A long-lived, straight-line windstorm associated with a line of thunderstorms is a derecho.
A derecho is a widespread convectively generated windstorm produced by a fast-moving mesoscale convective system. Its winds travel mainly in the direction of the storm’s movement rather than rotating around a narrow central vortex as tornado winds do. On weather radar, the storm often develops a curved bow-echo shape.
Derechos can remain organized for many hours and produce a broad, continuous damage swath. Their embedded downbursts may generate wind gusts exceeding hurricane strength, along with torrential rain, flash flooding, and occasional tornadoes. The term comes from the Spanish word for “straight,” emphasizing the storm’s straight-line wind damage.
A squall line is a band of thunderstorms, but not every squall line qualifies as a derecho. Downbursts and microbursts are localized wind events, usually much shorter in duration and smaller in geographic scale. The defining idea behind a derecho is sustained, widespread, long-lasting wind damage from an organized thunderstorm complex.