After hail, heavy rains and more than 30 tornadoes drenched the region, officials warned that a “generational flooding” disaster was possible.

© Brad J. Vest for The New York Times

At least two people were killed in Tennessee, officials said, and millions of people were under severe weather advisories. Flooding was reported in Nashville.

At least two people were killed in Tennessee, officials said, and millions of people were under severe weather advisories. Flooding was reported in Nashville.

© David Robert Elliott for The New York Times