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Published March 24, 2011
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
La Niña has weakened considerably over the past 30 days but continues to persist at a weak to moderate state. Sea surface temperatures (SSTs) over the eastern and central Pacific Ocean have warmed slightly to just 1.0 degree Celsius below average (up from -1.2 degrees C last month), indicative of weakening La Niña conditions. The atmosphere is lagging the changing SST conditions and continues to show a strong La Niña-like circulation pattern with stronger-than-average easterly winds along the equator and an above-average Southern Oscillation Index (SOI) value for this time of year. (Figure 13a). The International Research Institute for Climate and Society (IRI) notes that it is typical for the atmosphere to lag behind a weakening La Niña evident in warming SSTs, but that the lag should only last for a month or two. IRI also notes that the spring is a challenging time to forecast potential changes in the ENSO conditions for the upcoming spring and summer seasons, but there is growing evidence that the current La Niña event will continue to weaken, yielding to neutral conditions by summer.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through February 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, the 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 Dubois, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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