A thunderstorm is a local storm produced by a cumulonimbus cloud and always accompanied by lightning and thunder. It may also produce heavy rain, strong winds, hail, and occasionally tornadoes.

Thunderstorms form when moist air becomes unstable and rises vigorously. The updraft builds the cloud; the downdraft brings precipitation and cooler air to the surface. Most thunderstorms are short-lived, lasting less than an hour, yet organized systems can persist much longer and travel great distances.

They are most common in the tropics and during the warm season in mid-latitudes. Safety rules emphasize seeking substantial shelter when thunder is heard. Lightning is the most consistent hazard; flash flooding and damaging winds can also pose serious threats.

Radar and satellite monitoring allow continuous tracking of thunderstorm development and movement.