Thunderstorm, a violent, short-lived weather disturbance that is almost always associated with lightning, thunder, dense clouds, heavy rain or hail, and strong, gusty winds. Some thunderstorms can also bring tornadoes and/or hail. ... Thunderstorms are produced by cumulonimbus clouds and form when air rises rapidly.e when layers of warm, moist air rise in a large, swift updraft to cooler regions of the atmosphere. <br />Severe thunderstorms must meet at least one of three different criteria including strong winds winds in excess of 58 mph, hail larger than an inch, or a tornado. Lightning and heavy rain do not make a storm severe, but it doesn't mean they're any less dangerous
