Seasonal to Interannual Forecasts
July 2009 - 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?
Updated 23 July 2009 (posted July 24)
The climate outlook is reviewed monthly and updated as needed.
NOAA issued an "El Niño advisory" on 9 July, which is a statement that the present and anticipated climate in the equatorial Pacific Ocean is consistent with warm ENSO ("El Niño") conditions. A discussion of equatorial Pacific climate is provided below. Presuming that the warm ENSO continues to develop as forecast, the impacts of this phenomenon on Pacific Northwest (PNW; Washington, Oregon, Idaho) climate will be seen beginning in the Fall months.
The NOAA Climate Prediction Center August-September-October precipitation forecast is for a greater than 33% chance of below normal precipitation in central and northern Idaho, all of Washington and Oregon, and exceeding 40% in western Oregon. The temperature forecast for the same period is for an equal chance of below normal, normal, and above normal temperatures in the PNW. The forecasts represent a continuation of the drier than normal conditions that were experienced in June in the western and northern part of the PNW (see below).
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.
For More Information
The 30 days ending 18 July are characterized by drier than normal conditions west of the Cascades, significant preciptation in eastern Oregon and southern Idaho, and near normal temperatures throughout the Pacific Northwest (Precipitation total, departure from 1971-2000 mean; temperature departure from 1971-200 mean; WRCC).
The Office of the Washington State Climatologist offers a detailed documentation of the record dry conditions in western Washington State that began in late May (report). The last 3 months have seen both wetter and drier than normal conditions (analysis, UW), and an April-May-June seasonal mean that is below the 1971-2000 normal west of the Cascades and above normal in eastern Oregon and central and southern Idaho (analysis).
The wildland fire activity is not abnormal for this (early) part of the fire season. The wildland fire potential remains high for the Okanagon part of Washington State (analysis, NICC), consistent with the below normal snow pack in this region (analysis, NRCS.
Along the coast, the colder than normal May SSTs along Washington, Oregon, and California (May SST, PFEL) were replaced by smaller scale cold and warm anomalies along Washington and Oregon, and above normal SSTs along the California coast (June SST).
El Niño/Southern Oscillation (ENSO). The phase and strength of the El Niño/Southern Oscillation phenomenon is measured in terms of 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). NOAA has three criterion that must be met for an "El Niño advisory" to be declared, and these will be evaluated in the following.
1) The observed monthly Niño 3.4 SST anomaly must meet or exceed 0.5°C. The cold Niño 3.4 SST anomalies that peaked in January 2009 gave way to 0.28 and 0.57°C warm SST anomalies in May and June, respectively, relative to the 1971-2000 mean.
2) An atmospheric response typically associated with El Niño is observed over the equatorial Pacific Ocean. Winds in the western equatorial Pacific have shifted from westward to eastward in the last 3 months (NOAA Tropical Atmosphere Ocean array, not shown).
3) An expectation that the 3-month mean Niño 3.4 SST anomaly will meet or exceed 0.5°C. ENSO forecasts are made with two kinds of models: mechanistic models, which solve equations for ocean and atmosphere motions and radiative processes to forecast the future from present conditions; and statistical models, where the average past behavior of the system is characterized by regression coefficients, and the regression coefficients are applied to the present conditions to forecast the future. Agreement of the forecasts from these two types of models increases our confidence in the forecast. The International Research Institute for Climate and Society polled the results of 21 mechanistic and statistical models that were initialized with June ocean and atmosphere conditions, and 19 of the models forecast August-September-October mean Niño 3.4 SST anomalies greater than or equal to 0.5°C.
The fulfillment of these criteria led NOAA to declare an "El Niño advisory" on 9 July 2009. Fifteen of the 17 models that also made forecasts of December-January-February Niño 3.4 SST anomaly indicated that this index will remain greater than or equal to 0.5°C in that season. The NOAA advisory states that "current conditions and recent trends favor the continued development of a weak-to-moderate strength El Niño into the Northern Hemisphere Fall 2009, with further strengthening possible thereafter".
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. [For a normally distributed variable, only 32% of the values exceed one standard deviation in magnitude.] These large, negative PDO values were manifested along the North American coast as cold SST anomalies. The month of May saw a diminution of the negative PDO (-0.88 standard deviation) with negative SST anomalies still present along the coast (May SST, PFEL), and in June the PDO was further diminished to -0.31 standard deviations (June SST), with positive SST anomalies along the California coast that are consistent with weaker than normal upwelling.
