Courtesy of UCAR Digital Image Library
Thunderstorms are one of the most thrilling and dangerous types of weather phenomena. Over 40,000 thunderstorms occur throughout the world each day.
Thunderstorms form when very warm, moist air rises into cold air. As this humid air rises, water vapor condenses, forming huge cumulonimbus clouds.
There are two main types of thunderstorms: ordinary and severe. Ordinary thunderstorms are the common summer storm and usually last about one hour. The precipitation associated with these storms includes rain and occasionally small hail. With ordinary thunderstorms, cumulonimbus clouds can grow up to 12 kilometers high.
Severe thunderstorms are very dangerous. They are capable of producing baseball-sized hail, strong winds, intense rain, flash floods, and tornadoes. Severe thunderstorms can last several hours and can grow 18 kilometers high. Several phenomena are associated with severe thunderstorms, including gust fronts, microbursts, supercell thunderstorms, and the squall lines.
source: Windows to the universe