Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE - SEPTEMBER 2010

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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?

September 2010
Updated 20 September 2010 (posted 21 September)

The climate outlook is reviewed monthly and updated as needed.

"La Niña [cold ENSO] is expected to last through at least the Northern Hemisphere winter 2010-11" (9 September NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion). The forecasts of the eventual strength of the episode exhibit considerable range, from moderate to strong, and many of the models suggest that the episode will peak during October through January, slightly earlier than the typical ENSO episode. The analysis of historical Pacific Northwest ENSO variability suggests that the region will experience cooler and wetter than normal conditions in the coming months. A review of tropical Pacific observations and more recent ENSO forecasts is found below.

The NOAA Climate Prediction Center (CPC) forecast for October-November-December (OND) seasonal mean precipitation is for a greater than 33 percent chance of above normal precipitation throughout the Pacific Northwest, western Montana, northwest Wyoming, far northern Nevada, and northern California. Chances of above normal precipitation exceed 40% in north and central Idaho, all of Oregon with the exception of the southeast corner, and all of Washington. The chances of above normal precipitation exceed 50% in western Washington and northwest Oregon. The prediction of increased chances of above normal precipitation is consistent with storms bringing heavy precipitation amounts and significant flooding to western Washington and northwest Oregon.

The OND seasonal mean temperature forecast is for a greater than 33% chance of below normal temperatures to the west of the Oregon and Washington Cascades, with the chances of the same exceeding 40% in the coastal areas of the two states. The remainder of the PNW is forecast to have an equal chance of below, near, and above normal temperatures.

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. In general, seasonal precipitation forecasts only have skill during periods of significant ENSO variability like the present (CPC tools discussion).

For More Information

Recent Pacific Northwest Climate

The Pacific Northwest, Montana, western Wyoming, northern Utah, northern Nevada, and coastal, central, and northern California experienced below normal temperatures during the 30 days ending 19 September (1971-2000 mean, WRCC). The largest cold temperature departures in the PNW, in the range -2 to -4 °F ( -1 to -2 °C) and colder, were observed in smaller regions inland. The pattern of unseasonably cool temperatures in the region began in mid-March (1 April through 19 September mean; temperature timeseries for Lewiston, other cities, NCEP), and was interrupted by a period of above normal temperatures inland from mid-July through early August (24 July through 22 August mean).

The 30-day accumulated precipitation ending 19 September saw above average precipitation along the Washington coast, Puget Sound, Astoria and Portland Oregon, and near normal precipitation throughout the rest of the region (precipitation totals, departures, percent of 1971-2000 normal). Daily precipitation timeseries for selected cities provide additional information.

The Northwest Interagency Coordination Center (NWCC) maps the locations of "large wildland fires" (timber > 100 acres, grassland > 300 acres; 100 acres = 0.16 square miles) for Oregon and Washington, and the 17 September analysis (today's analysis) documented two fires in central eastern Oregon. Inciweb chronicles fires in Idaho, Oregon, and Washington and, on 20 September, Idaho had 11 fires greater than 100 acres in size (today's analysis for Oregon, Washington, and Idaho). The 14 September Drought Monitor identifies drought in south central Oregon and southeast Idaho, and it is little changed from last month.

August coastal sea surface temperatures (SSTs) continued the colder than normal pattern that has been observed since April of this year. SST departures were at least 1 °C colder than the 1985-97 mean from Vancouver Island to 30°N (Baja California), with larger magnitude temperature departures observed at the western end of the Straight of Juan de Fuca, the central and southern Oregon coast, and for several regions along the California coast. The mean northeast Pacific SST for the 30 days ending 18 September depicts the colder than normal SSTs extending 5° longitude offshore along the Washington coast, with the negative departures extending southwest to Hawaii, and eastward from this line to the coast (1982-96 mean, ESRL). Warm SST departures, in excess of 1°C, are observed between 25 and 45°N from Japan to the Gulf of Alaska.

Sources:

  • Western Regional Climate Center (WRCC)
  • National Centers for Environmental Prediction (NCEP)
  • Northwest Interagency Coordination Center (NWCC)
  • Incident Information System (InciWeb)
  • Drought Monitor
  • Pacific Fisheries Environmental Laboratory (PFEL)
  • Earth System Research Laboratory (ESRL)

  • Recent and Projected Changes in Key Indicators for Pacific Climate

    El Niño/Southern Oscillation (ENSO). The 9 September NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion summarized that "La Niña [cold ENSO] is expected to last through at least the Northern Hemisphere winter 2010-11." The SST departure from 1971-2000 averaged over 5°N-5°S, 170-120°W in the equatorial Pacific, in what is called the "Niño 3.4" region, is employed as a key indicator of ENSO variability. The ongoing cold ENSO, as measured by Nino 3.4 SST departures, intensified slightly from July (-0.99 °C) to August (-1.18 °C). The mean Nino 3.4 SST departure for June-July-August was -0.90 °C. The 3-month mean captures the seasonal evolution of ENSO conditions and it is used in the NOAA discussions to characterize the strength of the ENSO episode.

    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, and precipitation 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 3-month mean Nino 3.4 SST forecast from twenty-two ENSO models initialized with ocean and atmosphere data through August are summarized by the International Research Institute for Climate and Society. Twenty of the models forecast mean October-November-December (OND) Nino 3.4 SST anomalies in excess of -1.0 °C (moderate), twelve of the forecasts are for Nino 3.4 < -1.5 °C (strong), and the mean forecast is -1.6 °C. There is considerable spread in the SST predictions throughout the forecast period. The mean forecast Nino 3.4 for January-February-March and April-May-June 2011 are -1.2 and -0.5 °C, respectively.

    Pacific Decadal Oscillation (PDO). The continued cold SST departures along the west coast of North America and the intensification of warm departures in the central north Pacific, described above, contributed to a drop in the PDO value from -1.05 to -1.27 standard deviations from July to August (1900-90 reference period, PDO values). [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] August is the third consecutive month of negative PDO values following positive PDO values that were observed last winter and spring. ENSO variabilty is one of the mechanisms that can produce changes in the PDO, and the present cold ENSO can be expected to contribute to negative PDO values in the coming seasons.

    NOAA employs both statistical and mechanistic models to forecast the PDO and coastal ocean conditions. The statistical linear inverse model forecasts the PDO to be negative and of diminishing magnitude through the end of the forecast period in summer 2011. The NCEP coupled forecast system (a mechanistic ocean-atmosphere model) prediction issued on 20 September is for a continuation of the present pattern of cold SST anomalies along the eastern boundary north of 40°N (Cape Mendocino in California) and warm anomalies in the central north Pacific through March-April-May 2011 (20 September forecast, more recent forecasts). The recent model forecasts for next winter and spring have been judged to not be skillful for the central and southern California coast.

    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