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A polar vortex is engulfing the US. Here's what that really means, and why these events might be getting more common.

Business Insider logo Business Insider 1/31/2019 Aylin Woodward

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For the first time since 2014, the polar vortex is descending on North America. 

Windchill temperatures dropped to minus 66 degrees Fahrenheit in Minnesota Tuesday night. More than 83 million Americans in the Midwest and parts of New England will contend with subzero temperatures sometime between Wednesday and Monday, CNN reports.

Some areas in Minnesota and the Dakotas are facing temperatures 50 degrees below average for this time of year - that's life-threatening cold.

The National Weather Service's Chicago office reported windchill temperatures in the range of minus 45 to minus 55 degrees Fahrenheit on Wednesday morning. The office cautioned that the extreme cold would continue through Thursday.

The term polar vortex describes the mass of low-pressure cold air that circulates in the stratosphere above the Arctic and Antarctic regions. Sometimes the circulation of the polar vortex weakens during the winter, causing surges of frigid air to splinter off and drift south.

The freezing air is carried by the jet stream, a current of wind that extends around the hemisphere and divides the air masses in the polar region from those farther south.

This polar air mass has always been present, but scientists first dubbed it the "polar vortex" in 2014, when a similar (though less severe) cold snap hit a majority of the continental US.

Frostbite 'in a matter of minutes'

North America, Europe, and Asia can all experience polar-vortex events, which bring temperatures that are simply too cold for people to safely be outside.

"You're talking about frostbite and hypothermia issues very quickly, like in a matter of minutes, maybe seconds," Brian Hurley, a meteorologist with the Weather Prediction Center, told the Huffington Post.

a pile of snow

© AP
Hypothermia occurs when your body loses heat faster than you can produce it. Frostbite arises when skin and the tissues below freeze, or, in extreme cases, die.

Chicago's National Weather Service office said "dangerously cold wind chills could cause frostbite on exposed skin in as little as 5 minutes." The office suggests covering any exposed skin and bringing pets indoors.

Eight deaths have already been linked to the recent weather, CBS News reports. One Illinois man was fatally struck by a snow plow, two people died in a car accident in Indiana, a man collapsed and died in Milwaukee after shoveling snow outside, another man was found dead on the doorstep outside his Detroit home, and three deaths in Iowa were linked to the storm.

Schools are closed in Chicago and parts of eastern Iowa, in addition to closures in Michigan, Wisconsin, Ohio, and Minnesota. Several Midwest universities also closed, including the Ohio State University, the University of Notre Dame, the University of Minnesota, the University of Wisconsin, and Iowa State University.

Almost 1,500 flights were canceled at Chicago's O'Hare Airport, and another 326 were grounded at Midway Airport as of midday January 30, NBC Chicago reported. FlightAware, the airline tracing site, reported 1,971 flights within, leaving, or entering the US were canceled, and another 611 are delayed.

Even the US Postal Service suspended mail delivery service in nearly 100 zip codes in states including North and South Dakota, Nebraska, Kansas, Minnesota, Wisconsin, Iowa, and Illinois.

We might start seeing polar-vortex events more often

Despite President Donald Trump's assertions to the contrary on Twitter, the emergence of a polar vortex does not invalidate the scientific consensus on global warming.

The polar vortex creates weather events that take place regionally on dayslong or weeklong timescales. The latter is a planetwide phenomenon caused by increased concentrations of certain gases in Earth's atmosphere. Global average temperatures are still among the highest ever recorded, and oceans are the warmest they've been since we started keeping records.

In fact, recent research shows that the frequency of winter polar-vortex events has increased over the past four decades, perhaps because of climate change.

Although many questions remain, scientists have started to connect extreme cold waves to the warming Arctic, as Inside Climate News reported. Because temperatures are rising in the Arctic twice as fast as the rest of the globe, the difference between temperatures at the North Pole and continents at lower latitudes is decreasing, according to The Conversation. Less disparity in temperatures means less difference between air pressure levels, which weakens the jet stream. That can lead the jet stream to take longer, less direct paths.

If the jet stream wanders enough, that can disrupt the natural flow of the polar vortex.

Kevin Loria contributed to a past version of this story.

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