At least three tornadoes were reported in 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 400 flights nationwide were canceled by the evening, according to the flight tracker FlightAware.com. More than half were canceled into and out of Dallas/Fort Worth International Airport that got a few inches of snow.
Christmas lights also were knocked out with more than 100,000 customers without power in Texas, Arkansas, Oklahoma, Mississippi, Louisiana and Alabama.
In Louisiana, quarter-sized hail was reported early Tuesday in the western part of the state and a WDSU viewer sent a photo to the TV station of what appeared to be a waterspout around the Lake Pontchartrain Causeway in New Orleans. There were no reports of crashes or damage.
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.
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.
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.
The storm was moving quickly as it headed into through Louisiana and Mississippi and onto Alabama and eventually Georgia.
In Mississippi, Gov. Phil Bryant urged residents to have a plan for any severe weather.
"It only takes a few minutes, and it will help everyone have a safe Christmas," Bryant said.
Associated Press writers Jay Reeves in Birmingham, Ala., Ramit Plushnick-Masti in Houston, Chuck Bartels in Little Rock, Ark., and AP Business Writer Daniel Wagner in Washington, contributed to this report.