A La Nina event off the west coast of South America, which brought brutally cold and snowy weather to a large part of the country last winter, is expected to again influence conditions this winter, prompting especially harsh temperatures and snowfall across the Midwest and Great Lakes region, while the Northeast can expect winter 2011-2012 to be somewhat less extreme than last year, according to forecasters at AccuWeather.com.

“The way the jet stream is expected to be positioned during this winter’s La Nina will tend to drive storms through the Midwest and Great Lakes,” said AccuWeather.com meteorologist Heather Buchman. “Last year, the jet stream steered storms farther east along the Northeast coast, hammering the Interstate 95 corridor. Therefore, instead of New York City enduring the worst of winter this year, it will likely be Chicago.”

Bitter blasts of arctic air, along with above-normal snowfall averages, are expected in the northern Plains, Midwest and Great Lakes in December and January. The buildup of snow cover across the Midwest and Great Lakes could act to prolong the colder-than-normal weather beyond February and into early spring, the forecaster said.

While winter’s worst may not be focused over the major cities of the Northeast, there could be a few significant snow and ice storms that could pack a punch for the region, according to Paul Pastelok, leader of AccuWeather.com’s long-range forecasting team.

Snowfall is forecast to average near or slightly above normal south and east of the Appalachians from Virginia to Maine, with most of the snow expected to fall in December and January. The interior Northeast is predicted to be colder and snowier than areas closer to the coast, according to AccuWeather.com forecasters, who said an early, heavy lake-effect snow season will put areas from northwestern Pennsylvania into western New York into the zone of winter’s worst snow and cold. Precipitation is expected to be above normal throughout most of the Northeast in January and February.

AccuWeather.com forecasters said they expect ice events to be a problem from the southern Plains to the southern Appalachians this season and a severe weather threat to develop in the Lower Mississippi Valley in February. Much of Texas and the Southwest, which have been suffering through a severe drought, are forecast to have a “mild and dry” winter.

“The interior Southwest will be the driest area of the country through winter,” Pastelok said.

Weather Services International (WSI) recently said it expects the northern and eastern United States to experience cooler-than-normal temperatures through December (see Daily GPI, Sept. 21). The newly emerging La Nina event and a trend toward North Atlantic atmospheric blocking indicate below-normal temperatures becoming more common in the eastern U.S. in November and across all of the northern U.S. by December, according to Todd Crawford, chief meteorologist at WSI.

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