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Seasonal to Interannual Forecasts

Climate Outlook

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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?

December 2008
Updated December 19, 2008 (posted December 20)

The climate outlook is reviewed monthly and updated as needed.

The Pacific Northwest (Oregon, Washington, and Idaho; PNW) and the northcentral U.S. were gripped by extreme cold temperatures during mid-December, with temperature departures in excess of -5°C (-10°F) over Montana, North Dakota, northern Minnesota, southeastern Washington, and to the east of the Cascades in Oregon (map, 1971-2000 normal, HPRCC). Temperatures have been below freezing over almost all of the PNW (map). What precipitation has fallen has largely been snow, and the precipitation amounts have been below normal for this 7-day period (map). The upper atmosphere flow pattern (map, ESRL) documents a westward shift of the climatological ridge that normally resides over the PNW. Winds flow parallel to the contours, and the southward flow over western British Columbia brought arctic air into the PNW. This change in the atmospheric flow pattern is well characterized by the negative polarity of the Pacific/North American (PNA) pattern, and earlier studies have shown an increased chance of heavy snow and extreme cold in these situations (more information).

Examined over the past 30 days and the period since 1 October (the beginning of the Water Year), conditions have been drier and slightly warmer than normal (precipitation, temperature). The snow pack, as measured in terms of snow water equivalent, is less than 50% of normal for this point of the season throughout the Columbia Basin (18 December analysis, map legend, current analysis, NWRFC).

The recent cold ocean surface temperatures along the Washington, Oregon, and northern California coasts have diminished and are now slightly above the 1985-97 mean (analysis, PFEL). The broader equatorial and north Pacific sea surface temperatures (SSTs) (ESRL) remain generally colder than normal in the eastern portion of the basin, and warmer than normal in the central north Pacific. This pattern is well characterized as the cold polarity of the Pacific Decadal Oscillation (PDO) (more information). The November PDO value is -1.25 standard deviations relative to a 1900-93 climatology, and it is the eighth consecutive month of PDO values < -1 (digital values). [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.]

Sources:

  • High Plains Regional Climate Center (HPRCC)
  • Northwest River Forecast Center (NWRFC)
  • Pacific Fisheries Environmental Laboratory (PFEL)
  • Earth System Research Laboratory (ESRL)


    Current indicators for Pacific climate

    El Niño/Southern Oscillation (ENSO). The monthly mean Niño 3.4 region (5°N-5°S, 170-120°W) SST anomaly has been slightly cooler than the 1971-2000 climatology since September, and the September-October-November mean is -0.23°C. NOAA classified the present conditions as "ENSO-neutral" on 11 December (latest report, El Niño definition). Nineteen of the 23 ENSO forecast models polled by the International Research Institute for Climate and Society predict a January-February-March Nino 3.4 value in the range "-0.1 to -0.7°C," of which eight exceed the -0.5°C criterion of cold ENSO. The strong consensus of the models in the next several months diminishes by May-June-July.

    Pacific Decadal Oscillation (PDO). The conceptual model of PDO ocean variability has been very useful in characterizing the northeast Pacific Ocean conditions in 2008 (above), with the PDO in a significant cold phase. The NOAA Earth System Research Laboratory's statistical Linear Inverse Model PDO forecast is for continued cold polarity, but of smaller magnitude, through the end of the forecast period (December 2009) (forecast). The NOAA coupled forecast system model solves dynamical equations for ocean and atmosphere motions, and the forecast provides SST anomaly spatial information that complements the above ENSO and LIM PDO forecasts (forecast).

    For More Information


    What does the outlook mean for the PNW in coming months?

    The NOAA Climate Prediction Center (CPC) provides 14-day PNA forecasts (through 1 January, beyond 1 January). The red curves in the top panel indicate that the PNA pattern will persist through the forecast period.

    The longer-term January-February-March CPC climate forecast is for a greater than 33% chance of below normal temperatures north and west of Pocatello Idaho, with the probabilities exceeding 40% in northern Oregon, northern Idaho, and all of Washington (map). The precipitation forecast for the same months is for an even chance of below, equal to, and above normal precipitation throughout the PNW (map). The skill of the precipitation forecast is derived from ENSO-related changes in precipitation, and the model has no useful skill in ENSO neutral years. The 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

    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