible.

Heavy Snow: Depending on the region of the USA, this generally means that four or more
inches of snow has accumulated in 12 hours, or six or more inches of snow in 24 hours.

Height: The altitude above sea level at which a specified pressure is present, e.g. a 500 millibar
height may be 5640 meters in altitude. Lower values indicate an upper trough of low pressure
while higher values indicate an upper ridge of high pressure.

Helicity: A property of a moving fluid which represents the potential for helical flow (i.e. flow
which follows the pattern of a corkscrew) to evolve. Helicity is proportional to the strength of the
flow, the amount of vertical wind shear, and the amount of turning in the flow (i.e. vorticity).
Atmospheric helicity is computed from the vertical wind profile in the lower part of the
atmosphere (usually from the surface up to 3 km), and is measured relative to storm motion. This
value allows the forecaster to determine the rotational tendency of a thunderstorm. Higher values
of helicity (generally, around 150 m2/s2 or more) favor the development of mid-level rotation
(i.e. mesocyclones). Extreme values can exceed 600 m2/s2. It is dependent on the local
environmental wind profile in which a thunderstorm develops and the thunderstorm motion.

High: A region of high pressure, marked as a blue “H” on a weather map. A high is usually
associated with fair weather. See anticyclone.

High Clouds: These clouds have bases between 16,500 and 45,000 feet in the mid latitudes. At
this level they are composed of primarily of ice crystals. Some clouds at this level are cirrus,
cirrocumulus, and cirrostratus.

High Wind Advisory: This product is issued by local NWS Forecast Offices when high wind
speeds may pose a hazard. The criteria for this advisory varies from state to state.

High Wind Watch: This product is issued by local NWS Forecast Offices when there is the
potential of high wind speeds developing that may pose a hazard or is life threatening.

High Wind Warning: This product is issued by local NWS Forecast Offices when high wind
speeds may pose a hazard or is life threatening. The criteria for this warning varies from state to
state.
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Hook or Hook Echo: A pendant or hook on the right rear of a radar echo that often identifies
mesocyclones on the radar display. The hook is caused by precipitation drawn into a cyclonic
spiral by the winds, and the associated notch in the echo is caused by precipitation-free, warm,
moist air flowing into the storm. A hook often is associated with a mesocyclone, and indicates
favorable conditions for tornado development.

HMT (Hydrometeorological Technicians): Individuals who, at the technical level, have

knowledge in meteorology and hydrology. Among their duties are data collection, quality
control, gage network maintenance, as well as the gathering and disseminating of data and
products.

HP (High Precipitation) Storm or HP (High Precipitation) Supercell: A supercell

thunderstorm in which heavy precipitation (often including hail) falls on the trailing side of the
mesocyclone. Precipitation often totally envelops the region of rotation, making visual
identification of any embedded tornadoes difficult and very dangerous. HP storms often produce
extreme and prolonged downburst events, serious flash flooding, and very large damaging hail
events.

HPC: An acronym for the Hydrometeorological Prediction Center.

Humidity: Generally, a measure of the water vapor content of the air. Popularly, it is used
synonymously with relative humidity.

Hurricane: A warm-core tropical cyclone in which the maximum sustained surface wind (using
the U.S. 1-minute average) is 64 kt (74 mph or 119 kph) or more. The term hurricane is used for
Northern Hemisphere cyclones east of the International Dateline to the Greenwich Meridian. It
has a diameter of 250 to 500 miles and a cyclonic circulation typically extending to near 50,000
feet. It is called a Typhoon in the western Pacific north of the Equator and west of the
International Dateline, a Cyclone in the Indian Ocean, and Baguio in the Philippines area. See
Saffir-Simpson Hurricane Intensity Scale.

Hurricane Local Statement (HLS): This product is issued by a local NWS office when it is in
or near an area threatened by a tropical storm or a hurricane. This statement will take the place of
Special (SPS) and Severe (SVS) Statements, Flash Flood/Flood (FFS) Statements, Coastal Flood
Statements, and Marine Weather (MWS) Statements. This statement does not replace the tropical
storm or hurricane advisory from a hurricane center; rather, it complements the advisory with
crucial local information. Inland offices close to the coast may use HLSs if tropical storm or
hurricane conditions are forecasted or observed.

Hurricane Season: The portion of the year having a relatively high incidence of hurricanes. The
hurricane season in the Atlantic, Caribbean, and Gulf of Mexico runs from June 1 to November
30. The hurricane season in the Eastern Pacific basin runs from May 15 to November 30. The
hurricane season in the Central Pacific basin runs from June 1 to November 30.

Hurricane Warning: A warning that sustained winds 64 kt (74 mph or 119 kph) or higher
associated with a hurricane are expected in a specified coastal area in 24 hours or less. A
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hurricane warning can remain in effect when dangerously high water or a combination of
dangerously high water and exceptionally high waves continue, even though winds may be less
than hurricane force.

Hurricane Watch: An announcement of specific coastal areas that a hurricane or an incipient

hurricane condition poses a possible threat, generally within 36 hours.

Hydrologic Cycle: The constant movement of water above, on, and below the Earth's surface.
Processes such as precipitation, evaporation, condensation, infiltration, and runoff comprise the
cycle. Within the cycle, water changes forms in response to the Earth's climatic conditions.

Hydrologic Services: A general term referring to the operations, products, verbal

communications, and related forms of support provided by the NWS for the Nation's streams,
reservoirs, and other areas affected by surface water.

Hydrology: The applied science concerned with the waters of the earth, their occurrences,
distribution, and circulation through the unending hydrologic cycle of: Precipitation, consequent
runoff, infiltration, and storage; eventual evaporation; and so forth. It is concerned with the
physical and chemical reaction of water with the rest of the earth, and its relation to the life of the
earth.

Hydrometeor: A particle of condensed water (liquid, snow, ice, graupel, hail) in the atmosphere.

Hydrometeorological Prediction Center (HPC): This is one of 9 centers that comprises the
National Centers for Environmental Prediction (NCEP). This national center provides basic
hydrometeorological analysis and forecasts for NWS Field Offices and the entire meteorological
community. HPC meteorologists serve as experts in quantitative precipitation forecasting and
numerical model interpretation. Products provided by the HPC include surface analyses,
outlooks for heavy rain and snow, as well as guidance weather forecasts through five days.

Hydrometeorologists: Individuals who have the combined knowledge in the fields of both
meteorology and hydrology which enables them to study and solve hydrologic problems where
meteorology is a factor.

Hydrometeorology: The interdisciplinary science involving the study and analysis of the
interrelation between the atmospheric and land phases of water as it moves through the
hydrologic cycle.

Hygrometer: An instrument which measures the humidity of the air.

Ice Crystals (IC): A fall of unbranched (snow crystals are branched) ice crystals in the form of
needles, columns, or plates. They are also referred to as Diamond Dust.

Ice Fog: Occurs when the temperature is much below freezing and water vapor condenses
directly as ice crystals (sublimation). It is a radiational fog and the conditions for its formation
are the same as for radiational fog except that the temperature must be cold. It occurs mostly in
Arctic regions, but it is not unknown in middle latitudes during the cold season.
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Ice Pellets (PL): Precipitation of transparent and translucent pellets of ice, which are round or
irregular, rarely conical, and which have a diameter of 0.2” (5 mm), or less. Ice Pellets bounce
when they make contact with the ground. It is sometimes called “Sleet”. There are two main
types: 1 – Hard grains of ice consisting of frozen raindrops, or largely melted and refrozen
snowflakes. 2 – Pellets of snow encased in a thin layer of ice which have formed from the
freezing, either of droplets intercepted by the pellets, or of water resulting from the partial
melting of the pellets.

Ice Storm: Occasions when damaging accumulations of ice are expected during freezing rain
situations. Significant accumulations of ice pull down trees and utility lines resulting in the loss
of power and communications. These accumulations of ice make walking and driving extremely
dangerous. Significant ice accumulation are accumulations of 0.25” or greater.

Ice Storm Warning: This product is issued by the NWS when freezing rain produces a
significant and possibly damaging accumulation of ice. The criteria for this warning varies from
state to state.

Impulse: See upper level system.

Indian Summer: An unseasonably warm and calm period near the middle of autumn, usually
following a substantial period of cool weather. Usually referred to in northern climates.

Infrared (IR) Satellite Imagery: This satellite imagery senses surface and cloud top
temperatures by measuring the wavelength of electromagnetic radiation emitted from these
objects. This energy is called “infrared”. High clouds are very cold, so they appear white. Mid-
level clouds are somewhat warmer, so they will be a light gray shade. Low clouds are warmer
still, so they appear as a dark shade of gray or black. Often, low clouds are the same temperature
as the surrounding terrain and cannot be distinguished at all. This imagery can be used both
during the day and night.

Insolation: Incoming solar radiation. Solar heating; sunshine.

Instability (Unstable Air): A state of atmosphere in which the vertical distribution of

temperature allows rising, warm air to continue to rise and accelerate. This kind of motion is
conducive for thunderstorm development. Instability is a prerequisite for severe weather - the
greater the instability, the greater the potential for severe thunderstorms. See lifted index and
sounding.

Intertropical Convergence Zone (ITCZ): The boundary zone separating the northeast trade
winds of the Northern Hemisphere from the southeast trade winds of the Southern Hemisphere.
This region often contains convection along the zone.

Inversion: Generally, a departure from the usual increase or decrease in an atmospheric property
with altitude. Specifically it almost always refers to a temperature inversion, i.e., an increase in
temperature with height, or to the layer within which such an increase occurs. This occurs when

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warm air sits over cold air, possibly trapping moisture and pollutants in the surface air layer. An
inversion is present at the top of the marine layer and in the lower part of a cap.

IR: An acronym for Infrared. See Infrared Satellite Imagery.

Iridescent Clouds: Clouds that exhibit brilliant bright spots, bands, or borders of colors, usually
red and green, observed up to about 30 degrees from the sun. The coloration is due to the
diffraction with small cloud particles producing the effect. It is usually seen in thin cirrostratus,
cirrocumulus, and altocumulus clouds.

Island Effect (Bands): The effect that produces lines of convection in the lee of islands. As
winds are forced around the islands, they collide on the lee side and air is forced upward. In an
unstable air mass, this can produce convective showers, thunderstorms, waterspouts and funnel
clouds. See also Convergence Zone.

Isobar: A line of equal barometric pressure on a weather map.

Isolated: An NWS convective precipitation descriptor for a 10% chance of measurable

precipitation (0.01”). Isolated is used interchangeably with few. See Precipitation Probability
(PoP).

Isolated Storm: An individual cell or a group of cells that are identifiable and separate from
other cells in a geographic area.

Isotach: A line on a weather map connecting points of equal wind speed.

Isotherm: A line on a weather map connecting points of equal temperature.

Isothermal: Of equal or constant temperature with respect to either space or time.

Isothermal Atmosphere: An atmosphere in hydrostatic equilibrium in which the temperature is

constant with altitude and in which, the pressure decreases exponentially upward.

Isothermal Layer: Any layer where the temperature is constant with altitude, such that the
temperature lapse rate is zero. Specifically, the approximately isothermal region of the
atmosphere immediately above the tropopause.

ITCZ: Acronym for Inter-tropical Convergence Zone.

Jet Max (or Speed Max, Jet Streak): A point or area of relative maximum wind speeds within
a jet stream.

Jet Streak: A concentrated region within the jet stream where the wind speeds are the strongest.
It sets up unique wind currents in its vicinity which either enhance or diminish the likelihood of
clouds and precipitation. It will propagate downstream along the jet stream axis.

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Jet Stream: A narrow band of strong winds in the atmosphere that controls the movement of
high and low pressure systems and associated fronts. Jet Streams meander from time to time.
Wind speeds can reach 200 mph or higher in certain cases. It is usually found at 30,000 to 40,000
feet above the earth's surface. It owes its existence to the large temperature contrast between the
polar and equatorial regions. The position and orientation of jet streams vary from day to day.
General weather patterns (hot/cold, wet/dry) are related closely to the position, strength and
orientation of the jet stream (or jet streams).

Jetty: A structure (e.g.; a pier, or mole of wood or stone) extending into a sea, lake, or river to
influence the current or tide or to protect a harbor.

Katabatic Wind: A wind that blows down a topographic incline such as a hill, mountain, or
glacier as a result of cold, dense air flowing downhill.

Knot: Unit of speed used in aviation and marine activities which is equal to 1 nautical mile per
hour or about 1.15 statue miles an hour.

Land Breeze: A wind that blows from the land towards a body of water and caused by the
difference in surface temperature (heating) of the land and water. Also known as an offshore
breeze.

Landspout: Slang for a tornado that does not arise from organized storm-scale rotation and
therefore is not associated with a wall cloud (visually) or a mesocyclone (on radar). Landspouts
typically are observed beneath Cbs or towering cumulus clouds (often as no more than a dust
whirl), and essentially are the land-based equivalents of waterspouts. It is believed that most
California tornadoes are of the landspout variety.

La Niña: The cool phase of the Southern Oscillation (SO), or the opposite of El Niño.
Characterized by the cooling of the sea surface temperatures (SST) in the central and eastern
equatorial Pacific Ocean. See El Niño, Southern Oscillation and ENSO.

Lapse Rate: The rate of change of an atmospheric variable, usually temperature, with height. A
steep lapse rate implies a rapid decrease in temperature with height (a sign of instability) and a
steepening lapse rate implies that destabilization is occurring.

Large-scale: See synoptic-scale.

Lee Effect: The effect of topography on winds to the lee (downwind) side of an obstacle such as
a steep island, cliff, or mountain range.

Leeside: The downwind side of a mountain chain.

Leeside Low: Extratropical cyclones that form on the downwind (lee) side of a mountain chain.
In the United States, they frequently form on the eastern side of the Rockies and Sierra Nevada.

Left Front Quadrant: The area downstream from and to the left of an upper-level jet max (as
would be viewed looking along the direction of flow). Upward motion and severe thunderstorm
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potential sometimes are increased in this area relative to the wind speed maximum. Also, see
right rear quadrant.

Lightning: A sudden visible flash of energy and light caused by electrical discharges from
thunderstorms.

Lightning Flash: The total luminous phenomenon accompanying a lightning discharge. It may
be composed of one to a few tens of strokes that use essentially the same channel to ground.

Lightning Stroke: Any of a series of repeated electrical discharges comprising a single lightning
discharge (strike). Specifically, in the case of a cloud-to-ground discharge, a leader plus its
subsequent return streamer.

Likely: An NWS precipitation descriptor for a 60% or 70% chance of measurable precipitation
(0.01”). When the precipitation is showery or convective in nature, the term numerous will
occasionally be used. See Precipitation Probability (PoP).

Loaded Gun (Sounding): Slang for a sounding characterized by extreme instability but
containing a cap, such that explosive thunderstorm development can be expected if the cap can
be weakened or the air below it heated sufficiently to overcome it.

Local Flooding: Flooding conditions over a relatively limited (localized) area.

Local Storm Report (LSR): A product issued by local NWS offices to inform users of reports
of severe and/or significant weather-related events.

Longwave Trough: A trough in the prevailing westerly flow aloft which is characterized by
large length and (usually) long duration. Generally, there are no more than about five longwave
troughs around the Northern Hemisphere at any given time. Their position and intensity govern
general weather patterns (e.g., hot/cold, wet/dry) over periods of days, weeks, or months. Smaller
disturbances (e.g., shortwave troughs) typically move more rapidly through the broader flow of a
longwave trough, producing weather changes over shorter time periods (a day or less).

Low: A region of low pressure, marked as “L” on a weather map. A low center is usually
accompanied by precipitation, extensive cloudiness, and moderate winds. See cyclone.

Low Clouds: The bases of these clouds range from near the surface to about 6,500 feet in middle
latitudes. These clouds are almost entirely of water, but the water may be supercooled at sub-
freezing temperatures. Low clouds at sub-freezing temperatures can also contain snow and ice
particles. The two most common members of this family are stratus and stratocumulus.

Macroburst: One of 2 categories of downbursts (the other category is called a microburst). This
Downburst has an affected outflow area of at least 2.5 miles wide and peak winds lasting
between 5 and 20 minutes. Intense macrobursts may cause tornado-force damage up to F-3.

Main Stem: The reach of a river/stream formed by the tributaries that flow into it.

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Major Flooding: A general term including extensive inundation and property damage. (Usually
characterized by the evacuation of people and livestock and the closure of both primary and
secondary roads.)

Mammatus Clouds: Rounded, smooth, sack-like protrusions hanging from the underside of a
cloud (usually a thunderstorm anvil). Mammatus clouds often accompany severe thunderstorms,
but do not produce severe weather; they may accompany non-severe storms as well.

Marine Inversion: A temperature inversion created by the cooling of a warm air mass from
below by the cooler ocean.

Marine Weather Statement: The NWS will issue this statement: 1. To provide follow-up
information on Special Marine Warnings and to cancel all or part of a warning. 2. To describe
short duration, non-severe, but potentially hazardous conditions which sustained winds or
frequent gusts are less than 34 knots for 2 hours or less. Short-lived increases in winds, although
below threshold for Special Marine Warnings, that may make small craft handling difficult
especially for inexperienced boaters. 3. To provide information for a variety of conditions not
covered by warnings or routine forecasts (e.g., low water conditions, dense fog, etc.). 4. To
discuss increasing or decreasing winds and to convey details on possible later warnings.

Maritime Air Mass: A moist air mass originating over the ocean.

MB: An acronym for millibars.

Mean Low Water (MLW): The average height of the daily low tides recorded over a 19-year
period at a specific location.

Mean Lower Low Water (MLLW): The average height of the lower of the two low tides
occurring during a tidal cycle recorded over a 19-year period at a particular location.

Mean Sea Level (MSL): The average height of the surface of the sea at a particular location for
all stages of the tide over a 19-year period. This is usually determined from the hourly height
readings of the tide gage at that site.

Mean Temperature: The average of a series of temperatures taken over a period of time, such
as a day or a month.

Measurable: Precipitation of 0.01” or more.

Medium Range: In forecasting, (generally) three to seven days in advance.

Melting Level: The altitude which ice crystals and snowflakes melt as they descend through the
atmosphere.

Meniscus: The curved surface of the liquid at the open end of a capillary column, as in a rain
gage.

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Meridional Flow: Large-scale atmospheric flow in which the north-south component (i.e.,
longitudinal, or along a meridian) is pronounced. The accompanying zonal (east-west)
component often is weaker than normal. Compare with zonal flow.

Mesocyclone (MESO): A storm-scale region of rotation, typically around 2-6 miles in diameter
and often found in the right rear flank of a supercell (or often on the eastern, or front, flank of an
HP storm). The circulation of a mesocyclone covers an area much larger than the tornado that
may develop within it. Properly used, mesocyclone is a radar term; it is defined as a rotation
signature appearing on Doppler radar that meets specific criteria for magnitude, vertical depth,
and duration.

Mesonet: A regional network of observing stations (usually surface stations) designed to

diagnose mesoscale weather features and their associated processes.

Mesoscale: Size scale referring to weather systems smaller than synoptic-scale systems but
larger than storm-scale systems. Horizontal dimensions generally range from around 50 miles to
several hundred miles. Squall lines and large thunderstorm complexes are examples of mesoscale
weather systems.

METAR: A weather observation near ground level. It may include date and time, wind,
visibility, weather and obstructions to vision, sky condition, temperature and dew point, sea level
pressure, precipitation amount and other data used for aircraft operations.

Meteorology: The study of the atmosphere and atmospheric phenomena.

Microburst: One of 2 categories of downbursts (the other category is called a macroburst). This
downburst has an affected outflow area of less than 2.5 miles wide and peak winds lasting less
than 5 minutes. They may induce dangerous horizontal/vertical wind shears, which can adversely
affect aircraft performance and cause property damage. They can be sub-classified into either dry
or wet microburst depending on how much (or little) rain accompanies the microburst when it
reaches the ground. Most microbursts are rather short-lived (5 minutes or so), but on rare
occasions they have been known to last up to 6 times that long.

Middle Clouds: In the middle family are the altostratus, altocumulus, and nimbostratus clouds.
The height of the bases of these clouds ranges from 6,500 to 23,000 feet in middle latitudes.
These clouds are primarily water; however, much of the water may be supercooled and the
clouds can contain some ice crystals.

Mid-Latitude Areas: Areas between 30° and 60° north and south of the Equator.

Millibar (mb): Unit of atmospheric pressure. It is equal to 0.03” of mercury and 100 Pa (pascal).
One thousand millibars equals 29.55” of mercury on a barometer. Normal surface pressure is
approximately 1013 millibars.

Minor Flooding: A general term indicating minimal or no property damage but possibly some
public inconvenience.

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Minor Tidal Overflow: Minor flooding caused by high tides, which results in little if any
damage.

Mist (BR): A visible aggregate of minute water particles suspended in the atmosphere that
reduces visibility to less than 7 statue miles, but greater than or equal to 5/8 statue miles.

Mixing: Air movements (usually vertical) that make the properties of a parcel of air
homogeneous. It may result in a lapse rate approaching the moist or dry adiabatic rate.

Model: A mathematical representation of a process, system, or object developed to understand

its behavior or to make predictions. The representation always involves certain simplifications
and assumptions. Models are one of the primary forecasting tools used in the NWS.

