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Seasonal to Interannual Forecasts

Climate Outlook

ARCHIVE - JANUARY 2009

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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?

January 2009
Updated January 23, 2009 (posted January 25)

The climate outlook is reviewed monthly and updated as needed.

The Pacific Northwest (Oregon, Washington, and Idaho; PNW) experienced a wide variety of weather in the last 30 days, from the cold and snow of late December to the mild temperatures, heavy rains, and flooding of early January, to an extended strong inversion in mid-January where a layer of warmer air trapped cold, stagnant air at the surface. The temperature records over the region document the geographical extent of the different episodes (Seattle/Tacoma; Lewiston, Idaho; Pocatello (southeast) Idaho; Eugene Oregon (CPC)). The heavy precipitation of early January was mostly in Washington and central northern Idaho (map, 1971-2000 mean, HPRCC). More details on the associated flooding is available through the Office of the Washington State Climatologist. Additionally, Professor Cliff Mass at the University of Washington provides numerous analyses of the individual weather events during this period on his weather blog.

Seasonal mean temperatures since the beginning on the Water Year on 1 October have been near or slightly above normal (1971-2000). Total seasonal precipitation was dominated by the heavy precipitation of early January in Washington and northern Idaho (compare with the mid-December analysis). Snow pack, as measured in terms of snow water equivalent, is 10-25% above normal on the western flanks of the Cascades and 25-50% below normal on the eastern flanks, while a range of conditions exist over the remainder of the Columbia Basin (22 January analysis, map legend, current analysis, NWRFC). Despite the warm rains of early January, the snow conditions are much improved over those reported in mid-December.

The ocean surface temperatures during the same period (map, ESRL) are characterized by a continuation of cooler than normal sea surface temperatures (SSTs) along the west coast of North America and on the central and eastern equatorial Pacific, Above normal SSTs are found in the central north Pacific. The pattern in the north Pacific projects onto the negative polarity of the Pacific Decadal Oscillation (PDO). The December SST structure near the Washington, Oregon, and California coasts at 9km resolution (analysis, PFEL) is characterized by small, slightly positive anomalies along the Washington and Oregon coasts, and colder than normal SSTs along the California coast.

Sources:

  • NOAA Climate Prediction Center (CPC)
  • High Plains Regional Climate Center (HPRCC)
  • NOAA Northwest River Forecast Center (NWRFC)
  • NOAA Earth System Research Laboratory (ESRL)
  • NOAA Pacific Fisheries Environmental Laboratory (PFEL)


    Current indicators for Pacific climate

    El Niño/Southern Oscillation (ENSO). The monthly mean Niño 3.4 region (5°N-5°S, 170-120°W) SST anomalies were weakly negative in September, October, and November (average -0.23°C, 1971-2000 mean) and the anomalies intensified in December and early January (December average -0.73°C). In early January the NOAA Climate Prediction Center declared that the ocean was in "La Niña conditions" (defined as a monthly average anomaly less than -0.5°C along with constant atmospheric conditions and a forecast of persistence for 3 consecutive months; panel 21 of document). This declaration is consistent with the expectation that the ocean will evolve into a "La Niña episode" by the end of January, which requires a 3-month mean SST anomaly of less than -0.5°C (more information). The average February-March-April forecast anomaly of the 23 ENSO forecast models polled by the International Research Institute for Climate and Society is -0.5°C, just meeting the "La Niña episode" criterion, with the anomalies forecast to diminish in subsequent months.

    Pacific Decadal Oscillation (PDO). The PDO has exhibited negative monthly values since September 2007 (digital values), with values in excess of -1 standard deviation from April through November of 2008. [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] In December 2008 the strength of the PDO was slightly diminished with an index value of -0.87 standard deviations. "La Niña" is consistent with the development or continuation of negative PDO values. The NOAA Earth System Research Laboratory's statistical Linear Inverse Model PDO forecast is for continued cold polarity, but of smaller magnitude, through the end of the forecast period (December 2009) (forecast). The NOAA coupled forecast system model solves dynamical equations for ocean and atmosphere motions, and it predicts significant cold anomalies along the west coast of North America through April-May-June, with diminished anomalies thereafter (forecast).


    What does the outlook mean for the PNW in coming months?

    The lowland snows of December occurred at a time of significant negative amplitude of the Pacific/North American (PNA) pattern. Earlier studies have documented an increased chance of heavy snow and extreme cold during these periods (more information). The NOAA Climate Prediction Center (CPC) makes 14-day PNA forecasts (through 6 February, beyond 6 February). The PNA is presently negative and the red curves in the top panel indicate that the negative PNA polarity will persist through the forecast period.

    The longer-term February-March-April CPC climate forecast is for a greater than 33% chance of below normal temperatures north and west of Pocatello, Idaho, with the probabilities exceeding 40% in northern Oregon, northernmost Idaho, and all of Washington (map). The precipitation forecast for the same months is for an even chance of below, equal to, and above normal precipitation throughout the PNW (map). The skill of the precipitation forecast is derived from ENSO-related changes in precipitation, and the model has no useful skill in ENSO neutral periods. The 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.


    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