Tornados can be “a possible byproduct” of derechos, according to Eric Lenning, a meteorologist at the National Weather Service in Chicago. Tornados move in a circular direction and affect a smaller geographical region.
“The tornadoes would be more localized” than a derecho, he said.
Derechos occur a couple of times a year across the United States, but most do not usually produce wind speeds near 100 m.p.h., Mr. Marsh said. The powerful derecho on Monday was similar to the “Super Derecho” of May 8, 2009, which hit several states, including Kansas, Missouri, Illinois, Kentucky, Tennessee and Arkansas. Another powerful one occurred in 2012, he said.
Damage from a derecho can cover hundreds of miles. If wind damage covers 240 miles and includes numerous reports of wind gusts of at least 58 miles per hour, then “the event may be classified as a derecho,” according to the National Weather Service. Because they cover so much territory, Mr. Lenning said, derechos can last for several hours and travel across large portions of the country.
“We’ve had derechos that start in the Chicago area and hit Washington, D.C.,” he said.
Even after such storms pass, Mr. Lenning warned, there can be dangerous aftereffects. “Stay out of Lake Michigan, because the water levels could fluctuate rapidly because of the wind’s interaction with the water,” he said.
Randy Renstrom of Grinnell, Iowa, said there was extensive damage to houses and businesses in that city, which is about 55 miles east of Des Moines. His electric provider, Alliant Energy, estimated that his power would be out for two days.
Mr. Renstrom said his wife, Ashley Renstrom-Schaefer, 37, told him that the storm on Monday was similar to what she experienced when she was in Houston in 2008 and Hurricane Ike ripped through the city: The sky quickly grew dark and streets filled with roaring winds as trees were uprooted, flattened and bent in one direction.
While Mr. Renstrom, 40, said the damage to his home was limited to a few loosened shingles on the roof, his neighbors were not as lucky. One neighbor’s trailer tipped over. Across the street, another neighbor’s garage door and underside of her porch were damaged.
