Seasonal Climate Forecast
September – November 2025
Issued: August 21, 2025
Contact: ODF Lead Meteorologist Pete Parsons
503-945-7448 or peter.gj.parsons@odf.oregon.gov
ODA Team: Andy Zimmerman; Jenn Ambrose; Taylor Harding; Laura Passage
ODF Team: Julie Vondrachek; Kristin Cody; Sherri Pugh; Gary Votaw
El Niño vs La Niña
(SST Patterns in the Tropical Pacific Ocean)
Courtesy: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensocycle/ensocycle.shtml
Sea Surface Temperatures (SSTs)
Animated (PowerPoint only) SSTs (top) / Anomalies (bottom)
ENSO-neutral conditions continue
Courtesy: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/gsstanim.shtml
El Niño Southern Oscillation (ENSO)
Current Status and Forecast
◼ The July Southern Oscillation Index (SOI) of +0.6 indicated a slight
strengthening of trade winds across the equatorial Pacific Ocean but still
within the ENSO-neutral range.
◼ The May – July 2025 Oceanic Niño Index (ONI) remained at -0.1°C,
reflecting near-average tropical Pacific sea surface temperatures (“SSTs”).
◼ NOAA’s Climate Prediction Center (CPC) has issued a La Niña
Watch. They expect a brief period of La Niña conditions to develop this
fall and early winter before reverting to ENSO-neutral.
Note: This “Seasonal Climate Forecast” does not consider NOAA’s ENSO forecast. It uses only
historical and current ENSO conditions to find “analog years” that most-closely match the recent
evolution of the ENSO state.
https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
Southern Oscillation Index (SOI)
(1966-1967; 2005-2006; 2016-2017) July 2025 SOI
(+0.6)
reflected
ENSO-neutral
La Niña conditions
ENSO-neutral
July SOI
analogs were
El Niño all in the
ENSO-neutral
range
Oceanic Niño Index (ONI)
(1966-1967; 2005-2006; 2016-2017) May – July
2025 ONI
(-0.1°C) in the
ENSO-neutral
Strong range
Moderate El Niño
Weak
ENSO-neutral
Weak
Moderate La Niña
Strong May – July
ONI analogs
all in the
ENSO-neutral
range
The Pacific Decadal Oscillation (PDO)
(Reflects SST “Phase” in the North Pacific Ocean )
Positive (Warm) Negative (Cool)
“Phase” “Phase”
SST Anomalies
Courtesy: http://research.jisao.washington.edu/pdo/img/pdo_warm_cool.jpg
North Pacific Ocean
(Poleward of 20°N Latitude)
(1966-1967; 2005-2006; 2016-2017) July PDO
analogs in
Warm Phase “Neutral” or
“Cool” Phase
Neutral Phase
July 2025
PDO (-4.00)
Cool Phase dropped
deeply into
“Cool” Phase
SST Anomalies Comparison
July Analogs July 2025
◼ Analog composite of July SST anomalies (left) resembles the July 2025
SST anomalies (right). both reflect ENSO-neutral conditions, with the
latter having slightly cooler tropical Pacific SSTs.
El Niño & La Niña Impact
Global Temperatures...
El Niño
La Niña
Courtesy: http://www.drroyspencer.com/latest-global-temperatures/
Using El Niño & La Niña
To Find Analog Years
July 2025
Current Analogs
are 1967; 2006; 2017
Courtesy: http://www.drroyspencer.com/latest-global-temperatures/
Global Temperature Trends
Increase Error in Analog Forecasts!
July 2025
Warming of
≈0.15°C / Decade
Since 1979
Courtesy: http://www.drroyspencer.com/latest-global-temperatures/
September 2025 Forecast
Mean Upper-Air Pattern Upper-Air Anomalies
◼ 1967 had anomalous ridging over Oregon with 2006 & 2017 having
near-average upper-air ridging.
◼ The analog blend (above) has anomalous ridging extending southward
from Canada across Washington and most of Oregon.
September 2025 Forecast
Temperatures Precipitation
◼ Analog years had above-average temperatures with periods of 100+°F
heat in some western valley and eastern basin sites through mid-month.
◼ Precipitation near or below average. Dry years of 1967 & 2006 were
countered by a wetter 2017. Analogs all had showers near mid-month.
October 2025 Forecast
Mean Upper-Air Pattern Upper-Air Anomalies
◼ Analog upper-air patterns diverge by October...ranging from anomalous
troughing over Oregon, in 1967, to anomalous ridging in 2017.
