The most lethal were the storms of Dec. 24-26, 1982, when 29 tornadoes in Oklahoma, Missouri, Arkansas, Tennessee and Mississippi killed three people and injured 32; and those of Dec. 24-25, 1964, when two people were killed and about 30 people injured by 14 tornadoes in seven states.
In Mississippi, Gov. Phil Bryant urged residents to have a plan for any severe weather.
Quarter-sized hail reported early Tuesday in western Louisiana was expected to be just the start of a severe weather threat on the Gulf Coast, said meteorologist Mike Efferson at the weather service office in Slidell, La.
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. 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.
The storm was moving quickly as it headed into northeast Louisiana and Mississippi into the late afternoon and early evening, said Bill Adams at the weather service's Shreveport, La., office.
No day is good for severe weather, but Faulkner said Christmas adds extra challenges because people are visiting unfamiliar areas and often thinking more of snow than possible twisters.
Some mountainous areas of Arkansas' Ozark Mountains could get up to 10 inches of snow, which would make travel "very hazardous or impossible" in the northern tier of the state from near whiteout conditions, the National Weather Service said.
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.
At least three tornadoes were reported in Texas, though only one building was damaged and no injuries were reported, according to the National Weather Service. Tornado watches were in effect across southern Louisiana and Mississippi.
Elsewhere, areas of east Texas and Louisiana braced for possible thunderstorms as forecasters eyed a developing storm front expected to spread across the Gulf Coast to the Florida Panhandle.
"It only takes a few minutes, and it will help everyone have a safe Christmas," Bryant said.
NEW ORLEANS (AP) — Freezing rain and sleet made for a sloppy Christmas morning trek in parts of the nation's midsection on Tuesday, while residents along the Gulf Coast braced for thunderstorms, high winds and tornadoes.
AP Business Writer Daniel Wagner in Washington and Associated Press Writer Ramit Plushnick-Masti in Houston contributed to this report.
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.
In Alabama, the director of the Emergency Management Agency, Art Faulkner, said he has briefed both local officials and Gov. Robert Bentley on plans for dealing with a possible outbreak of storms.
Storms along the Gulf Coast could bring winds up to 70 mph, heavy rain, more large hail and dangerous lightning in Louisiana and Mississippi, Efferson said. Furthermore, warm, moist air colliding with a cold front could produce dangerous straight-line winds.
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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.
Authorities: Storm blamed for man's death in Texas