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Published August 25, 2010
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
The NOAA–Climate Prediction Center (CPC) has issued a La Niña Advisory, which means that a La Niña event has been observed and is expected to continue. In the last month, La Niña conditions continued to strengthen across the equatorial Pacific Ocean. Sea surface temperatures (SSTs) are now 1 degree Fahrenheit below average across the eastern Pacific Ocean, indicating a weak event is underway. The Southern Oscillation Index (SOI) rocketed to a value of 2 in July from a meager 0.1 in June (Figure 14a). This large swing in SOI values is evidence that the atmosphere has noticed the shift towards cooler SSTs in the Pacific Ocean and is responding with large-scale shifts in circulation patterns across the region. Winds from the east also have strengthened along the equator, driving more upwelling of cold water in the eastern tropical Pacific Ocean, which is serving to further strengthen the event.
Forecasts issued by the International Research Institute for Climate and Society (IRI) show a high probability that La Niña conditions will continue to persist and possibly strengthen over the next several months. The chance of the current La Niña event continuing through the upcoming winter season exceeds 90 percent, while there is only a 1 percent chance than an El Niño event will return during this period (Figure 14b). Seasonal precipitation forecasts issued by the CPC reflect the high probability for the La Niña event to continue this winter and show increased chances of drier-than-average conditions across all of Arizona and New Mexico.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from August 1980 through December 2009. 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.
The CLIMAS Web site contains official and non-official forecasts, as well as other information. While we make every effort to verify this information, please understand that we do not warrant the accuracy of any of these materials.... Read full disclaimer