A polar vortex dipping down from Siberia will bring a cold front with frigid temperatures to nearly 300 million Americans. See maps of the arctic blast.

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.

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.

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.

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

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

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.

Polar Vortex Set to Envelop Much of US in Freezing Temperatures By Hannah Lang and Brendan O'Brien (Reuters) - A blast of Arctic air is set to cover much of the United States with temperatures ...

Millions of Americans are bracing for life-threatening cold as an arctic blast driven by the polar vortex plunges temperatures across the country, reaching as far south as the Gulf Coast. The brutal cold,