Associated Press
FILE - In this June 29, 2012, file photo, Pete Michel, crew member for Jimmie Johnson, tries to hold down a tent as a storm blows through prior to the scheduled start of the NASCAR Nationwide Series auto race at Kentucky Speedway in Sparta, Ky. A gigantic line of powerful thunderstorms with tree-toppling winds is likely to threaten one in five Americans Wednesday is as it rumbles from Iowa to Maryland, meteorologists warn. The massive storms may even spawn an unusual weather event called a derecho, which is a massive storm of strong straight-line winds spanning at least 240 miles.(AP Photo/James Crisp, File)

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