CHICAGO (AP) -- A whirlpool of frigid, dense air known as a "polar vortex" is descending into much of the U.S., pummeling parts of the country with a dangerous cold that could break decades-old records.
For a big chunk of the Midwest, the subzero temperatures are following heavy snow and high winds. Officials have closed schools in cities including Chicago, St. Louis and Milwaukee and warned residents to stay indoors and avoid the frigid cold altogether.
The forecast is extreme: 32 below zero in Fargo, N.D.; minus 21 in Madison, Wis.; and 15 below zero in Minneapolis, Indianapolis and Chicago.
Wind chills could drop into the minus 50s and 60s.
It hasn't been this cold for almost two decades in many parts of the country.
Previous story - Sunday, January 5, 2013:
Temperatures not seen in years are likely to set records in the coming days across the Midwest, Northeast and South.
A "polar vortex" air mass will affect nearly half of the continental U.S. starting Sunday and into Monday and Tuesday, with wind chill warnings stretching from Montana to Alabama.
The bitterly cold temperatures already pushed into northern states Sunday morning. The National Weather Service reported a temperature of 9 below zero in Bismarck, N.D., and negative 21 at Duluth, Minn.
Snow preceded the polar air from Michigan to Kentucky. Forecasts called for up to a foot in eastern Missouri and parts of central Illinois.
Frostbite and hypothermia can set in quickly at 15 to 30 below zero. Medical experts say people should wear hats, face protection and layers of clothing.