Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE - APRIL 2008

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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 2008
Updated April 29, 2008 (posted April 30)

The climate outlook is reviewed monthly and updated as needed.

April temperatures (through the 28th) were at least 2°F (1.1°C) cooler than the 1971-2000 mean throughout the Pacific Northwest (PNW) (temperatures, temperature departures), with cold departures in excess of 4°F (2.2°C) over Idaho, and eastern Oregon and Washington (analyses: High Plains Regional Climate Center). This continued a pattern of colder than normal temperatures that was observed in March and, to a lesser extent, for the winter season as a whole (analyses: University of Washington). March coastal sea surface temperatures were at least 3.6°F (2°C) below the 1985-97 mean (source: NOAA Coastwatch).

April precipitation through 28 April was drier than the 1971-2000 mean throughout the PNW, with deficits exceeding 0.75 inches in magnitude in western Oregon and Washington (totals, departures, percent of normal). This pattern of dryness was also observed through the last 90 days, while for the water year (October through 28 April), the precipitation pattern was more varied. The precipitation that did fall during the past Winter produced an April 1st snowpack that was near or above normal for the Columbia Basin, and well above normal in the central Washington and Oregon Cascades (analysis: Natural Resources Conservation Service (NRCS)). Consistent with this heavy snowpack, streamflows are forecast to be near or above normal for Spring and Summer (NRCS).

Additional analyses of recent Pacific Northwest weather and climate are provided in the Office of the Washington State Climatologist Newsletter.

Current indicators for Pacific climate

El Niño/Southern Oscillation (ENSO). Cold ENSO conditions continue in the equatorial Pacific, with mean January-February-March sea surface temperatures (SSTs) 2.9°F (1.6°C) below the 1971-2000 normal in the Niño 3.4 region (5N-5S, 170-120W). The current cold ENSO conditions are characterized as "moderate-strength", and the cold ENSO is expected to "become weak and persist through May-June-July 2008. Thereafter, there is considerable spread in the forecasts, with nearly one-half indicating [cold ENSO] could continue well into the second half of the year" (National Centers for Environmental Prediction). (ENSO forecast plume.)

Pacific Decadal Oscillation (PDO). The March 2008 pattern of colder than normal SSTs along the west coast of North America and on the equator, and warmer than normal SSTs in the central north Pacific is characteristic of the cold polarity of the PDO phenomenon (analysis: University of Washington). The cold polarity of the PDO has been present since September 2007, and the January-February-March mean value of the PDO index was "-0.83" (almost a standard deviation in magnitude), which is within the range of typical fluctuations of the index. Continued cold ENSO conditions are consistent with continued cold PDO, and the NOAA Earth System Research Laboratory's statistical Linear Inverse Model PDO forecast is for a continuation of cold PDO throughout the rest of 2008 (forecast).

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

The Climate Prediction Center's (CPC) outlook for May-June-July temperature in western Washington is for April's cooler than normal temperatures to continue (greater than a 33% chance). For the remainder of the region, the CPC projects a greater than 33% chance of above normal May-June-July temperatures in southern and eastern Oregon and central Idaho, and a greater than 40% chance for the same in southeast Oregon and southern Idaho. The precipitation forecast is for a continuation of April's dry conditions throughout the region (greater than a 33% throughout the PNW, exceeding a 40% chance for the same in eastern Oregon and southern Idaho).

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. The forecasts tend to have most skill in years of significant warm or cold ENSO conditions, like this one.

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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 and North Pacific Conditions

The Current State of the Globe

Current and Predicted U.S. Conditions

Pacific Northwest Conditions

State Climatologist Offices

Special Areas