Violent tornadoes ripped through parts of the U.S., wiping out schools and toppling semitractor-trailers in several states.

Millions of Americans across the country are on alert for a severe weather outbreak with violent, long-track tornadoes with damaging winds of up to 80 mph and large hail

A powerful low-pressure system is likely to spawn a dangerous outbreak of severe thunderstorms in portions of the Midwest, South and East, where tornadoes, widespread damaging winds, large hail and flash flooding are all concerns.