The polar vortex has fractured, and the eastern U.S. faces a punishing stretch of winter weather

Forecasts call for a very cold and stormy pattern, just underway, to peak in a few weeks


Comparison of the polar vortex on Dec. 18, 2018 and Jan. 3. (earth.nullschool.net)
January 15 at 12:32 PM

The swirling winds tens of thousands of feet high in the sky above the Arctic — the dreaded polar vortex — broke apart into three parts to ring in 2019. Now the eastern half of the United States is about to feel the consequences.

Weather models project the onset of a severe and punishing winter weather pattern in just over 10 days, with extreme cold and heightened storminess. In fact, the transition to this harsh winter pattern has likely already begun.

Before and during the vortex disruption, locations east of the Rockies basked in unusually mild weather for weeks. Washington witnessed 28 days of warmer-than-normal weather, and the first half of January ranked among the top 10 warmest on record in Minneapolis and Milwaukee:

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But the polar vortex split, which forecasters predicted in December, has likely triggered a transition toward a much more wintry pattern.

Even though the vortex split around the start of the New Year, it often takes weeks for the effects to become apparent in day-to-day weather. The vortex zips around the North Pole high in the stratosphere about twice as high up as commercial aircraft fly, so its downward propagation through the atmosphere is a drawn out process.

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This past weekend’s storm which dumped 10 inches of snow in both St. Louis and Washington may have been one of the first indicators of the shift to harsher winter conditions.

“I think the snowstorm this weekend was related to the vortex split,” said Judah Cohen, a researcher at Atmospheric and Environmental Research in Boston, and polar vortex expert. “I think we’re seeing the impacts already.”

After the vortex fractures, it can fundamentally alter the flow in the atmosphere. Steering winds which blow from west to east — transporting mild air from the Pacific Ocean over the continental U.S. — shift to more north and south. Arctic air can more readily be drawn into the North America and Europe.

“The first order impact [of a vortex split] is that you slow the west to east flow and add more of a north-south component,” said Cohen. “There’s a much greater exchange of arctic air that’s moving south.”

A blast of a bitter Arctic air is forecast to plunge into the eastern U.S. late this week and this weekend, the coldest of the winter so far in some areas — another possible sign of the vortex disruption.

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