Model Output Statistics (MOS): A set of statistical equations that use model output to forecast
the probability of precipitation, high and low temperature, cloud cover, and precipitation amount
for many cities across the USA. The statistical equations were specifically tailored for each
location, taking into account factors such as each location's climate.

Monsoon: A persistent seasonal wind, often responsible for seasonal precipitation regime or a
wind which blows from opposite directions between winter and summer. Usually the wind blows
from land to sea in winter and from sea to land in summer. In the Southwest U.S. the “Southwest
Monsoon” occurs during late summer, producing usually diurnal thunderstorms. For many desert
locations, this is the cause of the majority of the annual rainfall.

MOS: An acronym for Model Output Statistics.

Mostly Clear:When the predominant/average sky condition is covered 1/8 to 2/8 with opaque
(not transparent) clouds. Sometime called Mostly Sunny if it is during the day.

Mostly Cloudy: When the predominant/average sky condition is covered by more than half, but
not completely covered by opaque (not transparent) clouds. In other words, 5/8 to 7/8 of the sky
is covered by opaque clouds.

Mostly Sunny: When the predominant/average daytime sky condition is covered 1/8 to 2/8 with
opaque (not transparent) clouds. Same as mostly clear.

MRF - Medium-Range Forecast model: The MRF was one of the main models forecasters use
for the medium range time period beyond 48 hours into the future. It is has been replaced by the
Global Forecast System (GFS).

MSLP: Acronym for Mean sea level pressure.

Muggy: Colloquially descriptive of warm and especially humid weather.

Multicell Thunderstorms: These thunderstorms are organized in clusters of at least 2-4 short-
lived cells. Each cell generates a cold air outflow and these individual outflows combine to form
a large gust front. Convergence along the gust front causes new cells to develop every 5 to 15
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minutes. The cells move roughly with the mean wind.

NAM: An acronym for the North American model. generated every 6 hours by NCEP.

National Environmental Satellite, Data, and Information Service (NESDIS): NESDIS

collects, processes, stores, analyzes, and disseminates various types of hydrologic, meteorologic,
and oceanic data. NESDIS is also responsible for the development of analytical and descriptive
products so as to meet the needs of its users.

National Oceanographic and Atmospheric Administration (NOAA): A branch of the US

Department of Commerce, NOAA is the parent organization of the NWS. Other agencies within
NOAA include: National Environmental Satellite, Data, and Information Service, the National
Marine Fisheries Service, and the National Ocean Service.

National Centers for Environmental Prediction (NCEP): The National Oceanic and
Atmospheric Administration created the National Centers for Environmental Prediction (NCEP)
to take advantage of improving technology and better serve the public and modernized NWS.
The NCEP's goal is to protect life and property, as well as mitigate economic loss, by providing
accurate forecasts and forecast guidance products to weather service field offices. The NCEP
prepares and makes available national forecasts and outlooks of weather and climate.
Meteorologists currently generate weather forecasts to seven days. Climate predictions are made
for two weeks out to a year. Nine national centers comprise the NCEP: Aviation Weather Center,
Climate Prediction Center, Environmental Modeling Center, Hydrometeorological Prediction
Center, NCEP Central Operations, Ocean Prediction Center, Space Environmental Center, Storm
Prediction Center, and Tropical Prediction Center.

National Climatic Data Center (NCDC): Located in Asheville, North Carolina, the agency that
archives and distributes climatic and forecast data.

National Fire Danger Rating System (NFDRS): A system that directly integrates the effects of
fuels, topography, and weather into components that associates with occurrence and fire behavior
potential. The system uses the components to derive indices that indicate the number of fires,
difficulty of containment, and finally, the total fire control job in a rating area. The system is
intended to provide guidance for short-range planning by evaluating the near upper limits of the
behavior of fires that might occur in an area during the rating period. It is not designed to serve
as a direct fire behavior forecast.

National Hurricane Center (NHC): This center maintains a continuous watch on tropical
cyclones over the Atlantic, Caribbean, Gulf of Mexico, and the Eastern Pacific from 15 May
through November 30. The Center prepares and distributes hurricane watches and warnings.
During the “off-season” NHC provides training for U.S. emergency managers and
representatives from many other countries that are affected by tropical cyclones. NHC also
conducts applied research to evaluate and improve hurricane forecasting techniques, and is
involved in public awareness programs.

National Weather Service (NWS): The National Weather Service (NWS) provides weather,
hydrologic, and climate forecasts and warnings for the United States, its territories, adjacent
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waters and ocean areas, for the protection of life and property and the enhancement of the
national economy. NWS data and products form a national information database and
infrastructure which can be used by other governmental agencies, the private sector, the public,
and the global community. This mission is accomplished by providing warnings and forecasts of
hazardous weather, including thunderstorms, flooding, hurricanes, tornadoes, winter weather,
tsunamis, and climate events. The NWS is the sole United States official voice for issuing
warnings during life-threatening weather situations.

Neap Tide: A minimum tide occurring at the first and third quarters of the moon.

Negative-Tilt Trough: An upper level system which is tilted to the west with increasing latitude
(i.e., with an axis from southeast to northwest). A negative-tilt trough often is a sign of a
developing or intensifying system.

Negative Vorticity Advection (NVA): A region of negative vorticity usually several hundred of
kilometers wide on a upper level chart that moves with the general wind flow. It aids in weather
prediction by showing where regions of sinking air. This is typically associated with clear skies.

NESDIS: An acronym for National Environmental Satellite, Data, and Information Service.

NEXRAD: An acronym that stands for NEXt generation of weather RADar. It is a

technologically-advanced weather radar. NEXRAD is a high-resolution Doppler radar with
increased emphasis on automation, including use of algorithms and automated volume scans.
NEXRAD units are known as WSR-88D.

Nimbostratus (Ns): A dark, gray cloud characterized by more or less continuously falling
precipitation. It is not accompanied by lightning, thunder, or hail. They normally occur between
6,500 and 23,000 feet above the ground.

NOAA: An acronym for National Oceanographic and Atmospheric Administration.

NOAAPORT Broadcast System: This provides a one-way broadcast communication of NOAA

environmental data and information in near-real time to NOAA and external users. This
broadcast service is implemented by a commercial provider of satellite communications utilizing
C-band. Weather data is collected by GOES satellite environmental sensors and NWS observing
systems, and processed to create products. The products are fed to the AWIPS Network Control
Facility (NCF) which routes the products to the appropriate NOAAPORT channel for uplink and
broadcast.

NOAA All-Hazards Radio: It is the voice of the NWS. NOAA All-Hazards Radio broadcasts
NWS warnings, watches, forecasts and other hazard information from other government
agencies 24 hours a day. It is provided as a public service by the Department of Commerce's
National Oceanic and Atmospheric Administration. The NOAA All-Hazards Radio network has
more than 700 stations.

NOAA Weather Wire Service (NWWS): The NOAA Weather Wire Service is the primary
telecommunications network for NWS forecasts, warnings and other products to the mass media
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(newspapers, radio stations, TV, etc.) and emergency management agencies. The NWWS is a
satellite communications system that transmits NWS products directly from NWS offices to
external users. The NWWS satellite communications system is operated by GTE Corp., under
contract to the NWS. The system uses satellite transmitting (i.e. “uplink”) equipment at more
than 58 major NWS forecast offices.

Noctilucent Clouds: Wavy, thin, bluish-white clouds that are best seen at twilight in polar
latitudes. They form at altitudes about 80 to 90 km above the Earth's surface.

North American Model (NAM): The North American model, which is generated every 6 hours
by NCEP. This model is more regional in nature and contains a higher spatial resolution than the
more global GFS model.

Normal: The long-term average value of a meteorological element for a certain area. For
example, “temperatures are normal for this time of year”. Usually averaged over 30 years.

Nowcast: A weather forecast, generally out to six hours or less. This is also called a Short Term
Forecast.

NVA: An acronym for Negative Vorticity Advection.

NSSL (National Severe Storms Laboratory): NSSL is one of NOAA's internationally known
Environmental Research Laboratories, leading the way in investigations of all aspects of severe
weather. Headquartered in Norman OK with staff in Colorado, Nevada, Washington, Utah, and
Wisconsin, the people of NSSL, in partnership with the NWS, are dedicated to improving severe
weather warnings and forecasts in order to save lives and reduce property damage.

Nucleus: A particle of any nature upon which molecules of water or ice accumulate.

Numerical Weather Prediction (NWP): Forecasting weather by the use of numerical models,
run on high speed computers. Most of the NWP for the NWS is done at the National Centers for
Environmental Prediction (NCEP).

Numerous: An NWS convective precipitation descriptor for a 60% or 70% chance of

measurable precipitation (0.01”). See Precipitation Probability (PoP).

NWP: An acronym for Numerical Weather Prediction.

NWS: An acronym for the National Weather Service.

Occluded Front (Occlusion): A complex frontal system that ideally forms when a cold front
overtakes a warm front. When the air is colder than the air ahead of it, the front is called a cold
occlusion. When the air behind the front is milder than the air ahead of it, it is called a warm
occlusion. These processes lead to the dissipation of the front in which there is no gradient in
temperature and moisture.

Ocean Prediction Center (OPC): This is one of 9 centers that comprise the National Centers
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for Environmental Prediction (NCEP). The Ocean Prediction Center (OPC) is an integral
component of NCEP. OPC is located at the NOAA Science Center in Camp Springs, MD. The
primary responsibility is the issuance of marine warnings, forecasts, and guidance in text and
graphical format for maritime users. Also, the OPC quality controls marine observations globally
from ship, buoy, and automated marine observations for gross errors prior to being assimilated
into computer model guidance. In addition OPC coordinates with the National Hurricane Center
(NHC) with forecast points for tropical cyclones in the Atlantic Ocean E of 65°W.

Offshore Flow: Air movement from the interior toward the ocean, usually associated with dry
weather. Can be caused by any combination of offshore pressure gradients (higher pressure over
the interior and lower pressure off the coast), temperature gradients (colder air over the interior
and warmer air off the coast), and/or northeast winds aloft that transfer to the surface. See Foehn
and Santa Ana.

Offshore Forecast (OFF): This marine forecast is designed to serve users who operate beyond
the coastal waters where it usually requires more than a day or more of sailing to and from port
(from 60 to 250 nautical miles). These users are mainly commercial fishermen and merchant
shipping and, to a lesser extent, government and research vessels and large recreational craft.

Omega: A term used to describe vertical motion in the atmosphere. Omega is determined by the
amount of spin (or large scale rotation) and warm (or cold) advection present in the atmosphere.
On a weather forecast chart, high values of omega (or a strong omega field) relate to upward
vertical motion in the atmosphere. If this upward vertical motion is strong enough and in a
sufficiently moist air mass, precipitation results.

Omega High: A blocking ridge of high pressure that forms in the middle or upper troposphere. It
looks like the Greek letter omega (Ω).

Onshore Flow: Air movement from the ocean across land. A sea breeze is indicative of onshore
flow. It usually indicates an increase in moisture. Can be caused by onshore pressure gradients
(higher pressure over the ocean and lower pressure over land).

Orographic: Related to, or caused by, physical geography (such as mountains or sloping
terrain).

Orographic Lifting (Upslope Flow): Occurs when air is forced to rise and cool due to terrain
features such as hills or mountains. If the cooling is sufficient, water vapor condenses into
clouds. Additional cooling results in rain or snow. It can cause extensive cloudiness and
increased amounts of precipitation in higher terrain.

Orographic Precipitation: Precipitation which is caused by hills or mountain ranges deflecting

the moisture-laden air masses upward, causing them to cool and precipitate their moisture.

Orphan Anvil: Slang for an anvil from a dissipated thunderstorm, below which no other clouds
remain.

Outflow Boundary: A storm-scale or mesoscale boundary separating thunderstorm-cooled air

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(outflow) from the surrounding air; similar in effect to a cold front, with passage marked by a
wind shift and usually a drop in temperature. Outflow boundaries may persist for 24 hours or
more after the thunderstorms that generated them dissipate, and may travel hundreds of miles
from their area of origin. New thunderstorms often develop along outflow boundaries, especially
near the point of intersection with another boundary (cold front, dry line, another outflow
boundary, etc.)

Overcast (OVC): An official sky cover classification for aviation weather observations, when
the sky is completely covered by an obscuring phenomenon. This is applied only when obscuring
phenomenon aloft are present--that is, not when obscuring phenomenon are surface-based, such
as fog.

Overrunning: A weather pattern in which a relatively warm air mass is in motion above another
air mass of greater density at the surface. Embedded thunderstorms sometimes develop in such a
pattern; severe thunderstorms (mainly with large hail) can occur, but tornadoes are unlikely.
Overrunning often is applied to the case of warm air riding up over a retreating layer of colder
air, as along the sloping surface of a warm front. Such use of the term technically is incorrect,
but in general it refers to a pattern characterized by widespread clouds and steady precipitation
on the cool side of a front or other boundary.

Overshooting: The failure of the radar to detect a target due to the radar beam passing above the
target.

Overshooting Top (or Penetrating Top): A dome-like protrusion above a thunderstorm anvil,
representing a very strong updraft and hence a higher potential for severe weather with that
storm. A persistent and/or large overshooting top (anvil dome) often is present on a supercell. A
short-lived overshooting top, or one that forms and dissipates in cycles, may indicate the
presence of a pulse storm or a cyclic storm.

Ozone: A nearly colorless (but faintly blue) gaseous form of oxygen, with a characteristic odor
like that of weak chlorine. Its chemical formula is O3. It is usually found in trace amounts in the
atmosphere, but it is primarily found at 30,000 to 150,000 feet above the ground. Its production
results from photochemical process involving ultraviolet radiation. Because it absorbs harmful
radiation at those heights, it is a very beneficial gas. However, photochemical processes
involving industrial/vehicle emissions can produce ozone near the ground. In this case, it can be
harmful to people with respiratory or heart problems.

Pacific High: A semipermanent anticyclone located in the Eastern North Pacific.

Palmer Drought Severity Index: An index whereby excesses or deficiencies of precipitation are
determined in relation to average climate values. The index takes in to account precipitation,
potential and actual evapotranspiration, infiltration of water into the soil, and runoff.

Partly Cloudy: When the predominant/average sky condition is covered 3/8 to 4/8 with opaque
(not transparent) clouds. Same as Partly Sunny.

Partly Sunny: When the predominant/average sky condition is covered 3/8 to 4/8 with opaque
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(not transparent) clouds. Same as Partly Cloudy.

Patchy or Patches of: Used with fog to denote random occurrence over relatively small areas.

Peak Wind Speed: The maximum instantaneous wind speed since the last observation that
exceeded 25 knots.

Pineapple Connection or Pineapple Express: Slang for a water vapor plume from the tropics.
Usually used on the West Coast describing a plume of water vapor extending from Hawaii.

Polar Front: A semipermanent, semicontinuous front that separates tropical air masses from
polar air masses.

Polar Jet Stream: A jet stream that is associated with the polar front in the middle and high
latitudes. It is usually located at altitudes between 9,000 and 12,000 km.

Polar Orbiting Satellite: A weather satellite which travels over both poles each time it orbits the
Earth. It orbits about 530 miles (850 km) above the Earth's surface.

Ponding: In flat areas, runoff collects, or ponds in depression and cannot drain out. Flood waters
must infiltrate slowly into the soil, evaporate, or be pumped out.

Popcorn Convection: Slang for showers and thunderstorms that form on a scattered basis with
little or no apparent organization, usually during the afternoon in response to diurnal heating.
Individual thunderstorms typically are of the type sometimes referred to as air-mass
thunderstorms. These thunderstorms are small, short-lived, very rarely severe, and they almost
always dissipate near or just after sunset. See Pulse Thunderstorm, Air Mass Thunderstorm and
Single Cell Thunderstorm.

Pops: An acronym for Probability of Precipitation or Precipitation Probabilities.

Positive-Tilt Trough: An upper level system which is tilted to the east with increasing latitude
(i.e., from southwest to northeast). A positive-tilt trough often is a sign of a weakening weather
system, and generally is less likely to result in severe weather than a negative-tilt trough if all
other factors are equal.

Positive Vorticity Advection (PVA): A region of positive vorticity usually several hundred of
kilometers wide on an upper level chart that moves with the general wind flow. It aids in weather
prediction by showing where regions of rising air occur. This usually results in clouds and
precipitation.

Precipitable Water (PW): It measures the depth of liquid water at the surface that would result
after precipitating all of the water vapor in a vertical column usually extending from the surface
to 300 mb.

Precipitation: 1. The process where water vapor condenses in the atmosphere to form water
droplets that fall to the Earth as rain, sleet, snow, hail, etc. 2. As used in hydrology, precipitation
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is the discharge of water, in a liquid or solid state, out of the atmosphere, generally onto a land or
water surface. It is the common process by which atmospheric water becomes surface, or
subsurface water. The term “precipitation” is also commonly used to designate the quantity of
water that is precipitated. Precipitation includes rainfall, snow, hail, and sleet, and is therefore a
more general term than rainfall.

Prescribed Burn: Fire applied to wildland fuels, in a definite place for a specific purpose under
exacting weather and fuel conditions (the prescription), to achieve a specific objective of
resource management.

Present Movement: The best estimate of the movement of the center of a tropical cyclone at a
given time and given position. This estimate does not reflect the short-period, small scale
oscillations of the cyclone center.

Pressure: The force exerted by the weight of the atmosphere, also known as atmospheric
pressure. When measured on a barometer, it is referred to as barometric pressure and it is
expressed in inches of mercury, millibars, or kiloPascals.

Pressure Gradient: The amount of pressure change occurring over a given distance.

Pressure Gradient Force: A three-dimensional force vector operating in the atmosphere that
accelerates air parcels away from regions of high pressure and toward regions of low pressure in
response to an air pressure gradient. Usually resolved into vertical and horizontal components.

Pressure Tendency: The character and amount of atmospheric pressure change during a
specified period of time, usually 3-hour period preceding an observation.

Prevailing Visibility: The visibility that is considered representative of conditions at the station;
the greatest distance that can be seen throughout at least half the horizon circle, not necessarily
continuous.

Prevailing Westerlies: Winds in the middle latitudes (approximately 30° to 60° N/S) that
generally blow from west to east.

Prevailing Wind: A wind that consistently blows from one direction more than from any other.

Precipitation Probabilities (PoP): It is defined as the likelihood of occurrence (expressed as a

percent) of a measurable amount of liquid precipitation (or the water equivalent of frozen
precipitation) during a specified period of time at any given point in the forecast area.
Measurable precipitation is defined as equal to or greater than 0.01” or 0.2 mm. Normally, the
period of time is 12 hours, unless specified otherwise.

Profiler: An instrument designed to measure horizontal winds directly above its location, and
thus measure the vertical wind profile. Profilers operate on the same principles as Doppler radar.

Psychrometer: An instrument used to measure the water vapor content of the air. It consists of
two thermometers, one of which is an ordinary glass thermometer, while the other has its bulb
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covered with a jacket of clean muslin which is saturated with distilled water prior to use. After
whirling the instrument, the dew point and relative humidity can be obtained with the aid of
tables.

Public Information Statement (PNS): This narrative statement can be used for a current or
expected nonhazardous event of general interest to the public that can usually be covered with a
single message. This may include: Unusual atmospheric phenomena such as sun dogs, halos,
rainbows, aurora borealis, lenticular clouds, and stories about a long-term dry/cold/wet/warm
spell; public educational information and activities, such as storm safety rules, awareness
activities, storm drills, etc, or information regarding service changes, service limitations,
interruptions due to reduced or lost power or equipment outages, or special information
clarifying interpretation of NWS data. For example, this product may be used to inform users of
radar equipment outages or special information clarifying interpretation of radar data originating
from an unusual source which may be mistaken for precipitation (such as chaff drops, smoke
plumes, etc., that produces echoes on the radar display.

Pulse Thunderstorm: A thunderstorm within which a brief period (pulse) of strong updraft
occurs, during and immediately after which the storm produces a short episode of severe
weather. These storms generally are not tornado producers, but often produce large hail and/or
damaging winds. Also, see Air Mass Thunderstorm, Popcorn Convection and Single Cell
Thunderstorm.

PVA: An acronym for Positive Vorticity Advection.

QPF (Quantitative Precipitation Forecast): A spatial and temporal precipitation forecast that
will predict the potential amount of future precipitation for a specified region, or area.

RADAR: An instrument used to detect precipitation by measuring the strength of the

electromagnetic signal reflected back. (RADAR= Radio Detection and Ranging)

Radar Beam: The straight line that a radar pulse travels along. As the radar beam gets further
away from the radar, it gets wider and wider. In order for a precipitation target to be detected by
the radar, it must fill the entire radar beam; therefore, the radar will have a difficult time
detecting small showers and thunderstorms at a great distance from the radar.

Radar Reflectivity: The sum of all backscattering cross-sections (e.g., precipitation particles) in
a pulse resolution volume divided by that volume.

Radiation: Energy emitted in the form of electromagnetic waves. Radiation has differing
characteristics depending upon the wavelength. Radiation from the sun has a short wavelength
(ultra-violet) while energy re-radiated from the Earth's surface and the atmosphere has a long
wavelength (infra-red).

