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Seasonal to Interannual Forecasts

Climate Outlook

February 2010 - 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?

February 2010
Updated 3 March 2010 (posted March 03)

The climate outlook is reviewed monthly and updated as needed.

The 4 February NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion anticipates the continuation of warm ENSO (El Niño) conditions through Northern Hemisphere Spring. A review of tropical Pacific observations and more recent ENSO forecasts is found below.

The NOAA Climate Prediction Center (CPC) seasonal forecast for March-April-May is for a continuation of the mild, drier than normal conditions the region has experienced this calendar year (temperature, precipitation forecasts). In particular, the CPC temperature forecast is for a greater than 40% chance of above normal temperatures over the PNW, with the probabilities of the same exceeding 50% in northern Idaho, northern Oregon, and Washington. The CPC precipitation forecast for March-April-May is for a greater than 33% chance of below normal precipitation in central Washington and northwest Oregon, with the probability of the same exceeding 40% in western Washington and the extreme northwest corner of Oregon. The remainder of the PNW is forecast to have an equal chance of below, equal to, or above normal precipiation in this period. This forecast pattern of temperature and precipitation deviations is consistent with the interpretation that ENSO will dominate the climate of the PNW in the coming months (analyses, UW).

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 significant ENSO conditions like the present.

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Recent Pacific Northwest Climate

The 30 days ending 22 February continued the regional pattern of significant warm temperature anomalies (>2 °F (1 °C) above the 1971-2000 mean) that began in mid-December (WRCC). The largest temperature anomalies, in excess of 4 °F (2 °C), were observed in central and eastern Washington and northern Idaho. The eastern Snake River Valley, including Pocatelllo, was the exception to this pattern and experienced slightly cooler than normal 30-day average temperatures (analysis, NCEP). The January-average Oregon, Washington, and Idaho state-average temperatures were in the 93rd and higher percentiles of the 116-year record (analysis, NCDC) and, several cities, including Bellingham and Seattle, broke long-standing temperature records (OWSC).

Precipitation summed over the 30-days ending 22 February was 50-75% of normal and drier west of the Cascades in Oregon and Washington and over much of Idaho (total, departure, percent normal). The recent weather contributed to continued diminished snowpack throughout the region (Snow Water Equivalent on 24 February, legend; today; NWRFC). The snowpack, as of 24 February, was near to slightly below normal (75-90%) in the Canadian portion of the Columbia Basin; 50-75% of normal throughout the eastern portion of the Basin; and 25-75% of normal for this part of the season in the Oregon and central Washington Cascades. The long-lived drought conditions to the west of Cascades persist (analysis, Drought Monitor).

Southerly winds associated with the January storms replaced the cold coastal sea surface temperature (SST) anomalies of December with warm anomalies in January (PFEL). January SSTs from Vancouver Island to Cape Blanco in southern Oregon (43 °N) were in excess of 1 °F (0.5 °C) above the 1985-97 normal, and in excess of 2 °F (1 °C) above normal along the southern Washington coast and in the Salish Sea. The Pacific SST anomalies for the more recent 30-day period ending 20 February (analysis, 1982-96 mean; ESRL) documents small SST anomalies near the coast and cool anomalies centered at 30°N to the west of 130°W.

Sources:

  • Western Regional Climate Center (WRCC)
  • National Centers for Environmental Prediction (NCEP)
  • National Climatic Data Center (NCDC)
  • Office of the Washington State Climatologist (OWSC)
  • 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) Diagnostic Discussion 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 for November, December, and January was 1.65, 1.78, and 1.62 °C, respectively, and the January value represents a diminution of the warm ENSO.

    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 November-December-January mean Nino 3.4 SST was 1.7°C, and the models are initialized with ocean and atmosphere data through January. The models exhibit a strong consensus that the present warm ENSO episode will diminish dramatically in the coming months, with a forecast March-April-May Nino 3.4 SST of 0.8°C. The system is forecast to become ENSO-neutral (Nino 3.4 SST < 0.5°C) in May-June-July.

    Pacific Decadal Oscillation (PDO). Much of the past 2.5 years has 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 ended in July of 2009, and the index was small in magnitude and usually positive through the remainder of 2009. The January 2010 index value was 0.88 standard deviations, which is consistent with the strong storms that were observed in that month (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 "El Niño" (warm ENSO) in the equatorial Pacific and its forecast persistence through the Northern Hemisphere Spring 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 May-June-July, and weak and negative by July-August-September. The coupled forecast system, a mechanistic ocean-atmosphere model, predicts warm SST anomalies along the Washington, Oregon, and California coasts through June-July-August. The warmest anomalies, in the range 0.5-1°C, are forecast for along the Oregon and Washington coasts through May-June-July. The current cool SST anomalies offshore (described above) are predicted to persist through the forecast period. This pattern of SST anomalies is consistent with the positive phase of the PDO (3 March forecast, more recent forecasts).

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    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