Weather Whys from Texas A&M Geosciences Center

Q:  On the forecast today, mention was made the possibility of a derecho in the Midwest. What is a derecho?
A:  A derecho is a severe windstorm that usually forms along a cluster of thunderstorms, explains Brent McRoberts of Texas A&M University. “The word is derived from the Spanish word meaning direct or straight,” McRoberts says. “Derechos are often formed with bow-shaped thunderstorms but they produce strong straight-line winds that can surpass 100 miles per hour in some cases. The storm system associated with derechos usually moves quickly, often at 50 miles per hour or more, and can last a long time So a derecho can be a very powerful storm with the capability of moving.”

Q: Where do they occur?
A: They can occur anywhere, but are most often seen in the Midwest and Great Plains, and they can form any time of day, McRoberts adds. “Winds in a derecho storm have been clocked at more than 110 miles per hour in Wisconsin and Michigan. A derecho that occurred in Memphis in 2003 was strong enough to leave over 300,000 homes without power,” he notes. “Derechos usually form in the summer months, so people who are outdoors are very much at risk, as are people in cars and in mobile homes. Also, there are numerous cases of people being killed or injured while in boats. A lake is certainly not a good place to be if a storm such as this occurs.”