If you're planning on celebrating Christmas in the Upper Midwest or the Dakotas this year, you're going to need to get a thicker coat.。

A true Arctic air mass -- the coldest of the season so far -- is projected to swirl down from the Far North, crossing the U.S. border with Canada as early as Wednesday, and potentially oozing its way all the way down to Texas, and east to New York City. 。

Right now, however, it appears the East Coast may escape the worst of the cold, at least initially.
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The precise details of this cold snap are still a bit fuzzy, specifically concerning whether a winter storm develops along the boundary separating the frigid air from more seasonable temperatures. It's conceivable that areas from Texas to New England could have a white or icy Christmas this year, though this won't become clear for another few days.
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In Denver, Christmas Eve could see temperatures as cold as 30 to 40 degrees Fahrenheit below average, according to computer model guidance. On Christmas Day itself, the core of the coldest air may be located over the big cities of the Midwest, including Minneapolis, Milwaukee, and Chicago. While low temperatures may plunge below zero Fahrenheit, this cold snap is not likely to break many records, in part because of the lack of widespread snow cover across the U.S.。

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As detailed in a post by the Washington Post's Capital Weather Gang blog, computer model projections do not yet agree on whether the frigid weather will move far enough east to affect the heavily-populated corridor from Washington, D.C. to Boston. 。

The cold blast will have the opposite affect in the Arctic, where unusually mild temperatures for this time of year (it will still be cold, just not as cold as usual) are forecast. Temperatures in Alaska could be 30 to 40 degrees Fahrenheit above average, while Arctic-wide temperatures also look to be far above average as well.
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The development of this warm Arctic, cold continents pattern is something researchers have been noticing that appears to be occurring more frequently during recent winters. The pattern is consistent with recent changes in the wintertime jet stream, which some scientists think is tied to the loss of Arctic sea ice. However, this is still an area of active research, with no clear consensus yet. 。

Computer model projection showing unusually mild air across Alaska and other parts of the Arctic Ocean on Dec. 23, 2017.Credit: weatherbell。

On Monday, the National Oceanic and Atmospheric Administration (NOAA) reported that the average Arctic sea ice extent during November was 11.6 percent below the 1981-2010 average. This was the third-smallest since records began in 1979.。

The average Arctic sea ice coverage in November was 11.6 percent below the 1981-2010 average, the third-smallest since records began in 1979. The Chukchi and Bering Seas off the northwest coast of Alaska were almost completely devoid of sea ice, which has been altering the weather across Alaska and adjacent parts of Russia as well.
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This is causing problems for animals as well as human populations that rely on the sea ice for hunting prey.。

This is causing problems for animals as well as human populations that rely on the sea ice for hunting prey. 。

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One of the main reasons for the cold snap will be a major northward bulge, or ridge, in the jet stream across the West, which will exacerbate California's wildfire problem. 。