Winter Forecast: Cold Winter More Likely For Some

http://www.weather.com/outlook/weather-news/news/articles/Winter-Forecast-Cold-Winter-More-Likely-For-Some_2012-11-29

"After an extended spell of above-normal temperatures across much of the U.S. during the past 18 months, the last few months have been characterized by below-normal temperatures across much of the eastern U.S., as a weak El Nino event has tried to emerge," said Dr. Todd Crawford, Chief Meteorologist at WSI, part of The Weather Company.

"While this El Nino event now appears to be a dud, most of our more skillful climate indicators suggest that very cold air will be in plentiful supply across western and central Canada this winter, with frequent border crossings into the northern U.S.," Crawford added. "Currently, we do not expect the kind of frequent atmospheric blocking in the North Atlantic that would result in more extreme and more widespread cold in the eastern U.S.  However, trends in some of the long-lead indicators suggest that this assumption may be challenged, and that the risk to the forecast in the eastern U.S. is towards the colder side."

Stu Ostro, senior meteorologist at The Weather Channel (Twitter | Facebook), notes that atmospheric blocking has been a major player in recent winters.

"That phenomenon of atmospheric 'blocking' by strong ridges of high pressure over Greenland and thereabouts is a key factor for winter weather downstream in the northeast United States, and it has been of overwhelming importance the past three winters," Ostro said.

"There was extreme blocking in 2009-10 and 2010-11, with arctic air and snowstorms repeatedly tackling the Northeast urban corridor. Then last winter, there was an equally extreme lack of Greenland blocking, in turn with relatively little cold air and snow in that and other parts of the U.S.

"Now, in autumn 2012, we've been seeing a tendency for a return of strong ridges over eastern Canada and Greenland.  That pattern is what forced Sandy to take the track it did, and was favorable for 'Athena' the following week and this week's systems bringing more coastal flooding to the Outer Banks.  We'll be watching very closely to see the extent to which this trend continues."

December Winter Forecast

The winter forecast for December calls for the coldest temperatures, relative to normal, to stretch from Seattle to Duluth, Minn. Unseasonably warm weather is expected from Phoenix to Houston.

January Outlook

The winter forecast for January calls for below-normal temperatures across the North, from Portland, Ore., to Portland, Maine. Unseasonably mild weather should prevail from Las Vegas and Denver to Dallas-Fort Worth.