(CNN) -- Powerful storms pounded cities and towns across the South on Christmas Day, leaving at least one man dead and others injured.
A 25-year-old man in Texas was killed after a tree fell on his pickup as he was driving on the northwest side of Houston, Harris County Sheriff's Deputy Thomas Gilliland said. Officials suspected high winds knocked the tree down.
A tornado struck Mobile, Alabama, according to the National Weather Service office there. A tower camera for CNN affiliate WALA showed a large wedge tornado moving through the city.
Mobile Fire-Rescue said on its Twitter page that one person was trapped under a fallen tree but was uninjured. It said crews were going door-to-door in affected areas to check on residents.
Several buildings, including a high school, were damaged by the tornado, and there were several car wrecks, said Steve Huffman, a public information officer for the Mobile Fire-Rescue Department.
"One female was transported to the hospital with pregnancy issues, but she was not injured," he said.
Nearly 17,500 customers in Mobile were without power, a spokesman for Alabama Power said. Statewide, there were 22,000 homes and business that were in the dark.
An apparent tornado touched down near downtown Alexandria, Louisiana, police said. One person was injured and more than a dozen buildings suffered significant damage, Lt. Paul Ellington of Alexandria police said.
Homes in Pearl River County in central Mississippi were damaged when a storm passed through Tuesday afternoon, the director of the county's emergency management department said. Danny Manley said one person suffered minor injuries and power was out in many homes. U.S. Highway 84 in Lawrence County was shut down because of downed power lines and debris.
Portions of Alabama, Louisiana and Mississippi were under a rare "particularly dangerous situation" tornado watch until 8 p.m. CT, the Storm Prediction Center in Norman, Oklahoma, said. Wind gusts up to 75 mph (120 kph) were possible, as well as powerful or long-lasting tornadoes, it said.
The portion of the country from East Texas to the Florida Panhandle will face severe weather throughout the day, said CNN Meteorologist Alexandra Steele.
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Major cities under severe weather threats on Christmas included Houston; New Orleans; Birmingham, Alabama; and Atlanta. The storm was moving eastward, putting northern Florida, Georgia and the Carolinas in its sights on Wednesday.
The biggest threat is for the possibility of tornadoes, Steele said. Straight-line winds may be as strong as 60-80 mph from Tuesday afternoon through the night.
A winter storm warning is in effect through at least midnight Tuesday for much of Oklahoma and Arkansas and parts of southern Missouri. By the time the storm is through, these areas could have 4 to 6 inches of sleet and snow.
Even without tornadoes, the Mississippi Emergency Management Agency said that state residents could see sustained winds between 70 and 80 mph, heavy rain and hail and dangerous lightning. The system is forecast to move through the state on Christmas.
A section of Interstate 40 in Oklahoma near Del City was temporarily closed Tuesday morning after an accident involving 20 vehicles, police said. Freezing rain was probably the cause of the chain reaction of vehicles, which included three big rigs, the Oklahoma Highway Patrol said. No life-threatening injuries were reported.
Passengers flying in and out of Oklahoma City's Will Rogers Airport are being urged to check with their airlines before going to the airport because of the weather there and elsewhere around the county. Delta Air Lines has already canceled four Christmas Day flights, and that carrier and United Airlines are waiving fees for passengers who want to change their scheduled tickets, the airport said in a news release.
A spokesman for the Bill and Hillary Clinton National Airport in Little Rock, Arkansas, said some airlines had canceled flights for Tuesday evening.
One reason for widespread delays this week: The weather is expected to be frightful in much of the United States, not just the Plains and Southeast.
A winter storm watch is in effect from Missouri through Vermont, a huge swath of territory where significant snows are expected to fall through Thursday.