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Published May 26, 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 that drove record dry conditions across parts of southeast Arizona and much of New Mexico this past winter has officially come to an end. The NOAA–Climate Prediction Center (NOAA–CPC) reports that sea surface temperatures (SSTs) have warmed to near-average levels across much of the eastern Pacific Ocean and are indicative of a return to ENSO-neutral conditions. The International Research Institute for Climate and Society (IRI) also notes that the Southern Oscillation Index (SOI) rapidly shifted from near-record levels in April to near-average values as of mid-May in concert with the warming SSTs (Figure 15a). The shift in the SOI indicates the atmosphere is rapidly adjusting back to an ENSO-neutral circulation pattern and that the lagging effects and impacts of the recent La Niña event may be short-lived.
IRI notes this is a particularly difficult time of year to develop longer-range ENSO forecasts, but short-term forecasts consistently point toward the persistence of ENSO-neutral conditions through at least the summer. IRI forecasts predict a 57 percent chance that neutral conditions will continue through the June–August period, with a 22 percent chance that La Niña conditions will return and a 21 percent that an El Niño event will develop (Figure 15b). These forecast probabilities remain relatively constant through next fall and winter. Some models have hinted at the possibility of a weak El Niño developing later this summer or fall, but forecast confidence is very low. ENSO-neutral conditions provide very little forecast guidance through the summer season in Arizona and New Mexico; this is reflected in the equal chances July–September precipitation outlook recently posted by NOAA–CPC
(see Figures 11a–d).
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through March 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, 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 Dubious, New Mexico State Climatologist
Please direct your Southwest Climate Outlook comments and suggestions to Zack Guido.
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