How to Decode METAR, TAF, and pilot reports.

A METAR is a codified observation message indicating an airfield

weather conditions observed at a given time.
Such a message is established every hour.

A SPECI message is identical to a METAR but is established

punctually instead of regularly. It is a special observation message
highlighting any significant change since the last METAR or SPECI
was issued.

A TAF is a terminal forcast. It is issued every few hours, and is

updated if necessary sooner.

Aviation Routine Weather Report (METAR)

Example:
METAR KRNO 210056Z 05012KT 10SM - BKN050 02/M08 A3016 RMK T00221083
SN AO2
SLP228
1 2 3 4 5 6 7 8 9 10 11

1. Message Type
· METAR: routine weather report
· SPECI: special weather report, triggered by a weather change
· AUTO will be first item for ASOS/AWOS generated reports
2. ICAO Identifier (4-letter)
3. Issuance Time DDHHMMz (UTC)
· COR (CCD in Canada) if correction to observation
4. Wind
· First 3 digits: True Wind direction or average if variable (VRB).
Note: If the wind direction varies 60° or more, the direction will be
indicated with a V (e.g. 180V250)
· Next 2 digits: Mean speed and units
- KT=knots, KMH=kilometers/hour, MPS=meters/second
· G (gust) as needed – 2 or 3 digit maximum speed
· Calm will be indicated by 00000KT
 · Example: 18012G22KT 150V240
5. Horizontal Visibility
· Prevailing Visibility (PV)
- Statue miles (SM) and fractions (US & Canada only) or,
- 4 digit minimum visibility in meters, and,
- Lowest value and direction, as required (shown as a remark)

· Runway Visual Range (RVR)

- R: Runway Designator, L/R/C as needed, “/”
- P/M: Plus/Minus (US only)
- 4 digit value (feet/meters)
- V (variability) with tendency U/D/N (up/down/no change)
- Example: R18R/1200FTV/U
6. Present Weather (Constructed sequentially):
· Intensity
· Descriptor
· Precipitation (Dominant type is listed first if more than one type
reported)
· Obscuration
· Other

Qualifier Weather Phenomena

Intensity or
Descriptor Precipitation Obscuration Other
Proximity
BC Patches DZ Drizzle BR Mist (1)
– Light Widespread DS Duststorm
BL Blowing (2) GR Hail (3) DU
Dust
Small Hail
Low Drifting Funnel
DR GS and/or snow FG Fog (6) FC
No (4) Clouds
Moderate pellets (5)
qualifier
Dust/Sand
FZ Freezing IC Ice Crystals FU Smoke PO
Whirls
MI Shallow PL Ice Pellets HZ Haze
+ Heavy SQ Squall(s)
PR Partial RA Rain SA Sand
 Snow
SH Shower(s) SG
Grains
Vicinity Volcanic
VC TS Thunderstorm SN Snow VA SS Sandstorm
(7) Ash
Unknown
UP
Precipitation
(1) Visibility at least 1000m (5/8SM) but not more than 9600m (6SM)
(2) 6 feet or more above the ground
(3) Hailstone diameter 5mm or greater
(4) Less than 6 feet above the ground
(5) Hailstone diameter less than 5mm
(6) Visibility less than 1000m (5/8SM)
(7) Within 8KM (5SM) of the aerodrome but not at the aerodrome

