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A rare and destructive weather event—known as a derecho—is expected to pummel the northern Plains and Upper Midwest on Monday evening, bringing wind gusts of up to 75 mph. Severe hail, heavy rainfall, and possible tornados are expected in parts of the region as well, according to the National Weather Service. Parts of South Dakota and Minnesota, where the Storm Prediction Center issued a Level 4 out of 5 risk, have issued storm warnings.
Here’s what to know and how to stay safe.
What is a derecho?
A derecho is a widespread windstorm often accompanied by rain or thunderstorms—and capable of producing destruction that rivals the strength of tornadoes.
“What sets the derecho apart from the storm systems that you might see on a more routine basis is intense wind speeds covering a large area, so a long swath of intense, damaging winds,” says Russ Schumacher, professor of atmospheric science at Colorado State University.
Whether or not the system developed into a derecho will be determined after the fact. According to the National Weather Service, a storm system must travel a distance of 240 miles and have wind gusts of at least 58 mph to be classified as a derecho. It doesn't occur very often— derechos are likely to occur only once a few times a year in the summer in the central and southern U.S..
The storm is being driven by the hot, humid air in the region. “In the summer, often there is high pressure and a lot of heat over the central and southern U.S., and then just on the north edge of that tends to be where the jet stream is, where there's a boundary between the extremely hot air to the south, and then cooler air to the north,” says Schumacher. ‘You get this ring of thunderstorms that can form.”
In 2012, a derecho traveled 700 miles in just 12 hours, knocking out power for millions of people—in some instances for over a week. A 2020 derecho killed four people and caused $11 billion worth of damages in the Midwest, making it the most expensive thunderstorm in modern U.S. history.
How do you stay safe during a derecho?
Much of the precautions you can take mirror what you might do during a tornado or thunderstorm. Stay indoors, ideally in a basement or interior room—like a bathroom or closet—and keep away from windows and doors.
Head all warnings from the National Weather Service. “On a day like today, those severe thunderstorm warnings need to be taken very seriously because of the kinds of damage that these storms can produce,” warns Schumacher.
Charge your devices in case of a power outage, and make sure you have more than one way to access any weather alerts from the National Weather Service. “Most people these days probably get those warnings on their phones,” says Schumacher. “But if the cell towers get knocked down or the power goes out, have another way to get that information, whether that's your local radio station or NOAA Weather Radio.”
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