What is a derecho? An atmospheric scientist explains these rare but dangerous storm systems
Thunderstorms are common across North America, especially in warm weather months. About 10% of them become severe, meaning they produce hail 1 inch or greater in diameter, winds gusting in excess of 50 knots (57.5 miles per hour), or a tornado.
The U.S. recently has experienced two rarer events: organized lines of thunderstorms with widespread damaging winds, known as derechos.
Derechos occur fairly regularly over large parts of the U.S. each year, most commonly from April through August.
Dennis Cain/NOAA
Derechos occur mainly across the central and eastern U.S., where many locations are affected one to two times per year on average. They can produce significant damage to structures and sometimes cause “blowdowns” of millions of trees. Pennsylvania and New Jersey received the brunt of a d...