Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE COPY - OCTOBER 2006
Special note: This outlook, prepared in October, was not posted at that time but is being made available in the Outlook 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. 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?

Early Fall 2006
Updated October 26, 2006

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

August and September were characterized by drier than normal conditions to the west of the Rockies (August, September), and warm (cool) temperatures departures from normal in the northern (southern) parts of the Pacific Northwest (August, September). The August and Septembertemperatures, averaged over the Pacific Northwest, are above normal and are a continuation of a pattern of warmer than normal late Summer - early Fall temperatures over the last two decades (NOAA).

Despite the October rains, most rivers in western Oregon and western Washington are experiencing very low to extremely low streamflows (moderate to extreme hydrological drought) compared to historic averages (USGS). Less severe, but below normal streamflows are seen throughout the rest of the Pacific Northwest. The rains and cooler temperatures have ended the "large incident" forest fires in the Pacific Northwest. The fair weather pattern has also induced stronger than average coastal upwelling for Oregon and Washington, and coastal ocean temperatures in August and September were generally 1 to 2° C below the long-term average from Central California to Vancouver Island (NOAA).

Current indicators for Pacific climate:

El Niño/Southern Oscillation (ENSO). The mean July-August-September sea surface temperaure in the central and eastern equatorial Pacific is 0.51C above normal, just crossing the NOAA definition of an El Niño episode. Fall is the time of the greatest skill in ENSO forecasts, and a simple linear model, capturing 79% of the variance, predicts a 23% amplification of the temperature departures by December-January-February, which will be a weak to moderate ENSO warm episode, followed by a diminution of anomalous conditions by March-April-May. Similar forecasts are provided with more sophisticated statistical and mechanistic models by the IRI and NOAA.

Pacific Decadal Oscillation (PDO). North Pacific SST anomalies trended towards the negative PDO pattern in September, October, and November 2005, but the PDO index was of small magnitude and positive sign in December 2005 through July 2006. Following an extended period with abnormally high sea level pressure across the North Pacific in July, August, and September, the PDO index for August and September dropped to -0.65 and -0.81, respectively. The expected continuation of weak-to-moderate intensity El Niño conditions through spring 2007 suggest that the PDO pattern will likely trend in a positive direction for the next few seasons (see note on PDO forecasting).

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What will it mean for the PNW in coming months?

The seasonal outlooks through spring 2007 suggest a tilt in the odds towards a continuation of warmer than average conditions throughout the region for the coming fall, winter, and spring seasons (based on NOAA/NCEP Forecasts from August 17). With expectations now pointing toward a weak-to-moderate intensity El Niño event for the next few seasons, seasonal outlooks through spring 2007 suggest a tilt in the odds towards an anomalously dry fall and winter for much of the region. Note that in the absence of strong El Niño or La Niña conditions, the forecast tools offer only marginal skill in predicting precipitation.

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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