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 on Monday afternoon and evening as a derecho blasted across multiple states with no sign of slowing down.
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 months and can vary by intensity. Monday’s derecho was in the upper echelon of intensity.
In what is considered one of the most dramatic ramp ups for severe thunderstorms so far this year, a morning that began with only a marginal concern for severe thunderstorms escalated quickly into the potential for a dangerous day ahead.
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Early Monday morning, these Midwest areas were considered at a Marginal Risk — meaning there was a chance for isolated, severe thunderstorms, but the risk wasn’t overly concerning. A Marginal Risk is considered a 1 out of 5 on the scale of severe weather risk.
By mid-morning, it became clear to meteorologists that the atmosphere was primed to support intense thunderstorms, so the area was upgraded to an Enhanced Risk, which is two jumps ahead — a 3 out of 5 on the severe weather scale.
By noon, the severe risk was upgraded even further to a Moderate Risk for severe weather, which is a 4 out of 5 on the scale. A “Particularly Dangerous Situation” severe thunderstorm watch was issued for parts of Iowa, Illinois, Wisconsin and Indiana that faced the potential for wind gusts up to 100 mph.
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. CT, 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. local time, the National Weather Service in Chicago tweeted this to warn folks of the 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.”
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.
Kathryn Prociv is a meteorologist and producer for NBC News.
The post Destructive derecho, a line of storms with 100 mph winds, slams Chicago and Midwest appeared first on NBC News.