The extreme weather is being caused by the polar vortex, an area of cold air that circulates around the Arctic.

The first major winter storm of the new year swept into the U.S. mid-Atlantic states on Monday morning, closing down federal offices and public schools in Washington, D.C., after dumping a foot of snow in parts of the Ohio Valley and Central Plains.

Millions were under weather advisories as the storm stretched from southern Illinois to Washington, D.C. Snow could fall at 1-2 inches per hour.

The severe weather, spanning from the Midwest to Washington DC, is a "potential disaster", says one forecaster.

Find out which cities have the highest winter storm impact rating as snow, ice and wind combine to cause hazardous conditions.