As crews in Mississippi and Alabama turned from search-and-rescue efforts to cleanup, forecasters began to downplay their initially dire predictions of a third round of deadly twisters on Tuesday.
Meterologists said the storm system had weakened substantially by evening, although some tornado watches and warnings were still in effect for isolated areas.
The storm system is the latest onslaught of severe weather a day after an 800m wide tornado carved a 130km path of destruction through the suburbs of Little Rock, Arkansas, killing at least 15.
Tornadoes or severe storms also killed one person in Oklahoma and two in Iowa on Sunday.
In North Carolina, the National Weather Service reported tornado touchdowns in five counties on Tuesday, but the twisters caused only moderate structural damage to homes and toppled some trees.
Two cities in the state reported extensive flooding from the storm system. No injuries were reported.
In Mississippi, officials said 12 people died on Monday, including nine in Winston County, where hard-hit Louisville is the county seat. Three others died in separate traffic incidents.
The Winston County tornado caused water damage and carved holes in the roof of a medical centre, where the emergency room was evacuated on Monday.
One victim was a woman who died in the day care centre she owned in the town of Louisville, county coroner Scott Gregory told the media. Authorities were returning to the centre on Tuesday.
One seriously injured child was evacuated, said state representative Michael Evans, who said authorities don't think any other children were in the centre during the storm.
In Tupelo, a community of about 35 000 in north-eastern Mississippi known as the birthplace of Elvis Presley, every building in a two-block area was damaged, officials on the scene said.
On Tuesday morning, a blanket of fog hung over the city as authorities switched from a search-and-rescue mission to cleanup duties.
In one residential neighbourhood, destroyed homes sat steps away from those left unscathed. Crews cleared trees tangled with power lines, fixed cracked roadway signs and removed debris from streets.
In Alabama, three people were reported dead, two in the northern part of the state and one in Tuscaloosa. There, officials say a University of Alabama student died on Monday when he took shelter in a home's basement and a retaining wall collapsed on him.
In southern Tennessee, two people were killed in a home when a suspected tornado hit on Monday night, authorities said.
The winds destroyed several other homes as well as a middle school in the county that borders Alabama, Hall said.