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Archive Copy - November 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?

Mid-Fall 2007
Updated November 13, 2007

The climate outlook is reviewed monthly and updated as needed.

Fires to the south of us, heat wave and drought in the eastern part of the country, and the Pacific Northwest (PNW; Oregon, Washington, and Idaho) has experienced a near normal Fall season with respect to the 1971-2000 climatology. The seasonal precipitation has returned (August-September-October amounts (in./month)), with amounts above normal in Oregon and southern Idaho, and below normal in Washington and northern Idaho (percentages of climatological precipitation). Larger fluctuations have been experienced in other parts of the country, with heavy rainfall in the northern plains and drought in the southeast in the same period (figure, note the different shading scale) [Source: High Plains Regional Climate Center (HPRCC)]. The multi-year drought conditions in Idaho and eastern Oregon continue (U.S. Drought Monitor).

Seaonally cooler temperatures returned to the Pacfic Northwest (map), which were cooler than normal but, as with the precipitation, represent smaller deviations from climatology than those experienced in other parts of the country (figure; source HPRCC). The temperature and precipitation anomalies in the eastern U.S. are consistent with an observed poleward shift of the storm track during the period (not shown).

Sea surface temperatures for the coastal regions, analyzed by the NOAA Pacific Fisheries Environmental Laboratory, indicated warm anomalies as large as 3C along the Oregon and Washington coast in August, which diminished appreciably in September, and are now slightly below normal (above normal) on the Washington (Oregon) coast (figure). On broader scales, below normal ocean temperatures are seen in the Gulf of Alaska (UW), and colder than normal temperatures (cold ENSO) are seen in the central and eastern equatorial Pacific. The colder ocean temperatures in the Gulf of Alaska have been present throughout this year and became significantly colder in October. The equatorial cold ENSO conditions first appeared in March, and intensified in September and October.

Current indicators for Pacific climate

El Niño/Southern Oscillation (ENSO). Cold ENSO conditions have developed significantly in the last 3 months with surface temperatures over 5N-5S, 170-120W averaging -0.48, -0.87, and -1.40C in August, September, and October, respectively. Model forecasts are for temperatures in the range of -0.5 to -1.7C through the December-January-February season, which make this a weak to moderate cold ENSO, respectively. It is likely that conditions will satisfy NOAA's La Niña definition in November. The model forecasts are for the cold conditions of winter to return to normal by early Summer (May-June-July).

Pacific Decadal Oscillation (PDO). The PDO Index values in August, September, and October were 0.50, -0.36, -1.45, respectively (with respect to a 1900-93 climatology), consistent with the changes in northeastern Pacific temperatures described above (digital values). The ongoing cold ENSO can be expected to contribute to continued negative PDO values (cold along the coast). NOAA's Earth System Research Laboratory experimental Pacific SST forecasts suggest that the PDO pattern will likely remain weakly negative through the forecast period (through October 2008).

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

The Climate Prediction Center's outlook for November-December-January (temperature | precipitation) is for a 33-40% chance of above normal temperatures for southern Idaho, with an equal chance of above, below, or normal temperature conditions for the remainder of the PNW. Precipitation probabilities for the period are for an equal chance of below normal, normal, or above normal precipitation in western Washington and the northern Oregon coast, and at least a 33% chance of increased precipitation in western Washington, Idaho, and central and eastern Oregon. Probabilities of above normal precipitation exceed 40% in southeastern Oregon and 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. One should also remember last November's record precipitation in western Washington, which was the opposite of what was expected during the then warm ENSO conditions. 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 Niña 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

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