Seasonal to Interannual Forecasts
November 2009 - 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. 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 19 November 2009 (posted November 26)
The climate outlook is reviewed monthly and updated as needed.
The NOAA El Niño Southern Oscillation (ENSO) alert system status is that of an "El Niño Advisory," indicating that tropical Pacific El Niño conditions exist and are expected to continue (5 November declaration). A review of tropical Pacific observations and ENSO forecasts is found below.
ENSO typically affects the climate of Oregon, Washington, and Idaho during the Fall through Spring. Guidance on what to expect in the coming months is also available through seasonal forecasts produced by the NOAA Climate Prediction Center (CPC). The December-January-February CPC temperature forecast is for a greater than 33% chance of above normal temperatures across the Pacific Northwest (PNW), with probabilities of above normal temperatures exceeding 40% in Idaho and the eastern portions of Washington and Oregon. The CPC precipitation forecast for the same period is for an equal chance of below normal, normal, or above normal precipitation in the southern latitudes of Oregon and Idaho. The northern areas of these states and Washington state are forecast to have a greater than 30% chance of below normal precipitation. The probability of below normal precipitation exceeds 40% in western Washington and the Idaho Panhandle.
Seasonal climate prediction is more skillful in years of significant ENSO episodes like this one, and forecasts initialized in the Fall can have skill into the Spring. The CPC March-April-May temperature and precipitation forecasts suggests an increased chance of the typical, warm-ENSO pattern of milder, drier than normal conditions for the PNW for the Spring.
The seasonal forecasts should be interpreted as the tilting of odds towards general categories of conditions, and should not be viewed as a guarantee that the specified conditions will be realized. The precipitation forecasts only have skill during periods of significant warm or cold ENSO conditions.
For More Information
Precipitation totals for the 30 days ending 17 November (total, departure from 1971-2000 normal, percent of 1971-2000 normal; WRCC) are characterized by exceptionally heavy seasonal rains west of the Cascades in Oregon and Washington, with precipitation in excess of 50% above normal over much of western Washington. As of 19 November, the Skokomish River near Potlatch (south and east of Olympic National Park) is above flood stage, and numerous rivers in western Washington and northwest Oregon are in excess of 90% "Bankful" (up-to-date observations and forecasts, 19 November observations and legend; NWRFC). River conditions change by the hour during heavy precipitation episodes.
The analyses also document below normal precipitation in much of the remainder of the Pacific Northwest. The precipitation deficit to the east of the Cascades acts to reinforce the drought conditions that were first identified in September (September Climate Outlook; 17 November analysis, Drought Monitor). PNW temperatures for the 30 days ending 17 November have been near normal (temperature departures).
October coastal sea surface temperatures were generally slightly cooler than the 1985-97 mean along Washington, warmer than normal along Oregon, and cooler than -1°C south to the California Bight (34°N) (analysis, PFEL). Temperature anomalies farther offshore were small in magnitude, and generally below the 1971-2000 mean (analysis, IRI).
El Niño/Southern Oscillation (ENSO).The NOAA El Niño/Southern Oscillation (ENSO) Alert System employs the average sea surface temperature (SST) anomaly over 5°N-5°S, 170-120°W in the equatorial Pacific, in what is called the "Niño 3.4" region, as a key indicator of tropical Pacific climate. The Nino 3.4 SST anomaly became positive in May, July through September monthly anomalies were near 0.8°C, and in October the temperature increased throughout the month for a monthly mean of 0.99°C (with respect to a 1971-2000 climatology).
The August-September-October mean Niño 3.4 value is 0.88°C, which is interpreted by NOAA as a weak El Niño. NOAA employs mechanistic and statistical models to forecast how ENSO will evolve over the next several seasons. Mechanistic models solve equations for ocean and atmosphere motions, precipitation, cloud and radiative processes to forecast the future from present conditions. Statistical models, on the otherhand, are constructed from observations of past climate, and apply regression coefficients to present climate conditions to forecast the future. Agreement of the forecasts from these two types of models increases our confidence in the forecast.
The ENSO model forecasts are summarized by the International Research Institute for Climate and Society. Twelve of the twenty-two mechanistic and statistical models that were initialized with October ocean and atmosphere conditions predict December-January-February mean Niño 3.4 SST anomalies in the range of 1.0-1.5 °C, which NOAA identifies as moderate "El Niño." The remainder of the forecasts for this period are evenly split between forecasts of weak and strong El Niño. Twenty of the models also produced March-April-May forecasts and half of the models predict that El Niño will be characterized as weak by this season. All of the models predict that Niño 3.4 anomalies will further diminish in June-July-August 2010.
Pacific Decadal Oscillation (PDO). Much of the past 2.5 years have seen strong negative PDO values relative to the 1900-93 mean, which was manifested by colder than normal temperatures along the North American coast. This run seems to have ended in August of this year, and the PDO has exhibited small positive values in each of the last 3 months (including October) (historical digital values in units of standard deviations). [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.]
The existence of the present weak "El Niño" (warm ENSO) in the equatorial Pacific and its forecast strengthening and diminution in the coming 8 months is consistent with the further development of a PDO warm phase during the same months.
NOAA employs both statistical and mechanistic models to forecast the PDO and coastal ocean conditions. The statistical linear inverse model forecast is for the PDO to be weak and positive through the forecast period (June-July-August 2010). The coupled forecast system, a mechanistic ocean-atmosphere model, predicts weak, warm SST anomalies along the Washington and Oregon coasts and the Gulf of Alaska through July 2010, and the forecast has no useful skill along the California coast during the same months (forecast).
For More Information
- Current conditions: Weekly NRCS drought monitor/snowpack update reports
- Read the latest expert analysis of the current state of ENSO from NOAA's Climate Prediction Center
- European Centre for Medium-Range Weather Forecasts ENSO forecast
- The International Research Institute for Climate and Society ENSO QuickLook
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 and Society
- Monitoring El Niño/La Niña (from NOAA’s Climate Prediction Center)
Predictions of Tropical Pacific and North Pacific Conditions
- Seasonal Niño3.4 sea surface temperature anomaly plume forecasts (from the European Center for Medium-Range Weather Forecasts)
- Statistical Probabilistic ENSO Predictions (from the International Research Institute for Climate and Society)
- Sea surface temperature forecasts (from the International Research Institute for Climate and Society)
- Experimental PDO and Pacific Seasonal Forecasts (from NOAA's Earth System Research Laboratory)
The Current State of the Globe
- Climate diagnostics bulletin (from NOAA’s Climate Prediction Center)
- The North Atlantic Oscillation (NAO) (from NOAA’s Climate Prediction Center)
- 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)
- State of the Climate report (from the National Climatic Data Center)
- Northern Hemisphere snow report (from the National Climatic Data Center)
- 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.
- Large fire incidents (from the National Interagency Fire Center)
- 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
- Temperature and precipitation maps (from the Western Regional Climate Center)
- Temperature and precipitation maps (from the High Plains Regional Climate Center)
- Western Washington water and snowpack (from Seattle City Light)
- Seattle water supply conditions and outlook (from Seattle Public Utilities)
- Wildland fires (from the Northwest Interagency Coordination Center)
- Coastal conditions (from NOAA’s CoastWatch)
- monthly snowpack maps for the region (from the National Resource Conservation Service)
State Climatologist Offices
- Drought in central and southwest Asia (from the International Research Institute for Climate and Society)