Radiation Fog: Fog produced from the air near the ground being cooled to saturation by contact
with the cold ground. The cooling of the ground results from night time loss of heat from the
Earth to space (terrestrial radiation). Favorable conditions for radiation fog are clear sky, little or
no wind, and high relative humidity. It occurs in stable air and is primarily a night time or early
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morning phenomenon. As the Earth and the lower layers of the atmosphere warm during the day,
air that was stable during the early morning hours may become unstable - at least in the lower
levels. For this reason visibility usually improves as the temperature rises during the day. Mixing
in the lower levels disperses the fog into a thicker layer, and eventually it evaporates into the
warmer air. When cloud layers form aloft over a radiation fog and retard heating from the sun,
visibility improvement is very slow. It is also known as Ground Fog and Valley Fog, and in
Central California as tule fog.

Radiation Inversion: It is a thermally produced, surface-based inversion formed by rapid

radiational cooling of the Earth's surface at night. It does not usually extend above the lower few
hundred feet. Conditions which are favorable for this type of inversion are: long nights, clear
skies, dry air, little or no wind, and a cold or snow covered surface.

Radiational Cooling: The cooling of the Earth's surface. At night, the Earth suffers a net heat
loss to space due to terrestrial cooling. This is more pronounced when you have a clear sky.

Radiosonde: An instrument attached to a weather balloon that transmits pressure, humidity,

temperature, and wind data to a ground-based receiving station as it ascends.

Rain (RA): Precipitation, either in the form of drops larger than 0.02” (0.5 mm), or smaller
drops, which in contrast to drizzle, are widely separated.

Rain Shadow: Areas of the leeward side of a mountain or mountain range which often receive
much less rain than the windward side.

Rainbow: An arc that exhibits in concentric bands the colors of the spectrum and is formed
opposite the sun by refraction and reflection of the sun's rays in rain drops.

RAOB: An acronym for Radiosonde Observation. See Radiosonde.

Record Report: This non-routine narrative product is issued by the NWS to report
meteorological and hydrological events that equal or exceed existing records.

Red Flag: This a fire weather program which highlights the onset of critical weather conditions
conducive to extensive wildfire occurrences.

Red Flag Warning: A term used by fire-weather forecasters to call attention to weather
conditions that may result in extreme burning conditions. It is issued when it is an on-going
event or the fire weather forecaster has a high degree of confidence that Red Flag criteria will
occur within 24 hours of issuance. Red Flag criteria occurs whenever the following forecast
weather parameters are forecasted to met: 1. A sustained wind average 15 mph or greater, 2.
Relative humidity less than or equal to 25%, and when dry lightning is expected.

Reflectivity: A radar product designed to determine the strength or the intensity of a

precipitation target. In order for the radar to calculate the reflectivity, it sends out a small burst of
energy. This energy strikes the small water particles located in the precipitation target. The more
of these particles located in the precipitation target, the greater the return of energy returned back
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to the radar. One will see a greater reflectivity return from heavy rain than light rain. Reflectivity
is expressed in the units of dBZ where dB stands for decibels and the Z stands for reflectivity.
See dBZ.

Relative Humidity: A dimensionless ratio, expressed in percent, of the amount of atmospheric

moisture present relative to the amount that would be present if the air were saturated. Since the
latter amount is dependent on temperature, relative humidity is a function of both moisture
content and temperature. As such, relative humidity by itself does not directly indicate the actual
amount of atmospheric moisture present. See dew point.

Retrogression (or Retrograde Motion): Movement of a weather system in a direction opposite

to that of the basic flow in which it is embedded, usually referring to a closed low or a longwave
trough which moves westward.

Return Flow: South winds on the back (west) side of an eastward-moving surface high pressure
system.

Rex Block: A blocking pattern where there is an upper level high located directly north of a
closed low.

RFC (River Forecast Center): Centers that serve groups of Weather Service Forecast offices in
providing hydrologic guidance and is the first echelon office for the preparation of river and
flood forecasts and warnings.

Ridge: An elongated area of high pressure in the atmosphere. Opposite of trough.

Right Rear Quadrant: The area upstream from and to the right of an upper-level jet max (as
would be viewed looking along the direction of flow). Upward motion and severe thunderstorm
potential sometimes are increased in this area relative to the wind speed maximum. Also, see left
front quadrant.

Rip Current: A strong, narrow current of surface water that flows seaward through the surf into
deeper water. Waves approaching the shoreline create a water buildup which results in a return
flow. This return flow (rip current) transports the excess water into deeper waters. Bubbles and
debris usually float on the surface of the rip current. Although this current is extremely localized,
they result in numerous deaths every year. These deaths are contributed to swimmers becoming
exhausted by trying to swim against the rip current. If you are a swimmer caught in a rip current,
wade sideways parallel to the beach until you are out of its pull. Another means of escape for
those who are good swimmers is to ride the current out beyond the surf zone where the rip
current dissipates then swim to shore outside the effects of the narrow current. This phenomenon
is sometimes mistakenly called a “rip tide” or an “undertow”.

River Basin: Drainage area of a river and its tributaries.

River Flood Statement (FLS): This product is used by the local NWS to update and expand the
information in the River Flood Warning. This statement may be used in lieu of a warning if
flooding is forecasted, imminent, or existing and it presents no threat to life or property. The
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statement will also be used to terminate a River Flood Warning.

River Flood Warning (FLW): This is product is issued by the local NWS when forecast points
(those that have formal gaging sites and established flood stages) at specific communities or
areas along rivers where flooding has been forecasted, is imminent, or is in progress. Flooding is
defined as the inundation of normally dry areas as a result of increased water levels in an
established water course. The flood warning normally specifies crest information. It usually
occurs 6 hours or later after the causative event and it is usually associated with widespread
heavy rain and/or snow melt or ice jams.

River Flooding: The rise of a river to an elevation such that the river overflows its natural banks
causing or threatening damage.

River Gage: A device for measuring the river stage.

Roll Cloud: A low, horizontal tube-shaped cloud associated with a thunderstorm gust front (or
sometimes with a cold front). Roll clouds are relatively rare; they are completely detached from
the thunderstorm base or other cloud features, thus differentiating them from the more familiar
shelf clouds. Roll clouds usually appear to be “rolling” about a horizontal axis, but should not be
confused with funnel clouds.

Rope (or Rope Funnel): A narrow, often contorted condensation funnel usually associated with
the decaying stage of a tornado. See rope stage.

Rope Cloud: In satellite meteorology, a narrow, rope-like band of clouds sometimes seen on
satellite images along a front or other boundary. The term sometimes is used synonymously with
rope or rope funnel.

Rope Stage: The dissipating stage of a tornado, characterized by thinning and shrinking of the
condensation funnel into a rope (or rope funnel). Damage still is possible during this stage.

Rotor Cloud: A turbulent cloud formation found in the lee of some large mountain barriers. The
air in the cloud rotates around an axis parallel to the mountain range.

RUC - Rapid Update Cycle: A numerical model run at NCEP that focuses on short-term (up to
12 hours) forecasts and small-scale weather features. Forecasts are prepared every 3 hours.

Runoff: That part of precipitation that flows toward streams on the surface of the ground or
within the ground. Runoff is composed of base flow and surface runoff.

Saffir-Simpson Hurricane Intensity Scale: This scale was developed in an effort to estimate
the possible damage a hurricane's sustained winds and storm surge could do to a coastal area.
The scale of numbers is based on actual conditions at some time during the life of the storm. As
the hurricane intensifies or weakens, the scale number is reassessed accordingly.

Sandstorm (SS): Particles of sand carried aloft by strong wind. The sand particles are mostly
confined to the lowest ten feet, and rarely rise more than fifty feet above the ground.
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Santa Ana Wind: A strong, hot, dry foehn-like wind that blows from the north, northeast, or
east into Southern California. Occasionally, the term is used even if the temperatures are low.
The winds are generated by surface high pressure (an anticyclone) located over the high deserts
of the Great Basin (Nevada) and produce warmth and dryness from compressional heating as the
air descends to lower elevations near the coast.

Scattered (SCT): 1. An official sky cover classification for aviation weather observations,
descriptive of a sky cover of 3/8 to 4/8. This is applied only when obscuring phenomenon aloft
are present--that is, not when obscuring phenomenon are surface-based, such as fog. 2. A NWS
convective precipitation descriptor for a 30%, 40%, and 50% chance of measurable precipitation
(> Trace). See Probability of Precipitation (PoP).

Scud (or Fractus): Small, ragged, low cloud fragments that are unattached to a larger cloud base
and often seen with and behind cold fronts and thunderstorm gust fronts. Such clouds generally
are associated with cool moist air, such as thunderstorm outflow.

Sea Breeze: A wind that blows from a sea or ocean towards a land mass as a result of
temperature and pressure gradients along the coastal interface. Also known as an onshore breeze.

Seas: This term is used in NWS Marine Forecasts to describe the combination or interaction of
wind waves and swells (combined seas) in which the separate components are not distinguished.
This includes the case when swells are negligible or are not considered in describing sea state.

Sea Level Pressure: The pressure value obtained by the theoretical reduction or increase of
barometric pressure to sea-level.

Sea Surface Temperature (SST): Surface temperature of ocean water. This data is collected
using IR satellite imagery, buoy and ship data.

Severe Thunderstorm: A strong thunderstorm with a tornado, wind gusts in excess of 58 mph
(50 knots), and/or hail with a diameter of 0.75” or more.

Severe Thunderstorm Warning (SVR): This is issued when either a severe thunderstorm is
indicated by the WSR-88D radar or a spotter reports a thunderstorm producing a hail 0.75” or
larger in diameter and/or winds equal or exceed 50 kts (58 mph); therefore, people in the affected
area should seek safe shelter immediately.

Severe Thunderstorm Watch (WWA): This is issued by the NWS when conditions are
favorable for the development of severe thunderstorms in and close to the watch area. The size of
the watch can vary depending on the weather situation. They are usually issued for a duration of
4 to 8 hours. They are normally issued well in advance of the actual occurrence of severe
weather. During the watch, people should review severe thunderstorm safety rules and be
prepared to move a place of safety if threatening weather approaches. The Watch is issued by the
Storm Prediction Center in Norman, Oklahoma. Prior to the issuance, SPC will usually contact
the affected local NWS Forecast Office and they will discuss what their current thinking is on the
weather situation. Afterwards, SPC will issue a preliminary Severe Thunderstorm Watch and
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then the affected NWFO will then adjust the watch (adding or eliminating counties) and issue it
to the public by way of a Watch Redefining Statement. During the watch, the local forecast
office will keep the you informed on what is happening in the watch area and also let the you
know when the watch has expired or been cancelled.

Severe Weather Statement (SVS): An NWS product which provides follow up information on
severe weather conditions (severe thunderstorm or tornadoes) which have occurred or are
currently occurring.

Shear: Variation in wind speed (speed shear) and/or direction (directional shear) over a short
distance. Shear usually refers to vertical wind shear, i.e., the change in wind with height.

Sheet Flow: Water flow that occurs overland in places where there are no defined channels; the
flood water spreads out over a large area at a uniform depth.

Shelf Cloud: A low, horizontal wedge-shaped arcus cloud, associated with a thunderstorm gust
front (or occasionally with a cold front, even in the absence of thunderstorms). Unlike the roll
cloud, the shelf cloud is attached to the base of the parent cloud above it (usually a
thunderstorm). Rising cloud motion often can be seen in the leading (outer) part of the shelf
cloud, while the underside often appears turbulent, boiling, and wind-torn. It is accompanied by
gusty, straight-line winds and is followed by precipitation.

Shoaling: The process whereby waves coming into shallow waters are slowed by bottom friction
and become closer together and steeper.

Short-Fuse Warning: A warning issued by the NWS for a local weather hazard of relatively
short duration. Short-fuse warnings include tornado warnings, severe thunderstorm warnings,
and flash flood warnings. Tornado and severe thunderstorm warnings typically are issued for
periods of an hour or less, flash flood warnings typically for three hours or less.

Short Term Forecast: This NWS narrative summary describes the weather in the local area and
includes a short-range forecast (not more than 6 hours). This product will be updated more
frequently when it is used during active weather. This product is also sometimes referred to as a
nowcast.

Shortwave (or Shortwave Trough): A disturbance in the mid or upper part of the atmosphere
which induces upward motion ahead of it. If other conditions are favorable, the upward motion
can contribute to thunderstorm development ahead of a shortwave.

Shower (SH): It implies short duration, intermittent, and scattered precipitation (rain, snow, ice
pellet) of a more unstable, convective nature.

SIGMET (SIGnificant METeorlogical Information): This NWS aviation product advises of

weather potentially hazardous to all aircraft other than convective activity. In the conterminous
U.S., SIGMETS covered are severe icing, severe or extreme turbulence, duststorms and
sandstorms lowering visibilities to less that three (3) miles, and/or volcanic ash.

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Significant Wave Height: The average height (trough to crest distance) of the one-third highest
waves. An experienced observer will most frequently report heights equivalent to the average of
the highest one-third of all waves observed.

Single Cell Thunderstorm: Generally, a thunderstorm not associated with a front or other type
of synoptic-scale forcing mechanism. Air mass thunderstorms typically are associated with
warm, humid air in the summer months; they develop during the afternoon in response to
insolation, and dissipate rather quickly after sunset. They generally are less likely to be severe
than other types of thunderstorms, but they still are capable of producing downbursts, brief heavy
rain, and (in extreme cases) hail over 0.75” in diameter. Also, see Air Mass Thunderstorm,
Popcorn Convection and Pulse Thunderstorm.

Sky Condition: Used in a forecast to describe the predominant/average sky condition based
upon octants (eighths) of the sky covered by opaque (not transparent) clouds. The usual
descriptors are: clear or sunny, 0/8, mostly clear or mostly sunny, 1/8 to 2/8, partly cloudy or
partly sunny, 3/8 to 4/8, mostly cloudy, 5/8 to 7/8, and cloudy, 8/8.

Sleet (PL): Describes solid grains of ice formed by the freezing of raindrops or the refreezing of
largely melted snowflakes. These grains usually bounce upon impact with the ground or
pavement. Heavy sleet is a relatively rare event defined as an accumulation of ice pellets
covering the ground to a depth of 0.5” or more. See Ice Pellets.

Slight Chance: An NWS precipitation descriptor for a 20 percent chance of measurable

precipitation (0.01”). When the precipitation is convective in nature, the term widely scattered or
isolated is used. See Precipitation Probability (PoP).

Small Craft Advisory: This is issued by the NWS to alert small boats to sustained (more than 2
hours) hazardous weather or sea conditions. These conditions may be either present or
forecasted. Winds in excess of 22 knots (25 mph), and less than 34 knots (39 mph), that may
cause hazardous conditions for operators of small vessels. The advisory may be issued for winds,
hazardous seas, or both.

Small Stream Flooding: Flooding of small creeks and streams.

Smog: Originally smog meant a mixture of smoke and fog. Now, it means air that has restricted
visibility due to pollution or pollution formed in the presence of sunlight--photochemical smog.

Smoke (FU): A suspension in the air of small particles produced by combustion. A transition to
haze may occur when smoke particles have traveled a great distance (25 to 100 miles or more)
and when the larger particles have settled out and the remaining particles have become widely
scattered through the atmosphere.

Snow (SN): Precipitation of frozen crystals, mostly branched in the form of six-pointed stars. It
usually falls steadily for several hours or more. Like drizzle, its intensity is based on visibility.
The amount of snow that falls is highly dependent upon temperature. For example, at 10°F, one
inch of precipitation will produce 30” of snow. At 20°F, one inch of precipitation will produce

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20” of snow. At 30°F, one inch of precipitation produces 10” of snow. At freezing, one inch
precipitation will produce approximately 6” of snow.

Snow Advisory: This product is issued by the NWS when a low pressure system produces snow
that may cause significant inconvenience, but do not meet warning criteria and if caution is not
exercised could lead to life threatening situations. The advisory criteria vary from area to area.

Snow and Blowing Snow Advisory: This product is issued by the NWS during situations that
cause significant inconvenience, but do not meet warning criteria and if caution is not exercised
could lead to life threatening situations. The warning criteria in this definition vary from area to
area.

Snow Depth: The combined total depth of both the old and new snow on the ground.

Snow Flurries: Intermittent light snowfalls of short duration (generally light snow showers) with
no measurable accumulation.

Snow Grains (SG): Precipitation of very small, white, and opaque grains of ice. They can be
distinguished from ice pellets, because ice pellets bounce and snow grains do not bounce at all.

Snow Pack: The combined layers of snow and ice on the ground at any one time. It is also called
snowcover.

Snow Pellets (GS): Precipitation of white, opaque grains of ice. The grains are round or
sometimes conical. Diameters range from about 0.08” to 0.2” (2mm to 5 mm).

Snow Shower (SHSN): It is a moderate snowfall of short duration. Some accumulation is

possible.

Sounding: A plot of the vertical profile of temperature and dew point (and often winds) above a
fixed location. Soundings are used extensively in weather forecasting, e.g., to determine
instability, locate temperature inversions, measure the strength of the cap, obtain the convective
temperature, measure the depth of the marine layer, etc.

Southern Oscillation (SO): A “see-saw” in surface pressure in the tropical Pacific characterized
by simultaneously opposite sea level pressure anomalies at Tahiti, in the eastern tropical Pacific
and Darwin, on the northwest coast of Australia. The SO was discovered by Sir Gilbert Walker
in the early 1920s. Later, the three-dimensional east-west circulation related to the SO was
discovered and named the “Walker Circulation”. The SO oscillates with a period of 2-5 years.
During one phase, when the sea level pressure is low at Tahiti and High at Darwin, the El Niño
occurs. The cold phase of the SO, called La Niña, is characterized by high pressure in the eastern
equatorial Pacific, low in the west, and by anomalously low sea surface temperature (SST) in the
central and eastern Pacific. This is called El Niño Southern Oscillation or ENSO.

Space Environment Center (SEC): This center provides real-time monitoring and forecasting
of solar and geophysical events, conducts research in solar-terrestrial physics, and develops
techniques for forecasting solar and geophysical disturbances. SEC's Space Weather Operations
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is jointly operated by NOAA and the U.S. Air Force and is the national and world warning center
for disturbances that can affect people and equipment working in the space environment.

SPC: An acronym for the Storm Prediction Center.

Special Marine Warning (SMW): This is issued by the NWS for hazardous weather conditions
over water (thunderstorms, funnel clouds, or waterspouts) usually of short duration (2 hours or
less) and producing sustained winds or frequent gusts of 34 knots or more.
These are tone alerted on NOAA All-Hazards Radio. Boaters can also get this information by
tuning into Coast Guard and commercial radio stations that transmit marine weather information.

Special Weather Statement (SPS): This is issued by the NWS to provide additional information
about expected or ongoing significant weather changes not covered in other statements. This
would include non-severe convective, winter weather, and non-precipitation events.

Specific Humidity: In a system of moist air, the ratio of the mass of water vapor to the total
mass of the system.

Speed Shear: The component of wind shear which is due to a change in wind speed with height,
e.g., southwesterly winds of 20 mph at 10,000 feet increasing to 50 mph at 20,000 feet. Speed
shear is an important factor in severe weather development, especially in the middle and upper
levels of the atmosphere.

Spot Forecasts: These are NWS site-specific fire weather forecasts. They are issued upon
request of User Agencies for wildfires, prescribed burns, hazardous material incidents, or special
projects.

Spray (PY): An ensemble of water droplets torn by the wind from the surface of the of an
extensive body of water, generally from crests of waves, and carried a short distance into the air.

Spring Tide: A tide higher than normal which occurs around the time of the new and full moon.

Squall (SQ): A strong wind characterized by a sudden onset in which the wind speed increases
at least 16 knots and is sustained more than 22 knots or more for at least one minute.

Squall Line: A line or narrow band of active thunderstorms. The line may extend across several
hundred miles. It forms along and ahead of an advancing cold front.

Stable: An atmospheric state with warm air above cold air which inhibits the vertical movement
of air.

Stable Air: Air with little or no tendency to rise.

Station Pressure: The pressure that is read from a barometer but is not adjusted to sea level.

Stationary Front: A front that barely moves with winds blowing in almost parallel, but in
opposite directions on each side of the front. Occasionally, these fronts can cause widespread
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flooding, because showers and thunderstorms moving along them will continue to move across
the same area. This weather situation is called “train echoing”.

Steam Fog: It forms as cold air moves over warm water. Water evaporates from the warm water
surface and immediately condenses in the cold air above. Heat from the water warms the lower
levels of the air creating a shallow layer of instability. It rises like smoke from the warm surface.
The low level convection can become quite turbulent. Steam fog is most common in Arctic
regions where it is called “Arctic Sea Smoke”, but it can and does occur occasionally at all
latitudes.

Steering Winds (or Steering Currents): A prevailing synoptic scale flow which governs the
movement of smaller features embedded within it.

Storm: Any disturbed state of the atmosphere, especially affecting the Earth's surface, and
strongly implying destructive and otherwise unpleasant weather. Storms range in scale from
tornadoes and thunderstorms through tropical cyclones to widespread extratropical cyclones. In
marine usage, winds 48 knots (55 mph) or greater.

Storm Motion: The speed and direction at which a thunderstorm travels.

