Seasonal to Interannual Forecasts
September 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 1 October 2009 (posted October 1)
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" of weak El Niño conditions in the tropical Pacific that are expected to develop into a weak-to-moderate strength El Niño through the Fall with the likelihood of at least a moderate strength El Niño this Winter. The impacts of this warm ENSO on Oregon, Washington, and Idaho are expected to be seen this Fall.
The NOAA Climate Prediction Center October-November-December temperature forecast is for a greater than 33% chance of above normal temperatures in Oregon, Washington, and Idaho, and as such represents a continuation of the warmer than normal conditions observed this summer (see below). The increased probability of above normal temperature is also seen for the broader region of the western contiguous U.S. and major portions of Alaska. The precipitation forecast for the same period is for a greater than 33% chance of below normal precipitation in all but the easternmost portions of Washington and Oregon, with the probability exceeding 40% in the western half of Washington and Oregon.
Winter seasonal climate prediction is more skillful in years of significant ENSO episodes like this one. The temperature and precipitation forecasts are for the typical warm ENSO pattern of a milder, drier winter in the PNW.
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
The 30 days ending 28 September saw PNW temperatures above the 1971-2000 mean and, with the exception of some coastal regions of California, warmer than normal temperatures over the entire western contiguous U.S. (analysis; WRCC). For the PNW, temperature departures west of the Cascades were less than 4 °F (2 °C) above the mean, while temperatures over eastern Oregon and most of Idaho were in excess of 4 °F (2 °C) above the mean. The last 30 days contributed to a 90 day mean temperature that was also above the long term mean over the entire PNW (analysis).
Precipitation averaged over the 30 days ending 28 September (total, percent of 1971-2000 normal) was characterized by below normal precipitation over Oregon, Idaho, and southern and eastern Washington. The northwestern corner and Chelan County of Washington State received above normal precipitation. Taken over the last 90 days, the precipitation for the region was again largely below normal, with the largest percentage precipitation deficits observed over the Oregon Cascades, the Columbia Basin of Washington State, and southcentral Idaho (analysis). The absence of rain in Washington State led the Governor to request the federal government to designate Chelan, Douglas, Ferry, Grant, Lincoln, and Okanogan Counties as farm disaster areas (Governor's statement, drought analysis, map of counties).
On 29 September there was one "large [wildland] fire" in the Oregon Wallowas and two in the southern Oregon Cascades (up-to-date analysis, definition; NICC). The occurrence and size of wildland fires can vary on a daily basis.
August Oregon and Washington coastal sea surface temperatures were generally warmer than the 1985-97 mean, with the exception of cold water at the mouth of the Columbia and along the north Oregon coast (analysis, PFEL). Temperatures farther offshore were above the 1982-96 mean to the west and south, and below the mean in the Gulf of Alaska (analysis; ESRL).
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, and the May through August monthly values have been 0.28, 0.57, 0.88, and 0.85°C, respectively (1971-2000 mean). The average anomaly over June, July, and August is 0.76°C.
NOAA declared an "El Niño Advisory" on 9 July, and the 10 September diagnostic discussion stated that "current conditions, trends, and model forecasts favor the continued development of a weak-to-moderate strength El Niño into the Northern Hemisphere Fall 2009, with the likelihood of at least a moderate strength El Niño during the Winter of 2009-10."
The ENSO model forecasts that NOAA evaluates are summarized by the International Research Institute for Climate and Society. ENSO forecasts are made with two kinds of models: mechanistic models, which solve equations for ocean and atmosphere motions and radiative processes to forecast the future from present conditions; and statistical models, where the average past behavior of the system is characterized by regression coefficients, and the regression coefficients are applied to the present conditions to forecast the future. Agreement of the forecasts from these two types of models increases our confidence in the forecast.
All twenty-two mechanistic and statistical models that were initialized with August ocean and atmosphere conditions predict October-November-December mean Niño 3.4 SST anomalies that exceed the NOAA criterion for a weak "El Niño" (0.5°C), and the mean prediction of 1.2°C for this season is categorized by NOAA as a moderate El Niño. The El Niño is forecast to maintain its strength in January-February-March (mean prediction of 1.1°C from seventeen models) and end by April-May-June of 2010.
Pacific Decadal Oscillation (PDO). The past two 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. The August PDO value, in contrast, was small and positive (0.09 standard deviations; historical digital values). [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.]
The development of "El Niño" (warm ENSO) in the equatorial Pacific is consistent with the onset of the warm phase of the PDO in the coming 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 for the forecast period of February through June 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)