7. Sky Cover
· Cloud Description
Amount in eights (octas)
-
SKC=Sky Clear (clear below 12,000 for ASOS/AWOS)
NSC=No significant clouds
FEW=Few (1/8 to 2/8 sky cover)
SCT=Scattered (3/8 to 4/8 sky cover)
BKN=Broken (5/8 to 7/8 sky cover)
OVC=Overcast (8/8 sky cover)
8. Terperature/Dewpoint (whole °C) (preceded by M=minus)
· First 2 digits = temperature
· Second 2 digits = dewpoint
9. Altimeter setting (QNH) and indicator (A=InHg, Q=hPa)
10. Supplementary Information
· RE = Recent weather followed by weather codes
· WS = Windshear, followed by:
- TKOF/LDG (takeoff/landing)
- RWY (2 digits runway identifier and designator L/R/C)
· RMK = Remark
- SLP = Sea Level Pressure
- T00221083 (Expanded temp/dewpoint)
1st, 5th digits: 0=plus, 1=minus
 2nd-4th digits: temp (decimal missing) (02.2)
6th-8th digits: dewpoint (decimal missing) (-8.3)
11. Trend Forecast (2 hours from time of observation) (Not used in US)
· PROB and 2 digits (30 or 40) = probability 30% or 40%
· Used to indicate the probability of occurance of alternate
element(s) or temporary fluctuations
· Change Indicator
- BECMG = Becoming (used where changes are expected to
reach or pass through specified values
- TEMPO = Temporary (fluctuations of less than one hour
duration
- NOSIG = No significant change

· Forecast Wind (same as item 4)

· Forecast Visibility (as item 5) (9999 indicates 10Kilometers vis or
greater)
· Forecast Weather (as item 6)
· Forecast Cloud (as item 7)

EIGHT FIGURE GROUP

An eight digit telegraphic code on runway conditions for some European airports
may be included at the end of hourly METAR messages:
Eight Figure Group
1st two digits Runway designator
3rd digit Runway deposits
4th digit Extent of runway contamination

5th and 6th digits Depth of deposit

7th and 8th digits Friction coefficient or braking action

The first two digits correspond to the runway designator. For parallel runways
LEFT is indicated by the designator only (18L would be displayed as 18) and
RIGHT has 50 added (18R would be displayed as 68). When all runways are
affected the figure group 88 will be used. If 99 appears as the first two digits the
information is a repetition of the last message because no new message has been
received in time for transmission.

Runway Deposits Extent of Runway Depth of Deposit

Contamination
0 Clear & Dry 1 <10% contaminated 00 Less than 1mm
(covered)
1 Damp 2 11% to 25% contaminated 01-90 Measurement in mm
2 Wet or water particles (covered) 92 10cm
3 Rime or frost covered 5 26%-50% contaminated 93 15cm
(normally > 1mm) (covered)
4 Dry Snow 9 51%-100% contaminated 94 20cm
5 Wet Snow (covered) 95 25cm
6 Slush / Not reported (runway 96 30cm
7 Ice clearance in progress) 97 35cm
8 Compacted or rolled 98 40cm or more
snow
9 Frozen ruts or ridges 99 Runway not operational
due to snow, slush, ice,
large drifts or runway
clearance, depth not
reported
/ Not reported (runway // Not operationally
clearance in progress) significant or not
measurable

Note: the quoted depth is the mean of a number of reading or if operationally

significant the greatest depth measured.

Friction Coefficient or Braking Action (7th and 8th digits)

28 Friction coefficient 0.28
35 Friction coefficient 0.35
91 Braking action poor
92 Braking action medium to poor
93 Braking action medium
94 Braking action medium to good
95 Braking action good
99 Figures unreliable
// Braking action not reported or runway not operations or airport closed.
Note: Where braking action is assessed at a number of points along the runway the
mean value will be transmitted or if operationally significant the lowest value.
If measuring equipment does not allow measurement of friction with satisfactory
reliability (such as contaminated by wet snow, slush or loose snow) the figure 99
will be used.

Automated Surface/Weather Observation System (ASOS/AWOS)

The Automated Surface Observation System (ASOS) and Automated Weather

Observation System (AWOS) observe and report altimeter setting, wind direction
and speed, temperature, dewpoint, visibility and ceiling/cloud height. Pilots may
use automated weather observation from ASOS/AWOS, provided the observations
from ASOS/AWOS, provided the observation includes all necessary weather
parameters, and that the system is installed, operated and maintained according to
applicable FAA standards.
Pilots may obtain the ASOS/AWOS reports through written, radio or telephone
methods. Refer to METAR section for ASOS/AWOS report format.
ASOS/AWOS observations may not be used as an authorized weather observation if
either the visibility or the wind is reported as missing.
ASOS/AWOS observation are unusable for the purpose of initiating or conducting
an instrument approach if the altimeter setting is reported as missing unless an
approved alternate source is noted on the applicable approach chart.

