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Published June 20, 2011
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
Sea surface temperatures (SSTs) are near average across much of the eastern equatorial Pacific Ocean and ENSO-neutral conditions are returning after the rapid retreat of La Niña in early May. The Southern Oscillation Index (SOI) values have also dropped toward near-average levels, which is additional evidence that neutral conditions are gaining a stronghold in the Pacific Ocean (Figure 13a). The NOAA-Climate Prediction Center (CPC) notes, however, that remnants of the recent La Niña event, albeit weak, are still persisting in the atmospheric circulation patterns, including slightly enhanced easterly winds along the equator. These conditions are expected to continue to weaken through June as the atmosphere catches up with the SSTs.
Forecasts issued by the International Research Institute for Climate and Society (IRI) show a high probability that neutral conditions will continue through the summer and well into next fall and winter. The chance of neutral conditions persisting is at least 70 percent for all time periods through next December, while El Niño and La Niña have a 15 percent chance of occurring (Figure 13b). IRI notes that some warmer-than-average subsurface water has emerged across the eastern Pacific, raising the prospect of an El Niño event developing, but forecast models do not support this development yet. Both CPC and IRI project neutral conditions through the rest of 2011. The lack of a strong ENSO signal does not clarify monsoon forecasts, which currently have equal chances of above-, below-, and average-precipitation for the monsoon season.
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through March 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.
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