On August 10, 2020, a wall of wind swept out of eastern Nebraska and tore across Iowa, Illinois, and Indiana in a matter of hours. By the time it dissipated, it had flattened an estimated 10 million acres of corn, knocked out power to well over a million people, and caused damage rivaling a major hurricane — all without a drop of ocean in sight. That storm was a derecho, and most people outside the affected states had never heard the word until it was on their doorstep.
A derecho (pronounced "deh-REY-cho," from the Spanish word for "straight") is one of the most destructive types of summer thunderstorm complex. Unlike a tornado, which carves a narrow path of spinning wind, a derecho delivers powerful straight-line winds across a swath that can be hundreds of miles long. Here's what it is, how it forms, and why forecasters take it so seriously.
Not every windy thunderstorm earns the title. Meteorologists apply a specific definition: a derecho is a widespread, long-lived windstorm associated with a band of fast-moving thunderstorms. To qualify, the damage swath must extend at least 240 miles (about 400 km), with wind gusts of at least 58 mph (93 km/h) along most of its length, and several well-separated gusts reaching 75 mph (121 km/h) or more.
In other words, it isn't the peak wind speed alone that defines a derecho — it's the combination of severe wind and the enormous distance it travels while staying intense. A single town getting a 70 mph gust is a severe thunderstorm. A 70 mph gust hitting town after town across three states is a derecho.
Derechos grow out of a mesoscale convective system — a large, organized cluster of thunderstorms. The engine behind the destructive wind is the downdraft: as rain falls through a storm, it drags cool air down with it. When that cool, dense air slams into the ground, it spreads outward at high speed, like water from a bucket hitting pavement.
In a derecho, these downdrafts become organized and self-reinforcing. The rush of cold air spreading out ahead of the storms — the gust front — lifts more warm, humid air into the system, feeding new thunderstorms along the leading edge. On radar, this often shows up as a distinctive bow echo: the line of storms bends forward in the middle, like an archer's bow, where the wind is pushing hardest. As long as the atmosphere ahead stays warm, moist, and unstable, the whole complex can march forward for many hours, sometimes covering more than 1,000 miles before it finally runs out of fuel.
Derechos are creatures of summer. In the United States they're most common from late spring through August, when hot, humid air provides the instability they feed on. There are two favored corridors: one running from the upper Midwest into the Ohio Valley, and another across the southern Plains into the Mid-South. They can and do happen elsewhere — including in Europe — but they need the same ingredients: heat, humidity, and a fast jet stream aloft to keep the storms organized and moving quickly.
| Event | What Happened |
|---|---|
| July 1995 — Northeast | A derecho roared across the Adirondacks, flattening huge areas of forest in minutes. |
| June 2012 — Mid-Atlantic | Traveled ~700 miles from the Midwest to the Atlantic coast, leaving millions without power during a brutal heat wave. |
| August 2020 — Midwest | The Iowa derecho: gusts over 100 mph (160 km/h), ~10 million acres of crops flattened, billions in damage. |
| May 2022 — Upper Midwest | A spring derecho spawned embedded tornadoes and blinding dust storms across the Plains. |
Very. Derecho winds routinely reach 80–100 mph (130–160 km/h), enough to uproot mature trees, peel roofs, topple high-profile vehicles, and bring down power lines across entire regions. Because the damage is so widespread, restoring power can take a week or more — which becomes life-threatening when a derecho strikes during a summer heat wave and air conditioning fails for millions at once. Falling trees and flying debris are the leading causes of derecho injuries and deaths.
Derechos can also spin up brief embedded tornadoes along their leading edge, and the leading gust front can kick up sudden dust storms that drop highway visibility to near zero in seconds.
Treat a severe thunderstorm warning seriously. When the warning text mentions 70–80 mph wind gusts or a "damaging wind threat," that's potential derecho language. Don't wait to see a funnel.
Get indoors and away from windows. The safest place is an interior room on the lowest floor, the same advice as for a tornado.
Avoid driving. If you're already on the road, the straight-line winds and sudden dust can be deadly. Pull off safely, away from trees and power lines, and wait it out.
Prepare for a long power outage. Charge devices, fill water containers, and have a plan for staying cool if the derecho hits during hot weather.
Watch the radar. A bow-shaped line of storms racing toward you is the classic signature. Knowing what a derecho is — before one is on your doorstep — is half the battle.
→ Check the current wind, gusts and storm conditions for your location on ClearCast