Thursday, June 13, 2013

What Is a Derecho, Anyway?

derecho outside chicago 

A derecho gathered outside Chicago in 2008.
You've probably heard that a massive system of storms is currently bearing down on the Midwest and expected to reach the mid-Atlantic on Thursday. Meteorologists are warning that the storms may turn into derechos, or "land hurricanes." Almost 75 million people are in the path of the storms, and forecasters believe that conditions are favorable for one or more derechos this week. So what can we expect from these intense storms?

What is a derecho? According to NOAA, a derecho is a "widespread, long-lived windstorm that is associated with a band of rapidly moving showers or thunderstorms." In order for a weather event to be classified as a derecho, the wind damage zone must extend more than 240 miles and include wind gusts of at least 58 miles per hour. In "super-derechos", wind gusts can top 100 miles per hour.  "You can think of a derecho as a tropical cyclone over land," NOAA research meteorologist Ken Pryor told Discovery News. "The impacts are very similar. There are damaging winds that cover a significant area." The storms are known to occur frequently at night, and they often bring hail, flooding, and tornadoes.

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