Scientists are predicting the lingering effects of La Niña weather conditions as the winter gets underway.

Last season’s incredible winter across almost all of North America was primarily the result of an El Niño pattern that produced heavy season-long snows from Taos to Whistler. La Niña, however, has typically meant wetter conditions in the northern part of the country while the southern states see drier conditions. No telling at this point if those conditions will hold true, or, more importantly, if La Niña will last into the new year.

Here’s the real science from the folks who know: ENSO-neutral conditions continued during August 2008, as recent increases in sea surface temperatures (SSTs) abated across the equatorial Pacific Ocean. Above-average SSTs in the east-central and eastern Pacific diminished, while below-average SSTs in the central Pacific strengthened slightly.

The subsurface oceanic heat content also decreased in response to the emergence of negative temperature anomalies at thermocline depth in the east-central Pacific.

Although ENSO-neutral conditions have been in place since June 2008, the atmospheric circulation over the western and central tropical Pacific continues to reflect lingering aspects of La Niña. Enhanced low-level easterly winds and upper-level westerly winds persist in this region, while convection remains generally suppressed over the central Pacific. Despite this lingering La Niña signal in the atmosphere, the overall atmospheric and oceanic system is consistent with ENSO-neutral conditions.
Most of the dynamical and statistical SST forecasts for the Niño 3.4 region indicate a continuation of ENSO-neutral conditions (−0.5°C to 0.5°C in the Niño-3.4 region) through the Northern Hemisphere Spring 2009. While the model spread continues to include the possibility of an El Niño, the decrease in subsurface and surface temperatures makes this outcome unlikely during the next several months. In addition, the redevelopment of negative temperature anomalies at thermocline depth and the historical tendency for multi-year La Niña episodes means that even a return to weak La Niña conditions is possible. However, based on current atmospheric and oceanic conditions, recent trends, and model forecasts, ENSO-neutral conditions are expected to continue through the end of 2008.