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Seasonal to Interannual Forecasts

Climate Outlook

Archive copy - Sept. 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?

Fall 2007
Updated September 26, 2007

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

A look back at summer: NOAA's National Climatic Data Center reported that U.S. and PNW temperatures (OR-WA-ID) for June-August 2007 were the 6th warmest on record since 1895. What seemed like an unusually cool summer this year across western Washington and Oregon was actually normal when compared to the 1971-2000 average. The common perception that this summer was cooler and wetter than normal in may be related to the fact that cloud cover was somewhat greater this summer than in recent summers. However, east of the Cascades temperatures were above normal, with the warmest area being southern Idaho, which which experienced its 3rd warmest summer on record (since 1895) with summer temperatures ranging from 3 to 5°F above the 1971-2000 average.

Summer precipitation varied across the region with above normal precipitation for the Washington coast and for Oregon's central and High Plateau regions. The east slopes of the WA Cascades along with northern and central ID experienced the greatest rainfall deficits and received less than 50% of normal summer precipitation.

Precipitation and temperature variations contributed to major wildfires (map) and drought across Idaho where nearly 2 million acres burned this year. As of September 1 many reservoir storage levels in Idaho remain low. Other major fires in the region included the 77,000 acre Hanford Reach National Monument fire, which threatened habitat for endangered pygmy rabbits and other wildlife. This year over 500,000 acres in both Washington and Oregon burned. Recent precipitation and the onset of autumn weather in mid-September has extinguished all but the Cascade Complex fire (current large fire incidents).

Satellite estimates of August sea-surface temperatures (SST) showed an anomalously warm band of water extending from northern California north to Vancouver Island (NOAA Pacific Fisheries Environmental Laboratory (PFEL)), a situation that was due in part to relatively weak upwelling winds this past summer.

Current indicators for Pacific climate

El Niño/Southern Oscillation (ENSO). Since May, there has been a persistent pattern of colder than normal eastern equatorial Pacific sea-surface temperatures (SSTs) (relative to the 1950-2007 mean), where the correlation of SST and PNW climate is strongest. Current SSTs in this region (NINO 3.4) are -0.9°C. NOAA's criteria for declaring a La Niña event call for Nino3.4 SST anomalies in 3 consecutive months to average less than -0.5°C, and it is highly likely that such a declaration will be made this fall. Currently, the majority of ENSO forecast models suggest weak to moderate La Niña conditions through 2007 with few models suggesting ENSO-neutral conditions.

Pacific Decadal Oscillation (PDO). The PDO Index Value decreased, but remained small and positive in August with respect to the 1900-1993 mean. NOAA's Earth System Research Laboratory experimental Pacific SST forecasts suggest that the PDO pattern will likely trend in a negative direction, which is consistent with the expected continuation of weak-to-moderate intensity La Niña conditions through 2007.

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

The Climate Prediction Center's outlook for October-November-December (temperature | precipitation) is for a slightly increased probability of above normal temperatures for Oregon and the majority of Idaho, with an equal chance of above, below, or normal temperature conditions for Washington and northern Idaho. Precipitation probabilities for the period are for increased chances above normal precipitation over the entire region with a greater than 40% probability for Washington, Oregon, and Northern Idaho, and only a slightly increased probability for southern Idaho.

The PNW forecast for winter (Dec-Jan-Feb) temperature calls for equal chance conditions and above normal precipitation for for the region, except along the northern Oregon coast and western Washington where equal chance conditions are expected. 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.

Historically, La Niña conditions have favored cooler than average winter temperatures around western Washington and western Oregon. However, the combination of long-term warming trends with the La Nina influence supports the CPC forecast for “equal chances” for above, below, and average winter temperatures in the PNW region.

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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