A line of fierce storms known as a derecho is threatening to move east from the upper Midwest through the mid-Atlantic states, bringing large hail and tree-breaking winds to a wide swath of the nation.
As many as one in five Americans live in the zone that is threatened by a line of squalls, a similar meteorological event to the one that that tore trough roughly the same region a year ago. A derecho can be as deadly as any outbreak of tornadoes, causing wind damage to structures and power lines.
Technically, a derecho is a wind storm associated with a band of rapidly moving thunderstorms. Unlike a tornado, which spins like a top, a derecho is a straight-line event. The line of storm carries winds in excess of 58 miles per hour along a front of at least 240 miles.
According to the National Weather Service, there is risk of severe weather hitting as many as 64 million people in 10 states including such major cities as Chicago, Indianapolis, Cincinnati and Columbus, Ohio. The band of storms will eventually travel through Detroit, Baltimore, Washington, Milwaukee, Pittsburgh and Louisville, Ky.