Big change coming for mid/late December?

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Weather bulletin boards have been abuzz for several days with discussions about a major change in the weather pattern coming later this month for the central and eastern United States, including the Southeast.

This could have major ramifications on a lot of people's travel plans over the Christmas and New Years holidays.

The consensus seems to be that two changes are headed our way:

-- Wetter conditions, which seems rather likely.

-- Colder weather, which is not quite a certain bet.

The computer models, for the most part, show a shift in the pattern at higher latitudes (i.e., Alaska, Canada, Greenland, northern Europe) that would allow much colder air to slide southward into the United States. Some of the models have been inconsistent on the details, but it seems likely that the colder air will at least reach the northern half of the country.

That, in turn, will push the storm track -- which has been north of the Carolinas -- a lot farther south. We could see a hint of that next week, with wetter conditions in parts of the Southeast.

Eventually, the thinking goes (at least for some meteorologists), colder air will seep even farther south. Add that to a much wetter pattern, and you have the chance of cold rain or frozen precipitation in parts of the south.

When will this happen?  The consensus seems to be somewhere around Dec. 20, just before Christmas.

My brother Michael, who I've written about before, has been harping about this to me for several days. He's much better at interpreting the models, and Michael insists a colder and stormy pattern will descend into the central and eastern part of the country as December progresses.  I'll take his word.  He correctly predicted the major pattern shift in mid-February 2011, when the Southeast turned balmy after 2 1/2 frigid months, and last winter's very mild conditions.

Some signs point to the eventual arrival of cold air in the Southeast. There's a negative North Atlantic Oscillation and Arctic Oscillation, and the computer models show signs of high pressure building in Alaska. Those are conditions that mean cold in the eastern United States.

But there also is a persistent trough in the Pacific, which has blocked the southward movement of cold air. 

I suspect this is a topic we'll be following closely over the next 10 to 14 days.