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Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE - OCTOBER 2010

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The Climate Impacts Group (CIG) translates global-scale climate forecasts and conditions into regional-scale climate forecasts for Pacific Northwest (PNW) resource managers and the general public. The El Niño/Southern Oscillation (ENSO) is the most important factor for seasonal forecasting, changing the odds for different types of winter and spring weather (e.g. warmer/drier, cooler/wetter) in the PNW. Another important climate variable for Pacific Northwest climate is the Pacific Decadal Oscillation (PDO). The climate outlook also provides the basis for natural resource forecasts, including the CIG's annual streamflow forecasts.


What's Next for the Pacific Northwest?

October 2010
Updated 21 October 2010 (posted 25 October)

The climate outlook is reviewed monthly and updated as needed.

The July-August-September mean sea surface temperature anomaly in the Niño 3.4 region is -1.25°C, which is consistent with moderate "La Niña" [cold El Niño / Southern Oscillation (ENSO)] conditions. The consideration of current conditions and model forecasts has led NOAA to expect that cold ENSO conditions will "last at least into Northern Hemisphere spring 2011" (7 October, NOAA). A discussion of current equatorial Pacific conditions and model forecasts is provided below.

The analysis of historical fall and winter Pacific Northwest climate for previous strong cold ENSO years suggests that the region will experience cooler and wetter than normal conditions in the coming months.

The NOAA Climate Prediction Center forecast for November-December-January (NDJ) precipitation is for a greater than 33 percent chance of above normal precipitation throughout the Pacific Northwest, western Montana and Wyoming, and the northern portions of Utah, Nevada, and California. Chances of above normal precipitation exceed 40% in north and central Idaho, western and northern Oregon, and all of Washington.

The NDJ temperature forecast is for a greater than 33% chance of below normal temperatures in northern, central, and western Washington, western Oregon, and in the coastal region of northern California. The changes of the same exceeding 40% in the coastal areas of Washington and Oregon. Idaho, southeast Washington, and eastern Oregon are forecast to have an equal chance of below, near, and above normal temperatures.

The existence and forecast persistence of a strong ENSO episode makes it useful to also discuss the climate forecast for later in the winter. The FMA precipitation forecast is qualitatively similar to the NDJ forecast. The FMA temperature forecast is highlighted by a greater than 50% chance of below normal temperatures for North Dakota, northern Montana and Idaho, all of Washington, and northern and western Oregon.

The seasonal forecasts should be interpreted as the tilting of odds towards general categories of conditions, and should not be viewed as a guarantee that the specified conditions will be realized.

For More Information

Recent Pacific Northwest Climate

The western U.S. experienced above normal temperatures during the 30-days ending 19 October (1971-2000 mean, WRCC). The largest temperature departures, in excess of 6°F (3°C), were observed in norhtwest Nevada, southeastern Oregon, central and southern Idaho, southern Montana, and Wyoming. For the Pacific Northwest, this represented a distinct shift from the cooler than normal temperatures that have dominated the region since spring (6-month average temperature; Climate Outlook archive).

The 30-day accumulated precipitation ending 19 October saw below average precipitation in western Oregon and southern Idaho, and above normal precipitation along the northern Washington coast (precipitation totals, departures, percent of 1971-2000 normal).

The cool, wet conditions throughout the growing season has led to Oregon and Washington grape harvests that are from 10-20 days later than usual. A consequence of the late harvest is that grape losses from migrating birds could be substantial (23 September, Tri-City Herald (Kennewick, Pasco, and Richland); 21 October, Oregonlive).

The Northwest Interagency Coordination Center (NWCC) maps the locations of "large wildland fires" (timber > 100 acres, grassland > 300 acres; 100 acres = 0.16 square miles) for Oregon and Washington. The fire season is drawing to a close and, on 21 October, there remain 5 large wildland fires in Idaho, 2 in Oregon, and none in Washington (Inciweb). The 19 October Drought Monitor identifies an increase in drought area and severity in south central Oregon and the onset of drought in southern Idaho. The enhanced drought conditions are consistent with the drier, warmer than normal climate in the drought regions during the last 30 days.

September coastal sea surface temperatures (SSTs) continued the pattern of below normal temperatures that have been observed since April of this year (PFEL). SST departures in excess of 1 °C colder than a 1985-97 mean were observed from Tatoosh Island at the northwest corner of Washington to Astoria in northern Oregon, and also to the south of Cape Blanco (42.83°) in southern Oregon.

