The Polar Vortex Is Unleashing Record Cold on 18 Million People in the U.S. What Is It?

The bitter cold temperatures that are descending across the northern tier of the United States are caused by a break in the polar vortex.

The Weather Channel reported on December 7 that "an arctic blast will accompany a barrage of clipper systems, plunging temperatures for millions." The "fresh blast of cold arctic air brought on by a clipper system" will extend across the Midwest and into the Northeastern U.S. On Friday, December 5, there were record cold temperatures in cities like Flint, MI, and Fort Wayne, Ind., according to the Weather Channel. More than 18 million people were under "winter weather alerts," CBS News reported on December 6, with the frigid temperatures unleashing throughout the northern tier on December 7 and 8.

But what is the polar vortex that is causing all of this, and why does it break?

The Polar Vortex Surrounds Both of the Earth's Poles, the National Weather Service Says

The polar vortex "is a large area of low pressure and cold air surrounding both of the Earth’s poles. It ALWAYS exists near the poles, but weakens in summer and strengthens in winter," according to the National Weather Service.

The term "vortex" refers to the "counter-clockwise flow of air that helps keep the colder air near the Poles. Many times during winter in the northern hemisphere, the polar vortex will expand, sending cold air southward with the jet stream (see graphic above)," NWS wrote.

"This occurs fairly regularly during wintertime and is often associated with large outbreaks of Arctic air in the United States. The one that occurred January 2014 is similar to many other cold outbreaks that have occurred in the past, including several notable colder outbreaks in 1977, 1982, 1985 and 1989," the NWS wrote.

NWS added that the polar vortex is not new. It's just talked about more, perhaps. And, it's not something that "exists at the Earth's service.

"When we feel extremely cold air from the Arctic regions at Earth’s surface, it is sometimes associated with the polar vortex. This is not confined to the United States," NWS wrote. "Portions of Europe and Asia also experience cold surges connected to the polar vortex. By itself, the only danger to humans is the magnitude of how cold temperatures will get when the polar vortex expands, sending Arctic air southward into areas that are not typically that cold."

According to Cincinnati.com, the polar vortex broke, which, again, is a common phenomenon. "The North Pole is covered by the polar vortex, a massive circular upper-air weather system in the Arctic," that newspaper explains. "It's a normal pattern that tends to contain the coldest weather close to the North Pole and is stronger in the winter."

A piece of it may "break off or drift south," the newspaper reported. The jet stream normally "locks in" the polar vortex. But weaker polar winds fail to keep the cold wins at the poles. The breaking of the polar vortex is caused by "a sudden warming of the Earth's stratosphere and a lack of strong wind activity around the pole," Cincinnati.com reports.

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