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Published April 27, 2011
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
La Niña continued to weaken over the past 30 days and is only hanging on by a thread at this point. Sea surface temperatures have warmed considerably across the equatorial Pacific Ocean and currently are only 0.6 degrees Celsius (about 1 degree Fahrenheit) below average in the eastern Pacific, where a large area of warmer-than-average water has been accumulating just below the surface. These conditions indicate that La Niña is severely diminished and neutral conditions will soon return. The International Research Institute for Climate and Society (IRI) notes that the atmosphere has not yet responded to the recent increases in sea surface temperatures and is still behaving as if a strong La Niña event were present, with above-average easterly winds along the equator and a highly positive Southern Oscillation Index (SOI) (Figure 14a). But the atmospheric response to changes in sea-surface temperatures is typically delayed. A weak La Niña event is expected to continue for the next month or two, with neutral conditions likely returning by early summer. IRI forecasts predict a greater than 50 percent chance that neutral conditions will return during the May–July period, with only a 27 percent chance that La Niña conditions will persist and a 15 percent chance that an El Niño will develop (Figure 14b). There is a slight increase in the odds for development of an El Niño later this summer. La Niña impacts on land may linger for several months, but will probably be of little consequence to Arizona and New Mexico, as May and June are historically hot and dry anyway.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
- 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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