Derecho
A derecho is a widespread, long-lived windstorm produced by fast-moving thunderstorms, known for long swaths of damaging straight-line winds.
What a derecho is
A derecho is a widespread, long-lived windstorm associated with a fast-moving line or cluster of severe thunderstorms. The name comes from the Spanish word for straight, because the damage is usually caused by straight-line winds rather than rotating tornado winds. A derecho can travel hundreds of miles while producing repeated severe wind gusts.
Straight-line wind damage
Derechos can produce damage that looks dramatic even when no tornado occurred. Trees, crops, power poles, roofs, and vehicles may be pushed in the same general direction across a long corridor. Tornado damage is often more chaotic and rotating, while derecho damage is usually broad and aligned with the storm's forward motion.
How derechos form
Many derechos develop from mesoscale convective systems, which are organized complexes of thunderstorms. Downdrafts inside the storms rush toward the ground and spread outward as damaging winds. If the storm system keeps regenerating and moving quickly, those wind bursts can merge into a long-lived corridor of severe wind.
Bow echoes and radar clues
On radar, derecho-producing storm lines often show bow echoes: curved segments that bulge forward where winds are strongest. Not every bow echo becomes a derecho, and not every damaging squall line reaches derecho criteria. Still, radar shape, storm speed, instability, wind shear, and reports of damage help forecasters assess the threat.
Warm-season and cool-season events
Derechos are often associated with warm, humid air and strong winds aloft, especially in spring and summer. They can also occur in cooler seasons when strong wind shear and organized storm lines are present. In the United States, derechos are most common in parts of the central and eastern states, but they can occur in other regions too.
Derecho versus tornado
Derechos and tornadoes can occur in the same severe-weather outbreak, but they are different hazards. A tornado is a rotating column of air in contact with the ground. A derecho is a long swath of damaging thunderstorm wind. Because derechos can affect many communities at once, they can cause power outages and cleanup problems over a very wide area.
Warnings and safety
A derecho may be covered by severe thunderstorm watches and warnings, sometimes with destructive wind language when the threat is extreme. Safety advice is similar to other severe thunderstorm wind events: move indoors, stay away from windows, avoid travel during the storm, and treat downed power lines as dangerous after the winds pass.
Why it matters
Derechos matter because they can be regional disasters even without the familiar labels of hurricane or tornado. Their fast movement, nighttime occurrence, long damage paths, and widespread power outages can catch people off guard. Understanding derechos helps people take severe thunderstorm warnings seriously.