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Published March 21, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
La Niña conditions weakened substantially during the past 30 days and the NOAA-Climate Prediction Center (CPC) states that March will probably be the last month with an active La Niña Advisory, as ENSO-neutral conditions are expected to return by the end of April.
During the last couple of months, a pool of cold water below the sea surface has been critical in supporting the La Niña. This below-surface water has substantially warmed in the eastern Pacific over the past 30 days and, in combination with rising sea surface temperatures (SSTs), indicate the days are numbered for the La Niña event. Ocean water is usually the leading indicator of changes in ENSO conditions and it will take the atmosphere several months to catch up. Current atmospheric circulation patterns remain very La Niña-like, with enhanced easterly winds and suppressed convection in the central Pacific. Consequently, the Southern Oscillation Index (SOI) remains positive (Figure 13a). This pattern should yield to typical atmospheric circulation patterns by the late spring and summer.
Official forecasts issued jointly by NOAA-CPC and the International Research Institute for Climate and Society (IRI) indicate greater than a 70 percent chance that ENSO-neutral conditions will develop in the April–June period (Figure 13b). Forecasts also indicate that ENSO-neutral conditions will likely persist through the upcoming summer and fall seasons. The chance of an El Niño event returning also rises by late summer, but confidence is low in the forecast. However, since 1900 there have been 10 two-year La Niña events. In four of these events, La Niña endured for a third consecutive winter, while El Niño developed in the other six winters.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through February 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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