thunderstorm
Severe storm of very heavy rain, thunder, and lightning. Thunderstorms are usually caused by the intense heating of the ground surface during summer. The warm air rises rapidly to form tall cumulonimbus clouds with a characteristic anvil-shaped top. Electrical charges accumulate in the clouds and are discharged to the ground as flashes of lightning. Air in the path of lightning becomes heated and expands rapidly, creating shock waves that are heard as a crash or rumble of thunder.
The rough distance between an observer and a lightning flash can be calculated by timing the number of seconds between the flash and the thunder. A gap of three seconds represents about a kilometre; five seconds represents about a mile.
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