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Published February 23, 2011
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
The La Niña event continues to reign across the equatorial Pacific Ocean but recently has shown signs of weakening. Sea surface temperatures (SSTs) this past week were still quite cool across the eastern Pacific, measuring 1.2 degrees Celsius (about 2 degrees Fahrenheit) below average but have slightly warmed since the end of January. The NOAA-Climate Prediction Center (CPC) also noted that the far eastern Pacific SSTs had warmed to near-average levels, and subsurface water temperatures also had warmed slightly. The weakening event is also evident in the atmosphere. Easterly winds at the surface along the equator are currently with less strength than in previous months. However, the atmosphere is still fully engaged and responding to the current La Niña event, which is evident in the strongly positive Southern Oscillation Index (SOI, Figure 13a).
Forecasts produced by the International Research Institute for Climate and Society (IRI) continue to indicate a high probability (greater than 90 percent) that La Niña conditions will continue into the early spring (Figure 13b). The chance of La Niña conditions persisting into the April–June period falls to 49 percent, while the chance of neutral conditions returning rises to 42 percent. IRI notes that late winter is the typical time for La Niña events to weaken, and that is reflected in forecasts for the remainder of the spring. However, this is the time of year when the El Niño Southern Oscillation (ENSO) forecast confidence is lowest, according to the CPC, so it is unclear whether neutral conditions will rapidly return later this spring or La Niña conditions will continue to linger. Some models suggest a high chance that La Niña will persist for another year.
The continuation of La Niña conditions in the short-term will continue to have profound impacts on the Southwest, likely delivering below-average precipitation to Arizona and New Mexico.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through January 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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