December weather has been relatively mild so far, but the nation’s northern tier can expect temperatures to average colder than normal until at least early spring, according to forecasters at Andover, MA-based Weather Services International (WSI).

From a gas demand perspective, the next three months could be the mildest since 2006, according to WSI, which forecast a 5.4% reduction in heating demand relative to last winter. Nevertheless, that would be a 4.3% increase relative to the 1981-2010 average. A much stronger polar vortex and the lack of any atmospheric blocking, which is the primary cause for colder eastern temperatures, has made the season different than the last two, the forecasters said.

“So far the heating season has been fairly mild across the major energy demand centers of the U.S. as a very strong polar vortex has kept most of the significant and sustained cold out of the eastern U.S.,” said WSI Chief Meteorologist Todd Crawford. “While no significant short-term change to this pattern is expected, we do foresee at least a slight weakening of the polar vortex heading into January. This will increase the odds of some colder spells in the Northeast.

“The general pattern for the remainder of winter will continue to be dominated by the current La Nina event, which favors below-normal temperatures across most of the northern and western U.S. and above-normal temperatures across most of the South.”

The National Oceanic and Atmospheric Administration (NOAA) also has said the current La Nina event will influence North American weather patterns (see Daily GPI, Nov. 18). NOAA expects the current La Nina, which formed in August, to gradually strengthen and continue through the winter. And 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).

Temperatures will average colder than normal across the Northern tier and in the Southwest in January, according to WSI, while warmer-than-normal temperatures are expected to be in place in the Southeast and South Central areas. That forecast is slightly bullish for natural gas demand, said Paul Flemming, Energy Security Analysis Inc. (ESAI) director of power and gas.

“Effective under the new Cross State Air Pollution Rule starting Jan. 1, new limits on SO2 (sulfur dioxide) and NOx (nitrogen oxide) emissions are also likely to have a measurable bullish impact on gas demand, in addition to the colder weather,” Flemming said in a statement issued in conjunction with WSI’s outlook. “Natural gas inventories are likely to experience significant drawdowns in January as a result of higher heating demand, although possibly less than in previous years. Increased demand expected in the Northern and Western regions will be somewhat offset by warmer-than-normal temperatures in the South.”

WSI’s temperature forecast remains unchanged in February, with colder-than-normal temperatures again expected to dominate the Northeast, North Central, Northwest and Southwest. But warmer-than-normal temperatures in portions of the Midwest, Mid-Atlantic and Southeast regions “should soften aggregate heating demand in February and are likely to soften delivered gas prices in the Northeast markets, relative to January,” Flemming said. “Milder weather and softer delivered natural gas prices will combine with lower loads to moderate power prices in the eastern markets.”

WSI expects warmer-than-normal temperatures to move into the Southwest by March, but temperatures will continue to average colder than normal across the northern tier.

“Late winter gas demand in March could be supportive of prices, although following milder February conditions and generally higher natural gas production expectations, bullish expectations for natural gas prices may be limited,” Flemming said. “Delivered gas prices to destination markets should decline as temperatures increase through March; and combined with marginally lower electric loads, power prices in most markets should be moderate.”

WSI is scheduled to issue its next seasonal outlook on Jan. 24.

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