"Some tornadoes could be long-lasting, adding to the danger, especially for those that occur after dark." The storm is expected to bring severe thunderstorms to the East Coast on Sunday,

Meanwhile, the severe weather threat will linger through Sunday from Florida northward into the upper Ohio River Valley, forecasters warned.

Millions of Americans across the country are on alert for a severe weather outbreak as violent, long-track tornadoes with damaging winds of up to 80 mph and large hail are expected across the Midwest and South with the cross-country storm moving east.