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Published April 25, 2012
El Niño Status and ForecastData Source(s): NOAA-Climate Prediction Center (CPC), International Research Institute for Climate and Society (IRI)
The La Niña conditions that have dominated since September and contributed to the dry conditions in the Southwest ceded ground to ENSO-neutral conditions in the first two weeks of April. Sea surface temperatures (SSTs) in the east-central tropical Pacific Ocean remain slightly negative at -0.3 degrees Celsius below average but are no longer cool enough to be characterized as La Niña. Several indicators point to conditions remaining ENSO-neutral over the next several months, including a large pool of warmer-than-average water just below the surface in the eastern Pacific Ocean. As this water makes its way to the surface, it will warm SSTs to near- or above-average temperatures, consistent with an ENSO-neutral state. Despite warming of the SSTs in recent weeks, the atmosphere is still reflecting La Niña-like circulation patterns and the Southern Oscillation Index (SOI) remains positive, according to the NOAA-Climate Prediction Center (NOAA-CPC; Figure 14a). Changes in the atmosphere typically lag behind changes in SSTs.
Overall, most models project that neutral conditions will persist through the upcoming summer months. The official forecast issued jointly by the CPC and International Research Institute for Climate and Society (IRI) indicates a high likelihood that ENSO-neutral conditions will be present during May–July and assigns greater than a 55 percent chance that neutral conditions will persist through the June–August season (Figure 14b). Also, several dynamical models are starting to pick up on the possibility of El Niño conditions developing as early as the July–September season. A shift towards El Niño this summer could decrease summer rains; there is a weak correlation between El Niño and below-average monsoon rain in southeastern areas of the region. Also, if El Niño continues into late 2012, the event will increase chances for above-average precipitation in the fall and winter.Notes:
The first figure shows the standardized three month running average values of the Southern Oscillation Index (SOI) from January 1980 through March 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
- 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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