TAF
Example:
TAF KRNO 202320Z 210024 04010G20KT P6SM -SN SCT060

1 2 3 4 5 6 7 8

FM0300 05008KT P6SM SCT060

1. Type of report (TAF)

2. ICAO Identifier (4 letter)
3. Issuance time (DDHHMMZ) UTC. May precede ICAO identifier at some
airports.
4. Day (DD). Hour begins (1st two digits XX) Hour ends (2nd two digits).
5. Wind. First 3 digits true wind direction or average if variable. If the wind varies
60° or more, the direction will be indicated with a V (e.g. 120V190). Next two
digits Mean speed and units (KT=knots, KMH=kilometers per hour, or
MPS=meters per second). G=gust as needed (2 or 3 digits). Calm will be
indicated by 00000XXX (XXX will be replaced by the appropriate units).
6. Horizontal visibility.
a. Prevailing visibility (PV)
- Statute Miles (SM) and fractions (US only), or
- 4 digit minimum visibility in meters, and
- Lowest value and direction, as required
b. Runway Visual Range (RVR)
- R=Runway Designator, L/R/C as needed, “/”
- P/M=Plus/Minus (US Only)
- 4 digit value (feet/meters)
- V(variability) with tendency U/D/N (up/down/no change)
7. Present Weather (constructed sequentially):
· Intensity
· Descriptor
· Precipitation (Dominant type is listed first if more than one type
reported)
· Obscuration
· Other

Qualifier Weather Phenomena

Intensity or
Descriptor Precipitation Obscuration Other
Proximity
BC Patches DZ Drizzle BR Mist (1)
– Light Widespread DS Duststorm
BL Blowing (2) GR Hail (3) DU
Dust
Small Hail
Low Drifting Funnel
DR GS and/or snow FG Fog (6) FC
No (4) Clouds
Moderate pellets (5)
qualifier
Dust/Sand
FZ Freezing IC Ice Crystals FU Smoke PO
Whirls
MI Shallow PL Ice Pellets HZ Haze
+ Heavy SQ Squall(s)
PR Partial RA Rain SA Sand
 Snow
SH Shower(s) SG
Grains
Vicinity Volcanic
VC TS Thunderstorm SN Snow VA SS Sandstorm
(7) Ash
Unknown
UP
Precipitation
(8) Visibility at least 1000m (5/8SM) but not more than 9600m (6SM)
(9) 6 feet or more above the ground
(10)Hailstone diameter 5mm or greater
(11)Less than 6 feet above the ground
(12)Hailstone diameter less than 5mm
(13)Visibility less than 1000m (5/8SM)
(14)Within 8KM (5SM) of the aerodrome but not at the aerodrome

