Polar vortex blasts U.S. Midwest with lethal cold air

The Midwest was the hardest-hit region, as temperatures plummeted below zero Fahrenheit (minus 17.8 degrees Celsius). By late afternoon, the mercury was hovering at 4F in Chicago (minus 16C), 10F (minus 12C) in Detroit and minus 15f (minus 26C) in Minneapolis. The brutal blast known as the polar vortex is a mass of freezing air that normally spins around the stratosphere over the North Pole, but whose current has been disrupted and is now pushing south into the United States.