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

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

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

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

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

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.

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

A lobe of the polar vortex will arrive in the United States this weekend, bringing the lowest temperatures in years and snow and ice to the East and Deep South.

So, as the Deep South grapples with the foreign language of snowflake icons making a (for some, repeat) appearance in weather apps, a reality check is in order.