8. Sky Cover
· Cloud Description
- Amount in eights (octas)
SKC=Sky Clear (clear below 12,000 for ASOS/AWOS)
NSC=No significant clouds
FEW=Few (1/8 to 2/8 sky cover)
SCT=Scattered (3/8 to 4/8 sky cover)
BKN=Broken (5/8 to 7/8 sky cover)
OVC=Overcast (8/8 sky cover)
- Height: 100s of feet (30m)
- Type CB (Cumulonimbus) or TCU (Towering cumulus) only.
· CAVOK – Ceiling and visibility OK (not used in US). Replaces
visibility/RVR, present weather, and clouds if:
- Visibility is 10KM or greater
- No CB and no cloud below 1500M (5000ft) or below highest
minimum sector altitude whichever is greater, and
- No precipitation, thunderstorm, sandstorm, duststorm, shallow fog,
or low drifting dust/sand/snow.
· Vertical visibility (when sky obscured) – VV100’s of feet (30m) (VV ///
means vertical visibility unavailable)
Optional groups (Forecast icing, Turbulence, & Temperature)
T= Temperature group indicator
Temperature: two digits (if below 0°, will be preceded by “M”),”/”
Expected time temperature will be reached: 2 digits, Z.
Icing Layer(s): 6 digits for each icing group (6WXXXY).
6: first digit of the icing group is always a 6.
Icing type: Second digit:
Icing Intensity Location
0 None None
1 Light Icing
2 Light Icing In cloud
3 Light Icing In precipitation
4 Moderate
5 Moderate In cloud
6 Moderate In precipitation
7 Severe
8 Severe In cloud
9 Severe In precipitation
Icing layer’s base: next 3 digits. (direct reading in 100s of ft/30s meters)
Thickness of icing layer: last digit:
Thickness of Layer
0 Up to top of cloud
1 300m/1000’
2 600m/2000’
3 900m/2000’
4 1200m/4000’
5 1500m/5000’
6 1800m/6000’
7 2100m/7000’
8 2400m/8000’
9 2700m/9000’

Turbulence Layer(s): 6 Digits (5WXXXY)

5: first digit of the turbulence group is always a 6.
Turbulence type: Second digit:
Intensity Weather Frequency
Condition
0 None
 1 Light
2 Moderate Clear Occasional
3 Moderate Clear Frequent
4 Moderate Cloud Occasional
5 Moderate Cloud Frequent
6 Severe Clear Occasional
7 Severe Clear Frequent
8 Severe Cloud Occasional
9 Severe Cloud Frequent
Turbulence layer’s base: next 3 digits. (direct reading in 100s of ft/30s
meters)
Thickness of turbulence layer: last digit:
Thickness of Layer
0 Up to top of cloud
1 300m/1000’
2 600m/2000’
3 900m/2000’
4 1200m/4000’
5 1500m/5000’
6 1800m/6000’
7 2100m/7000’
8 2400m/8000’
9 2700m/9000’

SIGNIFICANT CHANGES IN FORECAST

1. Probability groups(s)
- PROB and 2 digits (30 or 40).
- Probability 30% or 40% used to indicate the probability of
occurrence of alternate element(s) or temporary
fluctuations. (US will only use 40%). May also be listed as
TEMPO by some non US weather services.
- TIME (beginning 2 digits, ending 2 digits)
 - Forecast weather phenomena.
2. Forecast Change
o Indicators
§ BCMG=Becoming (used when changes are expected
to reach or pass through specified values)
§ FM = From and 2 digit time
§ TO = To and 2 digit time
§ TEMPO = Temporary fluctuation
o Forecast weather phenomena.

METAR /TAF Abbreviations / Cloud Types

A Hail AMOS Automatic Meteorological

ABM Abeam observing system
ABV Above AMS Air mass
AC Altocumulus ANLYS Analysis
ACCAS Altocumulus castellanus AO1 Automated observation
ACCUM Altocumulate with no precip
discriminator (rain/snow)
ACLD Above clouds AO2 Automated observation
ACSL Standing lenticular with precip discriminator
altocumulus (rain/snow)
ACTV Active AOA At or above
ACYC Anticyclonic AOB At or below
ADDN Addition AP Anomalous propagation
ADRNDCK Adirondack APCH Approach
ADVCTN Advection APRNT Apparent
ADVY Advisory AS Altostratus
AFDK After Dark ASOS Automated surface
observing system
AFT After ATLC Atlantic
AFTN Afternoon ATTM At this time
AGL Above Ground Level AURBO Aurora Borealis
AGN Again AUTOB Automatic weather
 reporting system
AHD Ahead AWOS Automatic weather
observing system
AIREP Air Report B Beginning of precipitation
AIRMET Airmen’s Meteorological (time in minutes (wx
Info reports only)
ALF Aloft BACLIN Baroclinic prognosis
ALG Along BATROP Barotropic or barotropic
prognosis
ALGHNY Allegheny BC British Columbia
ALQDS All quadrants BCFG Fog patches
ALSTG Altimeter setting BCKG Backing
ALTA Alberta BCM(G) Become (becoming)
ALUTN Alleutian BD Blowing dust (wx reports
only)
AMD Amended forecast BFDK Before dark
AMDT Amendment BINOVC Breaks in overcast

