Seasonal Climate Forecast

October – December 2015Issued: September 17, 2015

A cooperative product between the Oregon Department of Agriculture (ODA), and the Oregon

Department of Forestry (ODF).

Contact: ODF Meteorologist Pete Parsonsat 503-945-7448 or peter.gj.parsons@oregon.gov

Get related Seasonal Climate Forecast information at: http://www.oregon.gov/ODA/programs/NaturalResources/Pages/Weather.aspx

A cooperative product between the Oregon Department of Agriculture (ODA), and the Oregon

Department of Forestry (ODF).

Contact: ODF Meteorologist Pete Parsonsat 503-945-7448 or peter.gj.parsons@oregon.gov

Get related Seasonal Climate Forecast information at: http://www.oregon.gov/ODA/programs/NaturalResources/Pages/Weather.aspx

El Niño Southern Oscillation (ENSO)

Current Status and Forecast The Climate Prediction Center (CPC) has issued an El Niño Advisory. Equatorial Pacific Ocean SSTs have continued to warm and have entered the moderate El Niño range.

The Oceanic Niño Index (ONI) for the June-August period was +1.2°C. The CPC thresholds for a weak, moderate, and strong El Niño are +0.5°C, +1.0°C, and +1.5°C respectively.

CPC forecaster consensus unanimously favors El Niño becoming strong and peaking this late-fall/early-winter.

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

Forecast Method Notes…

The top analog years (1987; 1991; 2004) all had a strengthening El Niño, in the fall and winter, following a winter with positive ONI anomalies (like the 2014-15 period).

All three of the above years were weighted equally to generate the forecast graphics.

This forecast is based solely on historical weather data and does not utilize dynamic modeling (see Forecasting Methods).

Forecast Notes of Interest…

2015 has proven to be quite rare, in terms of Pacific Ocean SSTs. The corresponding weather patterns have been “extreme,” with Oregon experiencing record or near-record warm and dry conditions since last winter.

SST records, going back to 1950, show only one other year (1987) with an ONI for the June-July-August period of +1.0 or greater (like this year) following a winter with positive ONIs (like last winter).

El Niño is expected to peak late this fall or early winter, at strong intensity, which favors a continuation of warmer and drier-than-average weather and below-average mountain snow.

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

(bottom)

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

Well above average SSTs extend across much of the Gulf of Alaska and the

tropical Pacific Ocean.

Tropical Pacific OceanEl Niño has strengthened into the “moderate”

range...

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

SSTs are well above average across most of the tropical

Pacific Ocean

ENSO-neutral

Tropical Pacific Ocean

El Niño

La Niña

(2003-04; 1990-91; 1986-87)

Weak El Niño “Modoki” last

winter El Niño is strengthening...

ENSO-neutral

El Niño has strengthened into

the moderate range

El Niño

Tropical Pacific Ocean

(2003-04; 1990-91; 1986-87)

La Niña

Weak El Niño “Modoki” last

winter.

Weak

Moderate

Strong

Average

North Pacific Ocean

Warm

Cool

(2003-04; 1990-91; 1986-87)Last Winter Had The Highest PDO Values Since 1997

PDO dropped in August but is still well

above average

Model forecasts favor ENSO-neutral conditions through spring 2014; followed byEl Niño development.

ENSO Predictive Models El Niño is predicted to become strong this fall and

winter…

“Base” Graphic Courtesy: http://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

La Niña

El Niño

ENSO-neutral

Chart Updates

A time-series graphical comparison of “PDO” values was recently added. Predicted upper-air patterns and anomalies have also been added to help explain the reasons for the corresponding temperature and precipitation forecasts. Precipitation forecasts have changed from “departure from average” (in inches) to “percent of average” (with 100% being average). The color palettes have been updated for both the temperature and precipitation anomaly graphics.

October 2015 ForecastMean Upper-Air Pattern Upper-Air Anomalies

Stronger than average upper-level ridging is likely over the NW US.

Early-autumn storms will have a tendency to “split,” as they move onshore, with much of their energy directed north, into Canada, and south, into California.

October 2015 ForecastTemperatures Precipitation

Analog years suggest a continuation of generally mild and dry weather.

This “El Niño-driven” climate signal typically becomes more evident in the fall and winter months.

Northern zones will likely see the driest conditions (relative to average).

November 2015 ForecastMean Upper-Air Pattern Upper-Air Anomalies

Anomalous upper-level ridging is predicted to be centered over extreme SW Canada, which would weaken approaching fall storms.

A “split-flow” jet stream pattern will likely direct considerable storm energy south of Oregon, into California.

November 2015 ForecastTemperatures Precipitation

No major change - continued generally warmer and drier than average.

It is possible that the number of days with rain/snow will be near average but with decreased precipitation totals.

The likelihood of valley fog episodes is elevated.

December 2015 ForecastMean Upper-Air Pattern Upper-Air Anomalies

Upper-level ridging is likely to be stronger than average over the NW US and SW Canada, with an enhanced jet stream over California.

A “split-flow” jet stream is likely, which would bring weaker and less frequent storms, relative to average, onto the Oregon coast.

December 2015 ForecastTemperatures Precipitation

Expect a continuation of above average temperatures and below average precipitation. Best chance of storminess is early in the month.

Snow levels should generally be above average. Higher mountain sites may get near-average snowfall, but deficits are likely elsewhere.

October – December 2015 Forecast

Mean Upper-Air Pattern Upper-Air Anomalies

Strong anomalous upper-level ridging off the southern BC coast and anomalous troughing over southern California.

Expect a “split-flow” jet stream pattern, with considerable storm energy being directed both to the north and to the south of Oregon.

October – December 2015 Forecast

Temperatures Precipitation

A moderate-to-strong El Niño typically yields warmer and drier-than-average weather for Oregon during the autumn season.

“Cool” periods are usually brief but can bring an early mountain snowpack. However, winter snowpacks tend to fall short of average.

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

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

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

Australian Government Weekly Tropical Climate Note:http://www.bom.gov.au/climate/tropnote/tropnote.shtml

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

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

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

Water Supply Information NDMC U.S. Drought Monitor:http://droughtmonitor.unl.edu/

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

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

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

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

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

WRCC WestWideDroughtTracker:http://www.wrcc.dri.edu/wwdt/

Updated Monthly(around the 20th)

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

ODA Production support from Diana Walker and Andy Zimmerman

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

ODA Production support from Diana Walker and Andy Zimmerman

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