Derecho
A derecho is a widespread, long-lived windstorm produced by a fast-moving line or cluster of severe thunderstorms. Under the criteria the Storm Prediction Center uses, the swath of wind damage must be at least 250 miles (about 400 km) long, with gusts of at least 58 mph along its length and several well-separated gusts of 75 mph or greater.
Why It Matters
A derecho brings damaging wind to a far larger area than a tornado does. The winds blow in one direction along the path, so the result is called straight-line wind damage, and a single event can cross several states in one afternoon or night.
In the United States, derechos are most common from May through August, and more than 75% occur between April and August. They are most frequent along two corridors: one along the Corn Belt from the upper Mississippi Valley into the Ohio Valley, and one from the southern Plains northeast into the mid-Mississippi Valley.
Derecho Criteria Used by the Storm Prediction Center
| Criterion | Requirement |
|---|---|
| Length of the damage swath | At least 250 miles (about 400 km) |
| Wind gusts along the swath | At least 58 mph (93 km/h) |
| Stronger gusts | Several well-separated gusts of 75 mph (121 km/h) or greater |
| Parent storm system | A mesoscale convective system that moves faster than the mean wind, driven mainly by its cold pool |
SPC revised the definition in 2016 and again in 2025.
Types and Radar Signature
- A progressive derecho comes from a relatively short line of thunderstorms, typically 40 to 250 miles long.
- A serial derecho is produced by multiple bow echoes embedded in an extensive squall line, typically many hundreds of miles long.
- On radar, the signature is the bow echo: a line of storms that bulges forward where the strongest winds are pushing it.
Frequently Asked Questions
How long does a storm have to be to count as a derecho?
The swath of wind damage must be at least 250 miles (about 400 km) long. It also needs gusts of at least 58 mph along its length and several well-separated gusts of 75 mph or greater.
Is a derecho a tornado?
No. A tornado is a rotating column of air. A derecho is a straight-line windstorm: its winds blow outward from a line of thunderstorms in one general direction, across a path hundreds of miles long. The criteria require several gusts of 75 mph or greater, which is hurricane force.
When is derecho season?
May through August is the peak in the United States, and more than 75% of derechos occur between April and August. Cool-season derechos are less common and most likely from east Texas into the Southeast.
Related Terms
Bow Echo
A bow or crescent-shaped radar signature indicating strong straight-line winds. Bow echoes form when the center of a squall line accelerates ahead of its ends, often producing damaging winds exceeding 75 mph.
Squall Line
A squall line is a line of active thunderstorms, either continuous or with breaks, together with the rain areas the storms produce. Squall lines can extend for hundreds of miles and last for many hours. Their main hazard is straight-line wind damage, though tornadoes sometimes form along the leading edge.
Downburst
A strong downdraft that induces an outward burst of damaging winds at or near the surface. Downbursts can be either microbursts (less than 2.5 miles) or macrobursts (larger than 2.5 miles) and can cause damage similar to a tornado.
Microburst
A localized column of sinking air that produces damaging divergent winds at or near the surface. Microbursts can produce winds exceeding 100 mph in an area less than 2.5 miles across and are particularly hazardous to aircraft.
Shelf Cloud
A shelf cloud is a low, horizontal, wedge-shaped cloud attached to the base of a thunderstorm along its gust front, the leading edge of the storm's rain-cooled outflow. Rising cloud motion is often visible on its leading edge, while the underside looks turbulent and wind-torn. It means gusty winds are about to arrive.
SPC Outlook
Severe weather forecasts issued by the Storm Prediction Center categorizing risk levels from Marginal (1) to High (5). Outlooks cover tornadoes, damaging winds, and large hail for 1-3 days ahead and highlight where organized severe weather is most likely.
Derecho: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
In-depth guide
What Is a Derecho? The Inland Hurricane Explained
Learn what a derecho is, how it differs from tornadoes and hurricanes, why these long-lived windstorms are so destructive, and how to stay safe when one approaches.
Guides
SPC Outlooks Explained: Marginal, Slight, Enhanced, Moderate, High Risk
Learn how to read Storm Prediction Center outlooks, what SPC risk levels mean, and how tornado, hail, wind, moisture, instability, lift, and shear shape severe weather forecasts.
Weather Education
What Is a Heat Dome? How Stalled High Pressure Bakes a Region
Learn what a heat dome is, how a stalled upper-level high-pressure ridge traps sinking, warming air, why heat domes last for days, and how to stay safe in extreme heat.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Seasonal Hub
Severe Weather Season Guide
A seasonal hub for tornadoes, hail, damaging winds, and storm-prep reading.
Guide
Lightning Safety Guide
Know when lightning becomes dangerous, how far away it can strike, and when to move indoors.
Guide
What Causes Thunder and Lightning?
How lightning forms through charge separation, what causes thunder, and how to stay safe.
Tool
Wind Speed Converter
Convert between mph, km/h, knots, and m/s for wind reports and forecasts.
Sources
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Hail
Balls or irregular lumps of ice produced in severe thunderstorms. Hailstones form when updrafts carry raindrops into extremely cold areas of the atmosphere where they freeze. Repeated cycles through the updraft can create hailstones larger than softballs.
Wind Shear
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Debris Ball
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HRRR
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