BKN Broken CLD Cloud

BLDUP Build up CLR Clear
BLKHLS Black Hills CAS Clear and smooth
BLO Below CNL Cancel
BN Blowing sand (wx CNDN Canadian
reports only)
BNDRY Boundary CNTRL Central
BOVC Base of overcast CNVG Converge
BRAF Braking action fair CNVTV Convective
BRAG Braking action good CONT-DVD Continental Divide
BRAN Braking action nil CONTRAILS Condensation trails
BRAP Braking action poor CS Cirrostratus
BRF Brief CST Coast
BRKSHR Berkshire CTGY Category
BS Blowing snow (wx CTSKLS Catskills
reports only)
BTWN Between CU Cumulus
BY Blowing spray (wx CUF Cumuliform
reports only)
CA Clear above (PIREP CUFRA Cumulus fractus
only)
CAN Canada CYC Cyclonic
CARIB Caribbean CYCLGN Cyclogenesis
CASCDS Cascades D Dust (wx reports only)
CAVOK Ceiling and visibility DABRK Daybreak
OK
CAVU Ceiling and visibility DALGT Daylight
unlimited
CB Cumulonimbus DCAVU Clear or scattered cloud
CBMAM Cumulonimbus and vis greater than 10,
mammatus remainder or report
missing (wx reports
CC Cirrocumulus
only)
CCSL Standing lenticular DCR Decreased
cirrocumulus
CDFNT Cold Front DIAM Diameter
CFP Cold front passage DKTS Dakotas
CHC Chance DMSH Diminish
CHSPK Chesapeake DNS Dense
CIG Ceiling DNSLP Downslope

DNSTRM Downstream FLG Falling

DP Deep FLRY Flurry
DPNG Deepening FNT Front
DPTH Depth FNTGNS Frontogenesis
DRFT Drift FNTLYS Frontolysis
DRZL Drizzle FORNN Forenoon
DSIPT Dissipate FRMG Forming
DSNT Distant FROPA Frontal passage
DTRT Deteriorate FRST Frost
DRG During FRZ Freeze
DWNDFTS Downdrafts FRZLVL Freezing level
DWPNT Dew point FRZN Frozen
E Ending of precipitation FZRANO Freezing rain sensor not
(time in minutes)(wx operating
reports only) FT Terminal Forecast
E Equatorial (air mass) G Gusts reaching (knots)
(wx reports only)
E Estimated (wx reports GF Ground fog (wx reports
only) only)
ELNGT Elongate GFDEP Ground fog estimated
(feet) deep
EMBDD Embedded GICG Glaze icing
ENRT Enroute GLFALSK Gulf of Alaska
ENTR Entire GLFCAL Gulf of California
ERY Early CLFMEX Gulf of Mexico
EVE Evening GLFSTLAWR Gulf of St. Lawrence
EXCP Except GNDFG Ground Fog
EXPC Expect GRAD Gradient
EXTRM Extreme GRTLKS Great Lakes
F Fog (wx reports only) GSTS Gusts
FA Area Forecast GSTY Gusty
FAH Farenheit H Haze (wx reports only)
FAX Facsimile HCVIS High clouds visible
FIBI Filed but impracticable HDEP Haze layer estimated
to transmit (feet) deep
FINO Wx report will not be HDSVLY Hudson Valley
filed for transmission