Storm Prediction Center (SPC): A national forecast center in Norman, Oklahoma, which is
part of NCEP. The SPC is responsible for providing short-term forecast guidance for severe
convection, excessive rainfall (flash flooding), and severe winter weather over the contiguous
United States. This includes the issuance of Tornado and Severe Thunderstorm Watches.

Storm Relative: Measured relative to a moving thunderstorm, usually referring to winds, wind
shear, or helicity.

Storm Surge: A rise above the normal water level along a shore caused by strong onshore winds
and/or reduced atmospheric pressure. The surge height is the difference of the observed water
level minus the predicted tide. Most hurricane deaths are caused by the storm surge. It can be 50
or more miles wide and sweeps across the coastline around where the hurricane makes landfall.
The maximum rises in sea-level move from under the storm to the right of the storm's track,
reaching a maximum amplitude of 10 to 30 feet at the coast. The storm surge may even double or
more in height when the hurricane's track causes it to funnel water into a bay. The storm surge
increases substantially as it approaches the land because the normal water depth decreases
rapidly as it approaches the beaches. The moving water contains the same amount of energy;
thus, resulting in an increase of storm surge. Typically, the stronger the hurricane, the greater the
storm surge.

Storm Tide: The actual sea level resulting from astronomical tide combined with the storm
surge. This term is used interchangeably with “hurricane tide”.

Storm Track: The path that a low pressure area follows.

Storm Warning: A marine warning of sustained surface winds of 48 kt (55 mph or 88 kph) or
greater, either predicted or occurring, not directly associated with tropical cyclones.
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Straight Line Winds: Generally, any wind that is not associated with rotation, used mainly to
differentiate them from tornadic winds.

Stratiform: Descriptive of clouds of extensive horizontal development, as contrasted to the more

narrow and vertically developed cumuliform type. Stratiform clouds cover large areas but show
relatively little vertical development. Stratiform precipitation, in general, is relatively continuous
and uniform in intensity (i.e., steady rain versus rain showers).

Stratiform Rain: Horizontally widespread rain, uniform in character, typically associated with
macroscale fronts and pressure systems.

Stratocumulus (Sc): It has globular masses or rolls unlike the flat, sometimes definite, base of
stratus. This cloud often forms from stratus as the stratus is breaking up or from spreading out of
cumulus clouds. They usually consist of mainly water vapor and are located between the ground
and 6,500 feet. Stratocumulus often reveals the depth of the moist air at low levels, while the
speed of the cloud elements can reveal the strength of the low-level jet.

Stratosphere: The layer of the atmosphere above the troposphere, where temperature increases
with height.

Stratus (St): It is a low, uniform sheet-like cloud. Stratus may appear in the form of ragged
patches, but otherwise does not exhibit individual cloud elements as do cumulus and
stratocumulus clouds. It usually is located between the ground and 6,500 feet. It usually consists
of mainly water vapor. Fog is a stratus cloud with its base located at the ground.

Stream Gage: A site along a stream where the stage (water level) is read either by eye or
measured with recording equipment.

Sublimation: The change from ice (a solid) directly to water vapor (a gas) without going
through the liquid water phase. It is the opposite of Deposition.

Subrefraction: The bending of the radar beam in the vertical which is less than under standard
refractive conditions. This causes the beam to be higher than indicated, and lead to the
underestimation of cloud heights.

Subsidence: The slow sinking of air usually associated with high pressure areas. It is usually
over a broad area and is associated with warming air and little if any cloud formation.

Subsidence Inversion: It is produced by adiabatic heating of air as it sinks and is associated with
anticyclones (high pressure) and/or stable air masses. These inversions form between sinking
heated air and air below and they are characterized by temperature increase with height through
the inversion, while above the inversion, the temperature cools. The dew point temperature,
relative humidity, and mixing ratio values all decrease with height through the inversion.

Subtropical Jet: This branch of the jet stream is usually found between 20° and 30° latitude at
altitudes between 12 and 14 km.
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Supercell: A thunderstorm with a persistent rotating updraft. Supercells are responsible for a
remarkably high percentage of severe weather events - especially tornadoes, extremely large hail
and damaging straight-line winds. They frequently travel to the right of the main environmental
winds (i.e., they are right movers). Visual characteristics often include a rain-free base (with or
without a wall cloud), tail cloud, flanking line, overshooting top, and back-sheared anvil, all of
which normally are observed in or near the right rear or southwest part of the storm. Storms
exhibiting these characteristics often are called classic supercells; however HP storms and LP
storms also are supercell varieties.

Supercooled Liquid Water: In the atmosphere, liquid water can survive at temperatures lower
than 0°C (32°F); many vigorous storms contain large amounts of supercooled liquid water at low
temperatures. Important in the formation of graupel and hail.

Supersaturation: The condition which occurs in the atmosphere when the relative humidity is
greater than 100%.

Superrefraction: Bending of the radar beam in the vertical which is greater than sub-standard
refractive conditions. This causes the beam to be lower than indicated, and often results in
extensive ground clutter as well as an overestimation of cloud top heights.

Surface Pressure: The pressure that is read from a barometer but is not adjusted to sea level.

Surface Runoff: The part of runoff, caused by precipitation and/or snowmelt, that moves over
the soil surface to the nearest stream channel. Rain that falls on the stream channel is often
lumped with this quantity.

Sunny: When there are no opaque (not transparent) clouds. Same as clear.

Swell: Wind-generated waves that have traveled out of their generating area. Swells
characteristically exhibit smoother, more regular and uniform crests and a longer period than
wind waves.

Synoptic Chart: Chart showing meteorological conditions over a region at a given time; a
weather map.

Synoptic Scale (or Large Scale): The typical weather map scale that shows features such as
high and low pressure areas and fronts over a distance spanning a continent. Compare with
mesoscale and storm-scale.

TAF: An acronym for Terminal Aerodrome Forecast

TCU: An acronym for Towering Cumulus.

T. D.: An acronym for Tropical Depression.

Teleconnection: A strong statistical relationship between weather in different parts of the globe.
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For example, there appears to be a teleconnection between the tropics and North America during
El Niño.

Temperature: A measure of the warmth of the ambient air measured by a suitable instrument
such as a thermometer.

Terminal Aerodrome Forecast (TAF): This NWS aviation product is a concise statement of
the expected meteorological conditions at an airport during a specified period (usually 24 hours).
TAFs use the same weather code found in METAR weather reports.

Thermal: A relatively small-scale, rising air current produced when the Earth's surface is heated.
Thermals are a common source of low level turbulence for aircraft.

Thermal Highs: Areas of high pressure that are shallow in vertical extent and are produced
primarily by very low surface temperatures.

Thermal Lows: Areas of low pressure that are shallow in vertical extent and are produced
primarily by high surface temperatures.

Thermodynamic Chart (or Thermodynamic Diagram): A chart containing contours of

pressure, temperature, moisture, and potential temperature, all drawn relative to each other such
that basic thermodynamic laws are satisfied. Such a chart typically is used to plot atmospheric
soundings, and to estimate potential changes in temperature, moisture, etc. if air were displaced
vertically from a given level. A thermodynamic chart thus is a useful tool in diagnosing
atmospheric stability.

Thermodynamics: In general, the relationships between heat and other properties (such as
temperature, pressure, density, etc.) In forecast discussions, thermodynamics usually refers to the
distribution of temperature and moisture (both vertical and horizontal) as related to the diagnosis
of atmospheric instability.

Thermometer: An instrument for measuring temperature.

Thunder: The sound emitted by the rapidly expanding gases along the channel of a lightning
discharge. Thunder is seldom heard farther than about 15 miles from the lightning discharge,
with 25 miles an approximate upper limit and 10 miles a typical value.

Thunderstorm (TS): A local storm produced by cumulonimbus clouds. It is always

accompanied by lightning and thunder. It is estimated that nearly 2,000 thunderstorms occur
simultaneously around the Earth at any given instant. There are 3 types of thunderstorms:
1. Single Cell Thunderstorms, 2. Multicell Thunderstorms, and 3. Supercell Thunderstorm.

Tides: They are the periodic (occurring at regular intervals) variations in the surface water level
of the oceans, bays, gulfs, and inlets. Tides are the result of the gravitational attraction of the sun
and the moon on the earth, but mostly from the moon. Every 27.3 days, the earth and the moon
revolve around a common point. This means that the oceans and other water bodies which are
affected by the earth-moon system experience a new tidal cycle every 27.3 days. Because of the
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physical processes which occur to produce the tidal system, there are two high tides and two low
tides each day. Because of the angle of the moon with respect to the earth, the two high tides and
the two low tides each day do not have to be of equal height. Tides also differ in height on a
daily basis, due to the changing distance between the earth and the moon. Scientists use
measurements of the height of the water level to examine tides and the various phenomena which
influence tides, such as hurricanes and winter storms.

Tilted Storm or Tilted Updraft: A thunderstorm or cloud tower which is not purely vertical but
instead exhibits a slanted or tilted character. It is a sign of vertical wind shear, a favorable
condition for severe storm development.

Tipping-Bucket Rain Gage: A precipitation gage where collected water is funneled into a two
compartment bucket; 0.01”, 0.1 mm, or some other designed quantity of rain will fill one
compartment and overbalance the bucket so that it tips, emptying into a reservoir and moving the
second compartment into place beneath the funnel. As the bucket is tipped, it actuates an electric
circuit, recording the rainfall.

Tornado (+FC): A violently rotating column of air in contact with the ground and extending
from the base of a thunderstorm. A condensation funnel does not need to reach to the ground for
a tornado to be present; a debris cloud beneath a thunderstorm is all that is needed to confirm the
presence of a tornado, even in the total absence of a condensation funnel. It nearly always starts
as a funnel cloud and may be accompanied by a loud roaring noise. Tornadoes are classified by
the amount of damage that they cause. See Fujita Scale and Enhanced Fujita Scale.

Tornado Alley: The area of the United States in which tornadoes are most frequent. It
encompasses the great lowland areas of the Mississippi, the Ohio, and lower Missouri River
Valleys. Although no state is entirely free of tornadoes, they are most frequent in the Plains area
between the Rocky Mountains and Appalachians.

Tornado Warning (TOR): This is issued when a tornado is indicated by the WSR-88D radar or
sighted by spotters; therefore, people in the affected area should seek safe shelter immediately.
They can be issued without a Tornado Watch being already in effect. They are usually issued for
a duration of around 30 minutes. A Tornado Warning is issued by the local NWS office. It will
include where the tornado was located and what towns will be in its path. After it has been
issued, it will be followed up by periodic Severe Weather Statements. These statements will
contain updated information on the tornado and they will also let the public know when warning
is no longer in effect.

Tornado Watch (SEL): This is issued by the NWS when conditions are favorable for the
development of tornadoes in and close to the watch area. The watch is in a form of a rectangle
whose size and orientation varies depending on the weather situation. They are usually issued for
a duration of 4 to 8 hours. They normally are issued well in advance of the actual occurrence of
severe weather. During the watch, people should review tornado safety rules and be prepared to
move a place of safety if threatening weather approaches.

Tower: Short for towering cumulus.

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Towering Cumulus (TCU): It signifies a relatively deep layer of unstable air. The bases are flat
and usually appear darker than the bases of fair weather cumulus. They show considerable
vertical development and have billowing “cauliflower” tops. Showers can result from these
clouds. Same as cumulus congestus.

TPC: An acronym for the Tropical Prediction Center.

Trace: A rainfall amount less than 0.01”.

Track: The path that a storm or weather system follows.

Trade Winds: The winds that occupy most of the tropics and blow from subtropical highs to the
equatorial low.

Transcribed WEather Broadcasts (TWEBs): This NWS aviation product is similar to the Area
Forecast (FA) except information is contained in a route format. Forecast sky cover (height and
amount of cloud bases), cloud tops, visibility (including vertical visibility), weather, and
obstructions to vision are described for a corridor 25 miles either side of the route.

Transpiration: Water discharged into the atmosphere from plant surfaces.

Tropical Cyclone: It is a warm-core low pressure system which is non-frontal. It originates over
tropical and subtropical waters and a has an organized cyclonic (counter-clockwise) surface wind
circulation.

Tropical Depression: Cyclones that have maximum sustained winds of surface wind speed
(using the U.S. 1-minute average) is 33 kt (38 mph or 62 kph) or less. They are either located in
the tropics or subtropics. They characteristically have one or more closed isobars. They usually
intensify slowly and may dissipate before reaching Tropical Storm intensity.

Tropical Disturbance: A discrete tropical weather system of apparently organized convection--

generally 100 to 300 nautical miles in diameter---originating in the tropics or subtropics, having
a nonfrontal migratory character, and maintaining its identity for 24 hours or more. It may or
may not be associated with a detectable perturbation of the wind field. In successive stages of
intensification, it may be subsequently classified as a tropical wave, tropical depression, tropical
storm, or hurricane.

Tropical Prediction Center (TPC): One of NOAA's 9 National Centers for Environmental
Prediction (NCEP). The mission of the Tropical Prediction Center (TPC) is to save lives and
protect property by issuing watches, warnings, forecasts, and analyses of hazardous weather
conditions in the tropics. TPC products are generated for use in both the domestic and
international communities. To fulfill its mission, the TPC is comprised of the following
branches: The National Hurricane Center, Tropical Analysis and Forecast Branch (TAFB), and
the Technical Support Branch (TSB).

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Tropical Storm: It is a warm-core tropical cyclone that has maximum sustained surface wind
speed (using the U.S. 1-minute average) ranges from 34 kt (39 mph or 63 kph) to 63 kt (73 mph
or 118 kph).

Tropical Storm Warning: A warning for tropical storm conditions including sustained winds
within the range of 34 to 63 kt (39 to 73 mph or 63 to 118 kph) that are expected in a specified
coastal area within 24 hours or less.

Tropical Storm Watch: An announcement that a tropical storm poses or tropical storm
conditions pose a threat to coastal areas generally within 36 hours. A tropical storm watch should
normally not be issued if the system is forecast to attain hurricane strength.

Tropical Wave: A trough or cyclonic curvature maximum in the trade wind easterlies and it is
not classified as a tropical cyclone. The wave may reach maximum amplitude in the lower
middle troposphere.

Tropics: Areas of the Earth within 20°North/South of the Equator.

Tropopause: The upper boundary of the troposphere, usually characterized by an abrupt change
in lapse rate from positive (decreasing temperature with height) to neutral or negative
(temperature constant or increasing with height). It is also the boundary between the troposphere
and the stratosphere.

Troposphere: The layer of the atmosphere from the earth's surface up to the tropopause,
characterized by decreasing temperature with height (except, perhaps, in thin layers - see
inversion, cap), vertical wind motion, appreciable water vapor content, and sensible weather
(clouds, rain, etc.).

Trough: An elongated area of relatively low atmospheric pressure, usually not associated with a
closed circulation, and thus used to distinguish from a closed low. The opposite of ridge.

T.S.: An abbreviation for Tropical Storm.

Tsunami: An ocean wave produced by a sub-marine earthquake, landslide, or volcanic eruption.

These waves may reach enormous dimensions and have sufficient energy to travel across entire
oceans. (Sometimes referred to incorrectly as a tidal wave).

Tule Fog: Radiation fog in California’s Central Valley. It forms during night and morning hours
in late fall and winter months following rainfall. A leading cause of weather related casualties in
California.

Turbulence: Disrupted flow in the atmosphere that produces gusts and eddies.

Turkey Tower: Slang for a narrow, individual cloud tower that develops and falls apart rapidly.
The sudden development of turkey towers from small cumulus clouds may signify the breaking
of a cap.

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TWEB: Accronym for Transcribed WEather Broadcast.

Twister: In the United States, a colloquial term for a tornado.

Typhoon: A tropical cyclone of hurricane strength in the Western Pacific Ocean (west of the
international dateline).

UKMET: A medium-range (3 to 7 day) numerical weather prediction model operated by the

United Kingdom METeorological Agency. It has a resolution of 75 kilometers and covers the
entire northern hemisphere. Forecasters use this model along with the European and GFS in
making their extended forecasts (3 to 7 days).

Ultraviolet Radiation: The energy range just beyond the violet end of the visible spectrum.
Although ultraviolet radiation constitutes only about 5 percent of the total energy emitted from
the sun, it is the major energy source for the stratosphere and mesosphere, playing a dominant
role in both energy balance and chemical composition.

Unstable Air: An atmospheric state of warm air below cold air. Since warm air naturally rises
above cold air (due to warm air being less dense than cold air), vertical movement and mixing of
air layers can occur.

Updraft: Current(s) of air with marked vertical upward motion. If the air is sufficiently moist,
then the moisture condenses to become a cumulus cloud or an individual tower of a towering
cumulus or cumulonimbus.

Upper-Level Disturbance: A disturbance in the upper atmospheric flow pattern which is usually
associated with clouds and precipitation. This disturbance is characterized by distinct cyclonic
flow, a pocket of cold air, and sometimes a jet streak. These features make the air aloft more
unstable and conducive to clouds and precipitation.

Upper Level System: A general term for any large-scale or mesoscale disturbance capable of
producing upward motion (lift) in the middle or upper parts of the atmosphere. This term
sometimes is used interchangeably with impulse or shortwave.

Upslope Flow: Air that flows toward higher terrain, and hence is forced to rise. The added lift
often results in widespread low cloudiness and stratiform precipitation if the air is stable, or an
increased chance of thunderstorm development if the air is unstable.

Upwelling: The process by which cold waters from the depths of a lake or ocean rise to the
surface. This often occurs along the California coast during the summer and is an important
component in the development of coastal stratus clouds.

Urban & Small Stream Flood Advisory (FLS): This advisory alerts the public to flooding
which is generally only an inconvenience (not life-threatening) to those living in the affected
area. Issued when heavy rain will cause flooding of streets and low-lying places in urban areas.
Also used if small rural or urban streams are expected to reach or exceed bankfull. Some damage
to homes or roads could occur.
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Urban Flooding: Flooding of streets, underpasses, low lying areas, or storm drains. This type of
flooding is mainly an inconvenience and is generally not life threatening.

Urban Heat Island: The increased air temperatures in urban areas in contrast to cooler
surrounding rural areas due to the increased heat retention properties of concrete and pavement.

UTC: Coordinated Universal Time. The time in the zero degree meridian time zone.

UV (Ultraviolet) Index: This index provides important information to help you prevent
overexposure to the sun's rays. It was designed by the National Weather Service and the
Environmental Protection Agency (EPA). It is computed using forecasted ozone levels, a
computer model that relates ozone levels to UV incidence on the ground, forecasted cloud
amounts, and the elevation of the forecast cities.

Valley Winds: The tendency of wind to funnel down a pronounced valley. Also the movement
of air down the slopes of a valley at night (katabatic winds) or up the slopes of valley during the
day (anabatic winds).

Veering Wind: Wind which changes in a clockwise direction with time at a given location (e.g.,
from southerly to westerly), or which change direction in a clockwise sense with height (e.g.,
southeasterly at the surface turning to southwesterly aloft). Veering winds with height are
indicative of warm air advection (WAA).

Vertical Wind Shear: The rate of change of wind speed or direction, with a given change in
height. This is a critical factor in determining whether severe thunderstorms will develop.

Vertically Stacked System: A low-pressure system, usually a closed low or cutoff low, which is
not tilted with height, i.e., located similarly at all levels of the atmosphere. Such systems
typically are weakening and are slow-moving, and are less likely to produce severe weather than
tilted systems. However, cold pools aloft associated with vertically-stacked systems may
enhance instability enough to produce severe weather.

Virga: Precipitation that evaporates before it reaches the ground. It appears as wisps or streaks of
rain or snow falling out of a cloud. As the precipitation evaporates, it cools the air and starts a
down draft. In certain cases, shafts of virga may precede a microburst.

Visible (VIS) Satellite Imagery: This type of satellite imagery uses reflected sunlight (this is
actually reflected solar radiation) to see things in the atmosphere and on the Earth's surface.
Clouds and fresh snow are excellent reflectors, so they appear white on the imagery. Clouds can
be distinguished from snow, because clouds move and snow does not move. Meanwhile, the
ground reflects less sunlight, so it appears black on the imagery. The satellite uses its 0.55 to
0.75 micrometer (um) channel to detect this reflected sunlight. Since this imagery relies on
reflected imagery, it cannot be used during night.

Visibility: The greatest distance an observer can see and identify prominent objects.

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Visual Flight Rules (VFR): Refers to the general weather conditions pilots can expect at the
surface. VFR is ceiling greater than or equal to 1,000 feet and visibility greater than or equal to 3
miles. Marginal VFR (MVFR) is a sub-category of VFR (ceiling 1,000 - 3,000 feet and/or
visibility 3 to 5 miles).

Vort Max: This short for vorticity maximum. It is a center, or maximum, in the vorticity field of
a fluid.

Vortex: In its most general use, any flow possessing vorticity. More often the term refers to a
flow with closed streamlines.

Vorticity: A vector measure of the local rotation in a fluid flow. In weather analysis and
forecasting, it usually refers to the vertical component of rotation (i.e., rotation about a vertical
axis) and is used most often in reference to synoptic scale or mesoscale weather systems. By
convention, positive values indicate cyclonic rotation.

WAA: An acronym for Warm Air Advection.

