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Seasonal to Interannual Forecasts

Climate Outlook

August 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?

August 2009
Updated 24 August 2009 (posted August 24)

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," with statements that "an El Niño was present in July 2009" and "'is expected to strengthen and last through the Northern Hemisphere Winter 2009-2010." The impacts of this warm ENSO on the Oregon, Washington, and Idaho are expected to be seen beginning in the Fall months.

The NOAA Climate Prediction Center September-October-November temperature forecast is for a greater than 33% chance of above normal temperatures in western and central Oregon and western Washington, and as such represents a continuation of the warmer than normal conditions observed this summer (see below). The precipitation forecast for the same period is for a greater than 33% chance of below normal precipitation in Washington, Idaho, and central and eastern Oregon, with the chance exceeding 40% in southeast Washington, central Idaho, and eastern Oregon.

Winter seasonal climate prediction is more skillful in years of significant ENSO episodes, and the existence and forecast persistence of warm ENSO this year suggests the consideration of the December-January-February forecast products. 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.

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Recent Pacific Northwest Climate

The 30 days ending 18 August saw exceptionally warm temperatures in Washington, Oregon, and western Idaho (analysis, 1971-2000 mean; WRCC), with record warm daily-maximum temperatures met or set in Bellingham, Seattle, and Olympia on 29 July (96, 103, and 104°F, respectively; NCDC). Additional information on the daily temperature records during this heat wave are available from the Office of the Washington State Climatologist (documentation), and the weather blog written by Professor Cliff Mass discusses the meteorological conditions with a focus on Puget Sound / western Washington.

The unusual surface temperatures can be further documented in July-average statistics (UW). The warm departures over the PNW were part of a pattern of above normal temperatures along the west coast of North America, northern Mexico, and Texas; and below normal temperatures over central Canada and the eastern two-thirds of the contiguous United States. This temperature pattern was associated with a strengthening of the climatological upper-atmospheric ridge along the west coast (not shown). Record monthly-mean temperatues were experienced in cities in Alaska and Texas (warm); and Minnesota, Indiana, Wisconsin, and Illinois (cold; NCDC).

The last 30-days saw less than normal precipitation in the Columbia Basin, north central and south western Oregon, and southeast Idaho, while portions of eastern Oregon and central and northern Idaho experienced above normal precipitation (percentage of normal).

On 24 August there are three "large [wildland] fires" (up-to-date analysis, definition; NICC) on the eastern flank of the Washington Cascades. The fire potential remains high for the Okanagon region of Washington State.

July coastal sea surface temperatures are characterized by small-scale regions of below normal temperatures along Washington and Oregon, and above normal temperatures along California (analysis, 1985-97 mean; PFEL). Temperatures 2-5° longitude offshore are below normal, and temperatures farther offshore are above normal. (The larger-scale features are also present in the temperature analysis shown previously.)

Sources:

  • Western Regional Climate Center (WRCC)
  • National Climatic Data Center (NCDC)
  • Northwest Interagency Coordination Center (NICC)
  • Pacific Fisheries Environmental Laboratory (PFEL)

  • Recent and Projected Changes in Key Indicators for Pacific Climate

    El Niño/Southern Oscillation (ENSO). NOAA 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 in its "El Niño/Southern Oscillation (ENSO) Alert System." The Nino 3.4 SST anomaly became positive in May, and the May, June, and July values are 0.28, 0.57, and 0.88°C, respectively (1971-2000 mean). The average May-June-July anomaly is 0.58°C.

    NOAA declared an "El Niño Advisory" on 9 July, and the 6 August diagnostic discussion stated that "El Niño is expected to strengthen and last through the Northern Hemisphere Winter 2009-2010." The discussion also states that "current conditions 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 (3-month Niño-3.4 SST index of +1.0°C or greater) during the Northern Hemisphere Winter 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. Twenty-three mechanistic and statistical models that were initialized with July ocean and atmosphere conditions, and twenty-two of the models forecast September-October-November mean Niño 3.4 SST anomalies greater than or equal to 0.5°C, the Oceanic Niño Index "El Niño condition" criterion. Twenty of twenty-one December-January-February forecasts met this criterion.

    Pacific Decadal Oscillation (PDO). The PDO has exhibited negative monthly values since September 2007 (digital values), with values in excess of -1 standard deviation from April through November of 2008 and from January through April of this year. [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] These large, negative PDO values were manifested along the North American coast as cold SST anomalies.

    May, June, and July 2009 have seen weaker negative PDO values (-0.88, -0.31, and -0.53, respectively). The July ocean temperatures are warmer than normal over almost all of the northeast and equatorial Pacific (analysis). Although the PDO captures temperature variability along the west coast, it is defined by the difference between the temperatures near the coast and those in the central north Pacific. The contrast in temperatures between those two regions can more readily be seen if the global-mean ocean temperature is removed (analysis, UW).

    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. The NOAA coupled forecast system (a mechanistic ocean-atmosphere model) predicts weak, warm SST anomalies along the British Columbia, Washington, and Oregon coasts through the forecast period of February-March-April 2010. The California coast is forecast to experience weak, cool anomalies through December-January-February, and warm anomalies in the Spring of 2010 (forecast).

    For More Information


    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 and North Pacific Conditions

    The Current State of the Globe

    Current and Predicted U.S. Conditions

    Pacific Northwest Conditions

    State Climatologist Offices

    Special Areas