The current La Nina event — the cooling of Pacific Ocean surface temperatures off the coast of South America — remains unchanged and is expected to continue through the Northern Hemisphere’s winter season, influencing weather patterns across the United States for the next several months, according to the National Oceanic and Atmospheric Administration (NOAA).

Temperatures through February are expected to average below normal in California, Nevada, the Pacific Northwest and the northern Plains, with warmer-than-normal temperatures to be in place across much of the South, including the southern Ohio Valley and southern Mid-Atlantic areas, NOAA forecaster Jon Gottschalck said Thursday.

As it said last month, NOAA also expects La Nina and the less predictable Arctic Oscillation to extend drier-than-average weather conditions across a significant portion of the southern United States (see Daily GPI, Oct. 24).

NOAA expects the current La Nina, which formed in August, to gradually strengthen and continue through this winter.

Andover, MA-based forecaster Weather Services International (WSI) recently said it expects colder-than-normal temperatures to dominate the Northeast through at least January, although conditions indicate that the cold “will not be as extreme as it was during the last two winters” (see Daily GPI, Oct. 25). WSI forecasters said they believe “that the worst of the cold across the northern and eastern U.S. will be in December and January, and that the back half of winter could be significantly milder.” WSI’s forecast calls for a 6% reduction in heating demand relative to last winter, but a 5% increase relative to 1981-2010 averages. WSI is scheduled to issue its next seasonal outlook on Nov. 22.

Forecasters at AccuWeather.com have said they expect the La Nina event to prompt especially harsh temperatures and snowfall across the Midwest and Great Lakes region, while the Northeast can expect winter 2011-2012 to be less extreme than last year (see Daily GPI, Oct. 6).

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