HI High LABRDR Labrador

HLSTO Hailstones LFT Lift
HLYR Haze layer aloft LGT Light
HURCN Hurricane LIFR Low IFR (wx reports only)
HVY Heavy LK Lake
IC Ice crystal LSR Loose snow on runway
ICG Icing LST Local Standard Time
ICGIC Icing in clouds LTGCA Lightning cloud to air
ICGICIP Icing in clouds and LTGCC Lightning cloud to cloud
 precipitation
ICGIP Icing in precipitation LTGCCCG Lightning cloud to cloud,
cloud to ground
IF Ice fog LTGCG Lightning cloud to ground
IFR Instrument flight rules LTGCW Lightning cloud to water
INCR Increase LTGIC Lightning in clouds
INDC Indicate LTLCG Little change
INDEF Indefinite LTNG Lightning
INLD Inland LYR Layer or layered or layers
INSTBY Instability M Measured ceiling (wx
reports only)
INTR Interior M Missing (wx reports only)
INTR- Inter-mountain region MAN Manitoba
MTRGN
INTS Intense MDT Moderate
INTST Intensity METAR Scheduled aviation
observation
INVRN Inversion MEX Mexico
IOVC In overcast MHKVLY Mohawk Valley
IP Ice pellets (wx reports MIDN Midnight
only)
IR Ice on runway MIFG Patches of shallow fog not
deeper than 2 meters
JTSTR Jetstream MLTLVL Melting level
K Smoke MNLD Mainland
KDEP Smoke layer estimated MOGR Moderate or greater
(feet) deep
KLYR Smoke layer aloft MOV Move
KOCTY Smoke over city MRGL Marginal
L Drizzle (wx reports only) MRNG Morning

MRTM Maritime PGTSND Puget Sound

MSTLY Mostly PIBAL Pilot balloon observation
MTN Mountain PK WND Peak wind (wx report only)
MVFR Marginal VFR PNHDL Panhandle
NB New Brunswick PNO Rain gauge not operating
NEW ENG New England PPINA Radar weather report not
NFLD Newfoundland available or omitted
NGT Night PPINE Radar weather report no
echoes observed
NOSPL No special observations PPINO Radar weather report
taken (wx reports only) equipment inoperative due
to breakdown
NS Nimbostratus PPIOK Radar weather report
NS Nova Scotia equipment operation
resumed
NVA Negative vorticity PPIOM Radar weather report
advection equipment inoperative due
OBS Observation to maintenance
OBSC Obscure PRBLTY Probability
OCFNT Occluded front PRESFR Pressure falling rapidly
OCLD Occlude PRESRR Pressure rising rapidly
OCLN Occlusion PRJMP Pressure jump (wx reports
only)
OFP Occluded frontal passage PROG Prognosis or prognostic
OFSHR Offshore PSR Packed snow on runway
OMTNS Over mountains PTCHY Patchy
ONSHR On shore PTLY Partly
ONT Ontario PVA Positive vorticity advection
ORGPHC Orographic PWINO Precipitaion identifier
information not available
(wx reports only)
OTAS On top and smooth Q Squall (wx reports only)
OTLK Outlook QSTNRY Quasistationary
OVC Overcast QUE Quebec
OVR Over R Rain (wx reports only)
PAC Pacific RADAT Radiosonde observation
data
PCPN Precipitation RAOB Radiosonde observation
PDW Priority Delayed Weather RCKY Rocky Mountains
PEN Peninsula RDG Ridge
RGD Ragged TDWR Terminal Doppler Weather
Radar
RHINO Radar echo height TEMP Temperature
information not available
RHINO Radar range height THDR Thunder
indicator not operating
on scan
RIOGD Rio Grande THRU Through
RNFL Rainfall THRUT Throughout
ROBEPS Radar operating below THSD Thousand
prescribed standard
RPD Rapid TIL Until
RSG Rising TMW Tomorrow
RUF Rough TNGT Tonight
RVRNO Runway visual range TOP Cloud top
missing
RW Rain shower (wx reports TOVC Top of overcast
only)
S Snow (wx reports only) TPG Topping
SASK Saskatchewan TROF Trough
SAWRN Supplementary Aviation TROP Tropopause
Weather Reporting
System
SC Stratocumulus TRPCL Tropical
SCSL Stratocumulus standing TRRN Terrain
lenticular
SCT Scattered TSHWR Thundershower
SELS Severe local storms TSNO Lightning sensor not
available
SFERICS Atmospherics TSTM Thunderstorm
SG Snow grains (wx reports TURB Turbulence
only)
SHFT Shift (wx reports only) TURBC Turbulence
SHLW Shallow TWD Toward
SHWR Shower TWR Tower
SIERNEV Sierra Nevada TWRG Towering
SIR Snow and ice on runway TYPH Typhoon
SPECI Unscheduled aviation U Intensity unknown (wx
observation reports only)
SLF Sea level pressure UA Routine PIREP
SLPNO Sea level pressure not UDDF Up and down drafts
available
SNINCR Snow increasing rapidly UNSTBL Unstable
TCU Towering cumulus UNSTDY Unsteady
TDA Today UPR Upper

