What Is The Polar Vortex

Polar Vortex

Information sources and web definitions

1. A polar vortex is a persistent, large-scale cyclone located near one or both of a planet's geographical poles. On Earth, the polar vortices are located in the middle and upper troposphere and the stratosphere. They surround the polar highs and lie in the wake of the polar front. ...
   http://en.wikipedia.org/wiki/Polar_vortex

From NPR:  Washington Post weather editor Jason Samenow described the polar vortex this way:

"We're talking about a huge sprawling area of circulating cold air originating from the North Pole. It's a low-pressure center, and typically during the winter months it resides up there. At times, some tentacles of it will slip southward and bring cold air outbreaks into the U.S., but this year, we're seeing a huge chunk of it, most of it descending into the U.S."

High-pressure systems over Alaska and Greenland, Samenow added, are "allowing the jet stream to dive south over the U.S. and also for this polar vortex to drop south with the jet stream."

For a more visual image of what's happening, though, we suggest an analogy offered by science writer Andrew Freedman, "This is air that is circulating the Arctic," Freedman said. "In the last couple of days, it's sort of become lopsided — sort of like a figure skater that has extended their arms and then tripped.
"You know, when a figure skater pulls their arms in, they spin tighter and tighter and faster and faster. But when they put their arms out, they are a little bit slower and a little bit more wobbly and more prone to fall or stop skating at the end of their routine.

"What's happening now is that a piece of it is down on the other side of the globe, but a piece of it kind of got lopsided and came down on top of us."

The next logical question is why the vortex has weakened so much that a big piece of it has spun down over the U.S.

Along with the effects that those high-pressure systems over Alaska and Greenland are having, there's the possibility that climate change is also a factor.

"More and more Arctic sea ice is melting during summer months. The more ice that melts, the more the Arctic Ocean warms. The ocean radiates much of that excess heat back to the atmosphere in winter, which disrupts the polar vortex. Data taken over the past decade indicate that when a lot of Arctic sea ice disappears in the summer, the vortex has a tendency to weaken over the subsequent winter."

From USA TODAY:  A blast of brutally cold air - thanks to the polar vortex - is roaring across the central and eastern USA early this week, sending temperatures to levels not seen in 20 years.

The polar vortex is a strong area of low pressure that usually wanders around the Arctic throughout the winter. Counterclockwise winds around the vortex occasionally push waves of intensely cold air into the USA.

MORE: Subzero temperatures settle across USA
The vortex is strongest during the winter, and usually weakens or even disappears in the summer. The vortex tends to move very slowly or even stay stationary, and its position determines what part of the USA the Arctic air will invade.

This week, the core of the vortex has actually slipped all the way down over the USA. Essentially, the bitterly cold air that's typically over the Arctic is now over the central and eastern U.S.

The vortex was allowed to slip this far south in part due to a strong "blocking" area of high pressure over eastern Canada and Greenland.

Fortunately, this visit from the Arctic is expected to be short-lived, as the vortex is forecast to return to its proper location north of the border. This will allow temperatures to return to average or even above-average levels by the end of the week and the weekend.