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Published January 24, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
In the last 30 days, the average temperature in the upper 300 meters (about 1,000 feet) of the eastern Pacific Ocean cooled. The most recent average weekly sea surface temperature (SSTs) across parts of the tropical Pacific Ocean was about 1 degree Celsius below average, indicative of a weak to moderate La Niña event. Also, in this region the near-surface easterly winds strengthened over the central and west-central Pacific, and the Southern Oscillation Index (SOI), which measures the atmospheric circulation in the tropical Pacific Ocean, increased (Figure 13a). These conditions suggest the ocean and atmosphere are working in concert to maintain the La Niña event. This evolution is consistent with past events, in which the atmospheric components of La Niña become strongest and most well defined during the winter.
There is a strong likelihood that the weak to moderate strength of this event will continue for a month or more before it begins to weaken in late February and March, according to the International Research Institute for Climate and Society (IRI). Based on both statistical and dynamical forecast models, there is greater than a 95 percent chance that the La Niña will continue during the January–March period (Figure 13b). In the March–May period, chances become about equal for either a neutral event or a La Niña; by April–June it is likely that neutral conditions will return. Continued La Niña conditions likely will cause dry conditions in Arizona and New Mexico, according to the NOAA-Climate Prediction Center.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through December 2011. 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, 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
- Dan Ferguson, CLIMAS Program Director
- Gregg Garfin, Founding Editor, Institute of the Environment
- Zack Guido, CLIMAS Associate Staff Scientist
- Gigi Owen, CLIMAS Assistant Staff Scientist
- Nancy J. Selover, Arizona State Climatologist
- Jessica Swetish, CLIMAS Publications Assistant
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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