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Seasonal to Interannual Forecasts

Climate Outlook

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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 2011
Updated 2 February 2011 (posted 2 February)

The Climate Outlook is updated following the third Thursday of each month. The observations, forecasts, and discussions that are the inputs to the report are published on different days throughout the month. A little information on the content and release dates of the various inputs might be helpful to the reader interested in keeping apprised of the latest information, and this description follows.

The National Oceanic and Atmospheric Administration (NOAA) ENSO Diagnostic Discussion interprets the conditions in the month just concluded as well as ENSO forecasts issued during that month, and it is updated on the first Thursday of the month. The NOAA seasonal temperature and precipitation forecasts, and the International Research Institute for Climate and Society ENSO forecast summary are released on the third Thursday of the month. In recognition of the importance of ENSO variability to PNW winter climate, the Climate Outlook is issued after the publication of the ENSO forecasts.

The December equatorial Pacific Ocean climate exhibited "moderate-to-strong" La Niña [cold El Niño / Southern Oscillation (ENSO)] conditions (NOAA). Cold ENSO "is currently near its peak and is expected to persist into the Northern Hemisphere Spring 2011 at a lesser intensity."

The existence of a significant cold ENSO episode increases the likelihood of a wetter and colder than normal PNW winter climate. This can be seen in the analysis of PNW-average temperature and precipitation for individual calendar months, and also in November through April average maps of temperature and precipitation deviations from normal (reverse the sign of the departures in the map analyses for cold ENSO).

The NOAA February-March-April (FMA) precipitation forecast is for a greater than 33% chance of above normal precipitation in eastern Washington, northeast Oregon, and central and northern Idaho. The probability of the same exceeds 40% in the Bitterroot Mountains of Idaho, and the rest of the PNW is forecast to have an equal chance of precipitation below, near, or above the 1971-2000 normal.

The FMA temperature forecast is for Alaska, the PNW with the exclusion of southeast Idaho, western and northern California, Montana, the Dakotas, Minnesota, and much of Wisconsin to have a greater than 33% chance of below normal values. The forecast of PNW below normal temperatures exceeds the 50% probability in Washington, northern Idaho, and western and northern Oregon. Southeast Idaho is forecast to have an equal chance of temperatures that are below, near, or above the 1971-2000 normal.

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. A further discussion of equatorial ocean surface temperatures and a survey of the ENSO model seasonal forecasts is provided below.

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). Forecasts of the strength and sign of the PNA pattern are produced by the NOAA Climate Prediction Center

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Recent Pacific Northwest Climate

The 30 days ending 30 January saw near- to slightly above-normal temperatures over northwest Oregon and western Washington; positive temperature departures (typically 2-4°F (1-2 °C)) over the Oregon Coast Range, north central Oregon and eastern portions of Washington; and cold temperature departures (2-4 °F (1-2 °C)) over southeast Oregon and the Snake River Valley in northeast Oregon and southern Idaho (1971-2000 mean, WRCC). Examination of the daily time series for Portland, Yakima, Burns (eastern Oregon), and Boise documents varying degrees to which the shift from colder to warmer than normal conditions about 12 January affected individual locations (CPC).

The 30 days ending 30 January saw above normal precipitation in northwest Oregon and western Washington (in places the departures were in the range of 3-6 in. (6-12 cm)), and preciptation deficits of similar magnitude in the Oregon Coast Range and Oregon Coast (totals, departures, percent 1971-2000 normal). The remainder of the PNW experienced smaller magnitude precipitation departures. Southwest Oregon, as documented for Medford, observed a general lack of storms, while Spokane and Boise have had precipitation events in the period.

The 28 January snow pack, as measured in snow water content, is characterized by normal values in the eastern Columbia Basin, large deficits (50 to 90% of normal) in the northern Oregon through central Washington Cascades, and 25-50% greater than normal amounts in the Olympics (latest analysis, WRCC). The 25 January drought monitor documents the PNW as being free of drought, which is unusual (latest analysis).

