Seasonal to Interannual Forecasts
ARCHIVE COPY - APRIL 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?
Updated April 17, 2006
The climate outlook is reviewed after the 10th of each month and updated as needed.
Following an exceptionally warm January, February and March were characterized by near normal temperatures for the Northwest, and March precipitation contributed to wetter than normal conditions (90th percentile) for the January through March total. The April 17th SNOTEL observations indicate normal to 50% above normal snow pack over much of the Northwest with the exception of 50% below normal snowpack in the northern Coast Range of Oregon. In general the prospects for abundant spring and summer snow melt and river runoff are very good for the region.
Current indicators for Pacific climate:
El Niño/Southern Oscillation (ENSO). Cooler than average ocean temperatures in the tropical Pacific, along with stronger than average easterly trade winds, persistently wet conditions over Indonesia, the southwest Pacific, and Hawaii, and dry weather over the central equatorial Pacific are all characteristic of La Niña conditions. Based on NOAA's criteria for ENSO events, recent measures reflect conditions that are only modestly greater than the La Niña threshold (see NOAA press release). Most forecast models suggest that tropical climate will continue to have weak La Niña characteristics for the spring.
What happened to last fall's ENSO-neutral forecast? ENSO forecasts from last fall mostly called for near-neutral ENSO conditions, with a bias for slightly warmer than normal equatorial sea surface temperatures (SSTs). By November the forecasts were essentially equally split between slightly warmer and slightly cooler than average equatorial SST anomalies. Starting with December the forecasts caught up with the observations, and the forecasts are now for cooler than average conditions through spring (review the 2005-2006 ENSO forecast progression). There is now considerable spread between the most recent ENSO forecasts, with a general tendency for the forecasts to show a gradual weakening of the current cold SST anomalies in the tropical Pacific. By mid-summer, some forecasts indicate relatively weak positive SST anomalies in the equatorial Pacific. On average the forecasts suggest near-normal ENSO conditions by summer and into fall.
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?
Given the relatively weak intensity of the current La Niña, La Niña is expected to have a modest influence on PNW climate for the next few months. La Niña events increase the odds for cooler and wetter spring weather in the Pacific Northwest. NOAA's seasonal outlooks show odds that slightly favor above average temperature and "equal chances" of above, near, or below average precipitation this spring and early summer.
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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)