The U.S. National Weather Service is warning that much of the United States this week will see the coldest temperatures in almost 20 years.
The weather service says the widespread chill is the result of a relatively infrequent alignment of weather conditions, allowing the Arctic polar vortex to travel unusually far to the south.
A polar vortex is a counterclockwise rotating pool of cold, dense air that will affect more than half of the continental U.S. today and Tuesday, with wind chill warnings stretching from Montana in the north to Alabama in the south.
By Wednesday, nearly half the country will shudder in temperatures of below minus 17 degrees Celsius.
Several states in the Midwest already have received more than 30 centimeters of new snow, creating dangerous travel conditions and prompting church and school closures.
Meanwhile, the majority of the Western U.S. can expect relatively pleasant weather conditions through Tuesday.