The East Coast is bracing for severe thunderstorms on Monday from New York down to South Carolina, potentially impacting more than 60 million Americans.
The biggest threats are lightning, large hail and wind gusts up to 70 mph.
Airlines have cancelled more than 1,400 flights due to the severe weather, with airports in New York City, Boston and Atlanta getting hit the hardest.
A severe thunderstorm watch is in effect through Monday night for Baltimore and Washington, D.C., as well as parts of western New York, Pennsylvania, New Jersey and Delaware.
Damaging winds are expected to hit Washington, D.C., Philadelphia and New York City, while flood watches have been issued from Virginia to New York.
Meanwhile, more than 300,000 customers are without power across Tennessee, Kentucky, Arkansas, Georgia and Michigan in the wake of rough storms.
Severe weather this weekend spawned at least 20 reported tornadoes across the Midwest.
There were three confirmed tornadoes in Indiana, killing at least one person and damaging or destroying dozens of homes, local authorities said.
In Lonoke County, Arkansas, two people were killed when a tree fell on a mobile home, a coroner official told ABC News.
Another person was killed by a fallen tree in Fulton County, Georgia, local authorities said.
ABC News' Matt Foster, Mariama Jalloh, Emily Shapiro and Sam Sweeney contributed to this report.