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Seasonal to Interannual Forecasts

Climate Outlook

December 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?

December 2009
Updated 21 December 2009 (posted December 30)

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" that tropical Pacific El Niño conditions exist and are expected to continue. The 10 December ENSO diagnostic discussion characterized the conditions as a moderate El Niño which would persist through March-April-May 2010. A review of tropical Pacific observations and more recent 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 from seasonal forecasts produced by the NOAA Climate Prediction Center (CPC). The January-February-March CPC temperature forecast is for a greater than 50% chance of above normal temperatures in northern Idaho and eastern Washington; a greater than a 40% chance of the same in southern Idaho, central and western Washington, and northern and southeast Oregon; and a greater than a 33% chance of above normal temperatures in southwest Oregon. The CPC precipitation forecast for the same period is for a greater than 40% chance of below normal precipitation in northern Idaho, and northcentral and northeastern Washington; a greater than 33% chance of the same in central Idaho, the Olympic Peninsula and southern portions of Washington, and northern Oregon; and an equal chance of below normal, normal, or above normal precipitation in the southern latitudes of Oregon and Idaho. The temperature and precipitation forecasts for the PNW and the continental U.S. are consistent with the expectation that ENSO will be the dominant form of climate variability in the coming months (Observed typical November through April ENSO-related temperature and precipitation anomalies (UW).)

Seasonal climate prediction is more skillful in years of significant ENSO episodes like this one, and forecasts initialized in the Winter can have skill into the Spring. The CPC April-May-June temperature and precipitation forecasts suggests an increased probability of milder temperatures in the PNW, which is consistent with warm ENSO. Aside from PNW temperatures, the Spring forecast indicates that ENSO will have much less influence on U.S. climate during this season.

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

Recent Pacific Northwest Climate

The 30 days ending 20 December were drier and cooler than the 1971-2000 mean (precipitation total, departure, percent normal; temperature departure; WRCC). The precipitation amounts were 25-70% of normal over the region with the exception of slightly above-normal precipitation in southwest Idaho. The temperature was 2-4°F (1-2°C) below normal along the coastal portions of Oregon and southern Washington, and over much of the Columbia Basin to the east of the Cascades. The cooler than normal temperatures in the region have followed and coincided with cool temperature departures over much of the mountain and plains states during the last several months (60-day average, 90-day average).

The less than normal precipitation brought a welcome end to the flooding to the west of the Cascades (NWRFC), and reinforced the existing drought conditions to the east of the Cascades (drought monitor). The below normal precipitation also contributed to below normal snow water content (SWC) across the Pacific Northwest, where values are 50-97% of normal over the Columbia Basin (analysis, NRCS). A notable exception to the low SWC values is Hurricane Ridge in Olympic National Park, which has 43% higher SWC than normal for this time of the year.

November coastal sea surface temperatures were slightly warmer than the 1985-97 mean along Vancover Island and Washington; near normal along Oregon; in excess of 1°C above normal between Capes Blanco and Mendocino in southern Oregon and northern California (40°N); in excess of 1°C below normal from Cape Mendocino to Cape Conception (34°N), extending offshore some 5° longitude; and near normal in the California Bight (south of 34°N) (analysis, PFEL). On a broader scale, the Gulf of Alaska experienced cold anomalies, and the cold anomalies along California extend only a short ways out into the Pacific (analysis,1982-96 mean; ESRL).

Sources:

  • Western Regional Climate Center (WRCC)
  • Northwest River Forecast Center (NWRFC)
  • 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 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 July through September monthly anomalies were near 0.8°C (1971-2000 climatology). In October and November the conditions intensified with monthly-mean temperature anomalies of 1.01 and 1.65°C, respectively. The existence of one- and three-month mean Nino 3.4 anomalies in excess of 0.5°C, along with consistent changes in the tropical atmospheric circulation, defined conditions as those of a weak El Niño during the Summer, and the October and November observations of Nino 3.4 anomalies in excess of 1.0°C elevated the status to that of a moderate 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. The September-October-November mean Nino 3.4 SST was 1.2°C, and the models are initialized with ocean and atmosphere data through November. The average December-January-February Nino 3.4 SST forecast is 1.4°C, which represents a further enhancement of warm El Niño conditions. Only one of the 21 models forecast a Nino 3.4 value under 1°C for this forecast period. The El Niño is forecast to diminish to "weak" in March-April-May (average Nino 3.4 SST forecast of 0.8°C), and "neutral" in June-July-August (average Nino 3.4 SST forecast of 0.3°C).

    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 seemed to have ended in August of this year, and the PDO has exhibited small positive values in August, September, and October. The November PDO was small and negative (-0.40 standard deviations; 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 moderate "El Niño" (warm ENSO) in the equatorial Pacific and its forecast persistence through the next half-year is consistent with the development of a PDO warm phase 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, cold SST anomalies along the Washington, Oregon, and northern California coasts in January-February-March, with warm anomalies offshore; and then warmer than normal SSTs along with the west coast of North America in March-April-May and June-July-August 2010, consistent with warm PDO values (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