Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

December 2004 archive copy

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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. 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 2004 -Winter 2005
Updated December 10, 2004
The climate outlook is reviewed monthly and updated as needed.

Current ocean conditions

A variety of El Niño/Southern Oscillation (ENSO) forecast models continue to predict a weak warm phase of ENSO for now through the end of winter 2005. Recent observations support these forecasts. Sea surface temperatures in the central and western tropical Pacific have been mostly warmer than average since May 2004 and, after some delay, have spread eastward almost to the coast of South America, completing a previously missing piece of the usual El Nino pattern.

Seasonal to interannual forecasts of the state of the Pacific Decadal Oscillation (PDO) are an emerging science. A major source of uncertainty in developing PDO forecasts is our lack of understanding of what causes the observed multi-year persistence in the PDO and, more importantly, what triggers PDO regime shifts. However, the relative persistence of PDO phases over the 20th century and new evidence pointing to a statistical relationship with the state of ENSO provides a reasonable basis for providing seasonal projections of the PDO state.

The PDO index for sea surface temperatures in the north Pacific has been in a moderate warm phase since August 2002. Given this and the forecast for a moderate El Niño this winter, the CIG projects continuation of a weak to moderate warm phase PDO for winter 2004-05. There are presently no indications that a PDO phase shift will take place in the next year.

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What will it mean for the PNW in coming months?

Because of the high confidence that we're likely to continue experiencing a mild-to-modest intensity warm phase ENSO event for the remainder of this fall and winter, NOAA predicts that the higher than average odds for anomalously warm and dry fall and winter weather in the PNW (CPC precipitation, temperature outlooks). Conversely, NOAA predicts lower than average odds for a cool and wet fall and winter in the PNW. An additional factor informing the current one year lead time climate forecast for the U.S. is the clear trend to warmer fall and winter temperatures in the western part of the country (e.g., 8 of the last 10 winters have been at least 1 ° F warmer than "normal" in Washington state).

Like the ENSO forecast, the PDO forecast also affects the odds for certain climatic conditions in the PNW. A warm phase PDO typically increases the odds for warmer (by about 1°F on average) and drier (by about -10% on average) winter conditions in the PNW. It should be noted, however, that other factors coming into play in the 1990s may be affecting this relationship. Recent observations highlight an increased importance for a second major pattern of North Pacific sea surface temperature variations, the Victoria Pattern. More research is needed to determine if and how the Victoria Pattern affects PNW climate. For more information on the Victoria Pattern, please see Bond et al. 2003 and McKinnel 2003.

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In summary, expectations for continued mild warm-phase ENSO conditions, along with observed temperature trends, combine to support a forecast that has increased odds for mild temperatures and less than average precipitation for the PNW region.

It is critical to note that these climate forecasts indicate relatively subtle shifts in the odds for warmer/cooler temperatures and more/less precipitation in the PNW rather than a deterministic (or exact) climate prediction for the next 2 seasons. Simply stated, expectations for continued El Niño conditions in the tropics and trends for warmer winter PNW temperatures yield a climate outlook for the PNW that has higher than average odds for a warm and dry fall and winter, and lower than average (but not zero!) odds for a cool and wet fall and winter.

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