WASHINGTON - The fast-moving, long-lived, large and violent thunderstorms complex that battered in the Mid-Atlantic region is known as a derecho.
The Washington Post reports that derechos are most common between May and July in the Midwest and Great Lakes. The National Weather Service indicates they occur about once every four years in the Washington, D.C., area.
They form along the northern boundary of a hot-air mass, right along the jet stream, where upper-level winds zip along.
Friday's heat wave covered a region from the Midwest to the Southeast. This heat bubbled northward, clashing with a front draped from near Chicago to just north of Washington.
Thunderstorms erupted, then grew in coverage and intensity, powered by upper-level winds and fueled by the heat and humidity. This energy sustained the storms on along a 600-mile northwest-to-southeast path.
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