Q: The severe storms that hit the Northeast recently were called derechos? 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 up to 150 miles per hour. The storm system associated with derechos often moves quickly, often at 50 miles per hour and a few have been clocked at 70 miles per hour. They can also last a long time and move through several states. So a derecho can be a very powerful storm.”
Q: Where do they occur?
A: They can occur anywhere, but are most often seen in the Midwest and the prairie states, and they can form either in the daytime or at night, McRoberts adds. “Winds in a derecho storm have been clocked at more than 110 miles per hour in Wisconsin and Michigan, and a derecho that occurred in Memphis in 2003 was also believed to be that strong and knocked out much of the city’s 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.”
Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University.