The development of "El Niño" (warm ENSO) in the equatorial Pacific is consistent with the onset of the warm phase of the PDO in the coming months. NOAA employs both statistical and mechanistic models to forecast the PDO and coastal ocean conditions. The statistical linear inverse model forecast is for for the PDO to become positive and small in magnitude by October-November-December, and to remain positive and small in magnitude through the end of the forecast period in April-May-June 2010. The NOAA coupled forecast system (a mechanistic ocean-atmosphere model) predicts weak cold SST anomalies along the British Columbia, Washngton, and Oregon coasts through November-December-January 2009/10, and warmer than normal water in the same region in January-February-March 2010 (forecast). The model maintains warmer than normal SSTs in the central north Pacific throughout the forecast period which suggests that the north Pacific ocean climate in the next half year will be poorly captured by fluctuations in the PDO.
For More Information
- Current conditions: Weekly NRCS drought monitor/snowpack update reports
- Read the latest expert analysis of the current state of ENSO from NOAA's Climate Prediction Center
- European Centre for Medium-Range Weather Forecasts ENSO forecast
- View the International Research Institute for Climate Prediction's ENSO QuickLook
- How is an El Niņo/La Niņa event defined?
Pacific Northwest Resource Outlooks
- Water Resources Forecasts (streamflow and other hydrologic conditions)
- Salmon survival forecast
- Forecast of extreme weather events
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
- Real-time data from moored ocean buoys (from NOAA’s TAO array)
- ENSO diagnostic discussion (from NOAA’s Climate Prediction Center)
- NOAA El Niño and La Niña definitions (from NOAA’Climate Prediction Center)
- Weekly ENSO update (from NOAA’s Climate Prediction Center)
- ENSO Quick Look (from the International Research Institute for Climate Prediction)
- Monitoring El Niño/La Niña (from NOAA’s Climate Prediction Center)
Predictions of Tropical Pacific and North Pacific Conditions
- Seasonal Niño3.4 sea surface temperature anomaly plume forecasts (from the European Center for Medium-Range Weather Forecasts)
- Statistical Probabilistic ENSO Predictions (from the International Research Institute for Climate Prediction)
- Sea surface temperature forecasts (from the International Research Institute for Climate Prediction)
- Experimental PDO and Pacific Seasonal Forecasts (from NOAA's Earth System Research Laboratory)
The Current State of the Globe
- Climate diagnostics bulletin (from NOAA’s Climate Prediction Center)
- The North Atlantic Oscillation (NAO) (from NOAA’s Climate Prediction Center)
- Accumulated daily precipitation time series graphs (from NOAA’s Climate Prediction Center)
- Daily global and regional precipitation analysis (from NOAA’s Climate Prediction Center)
- Index of Climate Prediction Center’s climate monitoring activities and data
Current and Predicted U.S. Conditions
- Monthly to seasonal climate outlooks (from NOAA’s Climate Prediction Center)
- State of the Climate report (from the National Climatic Data Center)
- Northern Hemisphere snow report (from the National Climatic Data Center)
- Spring and summer streamflow forecasts (from the USDA Natural Resources Conservation Service)
- Drought in the US
- Water supply forecasts and snowpack conditions for the Western U.S.
- Large fire incidents (from the National Interagency Fire Center)
- Experimental seasonal fire risk forecasts (from the U.S. Forest Service)
- Western U.S. climate conditions and forecasts (from the Western Regional Climate Center)
Pacific Northwest Conditions
- Temperature and precipitation maps (from the Western Regional Climate Center)
- Temperature and precipitation maps (from the High Plains Regional Climate Center)
- Western Washington water and snowpack (from Seattle City Light)
- Seattle water supply conditions and outlook (from Seattle Public Utilities)
- Wildland fires (from the Northwest Interagency Coordination Center)
- Coastal conditions (from NOAA’s CoastWatch)
- monthly snowpack maps for the region (from the National Resource Conservation Service)
State Climatologist Offices
- Drought in central and southwest Asia (from the International Research Institute for Climate Prediction)