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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?

November 2010
Updated 23 November 2010 (posted 29 November)

The climate outlook is reviewed monthly and updated as needed.

Moderate "La Niña" [cold El Niño / Southern Oscillation (ENSO)] conditions are present in the equatorial Pacific (NOAA). ENSO is forecast to intensify to a "strong" episode in the next several months, and to last "at least into Northern Hemisphere spring 2011." The existence of a significant cold ENSO episode increases the likelihood of wetter and cooler than normal climate for the PNW in the coming months (historical analysis), and the NCEP forecasts, to be described next, are in-part consistent with this. The Climate Outlook is written in the days after the monthly release of ENSO forecasts. The newest ENSO forecasts, and current equatorial ocean surface temperatures are described below.

The skill of monthly and seasonal climate forecasts is tied to the existence of significant anomalous ocean surface temperature features. The skill of the NOAA seasonal temperature outlooks "peaks in the late winter" in the contiguous U.S. and precipitation skill, while usually marginal, can be as high as temperature skill during years of strong El Nino or La Nina [warm and cold ENSO, respectively] (NOAA).

The NOAA December temperature and precipitation forecasts are for an equally-likely chance of below-, near-, or above-normal temperatures, and an increased likelihood of above normal precipitation in the PNW. For precipitation, the PNW, Montana, Wyoming, and significant portions of the Dakotas are forecast to have a greater than 33% chance of above normal precipitation amounts. Washington state, Oregon with the exception of southcentral and southeast, and central and northern Idaho are forecast to have a greater than 40% of above normal precipitation in December. The one-month forecast, in this case for December, will be revised at the end of November / early December (NOAA).

Monthly and 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 NOAA December-January-February (DJF) precipitation forecast is for an increased likelihood of above normal precipitation for the PNW. The regions with greater than 33% and greater than 40% probability are the same as for the forecast for December. The DJF temperature forecast is for a greater than 33% chance of below normal temperatures in northwest Oregon, and western and northcentral Washington. The probability of below normal temperatures exceeds 40% in western Washington. The remainder of the PNW is forecast to have an equal likelihood of below-, near-, or above-normal temperatures.

On daily time scales, large magnitude values of the Pacific / North American pattern of atmospheric variability can be associated with extreme weather in the PNW. The 2.5 inches (6.3 cm) of snow that fell in Seattle on 22 November and the associated extreme cold temperatures occured during a period of large negative PNA values (strong offshore ridging of the upper atmosphere circulation, the contour field in the analysis; Center for Ocean-Land-Atmosphere Studies).

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Recent Pacific Northwest Climate

The western U.S. experienced above normal temperatures during the 30-days ending 21 November (1971-2000 mean, WRCC). The largest temperature departures, in excess of 2°F (1°C), were observed to the east of the Cascade Mountains in Oregon and Washington, and extended at least as far east as the central Dakotas. Northern Nevada and northwest Utah experienced similar magnitude departures. The preceding 30 days, ending 19 October, had a similar pattern of anomalies, but were of typical amplitudes of 6°F (3°C). For reference, the 60-day mean temperature departure ending 22 November 2010 is presented without discussion.

The PNW, California, Nevada, Utah, northwest Colorado, and Montana experienced above normal precipitation totals during the 30-days ending 21 November (precipitation totals, departures, percent of 1971-2000 normal). Precipitation was at least 50% above normal in several regions with climatologically modest rainfall, including eastern Oregon and much of Idaho (Burns OR, Pocatello ID; CPC). Precipitation notwithstanding, much of southern Idaho continues to be characterized as a drought region (16 November analysis, drought monitor). Southwest Washington and northwest Oregon, which are climatologically wetter than Burns or Pocatello, received > 30% above normal precipitation during the most recent 30-days (Astoria OR).

October coastal sea surface temperatures (SSTs) saw warm departures in excess of 2°F (1°C)) between Vancouver Island and Cape Blanco in southern Oregon (43°N), the Strait of Juan de Fuca, and Georgia Strait. Coastal temperatures south of Cape Mendocino in northern California (40°N) were in excess of 1°F (0.5 °C) colder than the mean. [SST analysis by PFEL; 1985-97 mean.]

North Pacific SST departures for the northeast Pacific SST for the 30 days ending 20 November (1971-2000 mean) documents the warm temperature departures described above as extending northward along the British Columbia and Alaska coasts as far west as Cordova AK (145°W). The north Pacific basin, however, is characterized by a complicated distribution of temperature departures, with the cold ENSO-related departures of the equatorial Pacific extending east and north to southern California and Baja California, another patch of cold departures centered south of the Gulf of Alaska (40°N, 140°W), and warm departures to the northwest of Hawaii, centered at 170°E, 40°N.

Sources:

  • Western Regional Climate Center (WRCC)
  • Climate Prediction Center (CPC)
  • 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). Sea surface temperature (SST) departures 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, are a key indicator of ENSO variability. The ongoing cold ENSO, as measured by Nino 3.4 SST departures, intensified from August (-1.18 °C) to September (-1.56°C) to October (-1.64°C). The mean Niño 3.4 SST departure for August-September-October (ASO) was -1.46°C, which NOAA categorizes as a moderate "La Niña" when accompanied by consistent atmospheric anomalies (NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion).

    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, in contrast, are constructed from observations of past climate, and they 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-three ENSO models initialized with ocean and atmosphere data through October are summarized by the International Research Institute for Climate and Society. The average forecast is for the cold ENSO to intensify from the observed ASO Niño 3.4 value of -1.46°C to a maximum negative value of -1.8°C in November-December-January. A 3-month Niño 3.4 SST anomaly value greater than or equal to -1.5°C is characterized as a "strong" La Niña (cold ENSO) by the NOAA criterion. Nineteen of the 23 models predict that ENSO will be "strong" in November-December-January, 17 in December-January-February, and 10 in January-February-March, with ENSO continuing to weaken in subsequent seasons. The model solutions diverge markedly by summer of 2011, when the mean prediction is for "La Niña" (cold ENSO) conditions to be over.

    Pacific Decadal Oscillation (PDO). October's PDO value was -1.06 standard deviations, making it the fourth consecutive month of PDO values in excess of -1 standard deviations (digital values, 1900-90 mean). Negative values of the PDO are associated with ocean surface temperature departures along the North America coast that are less than ocean surface temperature departures in the central north Pacific. For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude. 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 predicts the PDO to be negative, but of diminishing magnitude through the end of the forecast period in the fall of 2011. The NCEP coupled forecast system (a mechanistic ocean-atmosphere model) prediction issued on 23 November 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 the end of the forecast period in June-July-August 2011 (23 November forecast, more recent forecasts). The model forecasts for April-May-June 2011 are for cold anomalies (in excess of -0.5°C) along the Oregon, Washington, and British Columbia coasts, consistent with strong upwelling, and the forecasts are unskillful for the same period for the central and southern California coast.

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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