You're in the middle of a midwestern field right now. You feel a warm breeze gathering. Then wall of clouds starts heading in your direction. The wind gets stronger. Then a thunderstorm comes out of nowhere.
Amazingly, the wind gets even stronger. So strong that it damages a barn in a neighboring field. These aren't the soft and fluffy clouds of fairy tales. Ladies and gentleman, it's derecho season.
Derechos get their name from the Spanish word for "straight" because of the beeline path the combination wind/thunderstorm takes. They most frequently arrive in the U.S. beginning in late June and occur all the way through July. And a derecho will strike night or day—they don't discriminate.
Derechos in the U.S. generally occur through out the southern Plains, the Mississippi Valley, and the Ohio Valley. Derechos have also been known to occur in Brazil, Argentina, Canada, and even Germany.
Derechos can reach speeds up to 130mph and are at least 240 miles long. They can also travel hundreds of miles in a given direction. Most recently, a derecho struck in Marshalltown, IA, where it battered down the top of a grain silo (see above). That same derecho also moved through Indiana, Illinois and Ohio, with winds reaching speeds up to 80mph. Barns and mobile homes are frequent structural victims of derecho storms.
In case you're wondering, derechos and tornadoes can happen at the same time for double the disaster. There are even "super derechos" which can cause damage independent from the main wall of clouds. [NOAA and Mike Borland via Matt Hardigree]