Authorities in the Midwest say tornadoes and thunderstorms killed at least seven people and destroyed at least 50 homes on Sunday.
Multiple tornadoes in several states forced tens of thousands to take cover.
"The sirens had all sounded," Illinois resident Ron Smith recalled. "After we went downstairs, booms, everything broke loose, trees going anywhere, so a lot of damage."
In Ohio, just south of Toledo, tornadoes leveled dozens of homes.
Perhaps the most dramatic damage took place at one community's high school that lost its gym roof and back wall just hours before graduation.
The senior class valedictorian's father was killed in the storm. A rescuer said he left their basement shelter for a flashlight and never returned.
Severe weather also hit in Illinois, Michigan and Indiana.
In southeastern Michigan, high winds ripped siding off a building at the Fermi 2 nuclear plant, causing the facility to shut down automatically.
DTE Energy, the company which owns the plant, was still probing the extent of the damage. DTE spokesman Guy Cerullo said it's not clear when the plant will to go back into operation, adding that the reactor itself was not harmed, only other "plant-related equipment."