The rare Dixie winter storm stretched from Brownsville, Texas, through New Orleans to the Florida Panhandle and north to the Carolinas.
It brought 2 to 3 inches of snow and sheets of ice to Southern communities not equipped to deal with such conditions.
In all, six Southern states declared emergencies, and at least 12 deaths -- mostly from traffic accidents on slippery roads -- were blamed on the storm.
Schools and government offices were closed in most states Thursday, and officials urged businesses to let workers stay home.
Many roads, highways and bridges also remained closed. Some were still lined with cars and trucks that had collided with other vehicles, skidded off the road, run out of fuel or simply been abandoned Tuesday and Wednesday after the storm hit.
More than 800 flights were canceled as of early Thursday, including more than 200 at Hartsfield-Jackson Atlanta International Airport, the world's busiest, fight-tracking website FlightAware.com said. More than 1,600 flights were expected to be delayed, the website said.
Temperatures were forecast to rise above freezing, and to the 40s in some areas, by Thursday afternoon.
In Atlanta, the biggest city caught off-guard by the storm, National Guard and state troopers spent Wednesday returning more than 3,000 schoolchildren to their homes. The kids had been stranded since Tuesday at school or on school buses.
The state said all students were returned to their families late Wednesday afternoon.
In Alabama, more than 11,000 students, including more than 1,500 in Birmingham, spent Tuesday night at school.
Gov. Robert Bentley commended teachers for staying with the stranded students.
"Everybody's done extremely well," Bentley said in remarks to the teachers quoted by AL.com.
"You just have to improvise, and when emergency situations come up, you just have to make sure people are taken care of, and that's exactly what y'all did," he said.