◼ 1967 had prevailing SW flow aloft, while 2006 & 2017 both had more
ridging and subsequent NW flow aloft.
October 2025 Forecast
Temperatures Precipitation
◼ Analogs ranged from relatively cool to near-average temperatures.
◼ 2006 was drier than average, but 1967 & 2017 skewed wetter than
average. 1967 had a major windstorm, focused across the western
zones. All years had some mountain snow, especially 1967 & 2017.
November 2025 Forecast
Mean Upper-Air Pattern Upper-Air Anomalies
◼ Analogs diverge...2006 & 2017 had anomalous troughing from the
eastern Pacific Ocean extending inland over Oregon.
◼ In stark contrast, 1967 had strong ridging in the Gulf of Alaska with
positive anomalies extending all the way eastward to over Oregon.
November 2025 Forecast
Temperatures Precipitation
◼ Despite differences in their respective upper-air patterns, the analogs
were consistent in showing average or above-average temperatures.
◼ Low confidence in the precipitation forecast. Analogs varied from a dry
1967 to a wet 2006. The blend yields near-average rain/mountain snow.
September – November 2025 Forecast
Mean Upper-Air Pattern Upper-Air Anomalies
◼ Expect a transition from anomalous ridging, which prevailed this
summer, towards more typical upper-air patterns this fall.
◼ Analog solutions ranged from weak anomalous ridging (over Oregon) in
1967 to weak anomalous troughing in 2006.
September – November 2025 Forecast
Temperatures Precipitation
◼ Warmer-than-average in September, switching to slightly cooler-than-
average temperatures in October, followed by a mild November.
◼ Lowered confidence in a “near-average” precipitation forecast, due to
the wide range of analog solutions.
Forecast Highlights
◼ This forecast is based on weather that occurred during the (1967;
2006; 2017) analog years (the same years were used last month).
◼ Analogs maintained anomalously warm and dry conditions in
September with a continued threat of 100+°F temperatures through
mid-month.
◼ Expect a pronounced shift to more seasonal temperatures in October,
perhaps even cooler than average. Heightened chances of a significant
south-wind event for western zones, especially along the coast.
◼ November looks mild. Low confidence in the rain/mountain snow
forecast due to large differences among the analogs.
Disclaimer: This forecast is not associated with NOAA’s Climate Prediction Center (CPC). See
“Forecasting Methods…” at: https://www.oregon.gov/oda/natural-resources/pages/weather.aspx.
Forecast Resources
◼ ODA Seasonal Climate Forecast Home:
https://www.oregon.gov/oda/natural-resources/pages/weather.aspx
◼CPC Official US Three-Month Forecasts (Graphics):
https://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=01
◼ CPC US 30-Day & 90-Day Forecasts (Discussions):
https://www.cpc.ncep.noaa.gov/products/predictions/long_range/fxus07.html
◼ CPC Weekly & Monthly ENSO Discussions:
https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory
◼ Australian Government Climate Model Summary:
http://www.bom.gov.au/climate/model-summary/#region=NINO34&tabs=Overview
◼ Australian Government ENSO Wrap-Up:
http://www.bom.gov.au/climate/enso
◼ IRI ENSO Quick Look:
https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/
Water Supply / Fire-Potential Outlook
◼ CPC U.S. Seasonal Drought Outlook:
https://www.cpc.ncep.noaa.gov/products/expert_assessment/season_drought.png
◼ NRCS Snow Water Equivalent Oregon Map:
https://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/or_swepctnormal_update.pdf
◼ NRCS/USDA Snow Water Equivalent Products:
https://www.nrcs.usda.gov/wps/portal/wcc/home/snowClimateMonitoring/snowpack/
◼ NDMC U.S. Drought Monitor:
https://droughtmonitor.unl.edu/
◼ NIDIS North American Drought Portal:
https://www.drought.gov/nadm/content/percent-average-precipitation
◼ WRCC WestWideDroughtTracker:
https://www.wrcc.dri.edu/wwdt/
◼ NWCC Northwest Interagency Coordination Center (video)
https://gacc.nifc.gov/nwcc/predict/outlook.aspx
Updated Monthly
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Contact: Pete Parsons, ODF Lead Meteorologist
at 503-945-7448 or peter.gj.parsons@odf.oregon.gov
