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Published January 25, 2011
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
Moderate to strong La Niña conditions continue to dominate much of the equatorial Pacific Ocean, upholding the current A La Niña Advisory issued by the NOAA-Climate Prediction Center (CPC) in August 2010. Sea surface temperatures (SSTs) slightly cooled in early January, indicating the event is persisting and is showing no immediate signs of weakening. Across much of tropical Pacific Ocean SSTs were greater than 2 degrees Celsius (about 3.5 Fahrenheit) below average with isolated pools of temperatures greater than 2.5 degrees C (about 4.4 F) below average. The Southern Oscillation Index (SOI) and wind currents along the equator suggest a strong atmospheric response to the cold SSTs (Figure 13a). The International Institute for Climate and Society (IRI) notes that a large amount of unusually cold water lies just below the surface across much of the eastern Pacific Ocean. This cold reservoir most likely will make its way to the surface in coming months, helping to reinforce La Niña conditions through the upcoming spring season and perhaps prolong the event.
Official forecasts produced by IRI indicate a high probability that La Niña conditions will continue to persist into the spring season (Figure 13b). Current forecasts indicate a 98 percent chance that La Niña conditions will continue through the January–March period and a 67 percent chance for conditions persisting through the March–May period. The probability of neutral conditions returning to the Pacific Ocean rises to 50 percent by the May–July period. Given the strength of the current La Niña event and the high probability that it will continue through the remainder of the winter season, there is a high chance that the Southwest U.S. will continue to experience below-average precipitation, particularly in southern parts of the region where the influence of La Niña is most strongly felt. La Niña events typically cause winter season storms to track north of the region.
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through December 2010. The SOI measures the atmospheric response to SST changes across the Pacific Ocean Basin. The SOI is strongly associated with climate effects in the Southwest. Values greater than 0.5 represent La Niña conditions, which are frequently associated with dry winters and sometimes with wet summers. Values less than -0.5 represent El Niño conditions, which are often associated with wet winters.
The second figure shows the International Research Institute for Climate and Society (IRI) probabilistic El Niño-Southern Oscillation (ENSO) forecast for overlapping three month seasons. The forecast expresses the probabilities (chances) of the occurrence of three ocean conditions in the ENSO-sensitive Niño 3.4 region, as follows: El Niño, defined as the warmest 25 percent of Niño 3.4 sea-surface temperatures (SSTs) during the three month period in question; La Niña conditions, the coolest 25 percent of Niño 3.4 SSTs; and neutral conditions where SSTs fall within the remaining 50 percent of observations. The IRI probabilistic ENSO forecast is a subjective assessment of current model forecasts of Niño 3.4 SSTs that are made monthly. The forecast takes into account the indications of the individual forecast models (including expert knowledge of model skill), an average of the models, and other factors.
For a technical discussion of current El Niño conditions, visit:
For more information about El Niño and to access graphics similar to the figures on this page, visit:
Southwest Climate Outlook Staff
- Michael Crimmins, UA Extension Specialist
- Stephanie Doster, Institute of the Environment Editor
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, Managing Editor, CLIMAS Associate Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Dollin, CLIMAS Publications Assistant
- Dave Dubois, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
The CLIMAS Web site contains official and non-official forecasts, as well as other information. While we make every effort to verify this information, please understand that we do not warrant the accuracy of any of these materials.... Read full disclaimer