Seasonal to Interannual Forecasts
ARCHIVE COPY - September 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?
Early Fall 2006
Updated September 13, 2006 (posted 9.17.06)
The climate outlook is reviewed after the 10th of each month and updated as needed.
A look back at summer:
Seattle-Tacoma International Airport recorded 2.12 inches of rain in the months of June, July and August, but only 0.08 inch of that total has came after July 1. It was the second-driest July-August on record at Sea-Tac – in 1967, only 0.03 inch of rain was recorded for those two months. Bellingham had its driest July and August on record, with just 0.17 inch of rain, and Quileute, on the Pacific coast, also had a record-dry July and August, with just 1.21 inches of rain.
It was the third-driest July and August at Chelan, the fifth-driest in Yakima and the sixth-driest in Hoquiam. Even the rainy Olympic Peninsula has been severely affected. The sharply drier July and August held Quileute's total summer rainfall to just less than 4.5 inches, far below the normal of 8 inches.
July-August temperatures for the PNW (except the coastal areas of Washington and Oregon) were also well above average (the same was true for the rest of the continental U.S. except for southern Colorado, New Mexico, and southeastern Arizona).
NOAA's National Climatic Data Center reported that PNW temperatures (OR-WA-ID) for May-July 2006 were the warmest on record (June-July-August was 3rd warmest for the PNW on record), and the first seven months of 2006 was the warmest January-July of any year in the U.S. since records began in 1895 (Climate of July 2006 in historical perspective).
You can plot your own time series of monthly and seasonally averaged PNW temperature and precipitation at this NCDC link.
PNW resources affected by climate have experienced a number of notable extremes in recent months. As a consequence of the extended hot and dry summer and early snowmelt, most rivers in western Oregon and western Washington are experiencing very low to extremely low streamflows compared to historic averages for this time of year (as of this writing; see the USGS Streamflow information on Drought map). Large forest fires continue to burn throughout the PNW (9/17 note: cooler conditions and rain falling after 9/13 have significantly reduced the spread of these fires). The unusually fair weather pattern has also included stronger than average coastal upwelling for Oregon and Washington, and coastal ocean temperatures in August were generally 1 to 2° C below the long-term average from extreme Northern California to Vancouver Island (see NOAA's coastwatch page).
Current indicators for Pacific climate:
El Niño/Southern Oscillation (ENSO). Weak El Niño conditions have developed in the tropical Pacific, and they are likely to continue (and possibly intensify) into early 2007 (see NOAA's expert discussion for more details). Observed ocean temperature anomalies in the equatorial Pacific exceeded NOAA's El Niño criteria in the 4-week period from mid-August through mid-September 2006. Since early July weaker-than-average low-level equatorial easterly winds have been observed across most of the equatorial Pacific. In August the Southern Oscillation Index (SOI) was negative for the fourth consecutive month. Collectively, these oceanic and atmospheric anomalies are consistent with developing warm episode (El Niño) conditions in the tropical Pacific.
Most ENSO forecasts are now pointing to a weak-to-moderate intensity El Niño event for the coming fall and winter. Over the past several months most of the statistical and coupled model forecasts have trended towards warmer conditions in the tropical Pacific through the Northern Hemisphere winter (see the IRI Forecast Summary). The recent conditions and trends in the tropical atmosphere and ocean support these predictions.
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 and August, the PDO index for August dropped to -0.65. 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 ) .
For More Information
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
- Water Resources Forecasts (streamflow and other hydrologic conditions)
- Salmon survival forecast
- Forecast of extreme weather events
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
- Real-time data from moored ocean buoys (from NOAA’s TAO array)
- ENSO diagnostic discussion (from NOAA’s Climate Prediction Center)
- Weekly ENSO update (from NOAA’s Climate Prediction Center)
- ENSO Quick Look (from the International Research Institute for Climate Prediction)
- Monitoring El Niño/La Niña (from NOAA’s Climate Prediction Center)
Predictions of Tropical Pacific Conditions
- Seasonal Niño3 sea surface temperature anomaly plume forecasts (from the European Center for Medium-Range Weather Forecasts)
- ENSO forecast forum (from NOAA’s Climate Prediction Center)
- Statistical Probabilistic ENSO Predictions (from the International Research Institute for Climate Prediction)
- Sea surface temperature forecasts (from the International Research Institute for Climate Prediction)
The Current State of the Globe
- Climate diagnostics bulletin (from NOAA’s Climate Prediction Center)
- Monitoring climate in the Extratropics and Tropics (from NOAA’s Climate Prediction Center)
- The North Atlantic Oscillation (NAO) (from NOAA’s Climate Prediction Center)
- Monthly climate information digest (from the International Research Institute for Climate Prediction)
- Accumulated daily precipitation time series graphs (from NOAA’s Climate Prediction Center)
- Daily global and regional precipitation analysis (from NOAA’s Climate Prediction Center)
- Index of Climate Prediction Center’s climate monitoring activities and data
Current and Predicted U.S. Conditions
- Monthly to seasonal climate outlooks (from NOAA’s Climate Prediction Center)
- Northern Hemisphere snow report (updated monthly by NOAA/NCEP)
- Spring and summer streamflow forecasts (from the USDA Natural Resources Conservation Service)
- Drought in the US
- Water supply forecasts and snowpack conditions for the Western U.S.
- Experimental seasonal fire risk forecasts (from the U.S. Forest Service)
- Western U.S. climate conditions and forecasts (from the Western Regional Climate Center)
Pacific Northwest Conditions
- Western Washington water and snowpack (from Seattle City Light)
- Seattle water supply conditions and outlook (from Seattle Public Utilities)
- Coastal conditions (from NOAA’s CoastWatch)
- Data on PNW snowpack (from the Western Regional Climate Center)