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

According to the National Weather Service, a polar vortex will impact most of the country this weekend, here is what you need to know.

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.

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

A polar vortex is currently hitting the United States, with schools closed in many areas and at least four deaths caused by treacherous conditions.

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.

A lobe of the polar vortex, a stormy ring that typically keeps the coldest air locked up near the North Pole, will dip southward into the United States this weekend into next week. Polar air ...

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.

The Republican was accompanied by his family members including his wife Melania and youngest son Barron as they walked out of the Dulles Airport.

A series of cold fronts the last few weeks has kept Florida downright chilly, as another winter storm starts to take aim this weekend

A polar vortex could cause light snow over the weekend in Knoxville. A polar vortex is to blame for freezing temperatures.