Wall Cloud: It is formed in a supercell thunderstorm. A localized, persistent, often abrupt

lowering from a rain-free base. Wall clouds can range from a fraction of a mile up to nearly five
miles in diameter, and normally are found on the south or southwest (inflow) side of the
thunderstorm, attached to the rain free cloud base, and marks the strongest updraft in the
thunderstorm. Eventually, this updraft will pull air from the rain cooled area of the thunderstorm.
Since the rain cooled air is very humid, it will quickly condense in the updraft at a lower altitude
than the rain free cloud base. When seen from within several miles, many wall clouds exhibit
rapid upward motion and cyclonic rotation. However, not all wall clouds rotate. Rotating wall
clouds usually develop before strong or violent tornadoes, by anywhere from a few minutes up to
nearly an hour. Wall clouds should be monitored visually for signs of persistent, sustained
rotation and/or rapid vertical motion.

Warm Air Advection: Transport of warm air into an area by horizontal winds.

Warm Core Low: A low pressure area which is warmer at its center than at its periphery.
Tropical cyclones exhibit this temperature pattern. Unlike cold core lows, these lows produce
much of their cloud cover and precipitation during the nighttime.

Warm Front: A front that moves in such a way that warm air replaces cold air.

Warning: A type of product issued by NWS offices indicating that a particular weather hazard is
either imminent or has been reported. A warning indicates the need to take action to protect life
and property. The type of hazard is reflected in the type of warning (e.g., tornado warning,
blizzard warning). See short-fuse warning.

Warning Stage: The level of a river or stream which begins to cause flooding, and at which
concerned interests should take action.

Watch: A type of NWS product indicating that a particular hazard is possible, i.e., that
198
conditions are more favorable than usual for its occurrence. A watch is a recommendation for
planning, preparation, and increased awareness (i.e., to be alert for changing weather, listen for
further information, and think about what to do if the danger materializes).

Watch Redefining Statement (SLS): This product tells the public which areas are included in
the watch and is issued by the local NWS Forecast Office.

Water Equivalent: The liquid content of solid precipitation that has accumulated on the ground
(snow depth). The accumulation may consist of snow, ice formed by freezing precipitation,
freezing liquid precipitation, or ice formed by the refreezing of melted snow.

Watershed: The total area drained by a river and its tributaries. Sometimes called a basin.

Water Vapor (WV) Satellite Imagery: This satellite imagery uses that detects moisture
between 700 and 200 mb; therefore, it is good for determining mid and upper level moisture in
the atmosphere. Abundant water vapor appears white in this imagery. Meanwhile, dry air appears
black in this satellite imagery. This satellite imagery can be used both day and night.

Water Vapor Plume: This appears in the water vapor satellite imagery. It is a plume-like object
that extends from the Intertropical Convergence Zone (ITCZ) northward or southward into the
higher latitudes and is a favored region for very heavy rain. It is thought that the ice crystals
located in this plume help thunderstorms to become highly efficient rainfall producers. In North
America, this is sometimes called the “Mexican Connection” for moisture moving into the
southwestern US from Mexico or the “Pineapple Connection” for moisture moving into the west
coast from the tropics.

Waterspout: A violently rotating column of air, usually a pendant to a cumulus or

cumulonimbus cloud, over a body of water with its circulation reaching the water. Waterspouts
can be generated by thunderstorms, or can be cold air funnels, being generated by a cold air mass
passing over much warmer waters. Such waterspouts are generally much less intense than
tornadoes.

Wave: An identifiable, periodic disturbance or motion in a medium that shows displacement.

The most commonly referred medium is water, followed by the atmosphere. The forecasted
heights of waves in the oceans are those heights expected at the end of the fetch for that body of
water.

Weather Forecast Office (WFO): This National Weather Service office is responsible for
issuing advisories, warnings, statements, and short term forecasts for its county warning area.
There are 122 WFOs that cover the entire U.S. and its territories.

Weather balloon: Large balloon filled with helium or hydrogen that carries a radiosonde
(weather instrument) aloft to measure temperature pressure and humidity as the balloon rises
through the air. It is attached to a small parachute so that when the balloon inevitably breaks, the
radiosonde doesn't hurtle back to earth dangerously quickly.

Weather synopsis: A description of weather patterns affecting a large area.

199
West Coast and Alaska Tsunami Warning Center (WCATWC): The WCATWC provides
tsunami warning guidance for all U.S. coastal states (except Hawaii), and the Canadian coastal
provinces. It is located in Palmer, AK. A tsunami warning for California will come from this
center and will be relayed by the local NWS office.

Wet-Bulb Temperature: The lowest temperature that can be obtained by evaporating water into
air.

Wet-Bulb Zero (WBZ): The height where the wet-bulb temperature goes below 0°F. WBZ
heights between 7000 ft and 10,500 ft (above ground level) correlate well with large hail at the
surface when storms develop in an air mass primed for strong convection. It is also a good
indicator of the elevation of snowfall.

Wet Microburst: A microburst accompanied by heavy precipitation at the surface. A rain foot
may be a visible sign of a wet microburst. See dry microburst.

WFO: A National Weather Service Weather Forecast Office.

Whirlwind: A small, rotating column of air; may be visible as a dust devil.

Wildfire: Any free burning uncontainable wildland fire not prescribed for the area which
consumes the natural fuels and spreads in response to its environment.

Willy-Willy: A tropical cyclone of hurricane strength near Australia.

Wind: The horizontal motion of the air past a given point. Winds begin with differences in air
pressures. Pressure that's higher at one place than another sets up a force pushing from the high
toward the low pressure. The greater the difference in pressures, the stronger the force. The
distance between the area of high pressure and the area of low pressure also determines how fast
the moving air is accelerated. Meteorologists refer to the force that starts the wind flowing as the
pressure gradient force. High and low pressure are relative. There's no set number that divides
high and low pressure. Wind is used to describe the prevailing direction from which the wind is
blowing with the speed given usually in miles per hour or knots.

Wind Advisory: Issued for sustained winds strong enough to cause inconvenience or minor
damage. Criteria for Southern California are sustained winds 30 to 39 mph and/or gusts to 57
mph in coastal and valley areas, and sustained winds 35 to 44 mph and/or gusts to 57 mph in the
mountains and deserts.

Wind Aloft: The wind speeds and wind directions at various levels in the atmosphere above the
area of surface.

Wind Chill: The wind chill is the effect of the wind on people and animals. The wind chill
temperature is based on the rate of heat loss from exposed skin caused by wind and cold and
gives an approximation of how cold the air feels on your body. As the wind increases, it removes
heat from the body, driving down skin temperature and eventually the internal body temperature.
200
Therefore, the wind makes it FEEL much colder. If the temperature is 0°F and the wind is
blowing at 15 mph, the wind chill temperature is -19°F. At this level, exposed skin can freeze in
just a few minutes. The only effect wind chill has on inanimate objects, such as car radiators and
water pipes, is to shorten the amount of time for the object to cool. The inanimate object will not
cool below the actual air temperature. For example, if the temperature outside is -5°F and the
wind chill temperature is -31°F, then your car's radiator temperature will be no lower than the air
temperature of -5°F.

Wind Chill Advisory: The NWS issues this product when the wind chill becomes dangerous.
The criteria for this warning vary from state to state.

Wind Chill Warning: The NWS issues this product when the wind chill is life threatening. The
criteria for this warning vary from state to state.

Wind Direction: The true direction FROM which the wind is moving at a given location. It is
normally measured in tens of degrees from 10° to 360°.

Wind Gust: They are rapid fluctuations in the wind speed with a variation of 10 knots or more
between peaks and lulls. The speed of the gust will be the maximum instantaneous wind speed.

Wind Rose: A diagram that shows the percent of time that the wind blows from different
directions at a given location over a given time.

Wind Shear: The rate of change of wind speed and/or direction over a given distance. Also, see
shear.

Wind Shift: A change in wind direction of 45° or more in less than 15 minutes with sustained
wind speeds of 10 knots or more throughout the wind shift.

Wind Sock: A tapered fabric shaped like a cone that indicates wind direction by pointing away
from the wind. It is also called a wind cone.

Wind Speed: The rate at which air is moving horizontally past a given point. It may be a 2-
minute average speed (reported as wind speed) or an instantaneous speed (reported as a peak
wind speed, wind gust, or squall).

Wind Vane: An instrument that determines the direction from which a wind is blowing.

Wind Waves: Local, short period waves generated from the action of wind on the water surface
(as opposed to swell). Commonly referred to as waves.

Winter Storm Warning: Issued when more than one type of hazardous winter weather is
occurring, imminent, or highly likely over part or all of the forecast area. Winter storm warnings
are normally issued for the first period of the forecast but can be extended into the second period.
They are reissued whenever there is a change to the timing, areal extent, or expected condition.

201
Winter Storm Watch: Issued when conditions are favorable for hazardous winter weather
conditions to develop over part or all of the forecast area in the next 6-36 hours, but the
occurrence is still uncertain. Watches will be reissued whenever there is a change in the timing,
areal extent, or expected conditions. Winter storm watches either evolve into winter storm
warnings or advisories, or they are canceled.

WSR-88D: Weather Surveillance Radar - 1988 Doppler; NEXRAD unit.

Zone Forecast Product (ZFP): This NWS product will provide the general public with a clear
statement of the expected weather conditions within a given zone. The forecast will include: sky
condition, temperature, type of precipitation and its probability, and wind direction and speed
(probability of precipitation and winds are normally given only during the first 5 periods of the
forecast).

Zonal Flow: Large-scale atmospheric flow in which the east-west component (i.e., latitudinal) is
dominant. The accompanying meridional (north-south) component often is weaker than normal.
Compare with meridional flow.

Zulu (Z) Time: For practical purposes, the same as Coordinated Universal Time (UTC). The
notation formerly used to identify time Greenwich Mean Time. The word “Zulu” is notation in
the phonetic alphabet corresponding to the letter “Z” assigned to the time zone on the Greenwich
Prime Meridian.

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Appendix C - Weather Education Resources and Bibliography of
Local Weather
Education in person

Most colleges and universities offer courses in basic Meteorology. Many of these are part of the
Geography department in a Physical Geography course, which usually contain significant study
in weather and climate. In Southern California, the only university to offer a degree in
Atmospheric Science or Meteorology is UCLA.

Online Education

Many resources for learning more about weather in general are available online. Here are some
of our favorite weather education web sites on the Internet:

Online tutorials
www.srh.noaa.gov/jetstream
ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/home.rxml

Disaster Preparedness
www.fema.gov/hazard/index.shtm
emergency training courses: training.fema.gov

General weather basics education

wps.prenhall.com/esm_aguado_uwac_3
www.usatoday.com/weather/resources/basics/wworks0.htm
www.weatherworks.com
eo.ucar.edu/basics/index.html

Advanced weather education

A warehouse of great learning modules: meted.ucar.edu

Interpretation of weather models

meted.ucar.edu/nwp/course/modules.php
weather.unisys.com/model/details.html
www.theweatherprediction.com/models

Weather Books

Numerous books about weather and meteorology are available, including these finest examples:

Understanding Weather and Climate by Edward Aguado and James Burt. This book focuses on
explaining, rather than describing, the processes that produce Earth's weather and climate.
Companion web site available.

The Audubon Society Field Guide to North American Weather by David M. Ludlum can be
203
used to identify clouds and other sky phenomena in much the way a field guide to birds is used.

The USA TODAY Weather Book by Jack Williams explains the basics of meteorology with easy
to understand text and colorful graphics.

Meteorology Today: An Introduction to Weather, Climate, and the Environment by C. Donald

Ahrens, is one of the most popular college textbooks. It is designed for students who are not
planning to major in meteorology, which means little mathematical knowledge is required.

Meteorology: Understanding the Atmosphere by Steven Ackerman, John A. Knox. A college

text written by college professors containing generous graphics and photographs.

The Atmosphere: An Introduction to Meteorology by Frederick K. Lutgens, Edward J. Tarbuck

and Dennis Tasa. Using everyday, easy-to-grasp examples to reinforce basic concepts, this
highly regarded handbook remains the standard introduction to meteorology and the atmosphere
– components, problems, and applications.

Weatherwise is a weather magazine devoted to both professional and amateur weather

enthusiasts. See www.weatherwise.org.

Bibliography of Local Weather Research

(Archives of Western Region Technical Attachments and Technical Attachment-Lites since 1996
can be found at the Western Region web site at: www.wrh.noaa.gov/wrh/ta.php.)

Aldrich, John, and Meadows, Myra, 1962: Southland Weather Handbook. Brewster Publications.
51 pp.

Atkin, D.V., and Reynolds, J.A., 1995: Composite Maps of Selected Rainfall Events in San
Diego. Western Region Technical Attachment No. 95-06.

Atkin, D. V., and Dandrea, J.A., 1998: Composite Maps of Selected Warm Events in San Diego.
Western Region Technical Attachment No. 98-09.

Bailey, Harry P., 1966: Weather of Southern California. University of California Press. 87 pp.

Burger, M., 2003: An Analysis of the December 16, 2002 Grapevine Wind Event - A WES Case
Western Region Technical Attachment-Lite 03-48.

Carpenter, Ford A., 1913: The Climate and Weather of San Diego, California. San Diego
Chamber of Commerce.

Danielson, David, 2003: Southern California Wind Event 9-10 February 2003 - A WES Case
Study. Western Region Technical Attachment-Lite 03-22.

Danielson, David, 2003: Labor Day Weekend 2002: An Exercise Involving Flash Flood and
Lightning Potential Forecasts, “The Curve Fire”. Western Region Technical Attachment-Lite 03-
204
45.

Danielson, David, 2004: The Eastern Antelope Valley Eddy (EAVE) and Its Impact on Severe
Weather. Western Region Technical Attachment-Lite 04-45.

Evans, T.E., and Halvorson, D.A., 1998: Climate of San Diego, California. NOAA Technical
Memorandum, NWS WR-256.

Garza, A.L., and Atkin D. V., 1996: Southern California Severe Thunderstorm Event and a First
Look at Precipitation Data From the San Diego-Miramar WSR-88D. Western Region Technical
Attachment
No. 96-22.

Garza, A.L., 1999: 1985-1998 North Pacific tropical cyclones impacting the southwestern United
States and northern Mexico: An updated climatology. NOAA Technical Memorandum, NWS
WR-258.

Isla, E., and Lee, J., 2006: Climate of San Diego, California, Third edition. NOAA Technical
Memorandum, NWS WR-275.

Kurtz, Emil S., 1977, revised by Stitt, Whitlow and Tarczy 2002: Southern California Weather
for Small Boaters. NWS publication. 42 pp.

Markell, Jeff, 1997: Coastal Weather Guide for Southern California and Western Mexico.
Lighthouse Presss. 139 pp.

Martin, G., 1997: Applications of the RUC and Meso-ETA to Forecasting the Catalina Eddy.
Preprints of the 7th Conference on Aviation, Range, and Aerospace Meteorology.

Martin, G., 1998: An Outstanding Performance by the ETA-10 for the Southern California Storm
of 23 February 1998. Western Region Technical Attachment No. 98-36.

Maxwell, B., and Atkin, D.V., 1998: Chaff in the Vicinity of Thunderstorms in Southern
California on 6 June 1997. Western Region Technical Attachment No. 98-04.

Maxwell, B., 2000: Thunderstorms in San Diego and associated easterly wave of 20 July 1998.
Western Region Technical Attachment No. 00-02.

Maxwell, B., 2006: Analysis of the 22-23 July 2006 Extreme Heat in San Diego County.
Western Region Technical Attachment No. 06-12.

Small, I., 1995: Santa Ana Winds and the Fire Outbreak of Fall 1993. NOAA Technical
Memorandum NWS WR-230.

Small, I., Atkin, D.V., and Evans, T.E., 1998: Severe Hail Detection Using VIL Density and its
Application in the Western States. Western Region Technical Attachment No. 98-37.

205
Small, I., and Shah, A., 1999: A Case Study of a Wind Event In the Palm Springs Region.
Western Region Technical Attachment 99-17.

Small, I., 1999: An Observational Study of Island Effect Bands: Precipitation Producers in
Southern California. Western Region Technical Attachment 99-18.

Small, I., 1999: An Observational Study of a California Bight Coastal Convergence Zone
Produced by Flow Interaction with Mainland Topography: Precipitation Producer in Southern
California. Western Region Technical Attachment 99-19.

Small, I., Mackechnie, T., and Bower, B., 2000: Mesoscale Interactions Triggering Severe
Thunderstorms and Flash Flooding in Southwestern California July 1999. Western Regional
Technical Attachment 00-01.

Small, I., Martin, G., LaDochy, S., and Brown, J., 2002: Topographic and Synoptic Influences on
Cold Season Severe Weather Events in California. Preprints of the 16th Conference on
Probability and Statistics, Orlando, FL, Amer. Meteor Soc., 146-153.

Small, I., Atkin, D., 2002: Analysis of a Severe Thunderstorm using the Weather Event
Simulator (WES). Western Regional Technical Attachment-Lite 02-02.

Small, I., Atkin, D., 2003: A WES Simulation of the Extreme Santa Ana Wind Event of 6-7
January 2003. Western Regional Technical Attachment-Lite 03-08.

Small, I., 2003: A WES Simulation of the Interaction between a Trough in the Westerlies and
Monsoon Flow Leading to Flash Flooding in Southern California. Western Regional Technical
Attachment-Lite 03-42.

Small, I., Dandrea, J., 2003: A Low Level Blocking Ridge Along With Downward Motion Aloft
in the Right Front Quadrant of the Upper Level Jet - A Recipe for Minor Flooding and High
Winds. Western Regional Technical Attachment 03-05.

Small, I., Dandrea, J., 2004: Some Interesting Characteristics of Southern California Wildfires
and the Resulting Waterman Flash Flood/Mudslide Event of December 25, 2003. Western
Regional Technical Attachment-Lite 04-29.

Small, I., Atkin, D., 2004: A Pacific Storm As Seen Via The WES: Focus on a Gap Wind
Enhanced Convergence Zone and Associated Flooding. Western Regional Technical
Attachment-Lite 04-03.

Small, I., Gonsalves, P., 2005: A Dramatic Shift from a Warm Monsoonal Pattern to a Cold
Northwest Express Pattern. Western Regional Technical Attachment-Lite 05-05.

Small, I., Atkin, D., 2006: An Inside Slider with Very Low Elevation Snow and High Winds in
Extreme Southwestern California. Western Regional Technical Attachment-Lite 06-02.

Small, I., Dandrea, J., 2006: Characteristics of a Record Breaking Heat Wave and Monsoon
206
Event in Southern California during the Summer of 2006. Western Regional Technical
Attachment 06-08.

Tubbs, A.M., 1972: Summer thunderstorms over Southern California. Monthly Weather Review,
100, 799-807.

Wilson, Harlan L., 1959: Guide to Weather and Climate of San Diego. San Diego City Schools.
145 pp.

Zierer, Clifford, 1956: California and the Southwest. John Wiley & Sons. 376 pp. Chapter 4.

207
Appendix D - Product Cross Reference
The following chart is a cross references for weather products issued by the NWS with the World
Meteorological Organization (WMO) headers. The NWS identifier used is the final five or six
letters of the complete nine digit identifier. Actual issuance times may occur before the indicated
issuance times below.

Product NWS Header (for WMO Issuance Times

Weatherwire and Header
EMWIN)

Area Forecast Discussion AFDSGX FXUS66 330 am, 930 am, 230 pm,
930 pm, and as needed

Airport Weather Warning AWWSAN WWUS86 as needed

(Lindbergh Field only)

Climatological Report CLM XXX (XXX CSUX46 1st day of the month
(Monthly) dependent on
location)

Climatological Report CLIXXX (XXX CDUS46 2 am, 4 pm

(Daily) dependent on
location)

Coastal Flood Statement CFWSGX FZUS68 as needed

(incl. High Surf Advisory)

Coastal Waters Forecast CWFSGX FZUS56 330 am/pm, 930 am/pm

PDT (230 am/pm, 830
am/pm PST)

Coastal Weather CGRSGX SXUS8 7 am, 10 am, 1 pm,

Observations 4 pm, 7 pm, 10 pm,
(possibly 1 am, 4 am)

Earthquake Report EQREQI SEUS61 as needed

Fire Weather Planning FWFSGX FNUS56 400 am, 230 pm (during

Forecast season), as needed

Fire Weather Watch, Red RFWSGX WWUS86 as needed

Flag Warning

Flash Flood Warning FFWSGX WGUS56 as needed

Flood Watch (flash or river) FFASGX WGUS46 as needed

Flash Flood Statement FFSSGX WGUS76 as needed

208
Flood Potential Outlook ESFSGX FGUS76 as needed

Flood Statement or Advisory FLSSGX WGUS46 as needed

Flood Warning FLWSGX WGUS46 as needed

Hazardous Weather Outlook HWOSGX FLUS46 6 am, when needed

Hourly Weather Roundup RWRSGX ASUS46 hourly

Hurricane Local Statement HLSSGX WTUS84 as needed

Local Storm Report LSRSGX WWUS30 as needed

Marine Weather Statement MWSSGX FZUS76 as needed

Mexican Weather Roundup RWRMX AXUS46 hourly

Non Precipitation Warnings/ NPWSGX WWUS45 as needed

Watches/ Advisories

Offshore Waters Forecast OFFPZ6 FZPN26 330 am/pm, 930 am/pm

Public Information PNSSGX ABUS34 as needed

Statement

Quantitative Precipitation QPSSGX FSUS46 4 am/pm (1 Nov - 15 Apr),

Forecast as needed

Rainfall Storm Total RRMSGX SGUS46 as needed

Summary

Record Event Report RERSGX SXUS99 as needed

Red Flag Warning, Fire RFWSGX FXUS70 as needed

Weather Watch

Regional Max/Min Temp RTPSGX ASUS66 530 am, 430 pm, 530 pm,
and Precipitation Table and as needed

River Statement RVSSGX RWUS15 as needed

Tabular State Forecast for SFTSGX FOUS45 330 am, 230 pm

California

Severe Local Storm Watch SLSCA WWUS32 as needed

and Areal Outlook

Severe Thunderstorm SVRSGX WUUS56 as needed

Warning

209
Severe Weather Statement SVSSGX WWUS34 as needed

Short Term Forecast NOWSGX FPUS76 as needed

Special Marine Warning SMWSGX WMUS1 as needed

Special Weather Statement SPSSGX WWUS35 as needed

Surf Forecast SRFSGX FZUS56 2 am/pm

Tornado Warning TORSGX WFUS56 as needed

Tsunami Warning TSWSGX WEXX20 as needed

Tsunami Watch or Advisory TSASGX WEPA41 as needed

Tsunami Statement TSSSGX WEPA43 as needed

Winter Weather Warnings/ WSWSGX WWUS46 as needed

Watches/Advisories

Zone Forecast ZFPSGX FPUS56 330 am, 230 pm, and as

needed

210
Non- Routine Products
For the current Watches, Warnings and Advisories issued by the San Diego Weather Forecast
Office please use this link: www.wrh.noaa.gov/warnings.php?wfo=sgx.

