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Published July 25, 2011
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
Near-average sea surface temperatures (SSTs) reigned across the equatorial Pacific Ocean again this past month, reflecting ENSO-neutral conditions. Values of the Southern Oscillation Index (SOI), which tracks the atmospheric response to ENSO events, also dropped close to zero last month after peaking at record high values in April and May (Figure 14a). This also reflects a return to neutral conditions. There are some weak and lingering remnants of the La Niña event in the atmosphere, but they are having little impact on overall atmospheric circulation patterns, according to the NOAA-Climate Prediction Center (CPC).
Forecasts issued by the International Research Institute for Climate and Society (IRI) indicate a strong chance—greater than 80 percent—that neutral conditions will persist through the summer. This decreases in the fall to about 60 percent, while the chance that El Niño or La Niña will develop is 14 and 26 percent, respectively (Figure 14b). However, the combination of a weak but lingering La Niña pattern in the atmosphere and the emergence of slightly cooler-than-average water temperatures below the surface in the eastern Pacific suggest a possible return of La Niña conditions in the upcoming fall or winter. Most forecast models still paint the return of La Niña as an unlikely outcome, but the area of cool subsurface water will be monitored closely over the next several months. The return of La Niña conditions could be bad news for an already parched Southwest battered by a record dry winter and spring. La Niña events have a strong tendency to drive the winter storm track north and away from Arizona and New Mexico, as was the case this past winter.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through May 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
- 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 Dubious, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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