Derechos: definition and the largest US windstorms in the record

A derecho is a long-lived, fast-moving line of thunderstorms whose straight-line winds do damage along a path hundreds of miles long. Here is how forecasters define one, and the US storm days whose wind reports fit that pattern best.

The longest, most intense chain of damaging-wind reports in the NOAA Storm Prediction Center record since 1955 came on May 12, 2022: 413 reports linked over 507 miles across IA, MN, ND, NE, SD, 191 of them 75 mph or more. In all, 818 storm days had a chain at least 250 miles long with 3 or more reports of 75 mph+, and 79% of them fell from April through August.

What makes a windstorm a derecho

The NOAA Storm Prediction Center (Facts About Derechos, updated April 28, 2026) classifies an event as a derecho when all of these hold:

• The swath of wind damage is at least 250 miles (about 400 km) long.
• It has wind gusts of at least 58 mph along its length.
• It has several well-separated gusts of 75 mph or more.
• It comes from a cluster of thunderstorms (a mesoscale convective system) that moves faster than the mean wind, driven by its own pool of rain-cooled air.

SPC notes that derecho damage, though it can match a tornado's, typically runs in one direction along a fairly straight path, which is why it is often called straight-line wind damage. It says US derechos are most common from May through August, with more than 75% between April and August, and that warm-season derechos mostly follow two corridors: from the upper Mississippi Valley southeast into the Ohio Valley, and from the southern Plains northeast into the mid-Mississippi Valley.

How we find derecho-like days in the reports

Storm reports can't prove a derecho (the definition also depends on how the storm system moved and what drove it), but they show where long damage swaths happened. For each storm day we link damaging-wind reports that are within 50 miles and 90 minutes of each other into chains, then measure each chain end to end and count its 75 mph+ reports. Days ranked here are candidates; check the National Weather Service's event summaries before calling one a derecho.

Damaging wind reports on May 12, 2022

All 442 damaging wind reports that storm day. Storm reports for May 12, 2022 →

Storm days with the most 75 mph+ reports in one chain, since 1955

Candidate derecho days by month

Our 818 candidate days: 79% from April through August, in line with SPC's climatology above.

Recent candidate days since 2016

* Preliminary 2026 reports; many have no wind speed yet, so 75 mph counts may rise.

Related: US damaging wind history by state · tornado history · EF scale

Source: NOAA Storm Prediction Center (SPC) Severe Weather Database (SVRGIS) damaging-wind reports, 1955–2025, and SPC preliminary storm reports for 2026 (data through November 6, 2026). Wind speeds are measured or estimated by spotters, the public and NWS staff; SPC records them in knots and we show mph. 58 mph is the National Weather Service's severe-thunderstorm wind threshold.

Guide: Hail vs wind damage