A strong polar vortex in the stratosphere has brought subzero temperatures to the Midwest, Mid-Atlantic and deep into the South.

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

A blast of Arctic air is set to cover much of the United States with temperatures below freezing starting on Friday and into next week, impacting millions of Americans in nearly all of the contiguous states.

Despite a cold start to the day, most of the U.S. will experience seasonably mild temperatures on Thursday. However, dangerous changes are on the way as a polar vortex tightens its grip on the nation as sends temperatures tumbling below freezing starting this weekend.

In Indiana, around zero degrees was likely, the map showed, with temperatures of around three degrees possible in Northern Maine. Northern Georgia would see temperatures around 16, and in Colorado, the map showed that some areas would see -9.

Arctic air has brought chilling temperatures as low as 12 degrees in New York City on Monday night but are we in a polar vortex? A polar vortex settled its way over New York City and New Jersey following Sunday’s snow storm,

Meteorologist Travis Clark-Smith dives into what caused our recent cold snap.

This blast of frozen temperatures is tied to a polar vortex... but what is that? Air spins around the notoriously cold North and South Poles. When the air is spinning fast, it's stable, but when it is weakest,