December and January coastal sea surface temperatures (SSTs) were near the 1985-97 normal along southern Vancouver Island, Washington, Oregon and northern California. Cold departures in excess of 1 °C were observed in December over a broad region to the south of San Francisco. In January, cold departures of 1 °C were observed close to the coast between Willapa Bay (46°N) and the Columbia River, and in regions to the south of Point Arenas (39°N) (PFEL).

Average north Pacific SSTs for the 30 days ending 29 January (1971-2000 mean) also show near normal (albeit a different normal) SSTs along the Oregon, Washington, British Columbia, and Alaska coasts. Cold departures in excess of 0.5 °C are observed in the Gulf of Alaska, and a second patch extends south and southwest from southern California to the equator. Warm departures of similar magnitudes are found from Hawaii northwestward, and cold ENSO remains strong in the equatorial Pacific (PFEL).

The year 2010, when viewed globally, was tied with 2005 as the warmest years in the 131 year record maintained by the National Climatic Data Center (discussion; 1880-2010 temperature timeseries plot, plot of same data for 1990-2010, temperature dataset documentation). The 2010 PNW climate was warmer and wetter than the 1961-90 mean in the NCDC analysis.

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). December SSTs in the eastern equatorial Pacific were approximately 1.5 °C below the 1971-2000 normal, making this the 4th consecutive month of temperature departures near -1.5 °C. The October-November-December average temperature deviation in this "Niño 3.4" region (5°N-5°S, 170-120°W) was -1.55 °C and consideration of this temperature, along with the meteorological conditions, led NOAA to characterize the tropical Pacific climate state as that of a "moderate-to-strong La Niña."

    The anomalous state of the present tropical Pacific climate is more prominent in two other indices of ENSO variability. The Southern Oscillation Index (SOI) is the standardized difference between standardized departures of Darwin Australia (12°S, 131°E) and Tahiti (18°S, 150°W) sea level pressures, and it can be thought of as an indicator of the strength of the atmospheric part of the El Niño / Southern Oscillation. Three-month mean values of the SOI compiled by the Climate Prediction Center have equaled or exceeded 2 standard deviations since July-August-September. If the SOI is assumed to be a normally distributed variable, only 5% of the values can be expected to exceed this magnitude. The multivariate ENSO index, a metric constructed from both ocean and atmospheric variables, achieved some of the top ranked values in the 61-year record during the last months of 2010.

    To forecast the evolution of ENSO over the next several seasons NOAA employs mechanistic and statistical models. Mechanistic models use equations to describe the motions of the atmosphere and ocean, and also the contributions of cloud, precipitation, and radiative processes to the climate. In mechanistic models, these physically-based equations are used to forecast the future based on present conditions. Statistical models, in contrast, are constructed solely from observations of past climate, and they apply regression coefficients to forecast future climate from the present. Agreement between these two types of models increases our confidence in the forecast.

    The 3-month mean Niño 3.4 SST forecast from twenty-three ENSO models initialized with ocean and atmosphere data through December are summarized by the International Research Institute for Climate and Society. The average forecast is for the cold ENSO to diminish in strength, as measured by Niño 3.4 SST departures, from -1.55 °C in October-November-December to -1.1 °C in February-March-April -- so still a moderate cold ENSO -- and for an end of the ENSO alert in May-June-July (Niño 3.4 SST departure magnitude < 0.5 °C).

    Pacific Decadal Oscillation (PDO). December's PDO value was -1.21 standard deviations and it marked the seventh consecutive month of negative PDO values (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. To interpret the magnitude of the PDO value one should compare it with a normally distributed variable. Only 32% of the values exceed one standard deviation in magnitude for a normally distributed variable. 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 become increasingly negative 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 31 January is for cold SST departures in excess of -1°C to be found along the Alaskan Panhandle, British Columbia, Washington, Oregon, and California coasts during April-May-June, the season of upwelling onset. The forecast models exhibit no skill for SST forecasts along the Alaskan, British Columbia, Washington and Oregon coasts during July-August-September while California is forecast to have cold anomalies in excess of -0.5 °C (31 January 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