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Seasonal to Interannual Forecasts

Climate Outlook

July 2010 - Archive Copy

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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?

July 2010
Updated 20 July 2010 (posted 26 July)

The climate outlook is reviewed monthly and updated as needed.

The 8 July NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion indicates that "La Niña [cold ENSO] conditions are likely to develop during July-August 2010." At this early point in the ENSO cycle it is difficult to forecast the maximum magnitude of the cold event. The analysis of historical ENSO variability and the NOAA Climate Prediction Center (CPC) seasonal forecasts, to be described below, both indicate that the earliest the PNW will see the influence of the cold ENSO is this Fall. A review of tropical Pacific observations and more recent ENSO forecasts is found below.

The CPC forecast for August-September-October seasonal mean temperature is for a greater than 33 percent chance of above normal temperatures in southern and central Idaho, southeast Washington, and eastern Oregon; and an equal chance of below, near, and above normal temperatures in the remainder of the PNW. The seasonal mean precipitation forecast for the same period is for a greater than 33% chance of below normal precipitation in southeast Oregon and southern Idaho, with the chances of the same exceeding 40% on the southern border of Idaho. The remainder of the PNW is forecast to have an equal chance of below, near, and above normal precipitation. 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 ENSO models, described below, are predicting cold ENSO conditions through February-March-April (FMA) of 2011, and the forecast persistence of the anomalies is consistent with the analysis of historical equatorial Pacific ocean temperatures. The persistent nature of this phenomenon and its significant influence on PNW winter climate make it useful to examine the CPC seasonal forecasts for November-December-January (NDJ) and FMA. The CPC forecasts and a documentation of typical ENSO-related November through April mean temperatures and precipitation are linked below. The sign of the historical analyses should be reversed to described cold ENSO conditions.

Forecasts
NDJ temperature | precipitation
FMA temperature | precipitation

Historical analysis
NDJFMA temperature | precipitation

The forecast is for an increased probabilty of a cooler and wetter than normal winter, and this is consistent with the canonical pattern of temperature and preciitation anomalies for a cold ENSO. In general, seasonal precipitation forecasts only have skill during periods of significant ENSO variability, such as the one that is predicted to develop in the coming months (CPC tools discussion).

Storms during October, November, and December can bring heavy precipitation amounts and cause significant flooding in western Washington and northwest Oregon, and the tendency for these storms is enhanced in ENSO neutral and cold years. For this reason, it makes sense to examine specifically the CPC October-November-December seasonal precipitation forecast. The forecast is for a greater than 33% chance of above normal precipitation throughout the PNW, with the chances of the same exceeding 40% in north and central Idaho, western and northern Oregon, and all of Washington state. The temperature forecast for this season (not shown) is for equal chances of below, near, and above normal temperatures in the region.

For More Information

Recent Pacific Northwest Climate

The Pacific Northwest continues to experience unseasonably mild temperatures, in a pattern that began in March, while the precipitation over the 30 days ending on 14 July is below the 1971-2000 normal. The average temperature departure for 15 June - 14 July is in excess of -1 °F (-0.5 °C) over all but the coastal regions, and extends east through Montana and Wyoming (WRCC). Larger cool departures, in excess of -2 °F (-1 °C), were observed through much of the Columbia Basin and east central Idaho. The temperatures in the coastal regions of Oregon and Washington were near normal. The cool temperature departures for the most recent 30-day period are larger in magnitude than for the earlier averages (16 May - 14 June, 18 April - 17 May, 20 March - 18 April).

The precipiation summed over the 30 days ending 14 July (total, departure, percent normal) is 75 percent of normal and drier over most of the PNW as the region enters the climatological dry season. Northern and east central Idaho were the exception to this pattern, with above normal rainfall. To close out the documentation of June, Portland Oregon established a new June precipitation record of 4.21 inches (10.7 cm) (daily totals, NCEP), an amount that is more typical of February precipitation for the Rose City.

On 19 July there are two "large wildland fires" (fire area > 100 acres) in eastern Washington, none in Oregon (today's analysis, NWCC); and two wildfire incidents in southern Idaho (today's analysis, InciWeb). The 13 July drought monitor characterizes south central Oregon, and northern and southeastern Idaho as being in drought conditions, and this represents an improvement over the situation in the last several months (June, May; Drought Monitor).

June saw continued cooler than normal sea surface temperatures (SSTs) along Oregon, Washington, and Vancouver Island with departures near -1 °C at the coast and larger departures a degree offshore and west of 130°W (1985-97 mean, PFEL). Unseasonably cool waters also extend south along the California coast, with the exception of positive departures just south of Point Arena (39°N) and the California Bight (33-34°N). The negative coastal SST departures began in April. Over the northeast Pacific, SSTs in the Gulf of Alaska and between Baja and Hawaii are 0.5°C below the 1982-96 mean, with positive departures of equal magnitude to the north of Hawaii (ESRL).

Sources:

  • Western Regional Climate Center (WRCC)
  • National Centers for Environmental Prediction (NCEP)
  • Northwest Interagency Coordination Center (NWCC)
  • Incident Information System (InciWeb)
  • 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). The 8 July NOAA El Niño Southern Oscillation (ENSO) diagnostic discussion states that "La Niña [cold ENSO] conditions are likely to develop during July-August 2010." The average SST anomaly averaged over 5°N-5°S, 170-120°W in the equatorial Pacific, in what is called the "Niño 3.4" region, is employed as a key indicator of tropical Pacific climate in the discussion. The significant warm ENSO of last winter was replaced with anomalous cold conditions in May and June, as documented in Nino 3.4 SST values of -0.07 and -0.48 °C, respectively (1971-2000 mean). The rapid development of anomalous cold ocean conditions is depicted in this NCEP animation of weekly SST anomalies.

    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, on the otherhand, are constructed from observations of past climate, and 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 Nino 3.4 SST forecasts of twenty ENSO models initialized with ocean and atmosphere data through June are summarized by the International Research Institute for Climate and Society. Eighteen of the models forecast the development of negative August-September-October (ASO) Nino 3.4 SST anomalies equal to or in excess of -0.5 °C, twelve of the forecasts are for Nino 3.4 < -1.0 °C, and the mean forecast is -1.0 °C. There is considerable spread in the SST predictions for the ASO season and throughout the forecast period. The mean forecast Nino 3.4 is predicted to remain in excess of -0.5 °C through January-February-March of 2010.

    Pacific Decadal Oscillation (PDO). The PDO index was positive between December 2009 and May 2010, with typical anomalies of 0.7 standard deviations, and the June PDO value was -0.22 standard deviations (1900-90 reference period, PDO values). [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] Negative PDO values are consistent with below normal SST anomalies along the eastern portion of the north Pacific and positive SST anomalies in the central north Pacific. ENSO variabilty is one of the mechanisms that can produce changes in the PDO, and the forecast development of cold ENSO in the coming months can be expected to contribute to negative PDO values in the future.

    NOAA employs both statistical and mechanistic models to forecast the PDO and coastal ocean conditions. The statistical linear inverse model forecasts the PDO to be weak and negative through the end of the forecast period in Summer 2011. The NCEP coupled forecast system, a mechanistic ocean-atmosphere model, predicts a continuation of the present pattern of cold SST anomalies along the eastern boundary and warm anomalies in the central north Pacific through the December-January-February (DJF), with the forecast for subsequent months having less than useful skill along the eastern boundary (19 July forecast, more recent forecasts).

    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