On a broader scale and, with a cooler reference mean, SST departures for the northeast Pacific SST for the 30 days ending 16 October were warmer than a 1982-96 normal near the Washington and Oregon coast, near normal farther offshore, and cooler than the mean in the central Gulf of Alaska (centered at 45°N,145°W). Significant negative SST departures are present in the central and eastern Pacific, and to the south and east of Hawaii, and are associated with the ongoing cold ENSO episode.

Sources:

  • Western Regional Climate Center (WRCC)
  • National Centers for Environmental Prediction (NCEP)
  • Northwest Interagency Coordination Center (NWCC)
  • Incident Information System (InciWeb)
  • Drought Monitor
  • Pacific Fisheries Environmental Laboratory (PFEL)
  • Earth System Research Laboratory (ESRL)

  • Recent and Projected Changes in Key Indicators for Pacific Climate

    El Niño/Southern Oscillation (ENSO). Sea surface temperature (SST) departures from 1971-2000 averaged over 5°N-5°S, 170-120°W in the equatorial Pacific, in what is called the "Niño 3.4" region, are a key indicator of ENSO variability. The ongoing cold ENSO, as measured by Nino 3.4 SST departures, intensified from August (-1.18 °C) to September (-1.56°C). The mean Niño 3.4 SST departure for July-August-September (JAS) was -1.25°C, which NOAA categorizes as a moderate "La Niña" when accompanied by consistent atmospheric anomalies (NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion).

    NOAA employs mechanistic and statistical models to forecast how ENSO will evolve over the next several seasons. Mechanistic models solve equations for ocean and atmosphere motions, and precipitation and radiative processes to forecast the future from present conditions. Statistical models, in contrast, are constructed from observations of past climate, and they apply regression coefficients to present climate conditions to forecast the future. Agreement of the forecasts from these two types of models increases our confidence in the forecast.

    The 3-month mean Nino 3.4 SST forecast from twenty-three ENSO models initialized with ocean and atmosphere data through September are summarized by the International Research Institute for Climate and Society. The average forecast is for the cold ENSO to intensify from the observed JAS value of -1.25°C to a maximum negative value of -1.8°C in October-November-December. A 3-month Niño 3.4 SST anomaly value in excess of -1.5°C, would make this a "strong" La Niña (cold ENSO). The forecast for subsequent seasons is for the episode to diminish in intensity, with the "La Niña" rating to be that of "moderate" (Niño 3.4 > -1.5°C) in January-February-March, "weak" (Niño 3.4 > -1.0°C) in March-April-May, and a return of conditions to "neutral" (Niño 3.4 > -0.5°C) by next summer. There is considerable range in the forecasts Niño amplitudes, but good agreement on the trajectory of the episode.

    Pacific Decadal Oscillation (PDO). The continued intensification of positive SST departures in the central north Pacific during September contributed to a further intensification of negative PDO conditions during this month, resulting in a PDO value of -1.61 standard deviations (1900-90 reference period, PDO values). [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] September is the fourth consecutive month of negative PDO values following positive PDO values that were observed last winter and spring. ENSO variabilty is one of the mechanisms that can produce changes in the PDO, and the present cold ENSO can be expected to contribute to negative PDO values in the coming seasons.

    NOAA employs both statistical and mechanistic models to forecast the PDO and coastal ocean conditions. The statistical linear inverse model predicts the PDO to be negative and strengthening through the end of the forecast period in summer 2011. The NCEP coupled forecast system (a mechanistic ocean-atmosphere model) prediction issued on 21 October is for a continuation of the present pattern of cold SST anomalies along the eastern boundary north of 40°N (Cape Mendocino in California) and warm anomalies in the central north Pacific through March-April-May 2011 (21 October forecast, more recent forecasts). The model forecasts for next winter and spring have been judged to not be skillful for the central and southern California coast.

    For More Information


    Pacific Northwest Resource Outlooks

    Climate Prediction Resources

    The links below provide access to the latest information on the current state of global and regional climate, as well as links to global and regional climate predictions.

    The Current State of the Tropical Pacific

    Predictions of Tropical Pacific and North Pacific Conditions

    The Current State of the Globe

    Current and Predicted U.S. Conditions

    Pacific Northwest Conditions

    State Climatologist Offices

    Special Areas