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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?

December 2010
Updated 16 December 2010 (posted 23 December)

The climate outlook is reviewed monthly and updated as needed.

The November equatorial Pacific Ocean climate exhibited "moderate-to-strong" La Niña [cold El Niño / Southern Oscillation (ENSO)] conditions (NOAA). The cold ENSO departures from normal are forecast to peak in the November-December-January, and to remain cold "at least into Northern Hemisphere spring 2011." The existence of a significant cold ENSO episode increases the likelihood of a wetter and colder than normal PNW climate in the coming months (historical analysis). The NCEP seasonal forecasts, to be described next, are consistent with ENSO strongly influencing the climate in the contiguous U.S. during this period. A further discussion of equatorial ocean surface temperatures and a survey of the ENSO model forecasts is provided below.

The NOAA January-February-March (JFM) precipitation forecast is for a greater than 33% chance of above normal precipitation for the PNW. The probability of the same exceeds 40% throughout Washington state, in northern Oregon, and in north and central Idaho. The JFM temperatures for the PNW, with the exclusion of southeast Idaho, are forecast to have a greater than 33% chance of below normal values. The forecast of below normal temperatures exceeds the 40% probability in central and southwest Oregon, northern Idaho, and eastern Washington. The probability of the same exceeds 50% in northwest Oregon, and central and western Washington. Southeastern Idaho is forecast to have an equal chance of below-, near-, or above-normal temperatures during this period.

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.

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). Further documentation of that storm is available from the Office of the Washington State Climatologist and Cliff Mass's weather blog.

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Recent Pacific Northwest Climate

The 30 days ending 16 December saw cooler to near normal temperatures over the PNW (1971-2000 mean, WRCC). The largest cold temperature departures, in the range of 3 to 6°F (1.7 to 3.3°C), were observed in the Columbia Basin of Washington to the east of the Cascade Mountains. A cold, snow producing storm centered about 23-24 November and a warm, wet storm -- popularly referred to as a "Pineapple Express" -- centered about 12-14 December largely cancelled each other out in the determination of the temperature average. Daily temperature records for a selection of stations (Portland, Yakima, and Pocatello; CPC) document the large swings in temperature.

Late November and early December is a climatologically wet part of the year for the PNW. The 30 days ending 16 December saw precipitation totals between 1 and 4 inches (0.5 and 2 cm) to the east of the Cascades and throughout Idaho, and amounts in excess of 7 inches (3.5 cm) along the coasts, and within and to the west of the Washington and northern Oregon Cascades.

For almost all regions of the PNW, the precipitation accumulations were above the 1971-2000 mean. The northern Oregon coast, Washington coast, Olympic Penninsula, western Puget Sound, and southern Washington and northern Oregon Cascades experienced precipitation amounts more than 2 inches (1 cm) above climatology, which for most of these regions was 25 to 50% above normal (precipitation departures, percent normal). East central Oregon and southern Idaho experienced 1 to 2 inch (0.5 to 1 cm) precipitation surpluses during the same period, which represented at least 50% more precipitation than normal.

Daily timeseries for a selection of stations throughout the PNW document the progression of precipitation events during the last 90 days:Portland OR, Seattle WA, Burns OR, Pocatello ID. The heavy rain event of 11-14 December caused extensive flooding, land slides, road destruction, and power outages in western Washington. Documentation of this event can be found on Cliff Mass's Weather Blog, numerous online articles in the Seattle Times, and will be provided in the January 2011 Office of the Washington State Climatologist newsletter.

The variable weather over the last month has given rise to both surplus and deficit snowpack in the PNW, as documented in 17 December snow water content (WRCC). The Olympic Penninsula, and portions of southern Idaho had above normal amounts while eastern Washington and central Idaho are below normal for this time of the year. The interpretation of what contributes to snow amounts can be difficult, as the low snow water contents in eastern Washington occurred as Spokane broke a 55-year record with 25.9 inches of snow in November (65.8 cm, Seattle Times).

The long-standing drought conditions in southern Idaho and south central Oregon (16 November analysis) were eliminated and further weakened, respectively, in the past month (14 December analysis).

November coastal sea surface temperature (SST) departures from normal were similar to those observed in October, with warm departures from Vancouver Island to Cape Mendocino in northern California (41°N), and cooler than normal temperatures from Cape Mendocino to at least 30°N in Baja California. The largest magnitude departures, in excess of 2°F (1°C), are found between Vancouver Island and Grays Harbor in the central Washington coast (PFEL, 1985-97 mean).

The average north Pacific SST departures for the 30 days ending 18 December (1971-2000 mean) are characterized by generally cooler than normal conditions in the northeast Pacific and warmer than normal conditions in the central and western portions of the basin. The equatorial Pacific is dominated by the cold ENSO pattern of warm departures in the west, and large magnitude cold departures from the dateline to the Ecuador coast (ESRL). The different averaging periods and climatologies make it difficult to explain why the strong warm anomalies along the British Columbia and Washington coast in the coastal analysis aren't present in the global scale 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). 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. Niño 3.4 SST departures since August have been in excess of -1°C, with monthly values of -1.18, -1.57, -1.61, and -1.47 for August through November, respectively. The 3-month mean value for September-October-November is -1.55°C, which is cold enough for this to be categorized as a "strong" cold ENSO. The 9 December NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion, doesn't go quite so far, characterizing the episode at this stage as a "moderate-to-strong La Niña."

    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-two ENSO models initialized with ocean and atmosphere data through November are summarized by the International Research Institute for Climate and Society. The average forecast is for the cold ENSO to maintain its present intensity during December-January-February (mean Niño 3.4 value of -1.6°C), and to weaken thereafter. The mean forecast is for the episode to weaken to "moderate" (-0.5 to -1°C) by March-April-May,and to further weaken to "neutral" (-0.5 to 0.5°C) by June-July-August.

    Pacific Decadal Oscillation (PDO). November's PDO value was -0.82 standard deviations, and follows four 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. 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 21 December is for cold SST departures in excess of -0.5°C to be found along the British Columbia, Washington, Oregon, and California coasts through at the end of the forecast period of June-July-August (21 December 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