Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

May 2005 archive

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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?

Spring 2005
Updated May 5, 2005
The climate outlook is reviewed monthly and updated as needed.

Current indicators for Pacific climate:

The warm anomalies in the central equatorial Pacific abated a few months ago, and the coastal waters of South America near the equator which normally warm up this time of year have warmed more than normal (see Figure 1). The majority of current forecasts call for either near average or slightly above average SSTs in the eastern tropical Pacific for the next few seasons.

click image to enlarge

Global map, Warm Phase PDO

Figure 1 Five Day Zonal Wind, SST, and 20° C Isotherm Depth Anomalies

For more information on the current ENSO state and forecast, see the forecast summaries provided by the NOAA Climate Prediction Center and the International Research Institute for Climate Prediction .

Seasonal to interannual forecasts for the state of the Pacific Decadal Oscillation (PDO) index (based on a pattern of North Pacific SSTs) 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 index and, more importantly, what triggers PDO regime shifts. However, a strong tendency for year-to-year persistence of the PDO index along with a well-established statistical relationship with the state of ENSO provides a means for making skillful 1-year projections of the PDO index.

Using that simple statistical method with the observed PDO index values from July 2003-June 2004, combined with a prediction that SSTs in the NINO3.4 region of the tropical Pacific would be in the range of +0.4°C to +1.2°C, yields a prediction for a July 2004-June 2005 PDO index value ranging from ~ +0.5 to +1. Observed PDO index values for July 2004 to January 2005 are: 0.44, 0.85, 0.75, -0.11, -0.63, -0.17, 0.44 and 0.81 (averaging out to ~0.30). Note that the average value for the Nino34 index from July 2003-February 2004 is ~0.70, about in the middle of the range predicted last fall. (For more information on this one-year lead-time PDO forecast method, see Newman, M., G. P. Compo, and M. A. Alexander, 2003. ENSO-forced variability of the Pacific Decadal Oscillation, Journal of Climate 16: 3853-3857)

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What will it mean for the PNW in coming months?

The latest seasonal forecasts from NOAA's Climate Prediction Center call for a slight tilt in the odds favoring a warm spring and summer for the western parts of Oregon and Washington, and below-average summer precipitation. In short, odds are poor that the drought that developed (or in some areas continued) last winter will be erased by continued heavy precipitation. For an illustration of how the precipitation in the winter of 2005 stacked up, see these tables for Washington and Oregon.

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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