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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 is now provided by the Office of the Washington State Climatologist on a quarterly basis with the CIG newsletter.

Recent PNW Climate

May 2012
Updated3 19 April 2012 (posted 30 April)

The 90 days ending on April 15 were relatively cold for the western coast of the US, as shown in the average temperature departures from the 1971-2000 normal (Figure 1). Most locations in the Pacific Northwest west of the Cascades, as well as northern California, were 2-4°F below average with some areas in the Cascade Mountains even cooler. Further inland, the temperature departures from average were less, with temperatures only around 1-2°F below normal in eastern Washington and the Idaho panhandle. Eastern OR and the remainder of ID actually had above normal temperatures for the 90-day period, with temperatures about 1-2°F above normal. The most extreme temperature departures in the west can be found in eastern Montana, western North Dakota, and western South Dakota, where average temperatures ranged from 6 to 10°F above normal.

Precipitation during the last 90 days was extremely variable across the western US (Figure 2). The Pacific Northwest was wet, with western WA and western OR receiving 110 to 150%, and 150 to 200%, of normal precipitation, respectively. Similar departures from the normal ranges are shown for eastern WA and northern ID who received between 130 and 200% of average precipitation in the last 90 days. Precipitation was more variable in eastern OR and southern ID, with some isolated areas only receiving between 70 and 90% of normal. While most of the Pacific Northwest was experiencing above average rainfall, some other areas of the west were much below normal. Notably, Arizona and southern California received between 5 and 50% of the average rainfall for the past 90 days.

The cooler and wetter than normal conditions, especially since the beginning of March, brought substantial snowfall to the mountains of the Pacific Northwest. The snowpack, expressed as the percent of normal water content and shown in Figure 3, is normal (90-110%) throughout most of the Pacific Northwest and above normal in WA State (110-200%) as of April 18, 2012 (Figure 3). A few basins in eastern WA and southern ID, where the 90-day precipitation was below normal, have a snowpack between 50 and 90% of normal. The high snowpack bodes well for the summer water supply forecast for most of the Pacific Northwest, as the summer streamflow is projected to be above normal by the National Weather Service Northwest River Forecast Center in all of WA, and most of OR and ID (figure not shown). Below average numbers (between 40 and 89% of normal) are projected for some streams in southeastern OR and southern ID, where the snowpack is below normal (http://www.nwrfc.noaa.gov/ws/).

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ENSO Conditions

According to the Climate Prediction Center (CPC), last winter's weak-to-moderate La Niņa in the equatorial Pacific Ocean substantially weakened during March. In the last 90 days, the negative sea-surface temperature (SST) anomalies have decreased. This warming, relative to seasonal normals, extends through the upper 300 meters of the ocean. It is expected that ENSO will soon be in a neutral state, and that these conditions will persist through the summer. At this time, it is still too early to make a reliable ENSO prediction for next fall and winter.


Climate Outlook

As we transition to the spring and summer months, what can we expect for the Pacific Northwest? With ENSO conditions becoming neutral this spring, there is not much signal for the seasonal forecast. The CPC May-June-July (MJJ) temperature outlook calls for equal chances of below, equal to, or above normal temperatures for a majority of the Pacific Northwest (Figure 4). A higher chance of warmer than normal temperatures exists for southern ID and southeastern OR. Precipitation is expected to be below normal for most of the Pacific Northwest during the MJJ period, with the highest chances concentrated in far eastern WA, northeastern OR, and most of ID (Figure 5). West of the Cascades, however, is a toss up, with equal chances of below, equal to, or above normal precipitation.

 

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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