Big Chill in a Warmer World: What’s Going On?

Anchorage, Alaska, was warmer Tuesday than Jacksonville, Florida. The weather in the U.S. is that upside down. That's because the Arctic's deeply frigid weather escaped its regular atmospheric jail that traps the worst cold. It then meandered south to the central and eastern United States.

And this has been happening more often in recent times, scientists say.

Why Is It So Cold?

Super cold air is normally locked up in the Arctic in the polar vortex , which is a gigantic circular weather pattern around the North Pole. A strong polar vortex keeps that cold air hemmed in.

"Then when it weakens, it causes like a dam to burst," and the cold air heads south, said Judah Cohen, a winter storm expert for Atmospheric Environmental Research, a commercial firm outside Boston.

"This is not record-breaking for Canada or Alaska or northern Siberia, it's just misplaced," said Cohen, who had forecast a colder than normal winter for much of the U.S.

Is This Unusual?

Yes, but more for how long -- about 10 days -- the cold has lasted, than how cold it has been. On Tuesday, Boston tied its seven-day record for the most consecutive days at or below 20 degrees that was set exactly 100 years ago.

More than 1,600 daily records for cold were tied or broken in the last week of December, according to the National Oceanic and Atmospheric Administration. For Greg Carbin of the National Weather Service's Weather Prediction Center, the most meaningful statistics are how last week's average temperature was the second coldest in more than a century of record-keeping for Minneapolis, Chicago, Detroit and Kansas City, third coldest in Pittsburgh and fifth coldest in New York City.

Is It Just the U.S.?

Pretty much. While the United States has been in the deep freeze, the rest of the globe has been toastier than normal....

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