Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE COPY - APRIL 2009

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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?

April 2009 (no update required for May 2009)
Updated 23 April, 2009 (posted April 27)

The climate outlook is reviewed monthly and updated as needed.

The NOAA Climate Prediction Center May-June-July forecast is for a greater than 33% chance of above normal temperatures in eastern Oregon and southern Idaho, and a greater than 33% chance of below normal temperatures along the Oregon and Washington coasts (map) This forecast is a change from the cooler than normal conditions that enveloped the region in March-April (described below). The precipitation forecast is for an even chance of below, equal to, and above normal precipitation along the PNW coast; and a greater than 33% chance of below normal precipitation in the remainder of the region, exceeding 40% in central and southern Idaho.

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. The precipitation forecasts only have skill during periods of significant warm or cold ENSO conditions.

More on recent Pacific Northwest climate and recent and projected changes in key indicators for Pacific Northwest climate is provided below.

For More Information

Recent Pacific Northwest Climate

The Pacific Northwest (Oregon, Washington, and Idaho; PNW), as a whole, was cooler than the 1971-2000 mean during the last 30-, 60-, and 90-days ending 22 April (WRCC). The 60-day mean temperature departure documents the region-wide cooler than normal temperatures, and also negative surface temperature departures in excess of 1°C (2°F) in many portions of the region. In contrast, the winter (December-January-February) temperatures were more near the longterm mean over the PNW (not shown, HPRCC).

The precipitation during the last 60-days exhibited significant departures from the longterm mean in several geographic regions (total, departure, percent normal; WRCC). The northwest corner of Washington State was drier than normal; Mt. Hood in northern Oregon, much of the Columbia Basin, and Idaho experienced above normal precipitation; and the southeast high plains of Oregon has been drier than even its longterm mean (Burns Oregon precipitation, NCEP).

The April 1 snowpack (NRCS) largely reflects the dominant features of the 60-day precipitation departures discussed above. The Olympics, and the northern Washington and Canadian reaches of the Columbia Basin have significantly less snow than normal. The Oregon and southern Washington Cascades have normal to well-above normal snow for this date.

Along the coast, March sea surface temperatures were >1°C below the 1985-97 mean (analysis, PFEL) and represent a regional intensification of the existing pattern of colder than normal ocean temperatures along the west coast of North America and warmer than normal temperatures in the central north Pacific (analysis, 1982-96 mean; ESRL). This north Pacific temperature anomaly distribution is referred to as the Pacific Decadal Oscillation (PDO), and the ocean has been in this cold phase of the PDO since late 2007.

Sources:

  • Western Regional Climate Center (WRCC)
  • High Plains Regional Climate Center (HPRCC)
  • National Centers for Environmental Prediction (NCEP)
  • Natural Resources Conservation Service (NRCS)
  • 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). The phase and strength of the El Niño/Southern Oscillation phenomenon is characterized by the average sea surface temperature (SST) anomaly over 5°N-5°S, 170-120°W in the equatorial Pacific, in what is called the "Niño 3.4" region (NOAA El Niño definition). Cold Niño 3.4 SST anomalies peaked in January at -0.95°C, and February and March saw diminished anomalies (-0.64 and -0.50°C, respectively; 1971-2000 mean). The average of the three monthly values is -0.70°C, which exceeds the NOAA -0.50°C criterion for this to be a cold ENSO episode.

    ENSO forecasts are made with statistical models, which employ statistics of past variability to predict the future, and mechanistic models, which solve equations for ocean and atmosphere motions, to forecast the future from present conditions. Agreement of the forecasts from these two types of models increases our confidence in the forecast. The International Research Institute for Climate and Society polls the results of 23 models, both statistical and mechanistic, that are produced by research institutions around the world. The 23 forecasts, which were initialized with March ocean and atmosphere conditions, predict an average May-June-July Niño 3.4 value of -0.1°C, which is categorized as ENSO neutral. All ENSO forecast models have marginal skill at this time of the year and, with that strong disclaimer, the initial forecast for next winter is for slightly warmer than normal conditions (anomaly of 0.2°C).

    Pacific Decadal Oscillation (PDO). The PDO has exhibited negative monthly values since September 2007 (digital values), with values in excess of -1 standard deviation from April through November of 2008 and again since January of this year. [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] The "La Niña" (cold ENSO) of this past winter is consistent with the development or continuation of negative PDO values.

    The NOAA coupled forecast system model (a mechanistic ocean-atmosphere model) predicts that the present cold anomalies along with the west coast of North America will be reduced to a vestige by June-July-August, with a weak reemergence of the cold PDO pattern next winter (forecast).


    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