Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE COPY - APRIL/MAY 2007

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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/May 2007
Updated April 30, 2007 (posted 5.9.07)

The climate outlook is reviewed after the 20th of each month and updated as needed.

February and March were slightly warmer than normal over the Pacific Northwest (Idaho, Oregon, and Washington), and are a part of a broad region of warm anomalies spanning the contiguous U.S. and southern Canada (International Research Insitute for Climate and Society (IRI)). Temperatures along the coast were cooler than the 1950-2007 normal despite the weak El Niño of the early winter (University of Washington). The climatological stormtrack moved northward in March, with enhanced precipitation in British Columbia and Washington, and diminished precipitation in Oregon (IRI). Idaho was near normal in precipitation. The temperature and precipitation anomalies are consistent with positive values of the Northern Annular Mode (NAM), which is also called the Arctic Oscillation (AO), and the NAM was strong and of positive polarity in March (NOAA). The NAM has been large in amplitude, but varying in sign throughout the winter. Typical temperature and precipitation anomalies associated with positive values of the NAM are given in the following: temperature | precipitation (UW).

The April 1st snowpack reflects the temperature and precipitation over the entire winter, and is characterized by 90-109% of normal over the Washington Cascades and southeastern British Columbia (Kootenay); 70-89% in the Oregon Cascades and northern Idaho; and snowpack below 50% normal in southern Idaho and eastern Oregon. The precipitation since the beginning of the water year (1 October) has been within 10% of normal for Oregon and Idaho, and has been the 10th wettest (84th percentile) since 1951 for Washington. The poor Idaho and eastern Oregon snowpack are constistent with the above normal temperatures in February and March described above.

Current indicators for Pacific climate

El Niño/Southern Oscillation (ENSO). March equatorial Pacific sea surface temperatures were characterized by cold anomalies in the east and persistent warm anomalies in the west, adding up to neutral conditions in the central equatorial Pacific (relative to the 1950-2007 mean). The early indications of the 14 models summarized by the IRI is for weak, cool ENSO ("La Nina") conditions for next winter. Acceptance of the ENSO forecast should be tempered by the understanding that the models have their smallest amount of skill when initialized at this time of year.

Pacific Decadal Oscillation (PDO). The Winter PDO index values were small and positive, and in March shifted to negative with respect to the 1900-93 mean. The March value is consistent with the cooler than normal coastal SST described above. In the absence of a strong ENSO signal it is difficult to predict the amplitude and sign of the PDO in the coming months (PDO forecasting).

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

The Climate Prediction Center's outlook for May-June-July for is for a greater than 33% chance of warmer than normal temperatures for southeastern Oregon and southern Idaho, and equal chances for above, below, or near normal temperatures for the rest of the PNW. In the absence of strong ENSO conditions, the CPC precipitation forecast has negligible skill. 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.

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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 Conditions

The Current State of the Globe

Current and Predicted U.S. Conditions

Pacific Northwest Conditions

State Climatologist Offices

Special Areas