Freezing rain and sleet made for a sloppy Christmas trek in parts of the nation's midsection, while residents along the Gulf Coast braced for thunderstorms, high winds and tornadoes that were doing damage in some areas.
Winds toppled a tree onto a pickup truck in the Houston area, killing the driver.
Icy roads already were blamed for a 21-vehicle pileup in Oklahoma, where authorities warned would-be travelers to stay home.
Trees fell on a few houses in central Louisiana's Rapides Parish but there were no injuries reported so far and crews were cutting trees out of roadways to get to people in their homes, said sheriff's Lt. Tommy Carnline.
Fog blanketed highways, including arteries in the Atlanta area where motorists slowed as a precaution. In New Mexico, drivers across the eastern plains had to fight through snow, ice and low visibility.
At least three tornadoes were reported in parts of Texas, though only one building was damaged, according to the National Weather Service. Tornado watches were in effect across southern Louisiana and Mississippi.
More than 180 flights nationwide were canceled by midday, according to the flight tracker FlightAware.com.
More than half were canceled by American Airlines and its regional affiliate, American Eagle.
American is headquartered and has its biggest hub at Dallas/Fort Worth International Airport.
Meanwhile, a blizzard watch was posted for parts of Indiana and western Kentucky for storms expected to unfold Tuesday amid predictions of up to 4 to 7 inches of snow in coming hours.
Much of Oklahoma and Arkansas braced under a winter storm warning of an early mix of rain and sleet forecast to eventually turn to snow.
About a dozen counties in Missouri were under a blizzard warning from Tuesday night to noon Wednesday.
The holiday may conjure visions of snow and ice, but twisters this time of year are not unheard of.
Ten storm systems in the last 50 years have spawned at least one Christmastime tornado with winds of 113 mph or more in the South, said Chris Vaccaro, a National Weather Service spokesman in Washington, via email.