In June 2012 at least 13 people were killed and millions left without power after a Derecho swept through several US states.
A derecho is a widespread and long-lived, violent windstorm, convectively induced and running in a straight line. It can produce tornado-like damage and can reach gusts of up to 90mph. It is associated with a band of severe thunderstorms in the form of a squall line usually taking the form of a bow echo. Derechos blow in the direction of movement of their associated storms, similar to a gust front, except that the wind is sustained and generally increases in strength behind the "gust" front. A warm weather phenomenon, derechos occur mostly in summer, especially June and July in the Northern Hemisphere. They can occur at any time of the year and occur as frequently at night as in the daylight hours.
This particular derecho began in the Midwest, passed over the Appalachian Mountains and then drew new strength from a high pressure system as it hit the southeastern U.S.A. Brian Jackson of the US National Weather Service said "It's one of those storms," Jackson said. "It just plows through."