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Posted at 11:16 AM ET, 10/05/2011

AccuWeather: Expect second straight “brutal” winter in US north; slightly above normal snow, average temps in D.C.


AccuWeather winter outlook highlights. ( AccuWeather.com )
AccuWeather released its winter forecast this morning and is calling for a repeat performance of last winter’s harsh conditions, especially across the northern tier of the U.S. Like the winter of 2010-2011, La Nina, an episodic cooling of the tropical Pacific ocean, is the dominant player influencing its predictions.

La Nina events tend to favor a strong polar branch of the jet stream, which activates big cold air outbreaks. And when the cold air interacts with warm air coming up from the south, big storms often develop in the transition zone.

The State College-based forecast company anticipates the transition zone will set up slightly west of where it did last year, dealing winter’s most severe blow from the Ohio Valley to the Great Lakes and Northern Plains.

“The way the jet stream is expected to be positioned during this winter’s La Niña will tend to drive storms through the Midwest and Great Lakes,” AccuWeather said. “Last year, the jet stream steered storms farther east along the Northeast coast, hammering the Interstate 95 corridor.”

This year, cities like Detroit, Cleveland, Chicago and Minneapolis may be hardest hit.

Keep reading for what AccuWeather expects in the mid-Atlantic, including Washington, D.C., Northeast, and other parts of the country


AccuWeather winter outlook highlights for Northeast and mid-Atlantic. ( AccuWeather.com )
In the mid-Atlantic (including Washington, D.C.), AccuWeather senior meteorologist Paul Pastelok predicts winter will start off with a bang, but then gradually moderate. He examined analogs, past years with weather patterns similar to the present, and found the winter 2008-2009 closely mirrors what this region might expect.

“We saw most of our winter in the first half,” Pastelok said. “January then flipped, it became mild and we saw quite a bit of rainfall.”

During the second half of the winter, Pastelok believes the jet stream will migrate west, allowing the cold air to erode in the mid-Atlantic and Northeast. Such a shift would favor “Appalachian cutters,” storms tracking well to the west of the I-95 corridor. These storms usually bring rain and/or mixed precipitation along the Eastern seaboard rather than wsnow.

The second half of winter may also feature high pressure building over the Southeast as the jet stream shifts west, favoring occasional mild stretches Pastelok said.

Overall, here’s how Pastelok described the evolution of winter temperatures in the Washington, D.C. metro region:

December is probably going to be the coldest month - November back and forth a little bit. In January, I’m leaning a little bit cold, but February turns it around. We’re aiming at near normal temperatures. There will be ups and down, mostly downs the first part [of winter], mostly ups second half.

As for snowfall, using a combination of past analogs and computer model guidance, Pastelok is predicting slightly above average snow in the Washington, D.C. metro region.

“I could see snowfall this year reaching close to 20” but it would have to come earlier on,” Pastelok said.

While only 7.5” of snow fell during the 2008-2009 “analog” year in D.C., Pastelok sees signals in the Arctic sea ice evolution which may favor a negative phase of the North Atlantic Oscillation (NAO) pattern , conducive to cold, snowy weather during the first part of winter.

AccuWeather meteorologist Henry Margusity shared ideas similar to Pastelok on his Facebook page:

Overall, I like the forecast, just think the bulk of snow will be in the Appalachians and Northeast this year. Above normal snows for DC to NYC I believe. Also, St Louis, Chicago, Detroit, Cleveland also above normal.

Matt Ross, lead author for Capital Weather Gang’s winter outlook to be released around November 1, had this take on AccuWeather’s outlook

Although Accuweather’s outlook is a pretty cold and snowy one for the Midwest and west of the mountains, the key takeaway for our region is to expect a fairly typical La Nina pattern.  Quite cold at times, but with a prevalent storm track to our west, often dry when it does get cold

CWG’s winter weather expert Wes Junker sent along the following reaction:

I agree with Matt. The forecast is pretty much in line with a typical La Nina-like storm track to our west. La Ninas tend to have big swings in temperatures.... This year the complication is what the NAO will do as it’s been running negative for decent chunks during the last several winters. The same will probably hold this winter as we seem to have cycled into a period with more blocking in the North Atlantic than we had in the 1990s and early part of the decade. That blocking [negative NAO] probably will give us some chances for snow even with a La Nina. But with such a strong northern stream, we still may only get fringed with storms sort of like last year. Except for the Northern Plains, I don’t think this will be an easy year for seasonal forecasters.

Here are some additional summary points from the AccuWeather outlook:

Northeast U.S.: Not as extreme as 2010-2011; a few “significant impact” winter storms; much above normal snow north and west of the Appalachians. More info.

Southern States: More ice than snow for northeastern Texas and Oklahoma into Kentucky and Tennessee; significant severe weather and flood events in lower Mississippi Valley in February. More info.

Southwest and Texas: “Mild and dry”, more drought in Texas - with below average precipitation in entire region. More info.

West coast: Big temperature swings, starting warm in December, then cooling. Potentially a period active storminess with excessive rain and snow. More info.

By  |  11:16 AM ET, 10/05/2011

Categories:  Winter Storms, Latest

 
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