Meteorologists are warning that a gigantic line of powerful thunderstorms is likely to threaten one in five Americans.
The storm system packing tree-toppling winds is forecast to rumble Wednesday from Iowa to Maryland.
The continuous line of storms might even spawn an unusual weather event called a derecho. That's a massive storm of strong straight-line winds spanning at least 240 miles. A historic derecho last year killed 13 people and knocked out power to 4 million residents.