The polar vortex is a ring of cold air that typically circles the Arctic. A strong jet stream essentially acts like a fence, keeping it locked there. If there's any weakening in the jet stream (the fence), the frigid air can become unstable and spill out. This sends the normally trapped cold air much farther south.

A polar vortex is slated to sweep most of the continental US bringing winter storm warnings and a hazardous freeze to millions.

Many people across the United States may recall the polar vortex episode of early 2014. For the Midwest, it turned out to be the coldest winter in over 30 years. In Washington, D.C., January 2014 ...

People living "basically anywhere from the Rockies eastward" will see extremely cold temperatures over the next several days, a meteorologist says.

The most unusually cold air in the Northern Hemisphere will be over the United States early next week, bringing dangerously frigid conditions.

A brutal polar vortex is set to bury the Big Apple in snow Sunday and then deliver deadly single-digit temperatures that will feel like 15 degrees below zero. New

Americans were bracing Thursday for frigid temperatures that forecasters said could produce life-threatening conditions, with Donald Trump's inauguration expected to be the coldest in 40 years.

Although people from all over the country, of all ages and backgrounds, joined the People's March, one protester said no one felt like a stranger.

Another blast of winter weather is expected in parts of the U.S. in the coming days, including bone-chilling wind in the Northern Plains and unusual snow and ice in the Gulf Coast area.

Frigid arctic air due to a polar vortex is about to send temperatures plunging for millions of Americans across the U.S., and that could lead to one of the coldest Inauguration Days seen in decades.

A new blast of Arctic air sweeping from north to south will bring bone-chilling temperatures to millions of Americans this weekend and next week.