An intense line of thunderstorms moving at a pace of 75 mph. A 112-mph wind gust. Vehicles flipped on the interstates in Iowa. Embedded tornado warnings. This is what parts of the Midwest endured Monday as a derecho blasted across multiple states.
A derecho is a widespread, intense and long-lived wind storm. According to the NOAA's Storm Prediction Center, by strict definition, the swath of wind damage must extend for more than 250 miles and include wind gusts of at least 58 mph along most of its length. A derecho must also include several, well-separated 75 mph or greater gusts. It can produce destruction similar to a tornado, only the damage typically occurs in one direction along a relatively straight path.
"Derecho" is a Spanish word meaning "right," "direct" or "straight ahead." They typically happen during the summer and can vary by intensity. Monday's derecho was in the upper echelon of intensity.
The derecho began as a small thunderstorms cluster near the Nebraska and Iowa border early Monday morning, but as derechos typically do, it grew in size, picked up speed and gained intensity as it moved east.
By 4 p.m., the derecho reached the Chicago area, bringing with it wind gusts forecast to be 60-90 mph along with the risk for embedded tornadoes.
At 3:40 p.m., the National Weather Service in Chicago warned of imminent danger: "Very high winds likely headed for downtown #Chicago with pockets of 80 to 90 mph likely based on radar estimates! Stay away from windows and head indoors immediately if walking near high-rise buildings."
The gusts caused serious damage to residences and buildings in Iowa and Illinois, some caused by downed trees and power lines. More than 250,000 MidAmerican customers were facing power outages across the state of Iowa, NBC-affiliate WHO reported.
By the time it ripped through Iowa and Illinois, here were some of the strongest wind gusts:
- Midway, Iowa: 112 mph
- Le Grand, Iowa: 106 mph
- Hiawatha, Iowa: 100 mph
- Albion, Iowa: 99 mph
- Marshalltown, Iowa: 95 mph
- Dixon, Illinois: 92 mph
- Urbandale, Iowa: 85 mph
- Des Moines: 80 mph
- Chicago (Midway Airport): 72.5 mph
- Chicago (O'Hare): 62 mph
At times, 60+ mph winds persisted for 20-30 minutes straight.
The derecho was expected to continue to bring destructive winds to parts of the Midwest and Great Lakes as it races east, where severe thunderstorm warnings issued ahead of the line of storms are in effect until midnight. The National Weather Service even issued a warning for the eastern shore of Lake Michigan, warning the strong winds associated with the derecho could produce large and deadly waves for anyone on the beach.