The northern and western United States can expect slightly colder-than-normal conditions this winter, though overall temperatures will be more moderate this winter than in recent years, according to forecasters at Andover, MA-based Weather Services International (WSI).

WSI said it expects this to be the mildest winter the United States has seen since 2006-2007, forecasting a 7.5% reduction in heating demand relative to last winter, which would still be a 4% increase relative to the 1981-2010 average.

November has been fairly mild across major energy demand centers and no quick change to that pattern is expected, but “we do foresee a trend towards colder temperatures across much of the northern U.S., including the Midwest and Northeast, in December,” said WSI Chief Meteorologist Todd Crawford. “The winter pattern will be dominated by the current La Nina event, which favors below-normal temperatures across the northern U.S. and above-normal temperatures across most of the South.”

Temperatures across the eastern United States this winter will also be effected by the North Atlantic Oscillation (NAO), Crawford said. “During the last couple of years, a strong negative phase of the NAO has been dominant, which has resulted in very cold winters across much of the eastern U.S. It does not appear that this extreme negative NAO phase will occur again this winter, which we think will result in a milder winter across all of the eastern U.S. For the December-February aggregate period, we still feel that slightly below-normal temperatures will occur north of a Denver-Philadelphia line and across all of the western U.S.”

WSI’s forecast for both December and January calls for colder-than-normal temperatures across the nation’s northern tier and warmer-than-normal temperatures across the southern tier.

“With relatively mild temperatures expected through the end of November, the colder-than-normal temperatures in the Consuming East and Consuming West in December will create a sharp boost in gas demand. This will likely pressure gas prices higher,” said Energy Securities Analysis Inc. (ESAI) Senior Analyst Chris Kostas. “The December Nymex Henry Hub contract hit fresh life-of-contract lows in mid-November, trading as low as $3.33/MMBtu. Spot gas prices will likely trade higher than this level in December, once the below-normal temperatures take hold. Some of the increased demand from the North and West will be offset by the slightly warmer-than-normal temperatures that are expected throughout the South, however. Historically, a colder-than-normal December often translates into firm Henry Hub prices as traders with gas in storage are hesitant to sell significant volumes so early in the season.”

In January new limits on sulfur dioxide emissions are likely to slightly reduce coal-fired power generation and thereby slightly increase demand from gas-fired generations in the Midwest, Kostas said.

“Despite increased supplies from Marcellus Shale and robust drilling activity, natural gas inventories are likely to draw down meaningfully in January as a result of the cold. Though some of the increased demand expected in the North and West will be offset by warmer-than-normal temperatures in the South, the trend toward higher spot gas prices that we believe will begin in December should continue into January,” Kostas said.

Colder-than-normal temperatures will remain in place over the northern tier in February and are expected to move into the Southwest as well, while the Southeast and South Central areas will continue to average warmer than normal, according to WSI’s winter forecast.

“While New York, New England and the Great Lakes region are expected to run slightly colder-than-normal in February, a large portion of the Midwest and the Mid-Atlantic region will run slightly warmer than normal,” Kostas said. “Combined with warmer-than-normal temperatures throughout the Southeast, the mild temperatures should soften aggregate heating demand in February. This could soften delivered gas prices along the Northeast relative to January. The West Coast may not participate in the softer gas price trend of the East, however, as slightly colder-than-normal temperatures are expected in that region.”

The National Oceanic and Atmospheric Administration (NOAA) has also said the current La Nina event — the cooling of Pacific Ocean surface temperatures off the coast of South America — will influence North American weather patterns, but NOAA expects 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 (see Daily GPI, Nov. 18). NOAA expects the current La Nina, which formed in August, to gradually strengthen and continue through this winter.

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).

WSI is scheduled to issue its next seasonal outlook on Dec. 20.

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