SEVERE FLOODING NON- FIRE WINTER OTHER

WEATHER FLOOD WATCH PRECIPITATION WEATHER WEATHER SHORT TERM
TORNADO (LAXFFASGX) HAZARDS FIRE WEATHER WI NTER FORECAST
WATCH FLOOD (NPW) WATCH WEATHER (LAXNOWSGX)
(LAXWCNSGX) WARNING (LAXRFWSGX) OUTLOOK LOCAL STORM
WIND
TORNADO (LAXFLWSGX) RED FLAG (LAXSPSSGX) REPORT
HIGH WIND WATCH (LAXLSRSGX)
WARNING FLASH FLOOD WARNING WINTER
(LAXNPWSGX)
(LAXTORSGX) WATCH (LAXRFWSGX) WEATHER SPECIAL
(LAXFFASGX) HIGH WIND WEATHER
FUNNEL CLOUD
WARNING MARINE ADVISORY
(LAXSPSSGX) FLASH FLOOD (LAXWSWSGX) STATEMENT
(LAXNPWSGX) WATERSPOUT
SEVERE WARNING SNOW ADVISORY (LAXSPSSGX)
(LAXFFWSGX) WIND ADVISORY (LAXSMWSGX) (LAXWSWSGX) PUBLIC
THUNDERSTORM MARINE
(LAXNPWSGX) INFORMATION
WATCH FLASH FLOOD WEATHER SNOW AND
(LAXWCNSGX) STATEMENT FROST/FREEZE BLOWING SNOW STATEMENT
STATEMENT
SEVERE (LAXFFSSGX) FREEZE WARNING (LAXMWSSGX) ADVISORY (LAXPNSSGX)
THUNDERSTORM URBAN AND (LAXNPWSGX) (LAXWSWSGX) HAZARDOUS
SPECIAL
WARNING SMALL STREAM FROST ADVISORY WINTER STORM WEATHER
MARINE
(LAXSVRSGX) FLOOD (LAXNPWSGX) WARNING WATCH OUTLOOK
SEVERE ADVISORY HEAT (LAXSMWSGX) (LAXWSWSGX) (LAXHWOSGX)
WEATHER (LAXFLSSGX) EXCESSIVE HEAT WINTER STORM
STORM
STATEMENT FLOOD WATCH WARNING WARNING
(LAXSVSSGX) STATEMENT (LAXNPWSGX) Headlined in (LAXWSWSGX)
(LAXFLSSGX) EXCESSIVE HEAT (LAXCWFSGX) BLIZZARD
COASTAL WARNING GALE WARNING WARNING
FLOOD WATCH (LAXNPWSGX) Headlined in (LAXWSWSGX)
(LAXCFWSGX) (LAXCWFSGX) WIND CHILL
OTHER
COASTAL SMALL CRAFT ADVISORY
HIGH SURF
FLOOD ADVISORY (LAXWSWSGX)
WARNING ADVISORY
Headlined in WIND CHILL
(LAXCFWSGX) (LAXCFWSGX)
(LAXCWFSGX) WARNING
DENSE FOG
COASTAL (LAXWSWSGX)
ADVISORY AVIATION
FLOOD HEAVY SNOW
STATEMENT (LAXNPWSGX) AIRPORT
WARNING
(LAXCFWSGX) WEATHER
(LAXWSWSGX)
WARNING
(LAXAWWSAN)

211
Appendix E – Warning and Advisory Criteria
WIND

Location Wind Advisory (NPW) High Wind Warning (NPW)

Coastal Areas and Valleys Sustained 30 mph (26 kt) or Sustained 40 mph (35 kt) or more
more and/or gusts 35 mph (30 and/or gusts 58 mph (50 kt) or more
kt) or more

Desert and Mountains Sustained 35 mph (30 kt) or Sustained 45 mph (39 kt) or more
below 7000 ft more and/or gusts 45 mph (39 and/or gusts 58 mph (50 kt) or more
kt) or more

Mountains above 7000 ft Sustained 45 mph (39 kt) or Sustained 55 mph (48 kt) or more
more and/or gusts 55 mph (48 and/or gusts 75 mph (65 kt) or more
kt) or more

FOG

Location Dense Fog Advisory (NPW)

Usually for 2 or more locations Less than ½ mile visibility for any length of time

WINTER WEATHER

Location Snow and Blowing Snow Advisory Heavy Snow Warning

(WSW) (WSW)

Mountains above 7000 ft 4-7” in 12 hours with visibilities below 12” in 12 hours or 18” in
½ mile in strong wind 24 hours

Mountains below 7000 ft (3000- 4-7” in 12 hours with visibilities below 8” in 12 hours or 12” in
7000 ft) ½ mile in strong wind 24 hours

All other areas 1-4” in 12 hours with visibilities below 4” in 12 hours or 6” in 24

½ mile in strong wind hours

Location Wind Chill Wind Chill Blizzard Warning Blowing Snow Advisory
Warning (NPW) Advisory (NPW) (WSW) (WSW)

any -20 degree wind -10 to -19 degree Sustained wind 35 Widespread visibilities ½
chill wind chill mph (30 kt) or mile or less
more with visibility
1/4 mile or less for
3 hours or more

212
 Location Freezing Rain or Drizzle Advisory Ice Storm Warning (WSW)
(WSW)

any Freezing rain or drizzle accumulations of Freezing rain or drizzle accumulations of

a trace to less than 1/4” 1/4” or more

SEVERE THUNDERSTORM – TORNADO

Location Severe Thunderstorm Warning (SVR) Tornado Warning (TOR)

any Hail 3/4” or larger and/or winds 58 mph If tornado is sighted or if radar or other data
(50 kt) sustained or gusts suggest existence or formation is likely

TEMPERATURE

Location Excessive Heat Frost Advisory (NPW) Freeze Warning (NPW)

Warning (NPW)

Coastal Heat Index 105 Widespread temps from 28 to Widespread temps 28 degrees
Sections degrees or more 32 degrees or less

Valleys Heat Index 110 Widespread temps from 28 to Widespread temps 28 degrees
degrees or more 32 degrees or less

Apple and Heat Index 120 The 1st and 2nd time temp is The 1st and 2nd time temp is
Yucca degrees or more forecast to be 32 degrees or less forecast to be 28 degrees or less
Valleys for 2 or more consecutive hours for 2 or more consecutive hours
or anytime between 1 Mar and or anytime between 1 Mar and
15 Nov 15 Nov

Lower Heat Index 120 Widespread temps from 28 to Widespread temps 28 degrees
Deserts degrees or more 32 degrees or less

Mountains Heat Index 105 Not issued Not issued

(> 3 kft) degrees or more

MARINE

Small Craft Advisory (incl. for hazardous seas) Gale Warning Storm Warning

Wind 21 to 33 kt and/or combined seas 10 ft or more Wind 34 to 47 kt Wind 48 kt or more

These three hazards above are simply headlined in the text of the Coastal Waters Forecast (CWF)
High Surf Advisory (CFW) Tidal Overflow Statement (CFW)

Widespread breakers of 7 ft or more. Tides of 7 ft or more with little or no wave or

If high tides will be 5 ½ ft or more, a call to wind action. With higher wave or wind action,
action to protect beach property is required use Coastal Flooding products
213
Appendix F - Climate Data and Records
Official climate data suitable for insurance claims or for legal purposes must be certified by the
National Climatic Data Center (NCDC). These data are available in hourly, daily, monthly, or
seasonal breakdowns for nearly 100 locations in our area of responsibility and hundreds more
locations in the western U.S. These data can be obtained through the Western Regional Climate
Center in Reno, Nevada, and require a special request and a small fee. Contact them directly:

Western Regional Climate Center

2215 Raggio Parkway
Reno, Nevada 89512

email: wrcc@dri.edu
phone: 775-674-7010
fax: 775-674-7016
Internet address: www.wrcc.dri.edu

Southern California archives of climate normals are also available on the Western Regional
Climate Center’s web site at: www.wrcc.dri.edu/summary/climsmsca.html
For a narrative describing the monthly climate for the city of San Diego, click on:
www.wrh.noaa.gov/sgx/climate/san-san-month.htm

Many detailed (daily and hourly) historical weather conditions are available on our website
www.weather.gov/climate/index.php?wfo=sgx through the NOWData link (from our home
page, click on Climate – Local, then NOWData). Additional climate data are made available
through this web site for numerous sites in our area (Observed Weather tab). A wealth of various
other climate information data is available on the Local Data/Records tab. These data featured on
the web site are preliminary and not official data suitable for insurance claims or legal purposes.

The history or weather in Southern California can be viewed on a day-to-day basis each day and
is headlined on our home page as “This Day in History” with a link to the daily archive. More
weather history is available on our home page by clicking on “Weather History” on the left side
menu.

214
Appendix G – Weather Safety Tips for Southern California
For more information about these and other hazards, visit: weather.gov/safety.php

Flash Floods

• Get out of areas subject to flooding, such as dips, low spots, canyons, washes, etc. Climb to
higher ground.
• Do not let children play near storm drains.
• Avoid already flooded and high velocity flow areas. Do not attempt to cross flowing streams.
• If driving, be aware that the road bed may not be intact under flood waters. Turn around and
go another way. Never drive through flooded roadways.
• If the vehicle stalls, leave it immediately and seek higher ground. Rapidly rising water may
engulf the vehicle and its occupants and sweep them away.
• Be especially cautious at night when it is harder to recognize flood dangers.
• Do not camp or park your vehicle along streams and washes, particularly during threatening
conditions.
• If advised to evacuate, do so immediately.

Lightning

• Postpone outdoor activities if thunderstorms are imminent. This is your best way to avoid
being caught in a dangerous situation.
• Move to a sturdy building or car. Do not take shelter in small sheds, under isolated trees, or
in convertible automobiles. Stay away from tall objects such as towers, fences, telephone
poles, and power lines.
• If lightning is occurring and a sturdy shelter is not available, get inside a hard top automobile
and keep the windows up. Avoid touching any metal.
• Utility lines and metal pipes can conduct electricity. Unplug appliances not necessary for
obtaining weather information. Avoid using the telephone or any electrical appliances. Use
phones ONLY in an emergency.
• Do not take a bath or shower during a thunderstorm.
• Turn off air conditioners. Power surges from lightning can cause serious damage.

If caught outdoors and no shelter is nearby:

• Find a low spot away from trees, fences, and poles. Make sure the place you pick is not
subject to flooding.
• If you are in the woods, take shelter under the shorter trees.
• If you feel your skin tingle or your hair stand on end, squat low to the ground on the balls of
your feet. Place your hands over your ears and your head between your knees. Make yourself
the smallest target possible and minimize your contact with the ground. DO NOT lie down.
• If you are boating or swimming, get to land and find shelter immediately!

215
Tornadoes
• In a home or building, move to a pre-designated shelter, such as a basement.
• If an underground shelter is not available, move to a small interior room or hallway on the
lowest floor and get under a sturdy piece of furniture. Put as many walls as possible between
you and the outside.
• Stay away from windows.
• Get out of automobiles.
• Do not try to outrun a tornado in your car; instead, leave it immediately for safe shelter.
• If caught outside or in a vehicle, lie flat in a nearby ditch or depression and cover your head
with your hands.
• Be aware of flying debris. Flying debris from tornadoes causes most fatalities and injuries.
• Mobile homes, even if tied down, offer little protection from tornadoes. You should leave a
mobile home and go to the lowest floor of a sturdy nearby building or a storm shelter.

Winter Storms and Extreme Cold

Outside:

• Find shelter to stay dry. Cover all exposed body parts.

• If no shelter, build a lean-to, windbreak or snow cave for protection from the wind. Build a
fire for heat and to attract attention. Place rocks around the fire to absorb and reflect heat.
• Melt snow for drinking water. Eating snow will lower your body temperature.

In a Vehicle:

• Stay in the vehicle. You will become quickly disoriented in wind-driven snow and cold.
• Run the motor about 10 minutes each hour for heat.
• Open the window a little for fresh air to avoid carbon monoxide poisoning.
• Make sure the exhaust pipe is not blocked.
• Be visible to rescuers. Turn on the dome light at night when running the engine.
• Tie a colored cloth, preferably red, to your antenna or door.
• After snow stops falling, raise the hood to indicate you need help.
• Exercise. From time to time, move arms, legs, fingers and toes vigorously to keep blood
circulating and to keep warm.

Inside:

• Stay inside.
• When using alternate heat from a fireplace, wood stove, space heater, etc., use fire safeguards
and properly ventilate.
• If no heat: close off unneeded rooms, stuff towels or rags in cracks under doors, cover
windows at night. Eat and drink. Food provides the body with energy for producing its own
heat. Keep the body replenished with fluids to prevent dehydration. Wear layers of loose-
fitting, lightweight, warm clothing. Remove layers to avoid overheating, perspiration and
216
 subsequent chill.

Extreme Heat
• Slow down. Limit strenuous activities to the coolest time of the day.
• Dress for summer. Wear lightweight, light-colored clothing.
• Reduce the consumption of proteins to slow down metabolism and water loss.
• Drink plenty of water even if you are not thirsty. Avoid alcoholic beverages.
• Spend more time in air-conditioned places.
• Avoid too much exposure to the sun. Sunburn reduces the body’s ability to dissipate heat.

Boating

• Check NOAA All-Hazards Radio for latest warnings and forecasts.

• Watch for signs of approaching storms: dark, threatening clouds that may foretell a squall or
thunderstorm, a steady increase in wind or sea lightning flashes.
• An increase in wind opposite in direction to a strong tidal current may lead to steep waves
capable of broaching a boat.
• Heavy static on your AM radio may be an indication of nearby thunderstorm activity.
• If a thunderstorm is approaching, head for shore if possible. Get out of your boat and away
from the water. Find shelter immediately.
• If a thunderstorm catches you while afloat, remember that gusty winds and lightning pose a
threat to safety. Put on your personal flotation device and prepare for rough seas. Stay below
deck if possible. Keep away from metal objects that are not grounded to the boat's
protection system. Don't touch more than one grounded object at the same time (or you may
become a shortcut for electrical surges passing through the protection system).

Surf and Rip Currents

• Know how to swim.

• Always swim at guarded beaches and heed the beach patrol.
• Remain calm. If caught in a rip current remember it will not pull you under.
• Swim out of the current. Since the currents are relatively narrow, escape the flow by
swimming parallel to the shore until you break free, then swim diagonally toward the shore.
• Float if you cannot swim out of the current. Float until it dissipates, then swim diagonally
toward the shore or float and summon the beach patrol by waving your hands.
• Use a flotation device if you attempt to rescue someone.

217
Appendix H — Charts and Tables
Temperature Conversion
In the formulas below, / means to divide, * means to multiply, - means subtract, + means to add
and = is equal. Tc = temperature in degrees Celsius, Tf = temperature in degrees Fahrenheit.
To convert a Fahrenheit temperature into Celsius: Tc = (5/9)*(Tf-32)
To convert a Celsius temperature into degrees Fahrenheit: Tf = ((9/5)*Tc)+32

to C C or F to F to C C or F to F to C C or F to F to C C or F to F
-28.89 -20 -4 -6.67 20 68 15.56 60 140 37.78 100 212
-28.33 -19 -2.2 -6.11 21 69.8 16.11 61 141.8 38.33 101 213.8
-27.78 -18 -0.4 -5.56 22 71.6 16.67 62 143.6 38.89 102 215.6
-27.22 -17 1.4 -5 23 73.4 17.22 63 145.4 39.44 103 217.4
-26.67 -16 3.2 -4.44 24 75.2 17.78 64 147.2 40 104 219.2
-26.11 -15 5 -3.89 25 77 18.33 65 149 40.56 105 221
-25.56 -14 6.8 -3.33 26 78.8 18.89 66 150.8 41.11 106 222.8
-25 -13 8.6 -2.78 27 80.6 19.44 67 152.6 41.67 107 224.6
-24.44 -12 10.4 -2.22 28 82.4 20 68 154.4 42.22 108 226.4
-23.89 -11 12.2 -1.67 29 84.2 20.56 69 156.2 42.78 109 228.2
-23.33 -10 14 -1.11 30 86 21.11 70 158 43.33 110 230
-22.78 -9 15.8 -0.56 31 87.8 21.67 71 159.8 43.89 111 231.8
-22.22 -8 17.6 0 32 89.6 22.22 72 161.6 44.44 112 233.6
-21.67 -7 19.4 0.56 33 91.4 22.78 73 163.4 45 113 235.4
-21.11 -6 21.2 1.11 34 93.2 23.33 74 165.2 45.56 114 237.2
-20.56 -5 23 1.67 35 95 23.89 75 167 46.11 115 239
-20 -4 24.8 2.22 36 96.8 24.44 76 168.8 46.67 116 240.8
-19.44 -3 26.6 2.78 37 98.6 25 77 170.6 47.22 117 242.6
-18.89 -2 28.4 3.33 38 100.4 25.56 78 172.4 47.78 118 244.4
-18.33 -1 30.2 3.89 39 102.2 26.11 79 174.2 48.33 119 246.2
-17.78 0 32 4.44 40 104 26.67 80 176 48.89 120 248
-17.22 1 33.8 5 41 105.8 27.22 81 177.8 49.44 121 249.8
-16.67 2 35.6 5.56 42 107.6 27.78 82 179.6 50 122 251.6
-16.11 3 37.4 6.11 43 109.4 28.33 83 181.4 50.56 123 253.4
-15.56 4 39.2 6.67 44 111.2 28.89 84 183.2 51.11 124 255.2
-15 5 41 7.22 45 113 29.44 85 185 51.67 125 257
-14.44 6 42.8 7.78 46 114.8 30 86 186.8 52.22 126 258.8
-13.89 7 44.6 8.33 47 116.6 30.56 87 188.6 52.78 127 260.6
-13.33 8 46.4 8.89 48 118.4 31.11 88 190.4 53.33 128 262.4
-12.78 9 48.2 9.44 49 120.2 31.67 89 192.2 53.89 129 264.2
-12.22 10 50 10 50 122 32.22 90 194 54.44 130 266
-11.67 11 51.8 10.56 51 123.8 32.78 91 195.8 55 131 267.8
-11.11 12 53.6 11.11 52 125.6 33.33 92 197.6 55.56 132 269.6
-10.56 13 55.4 11.67 53 127.4 33.89 93 199.4 56.11 133 271.4
-10 14 57.2 12.22 54 129.2 34.44 94 201.2 56.67 134 273.2
-9.44 15 59 12.78 55 131 35 95 203 57.22 135 275
-8.89 16 60.8 13.33 56 132.8 35.56 96 204.8 57.78 136 276.8
-8.33 17 62.6 13.89 57 134.6 36.11 97 206.6 58.33 137 278.6
-7.78 18 64.4 14.44 58 136.4 36.67 98 208.4 58.89 138 280.4
-7.22 19 66.2 15 59 138.2 37.22 99 210.2 59.44 139 282.2

218
Wind Speed Conversion

1 mph = 0.87 knots; 1 knot = 1.15 mph

to Kt Kt or to mph to Kt Kt or to mph to Kt Kt or to mph to Kt Kt or to mph

mph mph mph mph
1 1 1 23 26 30 44 51 59 66 76 87
2 2 2 23 27 31 45 52 60 67 77 89
3 3 3 24 28 32 46 53 61 68 78 90
3 4 5 25 29 33 47 54 62 69 79 91
4 5 6 26 30 35 48 55 63 70 80 92
5 6 7 27 31 36 49 56 64 70 81 93
6 7 8 28 32 37 50 57 66 71 82 94
7 8 9 29 33 38 50 58 67 72 83 96
8 9 10 30 34 39 51 59 68 73 84 97
9 10 12 30 35 40 52 60 69 74 85 98
10 11 13 31 36 41 53 61 70 75 86 99
10 12 14 32 37 43 54 62 71 76 87 100
11 13 15 33 38 44 55 63 72 76 88 101
12 14 16 34 39 45 56 64 74 77 89 102
13 15 17 35 40 46 56 65 75 78 90 104
14 16 18 36 41 47 57 66 76 79 91 105
15 17 20 36 42 48 58 67 77 80 92 106
16 18 21 37 43 49 59 68 78 81 93 107
17 19 22 38 44 51 60 69 79 82 94 108
17 20 23 39 45 52 61 70 81 83 95 109
18 21 24 40 46 53 62 71 82 83 96 110
19 22 25 41 47 54 63 72 83 84 97 112
20 23 26 42 48 55 63 73 84 85 98 113
21 24 28 43 49 56 64 74 85 86 99 114
22 25 29 43 50 58 65 75 86 87 100 115

219
Beaufort Wind Scale

This scale is used to estimate wind speeds when no wind equipment is available.

