El Niño Status and Forecast

Moderate to strong La Niña conditions continue to dominate much of the equatorial Pacific Ocean, upholding the current A La Niña Advisory issued by the NOAA-Climate Prediction Center (CPC) in August 2010. Sea surface temperatures (SSTs) slightly cooled in early January, indicating the event is persisting and is showing no immediate signs of weakening. Across much of tropical Pacific Ocean SSTs were greater than 2 degrees Celsius (about 3.5 Fahrenheit) below average with isolated pools of temperatures greater than 2.5 degrees C (about 4.4 F) below average. The Southern Oscillation Index (SOI) and wind currents along the equator suggest a strong atmospheric response to the cold SSTs (Figure 13a). The International Institute for Climate and Society (IRI) notes that a large amount of unusually cold water lies just below the surface across much of the eastern Pacific Ocean. This cold reservoir most likely will make its way to the surface in coming months, helping to reinforce La Niña conditions through the upcoming spring season and perhaps prolong the event.

Official forecasts produced by IRI indicate a high probability that La Niña conditions will continue to persist into the spring season (Figure 13b). Current forecasts indicate a 98 percent chance that La Niña conditions will continue through the January–March period and a 67 percent chance for conditions persisting through the March–May period. The probability of neutral conditions returning to the Pacific Ocean rises to 50 percent by the May–July period. Given the strength of the current La Niña event and the high probability that it will continue through the remainder of the winter season, there is a high chance that the Southwest U.S. will continue to experience below-average precipitation, particularly in southern parts of the region where the influence of La Niña is most strongly felt. La Niña events typically cause winter season storms to track north of the region.