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Published February 22, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
The La Niña event is expected to continue for the next several months, according to the NOAA-Climate Prediction Center (CPC). Sea surface temperatures (SSTs) in the equatorial eastern Pacific Ocean in the last month were close to -1 degree Celsius below average, indicating a weak to moderate event. Above-average, near-surface easterly winds also persisted over the central and west-central Pacific, causing the Southern Oscillation Index (SOI), which measures the atmospheric circulation in the tropical Pacific Ocean, to remain positive (Figure 13a). Positive SOI values are also indicative of a La Niña event, but the event appears to be waning. Observations of warming SSTs in the far eastern Pacific Ocean and increasing subsurface water temperatures both suggest La Niña may be peaking or may have peaked. In addition, this is the time of year when ENSO events historically begin to lose strength.
The official forecast issued by the CPC and the International Research Institute for Climate and Society (IRI) indicates a 74 percent chance that La Niña will continue during the February–April period (Figure 13b). However, based on both statistical and dynamical forecast models, chances precipitously drop for the continuation of La Niña into the March–May period and beyond. The impacts of the La Niña event, including drier-than-average conditions in parts of the southern U.S., likely will continue through the remainder of the winter and into the spring—despite a weakening event—because changes in atmospheric circulation lag behind changes in SSTs. This is reflected in the recent seasonal forecasts that call for below-average precipitation for both Arizona and New Mexico through the upcoming spring.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through January 2012. 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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