Forecasts and Planning Tools

Seasonal to Interannual Forecasts

Climate Outlook

April 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?

April 2010
Updated 20 April 2010 (posted April 21)

The climate outlook is reviewed monthly and updated as needed.

The 8 April NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion is for ENSO "to continue through the Northern Hemisphere spring 2010 and transition to ENSO-neutral conditions by Northern Hemisphere summer 2010." A review of tropical Pacific observations and more recent ENSO forecasts is found below.

The NOAA Climate Prediction Center (CPC) May-June-July temperature forecast is for an equal chance of below, near, and above normal temperatures in the extreme eastern portion of Idaho, and a greater than 33% chance of above normal temperatures in the remainder of the PNW. The probability of greater than normal temperatures increases to over 40% in northern Oregon, northern Idaho, and Washington state. The CPC precipitation forecast is for an equal chance of below normal, near normal, or greater than normal May-June-July precipiation throughout 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 significant ENSO conditions and, as ENSO is forecast to diminish in the coming months, the above precipitation forecast is expected to have little skill.

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Recent Pacific Northwest Climate

The 30 days ending 18 April saw PNW temperatures near to slightly below the 1971-2000 normal (WRCC). Cold temperature departures between 2 and 4 °F (1 and 2 °C) were observed on the eastern slopes of the Oregon Cascades, southeast Oregon, and the southern half of Idaho. Daily records within these regions of below normal temperatures (Burns OR, Boise, and Pocatello; NCEP) document particularly cold temperatures between 30 March and 10 April. The 30-day averaged temperatures represent a return to more normal conditions after significant warm anomalies in the preceding 30-day periods (16 Feb. - 17 March, 24 Jan. - 22 Feb., 21 Dec. - 19 Jan.).

Precipitation summed over the 30-days ending 18 April was above normal in western Oregon, over most of Washington, and in northern Idaho (total, departure, percent normal). The NOAA regional climate center analysis (above) indicates precipitation 50-100% above normal in western Oregon, and daily records for Astoria (Oregon coast), Portland, and Eugene (central Willamette Valley) add further documenation. The long-lived drought conditions to the east of Cascades remain unchanged (13 April, Drought Monitor).

The snow resources are shown in 1 April snowpack (NRCS) and 20 April snow water equivalent (legend, NWRFC). The snowpack was aided by storms in early April (described above), but the snowpack is not significantly different than reported in the March Climate Outlook. 1 April snowpack in the 110-129% range occurred in southeast Oregon and southwest Idaho, and normal amounts were observed in the Olympic Penninsula and in several drainages on the eastern flank of the Washington Cascades. The remainder of the Columbia Basin has 1 April snow amounts in the 50-89% range and smaller.

The March coastal sea surface temperatures (SSTs) are above normal from at least central Vancouver Island to northern Baja within several hundred kilometers of the coast (1985-97 mean, PFEL). The largest SST departures, in excess of 1 °C, are along the Washington coast and within the Salish Seas, and are consistent with the slightly above normal temperatures in the adjacent coastal and Puget Sound land regions (see above). The 30-day mean SST anomalies for the north Pacific and beyond indicate small anomalies near the coast and cold anomalies at 10° of longitude and farther offshore (1982-96 mean, ESRL).

Sources:

  • Western Regional Climate Center (WRCC)
  • National Centers for Environmental Prediction (NCEP)
  • National Resources Conservation Service (NRCS)
  • 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 peaked in December at 1.78°C, and has declined in subsequent months, with January, February, and March values of 1.58, 1.24, and 1.12 °C, respectively.

    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 ENSO model forecasts are summarized by the International Research Institute for Climate and Society. The January-February-March mean Nino 3.4 SST was 1.26°C, and the models are initialized with ocean and atmosphere data through March. The models exhibit a consensus that the present warm ENSO episode will diminish into neutral ENSO conditions in April-May-June (3-month mean SST anomaly < 0.5°C), and the models forecast a continuation of neutral ENSO through the end of the forecast period in December-January-February, some 9 months from now. The models have diminishing skill at this time of the year, and little skill at forecasting second-half ENSO conditions from March conditions.

    Pacific Decadal Oscillation (PDO). The December, January, February, and March PDO values were 0.08, 0.83, 0.82, and 0.44 standard deviations relative to a 1900-90 mean, respectively. [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] The mean 21 March through 17 April SST anomalies, presented above, are near normal along the North American west coast and negative in the central north Pacific, and this is consistent with a weak positive PDO value.

    The existence of "El Niño" (warm ENSO) in the equatorial Pacific during the last half-year is consistent with the development of a PDO warm phase. 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 weak and positive through April-May-June, and then negative through at least December-January-February. The NCEP coupled forecast system, a mechanistic ocean-atmosphere model, predicts warm SST anomalies along the Alaska, British Columbia, Washington, Oregon, and California coasts, and cold SST anomalies in the central North Pacific through June-July-August. This pattern of SST anomalies is consistent with the positive phase of the PDO (20 April forecast, more recent forecasts).

    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