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Seasonal to Interannual Forecasts

Climate Outlook

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ARCHIVE COPY - June 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?

June 2009
Updated 23 June 2009 (posted June 24)

The climate outlook is reviewed monthly and updated as needed.

The NOAA Climate Prediction Center July-August-September temperature forecast is for an increased chance of above normal temperatures in the western contiguous U.S. with the notable exception of the coastal regions.

For regions within the Pacific Northwest this forecast is manifested as follows. The Oregon and Washington coastal areas are forecast to have an equal chance of below normal, normal, or above normal temperatures. Between the Coast Range and the Cascades there is a greater than 33% chance of above normal temperatures, and to the east of the Cascades the probability of above normal temperatures exceeds 40%. The chance of above normal temperatures exceeds 50% on the southern Idaho border.

The July-August-September precipitation forecast is for a greater than 33% chance of below normal precipitation in northern Oregon and northern Idaho, exceeding 40% in Washington and far northern Idaho.

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.

NOAA issued an "El Niño Watch" on 4 June as surface temperatures in the equatorial Pacific Ocean are now slightly above the 1971-2000 normal and the atmospheric conditions are consistent with the continued development of warm anomalies.

More on recent Pacific Northwest climate and recent and projected changes in key indicators for Pacific Northwest climate is provided below.

For More Information

Recent Pacific Northwest Climate

Washington, the northern two-thirds of Oregon, and the northern half of Idaho experienced unseasonably warm temperatures the first half of June (analysis, 1971-2000 mean, WRCC). Temperatures have since returned to more normal values. The warm spell contributed to 30-day mean temperatures in excess of 2°F (1°C) above the 1971-2000 normal over all 3 states, and in excess of 4°F (2°C) in portions of eastern Washington, eastern Oregon, and the northern two-thirds of Idaho. Seasonal (3-month average) temperatures are near normal.

The first half of June and 30-day mean precipitation were both characterized by below normal precipitation in the northern half of the PNW, extending eastward into Montana and North Dakota; and below normal precipitation along the Oregon and Washington coasts. The diminished coastal rainfall is also seen in the seasonal (3-month mean) precipitation and in the precipitation deficit since the beginning of the water year in October (map, UW). The water year precipitation analysis shows below normal precipitation along the British Columbia coast and also for the western U.S. The same analysis for 2007-08 documents a similar pattern of diminished precipitation (map).

The Spring has not seen significant wildland fires (NICC).

The Winter and Spring saw cold sea surface temperature (SST) anomalies in excess of 1°C along the west coast of North America, and these have been replaced from British Columbia to California by warm SST anomalies (>0.5°C) in the last several weeks (analysis, 1982-96 mean, ESRL).

Sources:

  • Western Regional Climate Center (WRCC)
  • Northwest Interagency Coordination Center (NICC)
  • Earth System Research Laboratory (ESRL)


    Recent and Projected Changes in Key Indicators for Pacific Climate

    El Niño/Southern Oscillation (ENSO). The phase and strength of the El Niño/Southern Oscillation phenomenon is characterized by 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 (NOAA El Niño definition). The cold Niño 3.4 SST anomalies that peaked in January have given way to 0.28°C warm SST anomalies in May, along with eastward winds in the western equatorial Pacific. The expectation of the development of "El Niño Conditions" in the next three months led NOAA to declare an El Niño Watch" on 4 June.

    ENSO forecasts are made with statistical models, which employ statistics of past variability to predict the future, and mechanistic models, which solve equations for ocean and atmosphere motions, to forecast the future from present conditions. Agreement of the forecasts from these two types of models increases our confidence in the forecast. The International Research Institute for Climate and Society polls the results of 23 models, both statistical and mechanistic, that are produced by research institutions around the world. Twenty of the 23 forecasts, which were initialized with May ocean and atmosphere conditions, predict that the equatorial Pacific will exceed the NOAA El Niño criterion (see above) by September-October-November with warm conditions extending into 2010.

    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 and from January through April of this year. The May PDO value was -0.88 standard deviations. [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] The development of "El Niño" (warm ENSO) in the equatorial Pacific is consistent with a diminution of the present cold PDO conditions and possible replacement by a warm phase of the PDO.

    NOAA employs both statistical and mechanistic models to forecast the PDO and coastal ocean conditions. The statistical linear inverse model forecast is for a continuation of the cold PDO phase, but of smaller magnitude, through the end of the forecast period (December 2009). The NOAA coupled forecast system model (a mechanistic ocean-atmosphere model) predicts weak cold SST anomalies along the British Columbia, Washngton, and Oregon coasts through September-October-November along with a generally weaker PDO pattern (forecast). The model skill is poor for coastal temperatures during the subsequent December-January-February.

    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