A polar vortex is a large pocket of very cold air, typically the coldest air in the Northern hemisphere, which sits over the polar region during the winter season.
The frigid air found its way into the United States when the polar vortex was pushed South, reaching southern Canada and the northern Plains, Midwest and northeastern portions of the United States.
"This is why we've had such extreme cold," Expert Meteorologist Brett Anderson said.
What Caused the Polar Vortex to Move?
"The polar vortex moves around at times during the course of the winter, but rarely do you see it get pushed this far south," Anderson said.
A large, powerful high pressure system originating in the Eastern Pacific is stretching to the North Pole, shoving the vortex farther south than is typical, allowing it to settle in Canada and the U.S.
"These high pressure systems can reach Alaska, but it is not typical to stretch all the way to the North Pole," Anderson said.
The vortex is threatening temperatures as low as minus 30 degrees Fahrenheit in the Plains and in the negative 20s and negative teens farther into the Midwest.
"The high pressure system, paired with the extensive snow cover over southern Canada and the northern United States, is allowing the air to stay very cold, according to Anderson.
According to the National Weather Service, the Upper Midwest, where some of the lowest temperatures are occurring, is currently more than 98 percent snow-covered.
The Upper Great Lakes region is 100 percent snow-covered, and the Midwest is more than 76 percent covered.
So, When Will the Cold Air Stop?
When the strong air from the Eastern Pacific weakens and falls apart, the polar vortex will retreat and go back into place near the North Pole.
Until then, temperatures across the northern Plains and Midwest will continue to be life-threateningly cold, shattering some all-time low record highs.
By Jillian MacMath, Staff Writer for AccuWeather.com