Speed Description - Visible Condition

(mph)

0 Calm: Smoke rises vertically

1-4 Light air: Direction of wind shown by smoke but not by wind vanes

4-7 Light breeze: Felt on face; leaves rustle; ordinary wind vane moved by wind

8 - 12 Gentle breeze: Leaves and small twigs in constant motion; wind extends light flag

13 - 18 Moderate breeze: Raises dust and loose paper; small branches are moved

19 - 24 Fresh breeze: Small trees in leaf begin to sway; crested wavelets form on inland
water

25 - 31 Strong breeze: Large branches in motion; telephone wires whistle; umbrellas used
with difficulty

32 - 38 Moderate gale: Whole trees in motion; inconvenience in walking against wind

39 - 46 Fresh gale: Breaks twigs off trees; generally impedes progress

47 - 54 Strong gale: Slight structural damage occurs; chimney pots and slates removed

55 - 63 Whole gale: Trees uprooted; considerable structural damage occurs

64 - 72 Storm: Very rarely experienced; accompanied by widespread damage

73+ Hurricane: Devastation occurs

220
Pressure Conversion

Standard Atmosphere conversion:

29.92 inches of mercury (Hg) = 1013.25 millibars

inches millibars inches millibars inches millibars inches millibars inches millibars

28.50 965.1 29.00 982.1 29.50 999.0 30.00 1015.9 30.50 1032.8
28.51 965.5 29.01 982.4 29.51 999.3 30.01 1016.3 30.51 1033.2
28.52 965.8 29.02 982.7 29.52 999.7 30.02 1016.6 30.52 1033.5
28.53 966.1 29.03 983.1 29.53 1000.0 30.03 1016.9 30.53 1033.9
28.54 966.5 29.04 983.4 29.54 1000.3 30.04 1017.3 30.54 1034.2
28.55 966.8 29.05 983.7 29.55 1000.7 30.05 1017.6 30.55 1034.5
28.56 967.2 29.06 984.1 29.56 1001.0 30.06 1017.9 30.56 1034.9
28.57 967.5 29.07 984.4 29.57 1001.4 30.07 1018.3 30.57 1035.2
28.58 967.8 29.08 984.8 29.58 1001.7 30.08 1018.6 30.58 1035.6
28.59 968.2 29.09 985.1 29.59 1002.0 30.09 1019.0 30.59 1035.9
28.60 968.5 29.10 985.4 29.60 1002.4 30.10 1019.3 30.60 1036.2
28.61 968.8 29.11 985.8 29.61 1002.7 30.11 1019.6 30.61 1036.6
28.62 969.2 29.12 986.1 29.62 1003.0 30.12 1020.0 30.62 1036.9
28.63 969.5 29.13 986.5 29.63 1003.4 30.13 1020.3 30.63 1037.3
28.64 969.9 29.14 986.8 29.64 1003.7 30.14 1020.7 30.64 1037.6
28.65 970.2 29.15 987.1 29.65 1004.1 30.15 1021.0 30.65 1037.9
28.66 970.5 29.16 987.5 29.66 1004.4 30.16 1021.3 30.66 1038.3
28.67 970.9 29.17 987.8 29.67 1004.7 30.17 1021.7 30.67 1038.6
28.68 971.2 29.18 988.1 29.68 1005.1 30.18 1022.0 30.68 1038.9
28.69 971.6 29.19 988.5 29.69 1005.4 30.19 1022.4 30.69 1039.3
28.70 971.9 29.20 988.8 29.70 1005.8 30.20 1022.7 30.70 1039.6
28.71 972.2 29.21 989.2 29.71 1006.1 30.21 1023.0 30.71 1040.0
28.72 972.6 29.22 989.5 29.72 1006.4 30.22 1023.4 30.72 1040.3
28.73 972.9 29.23 989.8 29.73 1006.8 30.23 1023.7 30.73 1040.6
28.74 973.2 29.24 990.2 29.74 1007.1 30.24 1024.0 30.74 1041.0
28.75 973.6 29.25 990.5 29.75 1007.5 30.25 1024.4 30.75 1041.3
28.76 973.9 29.26 990.8 29.76 1007.8 30.26 1024.7 30.76 1041.6
28.77 974.3 29.27 991.2 29.77 1008.1 30.27 1025.1 30.77 1042.0
28.78 974.6 29.28 991.5 29.78 1008.5 30.28 1025.4 30.78 1042.3
28.79 974.9 29.29 991.9 29.79 1008.8 30.29 1025.7 30.79 1042.7
28.80 975.3 29.30 992.2 29.80 1009.1 30.30 1026.1 30.80 1043.0
28.81 975.6 29.31 992.6 29.81 1009.5 30.31 1026.4 30.81 1043.3
28.82 976.0 29.32 992.9 29.82 1009.8 30.32 1026.8 30.82 1043.7
28.83 976.3 29.33 993.2 29.83 1010.2 30.33 1027.1 30.83 1044.0
28.84 976.6 29.34 992.6 29.84 1010.5 30.34 1027.4 30.84 1044.4
28.85 977.0 29.35 993.9 29.85 1010.8 30.35 1027.8 30.85 1044.7
28.86 977.3 29.36 994.2 29.86 1011.2 30.36 1028.1 30.86 1045.0
28.87 977.7 29.37 994.6 29.87 1011.5 30.37 1028.4 30.87 1045.4
28.88 978.0 29.38 994.9 29.88 1011.9 30.38 1028.8 30.88 1045.7
28.89 978.3 29.39 995.3 29.89 1012.2 30.39 1029.1 30.89 1046.1
28.90 978.7 29.40 995.6 29.90 1012.5 30.40 1029.5 30.90 1046.4
28.91 979.0 29.41 995.9 29.91 1012.9 30.41 1029.8 30.91 1046.7
28.92 979.3 29.42 996.3 29.92 1013.2 30.42 1030.1 30.92 1047.1
28.93 979.7 29.43 996.6 29.93 1013.5 30.43 1030.5 30.93 1047.4
28.94 980.0 29.44 997.0 29.94 1013.9 30.44 1030.8 30.94 1047.7
28.95 980.4 29.45 997.3 29.95 1014.2 30.45 1031.2 30.95 1048.1
28.96 980.7 29.46 997.6 29.96 1014.6 30.46 1031.5 30.96 1048.4
28.97 981.0 29.47 998.0 29.97 1014.9 30.47 1031.8 30.97 1048.8
28.98 981.4 29.48 998.3 29.98 1015.2 30.48 1032.2 30.98 1049.1
28.99 981.7 29.49 998.6 29.99 1015.6 30.49 1032.5 30.99 1049.4

221
Sunrise/Sunset Table and Tide Predictions for San Diego

Sunrise and Sunset Tables have been computed for any location by the U.S. Naval
Observatory. Click on: aa.usno.navy.mil/data/docs/RS_OneYear.html

The chart below shows the times of sunrise and sunset in San Diego for any year in
Pacific Standard Time. Add one hour for daylight time (between the second Sunday in
March and the first Sunday in November at 2 am).

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Rise Rise Rise Rise Rise Rise Rise Rise Rise Rise Rise Rise
Set Set Set Set Set Set Set Set Set Set Set Set

1 0651 0644 0617 0537 0502 0442 0444 0502 0523 0543 0606 0633
1653 1721 1746 1809 1830 1851 1901 1847 1814 1733 1658 1642

2 0651 0643 0615 0536 0501 0441 0445 0503 0524 0543 0607 0634
1654 1722 1746 1809 1831 1852 1900 1846 1812 1732 1657 1642

3 0651 0642 0614 0534 0500 0441 0445 0504 0524 0544 0608 0634
1655 1723 1747 1810 1832 1853 1900 1845 1811 1731 1656 1642

4 0651 0641 0613 0533 0459 0441 0445 0504 0525 0545 0609 0635
1656 1724 1748 1811 1832 1853 1900 1845 1810 1730 1655 1642

5 0652 0641 0612 0532 0458 0441 0446 0505 0526 0545 0610 0636
1657 1725 1749 1811 1833 1854 1900 1844 1808 1728 1654 1642

6 0652 0640 0611 0530 0457 0440 0446 0506 0526 0546 0610 0637
1657 1726 1750 1812 1834 1854 1900 1843 1807 1727 1654 1642

7 0652 0639 0609 0529 0456 0440 0447 0506 0527 0547 0611 0638
1658 1727 1750 1813 1835 1855 1900 1842 1806 1726 1653 1642

8 0652 0638 0608 0528 0455 0440 0447 0507 0528 0547 0612 0638
1659 1728 1751 1813 1835 1855 1900 1841 1804 1724 1652 1642

9 0652 0637 0607 0527 0454 0440 0448 0508 0528 0548 0613 0639
1700 1729 1752 1814 1836 1856 1859 1840 1803 1723 1651 1643

10 0652 0637 0606 0525 0454 0440 0448 0508 0529 0549 0614 0640
1701 1729 1753 1815 1837 1856 1859 1839 1802 1722 1651 1643

11 0652 0636 0604 0524 0453 0440 0449 0509 0530 0550 0615 0641
1702 1730 1753 1816 1837 1856 1859 1838 1800 1721 1650 1643

12 0652 0635 0603 0523 0452 0440 0450 0510 0530 0550 0616 0641
1702 1731 1754 1816 1838 1857 1859 1837 1759 1719 1649 1643

13 0651 0634 0602 0522 0451 0440 0450 0510 0531 0551 0617 0642
1703 1732 1755 1817 1839 1857 1858 1836 1758 1718 1649 1643

14 0651 0633 0600 0521 0451 0440 0451 0511 0531 0552 0618 0643
1704 1733 1756 1818 1840 1858 1858 1835 1756 1717 1648 1644

15 0651 0632 0559 0519 0450 0440 0451 0512 0532 0552 0618 0643
1705 1734 1756 1818 1840 1858 1857 1834 1755 1716 1648 1644

16 0651 0631 0558 0518 0449 0440 0452 0513 0533 0553 0619 0644
1706 1735 1757 1819 1841 1858 1857 1833 1754 1715 1647 1644

222
 17 0651 0630 0557 0517 0449 0440 0452 0513 0533 0554 0620 0645
1707 1736 1758 1820 1842 1859 1857 1832 1752 1713 1646 1645

18 0650 0629 0555 0516 0448 0440 0453 0514 0534 0555 0621 0645
1708 1737 1759 1821 1842 1859 1856 1830 1751 1712 1646 1645

19 0650 0628 0554 0515 0447 0441 0454 0515 0535 0555 0622 0646
1709 1737 1759 1821 1843 1859 1856 1829 1750 1711 1646 1646

20 0650 0627 0553 0513 0447 0441 0454 0515 0535 0556 0623 0646
1710 1738 1800 1822 1844 1859 1855 1828 1748 1710 1645 1646

21 0649 0626 0551 0512 0446 0441 0455 0516 0536 0557 0624 0647
1711 1739 1801 1823 1844 1900 1855 1827 1747 1709 1645 1646

22 0649 0625 0550 0511 0446 0441 0456 0517 0537 0558 0625 0647
1712 1740 1801 1823 1845 1900 1854 1826 1746 1708 1644 1647

23 0649 0624 0549 0510 0445 0441 0456 0517 0537 0559 0626 0648
1713 1741 1802 1824 1846 1900 1853 1825 1744 1707 1644 1647

24 0648 0622 0547 0509 0445 0442 0457 0518 0538 0559 0627 0648
1714 1742 1803 1825 1847 1900 1853 1823 1743 1706 1644 1648

25 0648 0621 0546 0508 0444 0442 0458 0519 0539 0600 0627 0649
1714 1742 1804 1826 1847 1900 1852 1822 1741 1705 1643 1649

26 0647 0620 0545 0507 0444 0442 0458 0519 0539 0601 0628 0649
1715 1743 1804 1826 1848 1900 1852 1821 1740 1704 1643 1649

27 0647 0619 0543 0506 0443 0443 0459 0520 0540 0602 0629 0649
1716 1744 1805 1827 1848 1900 1851 1820 1739 1703 1643 1650

28 0646 0618 0542 0505 0443 0443 0500 0520 0541 0603 0630 0650
1717 1745 1806 1828 1849 1901 1850 1819 1737 1702 1643 1650

29 0645 0541 0504 0443 0443 0500 0521 0541 0604 0631 0650
1718 1806 1829 1850 1901 1849 1817 1736 1701 1643 1651

30 0645 0540 0503 0442 0444 0501 0522 0542 0604 0632 0650
1719 1807 1829 1850 1901 1849 1816 1735 1700 1642 1652

31 0644 0538 0442 0502 0522 0605 0651

1720 1808 1851 1848 1815 1659 1653

Tide Predictions

Tide predictions for California and coastal locations throughout the country can be found
on the National Ocean Service’s web site: co-ops.nos.noaa.gov/tide_pred.html.

223
Heat Index

The NWS has devised the Heat Index, sometimes called the “apparent temperature.” It is the
temperature the body feels when the heat and humidity are combined. High relative humidity
inhibits the evaporation of perspiration and hence the body’s ability to cool itself. For more
information about the heat index: www.nws.noaa.gov/om/heat/index.shtml.
Note: Exposure to full sunshine can increase HI values by up to 15° F

HEAT INDEX °F
RELATIVE HUMIDITY (%)
Temp. 40 45 50 55 60 65 70 75 80 85 90 95 100
110 136
108 130 137
106 124 130 137
104 119 124 131 137
102 114 119 124 130 137
100 109 114 118 124 129 136
98 105 109 113 117 123 128 134
96 101 104 108 112 116 121 126 132
94 97 100 103 106 110 114 119 124 129 135
92 94 96 99 101 105 108 112 116 121 126 131
90 91 93 95 97 100 103 106 109 113 117 122 127 132
88 88 89 91 93 95 98 100 103 106 110 113 117 121
86 85 87 88 89 91 93 95 97 100 102 105 108 112
84 83 84 85 86 88 89 90 92 94 96 98 100 103
82 81 82 83 84 84 85 86 88 89 90 91 93 95
80 80 80 81 81 82 82 83 84 84 85 86 86 87

Category Heat Index Possible heat disorders for people in high risk groups
130°F or
Extreme higher
Heat stroke or sunstroke likely.
Danger (54°C or
higher)
105 - 129°F Sunstroke, muscle cramps, and/or heat exhaustion likely. Heatstroke possible with
Danger
(41 - 54°C) prolonged exposure and/or physical activity.
Extreme 90 - 105°F Sunstroke, muscle cramps, and/or heat exhaustion possible with prolonged exposure
Caution (32 - 41°C) and/or physical activity.
80 - 90°F
Caution Fatigue possible with prolonged exposure and/or physical activity.
(27 - 32°C)

224
Wind Chill

The wind chill temperature is how cold people and animals feel when outside. Wind chill
is based on the rate of heat loss from exposed skin caused by wind and cold. As the wind
increases, it draws heat from the body, lowering skin temperature and eventually the
internal body temperature. Therefore, the wind makes it feel much colder. See chart and
calculation formula below. Inanimate objects, such as car radiators and water pipes will
not cool below the actual air temperature. For more information about wind chill, click
on: www.nws.noaa.gov/om/windchill/index.shtml.

225
Ultraviolet Index

The Environmental Protection Agency (EPA) and the National Weather Service
developed the Ultraviolet Index (UVI) to provide important information to help you plan
your outdoor activities and prevent overexposure to the sun’s rays.

The UV Index can range from 0 (at night) to 15 or 16 (in the tropics at high elevations
under clear skies). UV radiation is greatest when the sun is highest in the sky and rapidly
decreases as the sun approaches the horizon. The higher the UV Index, the greater the
rate of skin-damaging (and eye damaging) UV radiation. Consequently, the higher the
UV Index, the shorter the time it takes before skin damage occurs. For more information
about the UVI, including forecast maps, click on:
www.epa.gov/sunwise/uvindex.html, also see
www.cpc.ncep.noaa.gov/products/stratosphere/uv_index.

The UV index is categorized by the EPA as follows:

UVI Exposure Level

012 Minimal

34 Low

56 Moderate

789 High

10 and greater Very High

226
Tropical Cyclones

Common Definitions

Tropical Depression Tropical Storm Hurricane

Wind speed less than 33 kt (39 Wind speed 34 to 63 kt (39- Wind speed greater than 63 kt
mph) 73 mph) (73 mph)

The Saffir-Simpson Hurricane Scale

The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane's present
intensity. This is used to give an estimate of the potential property damage and flooding
expected along the coast from a hurricane landfall. Wind speed is the determining factor
in the scale, as storm surge values are highly dependent on the slope of the continental
shelf in the landfall region. Note that all winds are using the U.S. 1-minute average. For
more information about hurricanes, click on: www.nhc.noaa.gov.

Category One Hurricane:

Winds 74-95 mph (64-82 kt or 119-153 km/hr). Storm surge generally 4-5 ft above
normal. No real damage to building structures. Damage primarily to unanchored mobile
homes, shrubbery, and trees. Some damage to poorly constructed signs. Also, some
coastal road flooding and minor pier damage. Hurricanes Allison of 1995 and Danny of
1997 were Category One hurricanes at peak intensity.

Category Two Hurricane:

Winds 96-110 mph (83-95 kt or 154-177 km/hr). Storm surge generally 6-8 feet above
normal. Some roofing material, door, and window damage of buildings. Considerable
damage to shrubbery and trees with some trees blown down. Considerable damage to
mobile homes, poorly constructed signs, and piers. Coastal and low-lying escape routes
flood 2-4 hours before arrival of the hurricane center. Small craft in unprotected
anchorages break moorings. Hurricane Bonnie of 1998 was a Category Two hurricane
when it hit the North Carolina coast, while Hurricane Georges of 1998 was a Category
Two Hurricane when it hit the Florida Keys and the Mississippi Gulf Coast.

Category Three Hurricane:

Winds 111-130 mph (96-113 kt or 178-209 km/hr). Storm surge generally 9-12 ft above
normal. Some structural damage to small residences and utility buildings with a minor
amount of curtainwall failures. Damage to shrubbery and trees with foliage blown off
trees and large tress blown down. Mobile homes and poorly constructed signs are
destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the
hurricane center. Flooding near the coast destroys smaller structures with larger structures
damaged by battering of floating debris. Terrain continuously lower than 5 ft above
mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying
residences with several blocks of the shoreline may be required. Hurricanes Roxanne of
1995 and Fran of 1996 were Category Three hurricanes at landfall on the Yucatan
Peninsula of Mexico and in North Carolina, respectively.
227
Category Four Hurricane:
Winds 131-155 mph (114-135 kt or 210-249 km/hr). Storm surge generally 13-18 ft
above normal. More extensive curtainwall failures with some complete roof structure
failures on small residences. Shrubs, trees, and all signs are blown down. Complete
destruction of mobile homes. Extensive damage to doors and windows. Low-lying escape
routes may be cut by rising water 3-5 hours before arrival of the hurricane center. Major
damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea
level may be flooded requiring massive evacuation of residential areas as far inland as
6 miles (10 km). Hurricane Luis of 1995 was a Category Four hurricane while moving
over the Leeward Islands. Hurricanes Felix and Opal of 1995 also reached Category Four
status at peak intensity.

Category Five Hurricane:

Winds greater than 155 mph (135 kt or 249 km/hr). Storm surge generally greater than 18
ft above normal. Complete roof failure on many residences and industrial buildings.
Some complete building failures with small utility buildings blown over or away. All
shrubs, trees, and signs blown down. Complete destructon of mobile homes. Severe and
extensive window and door damage. Low-lying escape routes are cut by rising water 3-5
hours before arrival of the hurricane center. Major damage to lower floors of all
structures located less than 15 ft above sea level and within 500 yards of the
shoreline. Massive evacuation of residential areas on low ground within 5-10 miles (8-16
km) of the shoreline may be required. Hurricane Mitch of 1998 was a Category Five
hurricane at peak intensity over the western Caribbean. Hurricane Gilbert of 1988 was a
Category Five hurricane at peak intensity and is the strongest Atlantic tropical cyclone of
record.