UTC Universal coordinated WND Wind

time
UUA Urgent PIREP WRM Warm
V Variable (wx reports WRMFNT Warm front
only)
VCSH Showers in vicinity WRNG Warning
VCTY Vicinity WSHFT Wind shift
VFR Visual flight rules WW Severe weather forecast
VLY Valley WX Weather
VRBL Variable X Obscured sky condition
VSBY Visibility XCP Except
WDLY Widely YDA Yesterday
WEA Weather Z UTC
WFP Warm front passage ZRNO Freezing rain information
WK Weak not available (wx reports
only)
WKN Weaken
WL Will

AIRMETs
Hazardous weather advisories of moderate intensity will be issued as AIRMETs.
AIRMETs are issued when the following conditions are expected to cover an area
of at least 3000 square miles:
Moderate icing.
Moderate turbulence.
Sustained surface winds of 30 knots or more.
Ceilings less than 1,000 ft. and/or visibility less than 3 miles affecting 50%
of an area at one time.
Extensive mountain obscuration.

SIGMET's

Hazardous weather advisories of severe intensity will be issued as SIGMETs.

SIGMETs are reported as convective or nonconvective.
Convective SIGMETs report only thunderstorms and related phenomena
(tornadoes, heavy precipitation, hail and high surface winds.
Nonconvective SIGMETs are issued when the following conditions occur or are
expected to cover an area of at least 3,000 square miles:
Severe or extreme turbulence or clear air turbulence (CAT) not
associated with thunderstorms.
Severe icing not associated with thunderstorms.
Widespread duststorms, sandstorms, or volcanic ash lowering
surface or inflight visibilities to below three miles.
Volcanic eruption.

Volcanic eruption SIGMET's are identified by an alphanumeric designator which

consists of an alphabetic identifier and issuance number. The first time an advisory
is issued for a phenomenon associated with a particular weather system, it will be
given the next alphabetic designator in the series and will be numbered as the first
for that designator. Subsequent advisories will retain the same alphabetic designator
until the phenomenon ends. In the conterminous U.S., this means that a
phenomenon that is assigned an alphabetic designator in one area will retain that
designator as it moves within the area or into one or more other areas. Issuance’s for
the same phenomenon will be sequentially numbered, using the same alphabetic
designator until the phenomenon no longer exists. Alphabetic designators
NOVEMBER through YANKEE, except SIERRA and TANGO are only used for
SIGMET's, while designators SIERRA, TANGO and ZULU are used for
AIRMET's.

Pilot Weather Report (PIREP)

Pilots must report any significant weather or flight condition to ATC as soon as
possible. Additionally, all significant weather or flight conditions that clearly differ
from the forecast should be reported to Dispatch. There is no specific format for
this type of report.
NOTE: Report windshear encountered during departure or approach to the tower
controller as soon as possible.Use the term PIREP to ensure that it is
rebroadcast.