After an EF-1 tornado struck the south Indianapolis suburb of Greenwood, television stations showed pictures of damage including a portion of a roof blown off a veterinary office.
The Tennessee Department of Health confirmed Wednesday night that two people were killed in severe storms. Officials said the deaths -- one male and one female -- occurred in Perry County. No further details were available.
The biggest threat for tornadoes was in a region of 3.7 million people in Mississippi, Tennessee and Arkansas and parts of Missouri, Illinois, and Kentucky, according to the national Storm Prediction Center in Oklahoma. The center issued a "particularly dangerous situation" alert for the first time since June 2014, when two massive EF4 twisters devastated a rural Nebraska town, killing two people.
The greatest risk for a few "intense, long-tracked tornadoes" will be through Wednesday night.
About 120 miles (193 kilometers) east of the tornado, Brandi Holland, a convenience store clerk in Tupelo, Mississippi, said people were reminded of a tornado that damaged or destroyed more than 2,000 homes and businesses in April 2014.
"They're opening all our tornado shelters because they say there's an 80 percent chance of a tornado today," Holland said.
Elsewhere, skiers on the slopes out West got a fresh taste of powder and most people in the Northeast enjoyed spring-like temperatures as they finished up last-minute Christmas shopping.
"It's too warm for me. I don't like it. I prefer the cold in the winter, in December. Gives you more of that Christmas feel," said Daniel Flores, a concierge in New York, his light jacket zipped open as he shopped in Manhattan with his three children.
Only about half of the nation, mostly in the West, should expect the possibility of a white Christmas.
In the small coastal town of Loxley, Alabama, Mandy Wilson watched the angry gray sky and told drivers to be careful as she worked a cash register at Love's Travel Stop.
"It's very ugly; it's very scary," Wilson said. "There's an 18-wheeler turned over on I-10. There's water standing really bad. It's a really interesting way to spend Christmas Eve eve."
In parts of Georgia, including Atlanta, a flood watch was posted through Friday evening as more than 4 inches (102 millimeters) was expected, the National Weather Service said.