Tropical Cyclone Names

Names have been given to tropical cyclones attaining tropical storm status by the
National Hurricane Center since 1953. Currently, the name lists are maintained and
updated by an international committee of the World Meteorological Organization. The
lists featured only women's names until 1979. Since then, men's and women's names have
been alternated. When a hurricane is particularly deadly or costly, the name is retired and
a new name is chosen to replace it. These lists are recycled every six years (e.g., the 2004
list will be used again in 2010). For these lists and more information about the naming of
tropical cyclones and hurricanes, click on: www.nhc.noaa.gov/aboutnames.shtml.

228
Tornadoes - The Enhanced Fujita (EF) Scale

The original Fujita (F) Scale was developed in 1971 by T. Theodore Fujita of the
University of Chicago. It is a scale that measures the severity of tornadoes based on
extent of damage. In 2007 the NWS implemented the Enhanced Fujita Scale as an update.
It continues to support and maintain the original tornado database.
For more information about tornadoes, click on: www.spc.noaa.gov/faq/tornado.

EF - Scale Wind Estimate* Typical Damage

(3 second gust)
(mph)

EF0 65-85 Light damage. Some damage to chimneys; branches

broken off trees; shallow-rooted trees pushed over; sign
boards damaged.

EF1 86-110 Moderate damage. Peels surface off roofs; mobile

homes pushed off foundations or overturned; moving
autos blown off roads.

EF2 111-135 Considerable damage. Roofs torn off frame houses;

mobile homes demolished; boxcars overturned; large
trees snapped or uprooted; light-object missiles
generated; cars lifted off ground.

EF3 136-165 Severe damage. Roofs and some walls torn off well-
constructed houses; trains overturned; most trees in
forest uprooted; heavy cars lifted off the ground and
thrown.

EF4 166-200 Devastating damage. Well-constructed houses leveled;

structures with weak foundations blown away some
distance; cars thrown and large missiles generated.

EF5 Over 200 Incredible damage. Strong frame houses leveled off
foundations and swept away; automobile-sized missiles
fly through the air in excess of 100 meters (109 yards);
trees debarked; incredible phenomena will occur.

* IMPORTANT NOTE ABOUT EF-SCALE WINDS: The Enhanced F-scale still is a set
of wind estimates (not measurements) based on damage. Its uses three-second gusts
estimated at the point of damage based on a judgment of 8 levels of damage to 28
indicators. These estimates vary with height and exposure. Important: The 3 second gust
is not the same wind as in standard surface observations. Standard measurements are
taken by weather stations in open exposures, using a directly measured, “one minute
mile” speed.

229
Earthquake Magnitude Classes (based on the Richter Scale)

Although the National Weather Service has no earthquake responsibility, earthquake

information can be relayed through the agency’s communications networks. For more
information on earthquakes, with a focus on Southern California, click on:
earthquake.usgs.gov/regional/sca.

Classes Magnitude

Great Greater than or equal to 8

Major 7 to 7.9

Strong 6 to 6.9

Moderate 5 to 5.9

Light 4 to 4.9

Minor 3 to 3.9

Micro Less than 3

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Time Zone Conversions (UTC, GMT, Z) Conversions from UTC to US time zones:
* = previous day

UTC PACIFIC MOUNTAIN CENTRAL EASTERN

(GMT) Standard/Daylight Standard/Daylight Standard/Daylight Standard/Daylight

00 4 pm* / 5 pm* 5 pm* / 6 pm* 6 pm* / 7 pm* 7 pm* / 8 pm*

01 5 pm* / 6 pm* 6 pm* / 7 pm* 7 pm* / 8 pm* 8 pm* / 9 pm*

02 6 pm* / 7 pm* 7 pm* / 8 pm* 8 pm* / 9 pm* 9 pm* / 10 pm*

03 7 pm* / 8 pm* 8 pm* / 9 pm* 9 pm* / 10 pm* 10 pm* / 11 pm*

04 8 pm* / 9 pm* 9 pm* / 10 pm* 10 pm* / 11 pm* 11 pm* / 12 am

05 9 pm* / 10 pm* 10 pm* / 11 pm* 11 pm* / 12 am 12 mid / 1 am

06 10 pm* / 11 pm* 11 pm* / 12 am 12 mid / 1 am 1 am / 2 am

07 11 pm* / 12 am 12 mid / 1 am 1 am / 2 am 2 am / 3 am

08 12 mid / 1 am 1 am / 2 am 2 am / 3 am 3 am / 4 am

09 1 am / 2 am 2 am / 3 am 3 am / 4 am 4 am / 5 am

10 2 am / 3 am 3 am / 4 am 4 am / 5 am 5 am / 6 am

11 3 am / 4 am 4 am / 5 am 5 am / 6 am 6 am / 7 am

12 4 am / 5 am 5 am / 6 am 6 am / 7 am 7 am / 8 am

13 5 am / 6 am 6 am / 7 am 7 am / 8 am 8 am / 9 am

14 6 am / 7 am 7 am / 8 am 8 am / 9 am 9 am / 10 am

15 7 am / 8 am 8 am / 9 am 9 am / 10 am 10 am / 11 am

16 8 am / 9 am 9 am / 10 am 10 am / 11 am 11 am / 12 pm

17 9 am / 10 am 10 am / 11 am 11 am / 12 pm 12 pm / 1 pm

18 10 am / 11 am 11 am / 12 pm 12 pm / 1 pm 1 pm / 2 pm

19 11 am / 12 pm 12 pm / 1 pm 1 pm / 2 pm 2 pm / 3 pm

20 12 pm / 1 pm 1 pm / 2 pm 2 pm / 3 pm 3 pm / 4 pm

21 1 pm / 2 pm 2 pm / 3 pm 3 pm / 4 pm 4 pm / 5 pm

22 2 pm / 3 pm 3 pm / 4 pm 4 pm / 5 pm 5 pm / 6 pm

23 3 pm / 4 pm 4 pm / 5 pm 5 pm / 6 pm 6 pm / 7 pm
Appendix I – Weather Extremes

Temperature

The world’s highest temperature on record was 136° at Al Aziziyah, Libya, on September 13,
1922.

Vostok, Antarctica holds the world's record for coldest temperature: -129° on July 21, 1983.

On January 22, 1943 in Spearfish, SD: The temperature rose 49 degrees in two minutes, from - 4
to 45; later the same morning, it dropped 60 degrees in 27 minutes, from 56° to - 4°. Plate glass
windows cracked as a result of the wild fluctuation in temperatures caused by Chinook winds.

The greatest 24- hour U.S. temperature difference in one place was set January 23- 24, 1916, in
Browning, MT, at 100 degrees when it went from a low of -56° to a high of 44°.

Alaska and Hawaii share the same record high temperature of 100°. Pahala, Hawaii, reached that
temperature on April 27, 1913; Fort Yukon, Alaska, hit 100° on June 27, 1915.

It was 134° at Death Valley on July 10, 1913. It remains the highest reading on record for the
Western Hemisphere, the nation’s highest temperature on record for July, and the second highest
reading in the world. Sandstorm conditions accompanied the heat.

The greatest diurnal range of temperature on record for the U.S. is 65 degrees, at Deeth, NV.
After a morning low of 12°, the mercury rose to 87° on 9.21.1954.

Precipitation

Dry

Arica, Chile is the world’s driest place, receiving 0.03” of rain annually. It never rained at all in
one 14- year period.

Death Valley is the driest place in the United States, receiving 2.33” annually (1971-2000
normals). In 1929, it did not rain at all.

Bagdad, California holds the U.S. record for continuous days without rain at 767.

The driest state in the U.S. is Nevada, with an average annual rainfall of 9.0”.

Wet

The wettest locations in the world according to the most average annual rainfall are Mawsynram,
India: 467.4 inches, Tutunendo, Colombia: 463.4 inches, and Mt. Waialeale, Kauai, Hawaii: 460
inches. At Mt. Waialeale it averages more than one inch a day, on the average of 355 days a
year. In India, most of the rainfall occurs in a six month period.

232
Greatest one minute rainfall in the world: 1.5 inches in Guadeloupe, West Indies, on Nov 26,
1970.
In the U.S.: 1.23 inches in Unionville, MD, on July 4, 1956.

Greatest one hour rainfall in the world: 15.78 inches in Muduocaidoang, Inner Mongolia, on Aug
1, 1977.
In the U.S.: 12.0 inches in Holt, MO, in June 1947.

Greatest 24- hour rainfall in the world: 73.62 inches at La Reunion Island, Indian Ocean, on
March 15- 16, 1952.
In the U.S.: 43 inches in Alvin, Texas, on July 25- 26, 1979.

Greatest one month rainfall in the world: 366 inches in Cherrapunji, India, in July 1861.
In the U.S.: 107 inches in Kukui, Hawaii, in March 1942.

Greatest one year rainfall in the world: 1,042 inches in Cherrapunji, India, in 1860- 1861.
In the U.S.: 739 inches in Kukui, Hawaii, in 1981- 1982.

Hail

Large hailstones fall at speeds faster than 100 mph.

Hailstones sometimes contain foreign matter such as pebbles, leaves, twigs, nuts, and insects.

The costliest U.S. hailstorm occurred in Denver, Colorado, on July 11, 1990. Total damage was
$625 million.

The most deadly international hailstorm on record occurred in India on April 30, 1888. This
hailstorm killed 230 people at Moradabad, about 100 miles east of Delhi, and 16 others at
Bareilly.

The heaviest hailstones on record reportedly weighed 2.25 pounds and killed 92 people in
Gopalganj, a district of Bangladesh, on April 14, 1986.

A hailstone that fell June 22, 2003 at Aurora, NE, measured 7.0 inches in diameter and 18.75
inches in circumference. This was the largest hailstone ever recorded in the state of Nebraska,
and the largest hailstone ever documented in the U.S. and the world. Another hailstone from the
same storm measured 6.5 inches in diameter, with a circumference of 17.3 inches, and weighed
1.33 pounds. The previous U.S. record was held by a Coffeyville, KS hailstone, which fell on
September 3, 1970. It measured 5.7 inches in diameter, had a circumference of 17.5 inches, and
weighed 1.67 pounds. A Potter, NE hailstone that fell on July 6, 1928, held the U.S. record for
42 years. It measured around 7 inches in diameter and weighed about 1.5 pounds.

A 1959 hailstorm in northwestern Kansas lasted 1.5 hours and covered an area of 54 square
miles with hailstones 18 inches deep.

233
Hail was swept into drifts in Iowa on August 6, 1890. The hail was so deep in some protected
areas that hail remained on the ground for 26 days.

Snow

Greatest 24- hour snowfall in the world: 75.8 inches at Silver Lake, Colorado, on April 14- 15,
1921.

Greatest one storm snowfall in the world: 189 inches at Mt. Shasta Ski Bowl, California, on
February 13- 19, 1959.

Greatest one month snowfall in the world: 390 inches at Tamarack, California, in January 1911.

Greatest one season snowfall in the world: 1140 inches at Mt. Baker, Washington, in 1998- 99.
The largest reported snowflake on record fell at Bratsk, Siberia, in 1971 and was 12 inches
across.

Wind

The highest surface wind speed of 231 mph was recorded at Mt. Washington, New Hampshire
on April 12, 1934. Its average wind speed is 35 mph.

Tornadoes

75% of the world=s tornadoes occur in the United States.

In 1990, there were 1126 tornadoes reported in the U.S., a record for a single year.

In the year 2005, California was hit by 27 tornadoes, while Oklahoma managed only 25.

Thunderstorms

At any given time, there are nearly 2,000 thunderstorms occurring over the planet.
The U.S. has over 100,000 thunderstorms annually.

The estimated number of global thunderstorms in a single year is about 16 million.

Hurricanes

Hurricane Andrew was the costliest hurricane on record, leaving $25-30 billion in damage on
August 24, 1992. It left a quarter of a million people homeless before it died. Only 40 lives were
lost thanks to advanced warning.

The deadliest weather event in U.S. history was the Galveston Hurricane that hit Galveston,
Texas, on September 8, 1900. More that 8,000 people (some estimates say nearly 12,000) lost
their lives.

234
Typhoon Tip in the Northwest Pacific Ocean on October 12, 1979 was measured to have the
lowest central pressure on record of 870 mb and estimated surface sustained winds of 190 mph.

Hurricane Gilbert's 888 mb lowest pressure in mid-September 1988 is the most intense [as
measured by lowest sea level pressure] for the Atlantic basin.

The most deadly tropical cyclone was the infamous Bangladesh Cyclone of 1970. The death toll
has had several estimates, some wildly speculative, but it seems certain that at least 300,000
people died from the associated storm tide [surge] in the low-lying deltas.

Pressure

The world’s highest barometric reading at sea level was 32.01 inches (1083.6 mb) recorded on
December 31, 1968 at Agata, U.S.S.R (Siberia). The station elevation is 263 meters; the
temperature was -46° C. Extraordinarily high surface pressures observed nearby at the same time
corroborated the record measurement.

The North American record for high pressure was 31.85 inches (1078.4 mb) set on January
31,1989, in Northway Alaska (on the Alaska highway in east central Alaska). When pressures
occur in this range, many commercial aircraft are grounded because their altimeters aren’t
designed for such high settings.

The lowest pressure ever recorded was 25.69 inches (870 mb) in the eye of Typhoon Tip, in the
tropical western Pacific Ocean, on October 12, 1979. Since average sea level pressure is 29.92
inches (1013.25 mb), this record pressure was more than 14% lower than average.

The lowest pressure ever recorded in the United States was 26.35 inches (892.3 mb), recorded at
Matecumbe Key, Florida, on September 2, 1935.

San Diego, because of its unique location and favorable latitude, has the U.S. record for the least
difference or “shortest” barometer between the record high and record low. It is only 1.16 inches
of mercury. The highest sea level pressure recorded in the downtown area was 30.53 inches of
mercury on February 17, 1883 and the lowest was 29.37 inches of mercury, 100 years later on
March 3, 1983.

235
Appendix J - Web Sites for Weather Information
Forecasts, Current Conditions, Maps, Satellite, Radar, Etc.
National Weather Service (NWS) San Diego weather.gov/sandiego

Servicio Meteorológico Nacional - San Diego www.wrh.noaa.gov/sgx/spanish/spanish.php?wfo=sgx

NWS Forecast Office Web Pages Nationwide weather.gov/organization.php

NWS National Home Page weather.gov

NWS Internet Weather Source weather.noaa.gov

Weather Maps - Models

Selection of Weather Maps www.hpc.ncep.noaa.gov

Environmental Modeling Center www.emc.ncep.noaa.gov

List of Numerical Weather Prediction Sites www.nhc.noaa.gov/aboutlinkmodel.html

Guide to Reading Weather Maps ww2010.atmos.uiuc.edu/(Gh)/guides/maps/home.rxml

Advanced Meteorology Education Modules meted.ucar.edu

Understanding NWP Models meted.ucar.edu/nwp/course/modules.php

Unisys Forecast Model Details weather.unisys.com/model/details.html

The Weather Prediction - Models www.theweatherprediction.com/models

Weather Learning - Education and Research

NWS Weather Tutorial www.srh.weather.gov/jetstream

NWS Office of Climate, Water and Weather www.nws.noaa.gov/om

Services

Online Weather Tutorial (Univ. of Illinois) ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/home.rxml

Understanding Weather and Climate online wps.prenhall.com/esm_aguado_uwac_3

USA Today Weather Basics Page www.usatoday.com/weather/basics/wworks0.htm

Resources for Educators www.nssl.noaa.gov/edu/resources

How the Weather Works Homepage www.weatherworks.com

National Center for Atmospheric Research www.ncar.ucar.edu

236
 University Corp. for Atmospheric Research www.eo.ucar.edu

NOAA Research www.oar.noaa.gov

NOAA Hurricane Research Division www.aoml.noaa.gov/hrd

Center for Ocean-Land-Atmospheric Studies wxmaps.org

NOAA Climate Page www.noaa.gov/climate.html

EPA – Climate change www.epa.gov/climatechange

NCDC Climate Change Research www.ncdc.noaa.gov/oa/climate/climateextremes.html

NCDC Global Warming FAQ www.ncdc.noaa.gov/oa/climate/globalwarming.html

Listing of Meteorology Schools Nationwide www.srh.noaa.gov/jetstream/nws/schools_map.htm

UCLA Department of Atmospheric Sciences www.atmos.ucla.edu

AMS Meteorology Career Guide www.ametsoc.org/atmoscareers/index.html

NOAA Career Page www.careers.noaa.gov

Weather for Young Students and Their Teachers

NOAA Play Time For Kids www.nws.noaa.gov/om/reachout/kidspage.shtml

NOAA Weather Education www.education.noaa.gov

National Severe Storms Laboratory www.nssl.noaa.gov/edu

FEMA for Kids www.fema.gov/kids

Dan’s Wild Wild Weather Page for Kids www.wildwildweather.com

The Weather Dude www.wxdude.com

Discovery School Weather school.discovery.com/lessonplans/weather.html

Severe Weather Plan for Schools www.nws.noaa.gov/er/lwx/swep/index.htm

Univ. of Illinois Weather links for kids www.illiniweather.com/pages/kids_weather_links.htm

Stormy Weather and Disaster Preparedness

NWS Winter Weather Awareness www.nws.noaa.gov/om/winter

Storm Prediction Center www.spc.noaa.gov

National Severe Storms Laboratory www.nssl.noaa.gov

237
 The Tornado Project www.tornadoproject.com

Stormtrack Storm Chaser Homepage www.stormtrack.org

National Lightning Safety Institute www.lightningsafety.com

Severe Weather Awareness www.nws.noaa.gov/om/severeweather

StormReady www.nws.noaa.gov/stormready

Spotter and Skywarn Page - San Diego www.wrh.noaa.gov/sgx/spotter/spotter.php

Federal Emergency Mgmt. Agency www.fema.gov

The Disaster Center www.disastercenter.com

Hurricanes and Tropical Weather

Tropical Storm Tracker www.solar.ifa.hawaii.edu/Tropical/tropical.html

National Hurricane Center www.nhc.noaa.gov

Central Pacific Hurricane Center www.prh.noaa.gov/hnl/cphc

Atlantic Tropical Weather Center www.atwc.org

NWS Hurricane Awareness www.weather.gov/om/hurricane

NRL Navy Monterey Tropical Cyclone Page www.nrlmry.navy.mil/tc_pages/tc_home.html

Good Hurricane Resources ggweather.com/hurricane.htm

Rainfall, Floods and Drought

Local Rainfall Maps and Charts www.wrh.noaa.gov/sgx/obs/rainobs.php?wfo=sgx

California-Nevada River Forecast Center www.cnrfc.noaa.gov

Hydrometeorological Prediction Center www.hpc.ncep.noaa.gov

California Data Exchange Center cdec.water.ca.gov

California Department of Water Resources www.dwr.water.ca.gov

Climate Diagnostics Center www.cdc.noaa.gov/ClimateInfo/drought.html

NOAA’s Drought Information Center www.drought.noaa.gov

National Drought Mitigation Center www.drought.unl.edu

238
Climate Data and Long Term Prediction
Climate Diagnostics Center (El Niño-La Nina) www.cdc.noaa.gov

NOAA’s El Niño Theme Page www.pmel.noaa.gov/tao/elnino/nino-home.html

Climate Prediction Center www.cpc.noaa.gov

Seasonal Outlooks from CPC www.cpc.ncep.noaa.gov/products/forecasts

Western Regional Climate Center www.wrcc.dri.edu

National Climatic Data Center www.ncdc.noaa.gov

Weatherbase Climate Data www.weatherbase.com

Aviation Weather
Aviation Digital Data Service adds.aviationweather.noaa.gov

Aviation Weather Center aviationweather.noaa.gov

NWS Aviation Program www.weather.gov/os/aviation.shtml

NWS San Diego Aviation Page www.wrh.noaa.gov/sgx/aviation/aviation.php?wfo=sgx

USA Today Aviation Weather www.usatoday.com/weather/wpilots0.htm

Air Traffic Control System Command Center www.fly.faa.gov/flyfaa/usmap.jsp

Marine Weather and Surf

NWS Marine Weather Homepage www.nws.noaa.gov/om/marine/home.htm

Ocean Prediction Center www.opc.ncep.noaa.gov

Guide to Marine Weather Services www.nws.noaa.gov/om/marine/marine.shtml

National Data Buoy Center www.ndbc.noaa.gov

NWS San Diego Marine Page www.wrh.noaa.gov/sgx/marine/marine.php?wfo=sgx

La Jolla Surfing Weather www.lajollasurf.org/weather.shtml

Scripps Inst. of Oceanography sio.ucsd.edu/research/atmosphere.cfm

Coastwatch Program - West Coast coastwatch.noaa.gov/cw_index.html

Tsunami Warning Centers tsunami.gov

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Weather Organizations, Publications
National Weather Service weather.gov

Nat.Oceanic and Atmospheric Admin. www.noaa.gov

World Meteorological Organization www.wmo.ch

Foreign Weather Services www.nhc.noaa.gov/aboutlinkabroad_short.html

American Meteorological Society www.ametsoc.org

National Weather Association www.nwas.org

Weatherwise Magazine www.weatherwise.org

Mariners Weather Log Magazine www.vos.noaa.gov/mwl.shtml

Weather Books from USA Today www.usatoday.com/weather/science/books/books0.htm

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