Pub. date: 2008 | Online Pub. Date: April 25, 2008 | DOI: 10.4135/9781412963893 | Print ISBN: 9781412958783 | Online ISBN: 9781412963893| Publisher:SAGE Publications, Inc.About this encyclopedia
A THUNDERSTORM IS a localized storm that is produced by a cumulonimbus cloud and always contains thunder and lightning. Thunderstorms form in conditionally unstable environments, meaning there is cold, dry air aloft over warm, moist surface air. This causes the air to become buoyant and allows for rising air motion. A lifting mechanism is also needed to start the air moving. Such lifting mechanisms include surface heating, surface convergence, lifting caused by mountains, or lifting along frontal boundaries. The heat and the humidity of the summertime can often produce what are called ordinary thunderstorms or air mass thunderstorms. These are the type of thunderstorms that seem to suddenly pop up, last less than an hour, and are rarely severe. A severe thunderstorm is defined by the National Weather Service as having three-quarter-inch diameter hail or surface winds exceeding 58 mi. (93 km.) per hour or producing a tornado. Ordinary thunderstorms ...