Derecho - A damaging wind

Today's question comes to us from Micki, who wants to know "what were those damaging winds that blasted across Alabama earlier in the week. They called them a name I hadn't heard before".

Thanks Micki, those damaging winds were called a "Derecho", a widespread and long lived windstorm that is associated with a band of rapidly moving showers or thunderstorms.

Derecho is a Spanish word which can be defined as "direct" or "straight ahead", and these powerful straight-line winds can do considerable damage, and the area of damage can extends for hundreds of miles.

To see the impact they had on Alabama earlier in the week, try the following link. http://www.nbc13.com/vtm/news/local/article/alabama_storm_damage_caused_by_derecho/71027/

Derechos are associated with bands of thunderstorms (which may include some supercells thunderstorms), which show up as a curved shape (or "bow echo") on radar screens. To see 2 bow echoes on radar, point your browser to this link:
http://www.ask.com/bar?q=bow+echo&page=1&qsrc=0&ab=2&u=http%3A%2F%2Fwww.theweatherprediction.com%2Fhabyhints2%2F386%2F

So, how strong can they be? To start with, winds in a derecho have to meet the National Weather Service's requirement for severe thunderstorm winds (58 mph or stronger) at most points along the path of the storm.

Gusts stronger than 100 mph have been reported.

Derechos in the United States are most common in the late spring and summer (May through August) and typically in two general areas. One reaches through the "corn belt" from the upper Mississippi Valley into the Ohio Valley. The other one stretches from the mid Mississippi Valley into the southern Plains. During the cool season (September through April) derechos can still occur from eastern Texas into the southeastern states.

Besides the United States, derechos have been reported in eastern Germany, Bangladesh and portions of India. (and, by the way, they can occur at the same time as tornadoes).

That's only the beginning of a very interesting topic, and for more information, take a look at this information from the Storm Prediction Center in Norman Oklahoma. http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm

Hopefully, you'll only get to study them from a distance