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Published October 24, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
The shift towards El Niño conditions continued to slow during the past thirty days, introducing some doubt on when and if an official El Niño event would develop this fall. While the NOAA Climate Prediction Center (CPC) continues to issue an ‘El Niño watch,’ meaning an El Niño is expected to materialize in coming months, discussions among forecasters indicate that the expectation is for a weak event at best. Forecasters cite evidence that the sea-surface temperature (SST) pattern across the equatorial Pacific Ocean has cooled to near-average conditions over the past month. The CPC also notes that atmospheric circulation patterns do not look characteristic of the beginning of an El Niño event, and the pattern is not helping to jumpstart warming SSTs across the eastern Pacific Ocean—the Southern Oscillation Index (SOI) remains in ENSO-neutral values (Figure 11a). One favorable sign pointing toward the development of an El Niño is the existence of thunderstorm activity along the equator near the International Date Line. There is a small chance that this activity could spread eastward and help strengthen the El Niño event.
Official forecasts issued jointly by CPC and the International Research Institute for Climate and Society (IRI) show declining chances of an El Niño event forming in the next several months, but they still remain above 50 percent (Figure 11b). In the October–December period, forecasts call for a 56 percent chance that El Niño will occur, down from 69 percent issued last month. If El Niño does take hold, it is expected to be short-lived, and neutral conditions are expected to be back in control by mid-winter. The bottom line is that even if El Niño does materialize, it will likely not be a big player in weather across the Southwest this winter.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through September 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
- 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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