The threat of flash flooding on Sunday afternoon was focused over parts of the Midwest, where flood watches have been posted from Missouri to West Virginia, including the cities of Indianapolis and Cincinnati. Rounds of heavy rain and thunderstorms are forecast to sweep across the Midwest region over the next 24 hours.

Slow-moving storms could bring up to 11 inches of rain, raising the risk of flash floods on Sunday, particularly in Illinois and Indiana, forecasters said.

Much of the eastern U.S. and Midwest was facing the threat of severe thunderstorms and heavy rainfall, while heat alerts were issued Sunday for over 50 million people from Kansas to the Carolinas. The big picture: NOAA's Weather Prediction Center issued a Level 3 out of 4 risk for excessive rainfall over parts of the Ohio Valley through Monday morning,