Seasonal Climate ForecastJanuary – March 2021

Issued: December 17, 2020

Contact: ODF Meteorologist Pete Parsons503-945-7448 or peter.gj.parsons@oregon.gov

Oregon Department of Agriculture (ODA) - Oregon Department of Forestry (ODF)Production support: Diana Walker; Jacob Cruser; Andy Zimmerman; Julie Waters

El Niño Southern Oscillation (ENSO)Current Status and Forecast

n The September – November 2020 Oceanic Niño Index (ONI) cooled into the moderate La Niña range (-1.2°C).

n The ONI lags real-time sea-surface temperatures (SSTs), which are also in the moderate La Niña range across the tropical Pacific.

n NOAA’s Climate Prediction Center (CPC) has issued a La Niña Advisory and expects La Niña to continue into this coming spring.

n Tropical Pacific SSTs are much colder than they were the past two winters, which displayed El Niño conditions.

IMPORTANT NOTE: Beginning with the October 2017 update, ONI values use ERSSTv5 data (Huang et al. 2017, J. Climate, vol. 30, 8179-8205).

https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

Forecast Highlightsn Two of the analog years (1971 & 1996) are unchanged from last month. However, 2008 replaces 1960, due to the strengthening La Niña.

n Expect considerably more storminess than we had during the past two winters, which were influenced by El Niño conditions.

n The chances for cold-air outbreaks and valley snowfall are much higher this winter, compared to the past two winters.

n Near-or-above-normal mountain snowfall is likely.

n La Niña can produce wide-ranging weather patterns, even within the same month, so volatility should be expected this winter.

IMPORTANT NOTE: This forecast is based on past and current weather data and is not associated with CPC predictions (see “Forecasting Methods…” at: https://oda.direct/Weather) nor the official CPC “Three-Month Outlooks,” which are available here: https://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=1

Pacific OceanAnimated (PowerPoint only) SSTs (top) / Anomalies (bottom)

Courtesy: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/gsstanim.shtml

Tropical Pacific SSTs remain in moderate La Niña territory

Tropical Pacific OceanLa Niña Conditions Present

Courtesy: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstweek_c.gif

Current SSTs are in the moderate La Niña range)

Strong

Moderate

ENSO-neutral

El Niño

Tropical Pacific Ocean

(1969-70; 1994-95; 2006-07)

La Niña

Weak

Strong

Moderate

Sept. – Nov. analog ONIs were all in theLa Niña range

Weak

Sept. – Nov. ONI (-1.2°C)

reflected moderate

La Niñaconditions

ENSO-neutral

Tropical Pacific Ocean

El Niño

La Niña

(1969-70; 1994-95; 2006-07)

Nov. SOI (0.7) rose

slightly, close to the La Niña

range

Nov. analog SOIs ranged

fromLa Niña to

ENSO-neutral

North Pacific Ocean(Poleward of 20°N Latitude)

Cool

(1969-70; 1994-95; 2006-07)

Nov. PDO (-1.12) dropped into the “Cool”

zone

Nov. PDO analogs ranged from “Neutral”

to “Cool”

Warm

Neutral

SST Anomalies ComparisonNov. Analog Composite November 2020

n The SST anomalies from the November analog composite (left) and from this past November (right) both show La Niña conditions across the tropical Pacific of similar strength (moderate).

January 2021 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n The analog years all had negative temperature anomalies over western Canada, which increases the chances for Arctic intrusions into Oregon.

n This pattern also favors ample mountain snowfall & stormy periods, especially for the coast and western zones.

January 2021 ForecastTemperatures Precipitation

n Above-average precipitation and near-to-above-average mountain snow. Increased chances for windstorms, especially along the coast.

n Temperature forecast is tricky, with transitions between more-mild stormy and cold periods. Heightened chances for low-elevation snow.

February 2021 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n Analogs solutions begin to diverge, with 1971 and 2008 most-closely resembling the mean pattern shown above.

n Cold-air dumps will likely continue east of the Rockies but could also impact the Pacific Northwest.This pattern has the potential to produce a high variety of outcomes,

February 2021 ForecastTemperatures Precipitation

n Large overall departures from average conditions are not indicated, but week-to-week variations could be significant.

n Rapid transitions from cold/dry to mild/wet periods are possible. Mountain snowpacks should finish the month near or above average.

March 2021 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n A general continuation February’s pattern is predicted by the analogs, with 1971 and 2008 most-closely resembling the mean pattern shown.

n This keeps the door open for cold-air dumps into the northern U.S. Cold-air outbreaks may even impact the Pacific Northwest.

March 2021 ForecastTemperatures Precipitation

n Cooler-than-normal conditions, with near-average precipitation.n Mountain snowpacks should be near or above normal at month’s end.

January – March 2021 ForecastMean Upper-Air Pattern Upper-Air Anomalies

n Analogs all show a similar mean upper-air pattern (left) and anomalies (right) for the 3-month period, with more month-to-month variability.

n This pattern opens the door for cold air masses to drop southward into the northern U.S. and possibly into the Pacific Northwest.A wide variety of weather patterns are likely during the period.

January – March 2021 ForecastTemperatures Precipitation

n Cooler than average, especially at higher elevations. More storminess than the previous two January-March periods.

n Mountain snowpacks should be near or above average. Elevated chances for low-elevation snow, but that is not a certainty.

January – March 2021 Insights

n Unlike the past two winters, which had El Niño conditions, La Niña conditions should promote stormy periods along with an increased chance of “extreme” weather events.

n Expect a transition to generally colder and wetter weather than average with ample mountain snowpacks.

n Valley cold-air outbreaks and snowfall are not guaranteed, but the chances for such events are elevated.

n Heightened chances for windstorms and flooding across western Oregon, especially along the coast.

Oregon Department of Agriculturehttp://www.oregon.gov/ODA/programs/NaturalResources/Pages/Weather.aspx

Forecast Resourcesn CPC Official US Three-Month Forecasts (Graphics):https://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=01

n CPC US 30-Day & 90-Day Forecasts (Discussions):https://www.cpc.ncep.noaa.gov/products/predictions/long_range/fxus07.html

n CPC Weekly & Monthly ENSO Discussions: https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory

n Australian Government Climate Model Summary:http://www.bom.gov.au/climate/model-summary/#region=NINO34&tabs=Overview

n Australian Government ENSO Wrap-Up:http://www.bom.gov.au/climate/enso

n IRI ENSO Quick Look:https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

n ODA Seasonal Climate Forecast Home:http://www.oregon.gov/ODA/programs/NaturalResources/Pages/Weather.aspx

Water Supply Informationn NDMC U.S. Drought Monitor:https://droughtmonitor.unl.edu/

n NIDIS North American Drought Portal:https://www.drought.gov/nadm/content/percent-average-precipitation

n NRCS Snow Water Equivalent Oregon Map:https://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/or_swepctnormal_update.pdf

n NRCS Snow Water Equivalent Products:https://www.wcc.nrcs.usda.gov/snow/snotel-wereports.html

n NRCS Weekly Water and Climate Update:https://www.wcc.nrcs.usda.gov/cgibin/water/drought/wdr.pl

n NRCS Western Snowpack Data & Water Supply Forecast:https://www.wcc.nrcs.usda.gov/cgibin/westsnowsummary.pl

n WRCC WestWideDroughtTracker:https://www.wrcc.dri.edu/wwdt/

Updated Monthly(Around the 20th)

Contact: Pete Parsons, ODF Meteorologistat 503-945-7448 or peter.gj.parsons@oregon.gov

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