Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE COPY MAY 2006

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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?

Spring 2006
Updated May 20, 2006

The climate outlook is reviewed after the 10th of each month and updated as needed.

Current indicators for Pacific climate:

El Niño/Southern Oscillation (ENSO). The short-lived almost-La Niña conditions have ended and the Pacific Ocean has returned to near-neutral conditions. Forecasts of tropical Pacific sea surface temperature (SST) suggest that near-neutral conditions are likely to prevail during the next year, with the International Research Institute for Climate Prediction suggesting the following probabilities for fall 2006: a 60% chance of ENSO neutral conditions, a 30% chance of an El Niño, and only a 10% chance of a La Niña.

Recent history of forecasts. In the fall of 2005, most forecasts of ENSO called for continued near-neutral conditions. However, some conditions indicative of a cool phase of ENSO (La Niña) developed during the winter. Models underestimated both the rapidity of development of cool conditions and the rapidity of their recent demise.

Pacific Decadal Oscillation (PDO). North Pacific SST anomalies trended towards the negative PDO pattern in September, October, and November, but changed to a near-neutral PDO state in December. January and February had positive PDO index values (+1 and +0.66, respectively). These relatively large changes in North Pacific SSTs were directly related to a persistently positive Pacific North America pattern of atmospheric circulation in the month of December and again in the first 2 weeks of February (view the PNA index). Persistently negative PNA index values from mid-February to mid-March likely caused the decline of the PDO in March to 0.05. Given the state of the tropics and the expected continuation of ENSO-neutral to weak La Niña characteristics, it is likely that the PDO will return to near-zero values for spring (see note on PDO forecasting).

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What will it mean for the PNW in coming months?

The seasonal outlooks for spring and summer suggest a tilt in the odds toward warmer, drier conditions for most of the Northwest. With the disappearance of quasi-La Niña conditions, the likelihood of above-average precipitation dropped.

Brief hydrologic outlook. As of May 19, snowpack in most of the Northwest is near to above normal for this time of year. UW's west-wide hydrologic forecast suggests April-September flows on the Columbia River at The Dalles will be 5-10% above average, mainly as a result of wetter and slightly colder than average conditions in the southern and eastern portions of the Snake River basin.

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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