Powerful derecho blasts Midwest, swarming Chicago with tornadoes (2024)

The National Weather Service received one report of a fatality in northwestern Indiana, where a tree fell on a residence in Cedar Lake, killing a 44-year-old woman.

The well-anticipated storm complex was a derecho, or a fast-moving squall line that gobbles up heat and humidity and produces a trail of destructive wind gusts. Storms began generating 60-plus mph winds east of Des Moines around 7 p.m. Central time, then continued through northeastern Indiana along a 500-mile-long path before dissipating around 1 or 2 a.m. Tuesday.

The derecho toppled hundreds of trees — some onto homes — as well as dozens of wires and power poles, while ripping off roofs and damaging vehicles.

At one point, forecasters at the National Weather Service in Chicago had to abandon their posts as a tornado approached, transferring responsibility for issuing warnings to a sister office in Gaylord, Mich.

As the storms plowed through the greater Chicago metro area, so many tornadic circulations spun up that meteorologists opted to issue blanket warnings. That meant they weren’t issuing tornado warnings for individual areas of rotation, but rather entire segments of the squall line.

A local news station broadcast live coverage with the chyron “possible tornadoes almost everywhere in Chicagoland” at a time when multiple confirmed tornadoes were ongoing. No fewer than eight “couplets,” or areas of tight rotation, were visible on radar.

“We are seeing power flashes on both the O’Hare and Midway Airport webcams due to likely tornadoes and/or destructive wind gusts near those areas,” the National Weather Service in Chicago posted on X.

Here’s a roundup of some of the strongest winds measured:

Storms first erupted during the mid-evening hours in central and eastern Iowa, bringing tennis-ball-size hail in Crawford. Initial storms began as rotating supercells, including one that spawned a tornado near Des Moines.

Storms then congealed into a cluster, which towered to 55,000 feet in height. The cluster began feeling jet stream winds aloft and fanned out into an arcing squall line reminiscent of an archers bow.

From there, the storms charged east, riding along a stalled frontal boundary. Cooler air was present to the north, with very warm, moist air to the south. Storms tend to straddle boundaries, riding them like rail cars on a train track. That steered them into northern and central Illinois and then Chicago.

Chicago was particularly prone to tornadoes due to the presence of a “northern bookend vortex.” The northern end of one segment within the squall line curled back on itself, acquired counterclockwise rotation and began producing intermittent tornadoes.

At 9:04 p.m. Central time, three tornadoes were simultaneously on the ground in the southwestern Chicago metro. Two were sighted by radar near Aurora, Ill., while a third occurred near Oswego. Doppler radar detected debris lofted by the tornadoes, which appeared as blue splotches on weather maps.

Significant tornado damage was reported around Elwood and Channahon, Ill., about 35 to 40 miles south of Chicago.

Summertime windstorms and derechos aren’t terribly unusual; they happen across the Corn Belt, Great Lakes and Midwest roughly once per summer on average. They ordinarily form on the northern periphery of “heat domes,” or sprawling ridges of high pressure. Storm complexes take advantage of the hot, humid air, while surfing the jet stream eastward.

On Aug. 10, 2020, an extreme derecho brought 130 mph gusts to parts of Iowa. It was the most costly thunderstorm disaster in United States history, damaging or destroying hundreds of homes and flattening millions of acres of the state’s corn crop. The derecho also produced damaging winds in Chicago.

Jason Samenow contributed to this report.