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associated with a heavy or severe thunderstorm over Enschede , The Netherlands .]] A thunderstorm, or an '''electrical storm''', is a form of Weather characterized by the presence of Lightning and its attendant Thunder . It is usually accompanied by copious Rain fall, Hail , or rarely, Snow fall in the winter months, sometimes termed Thundersnow . Thunderstorms occur throughout the world, even in the polar reigons, with the greatest frequency in Tropical Rainforest areas, where they may occur nearly daily. Kampala and Tororo in Uganda have each been mentioned as the most thunderous places on Earth, an accolade which has also been bestowed upon Bogor on Java , Indonesia . In temperate regions, they are most frequent in spring and summer, though can occur in Cold Front s at any time of year. Probably the most thunderous region outside of the Tropics is Florida . During the summer, violent thunderstorms are an almost daily occurrence over central and southern parts of the state. The most powerful and dangerous severe thunderstorms also occur over the USA, particularly in the Midwest and the southern States. These storms can produce very large Hail and powerful Tornadoes . Thunderstorms form when significant condensation—resulting in the production of a wide range of water droplets and ice crystals—occurs in an atmosphere that is unstable and supports deep, rapid upward motion. This often occurs in the presence of three conditions: sufficient moisture accumulated in the lower Atmosphere , reflected by high Dewpoint temperatures; a significant fall in air Temperature with increasing height, known as a steep Adiabatic Lapse Rate ; and a force such as mechanical Convergence along a cold front to focus the lift. Thunderstorms have had a lasting and powerful influence on early civilizations. Romans thought them to be battles waged by Jupiter , who hurled lightning bolts forged by Vulcan . Thunderstorms were associated with the Thunderbirds , held by Native Americans to be a servant of the Great Spirit . In more contemporary times, thunderstorms now have taken on the role of a curiosity. Every spring, Storm Chasers head to the Great Plains of the United States and the Canadian Prairies to explore the visual and scientific aspects of storms and tornadoes. According to Encyclopedia Britannica, if the quantity of water that is condensed in and subsequently precipitated from a cloud is known, then the total energy of a thunderstorm can be calculated. In an average thunderstorm, the energy released amounts to about 10,000,000 kilowatt-hours, which is equivalent to a 20-kiloton nuclear warhead. A large, severe thunderstorm might be 10 to 100 times more energetic. CLASSIFICATION There are four main types of thunderstorms: single cell, '''multicell''', '''squall line''' (also called multicell line) and '''supercell'''. Which type forms depends on the instability and relative wind conditions at different layers of the atmosphere (" Wind Shear "):
Multicell or squall line systems may form a meteorologically important feature known as ''mesoscale convective system'' (MCS) stretching for hundreds of kilometres. ''Mesoscale convective complex'' is another term for this phenomenom. They are large enough to have a pronounced effect on the upper-level and surface weather pattern, and may influence forecasts over a large area. MCS systems are common in the Midwest region of the United States and the Canadian Prairies during the summer months and produce much of the region's important agricultural rainfall. Severe thunderstorm A severe thunderstorm is a thunderstorm with winds 90 km/h (55 mph) or greater, 2 cm or larger hail, funnel clouds or tornadoes. These storms may contain frequent cloud-to-ground lightning and heavy downpours which can lead to localized flooding. This is a general definition which varies by country and is somewhat contentious. An otherwise weak thunderstorm which produces a wind gust of the required strength would be defined as 'severe' whereas a very violent thunderstorm with continuous lightning and very heavy rain (but without the required wind gusts, hail or tornado/funnel cloud) would not. Many of the violent local thunderstorms which affect Florida so frequently during the summer months would not be defined as severe. Severe thunderstorms may occur as Supercell Thunderstorm s, although multicell and squall lines are the most common forms. LIFE CYCLE A given cell of a thunderstorm goes through three stages: the ''cumulus stage'', the ''mature stage'', and the ''dissipation stage''. In the ''cumulus stage'' of a thunderstorm cell, masses of moisture are pushed upwards. The trigger for this can be solar Insolation heating the ground producing Thermals , areas where two winds converge forcing air upwards, or where winds blow over areas of high ground. The moisture rapidly cools into liquid drops of water, which appears as ''cumulus'' Cloud s. As the water vapour condenses into liquid, Latent Heat is released which warms the air, causing it to become less dense than the surrounding dry air, and so the air will tend to rise in an ''updraft'' due to the process of Convection (hence the term Convective Precipitation ). This creates a low-pressure zone beneath the forming thunderstorm. In a typical thunderstorm, some 5×108 Kg of water vapour are lifted and the amount of Energy released when this condenses is about equal to the energy used by a City ( US - 2002 ) of 100,000 over a Month . In the ''mature stage'', the warmed air continues to rise until it reaches existing air which is itself warmer, and the air can rise no further. Often this 'cap' is the Tropopause . The air is instead forced to spread out, giving the storm a characteristic anvil shape. The resulting cloud is called '' Cumulonimbus Incus ''. The water droplets Coalesce into heavy droplets and freeze to become ice particles. As these fall they melt, to become Rain . If the updraft is strong enough, the droplets are held aloft long enough to be so large that they do not melt completely as they fall and fall as Hail . While updrafts are still present, the falling rain creates ''downdrafts'' as well. The presence of both updrafts and downdrafts during this stage can cause considerable internal Turbulence in the storm system, which sometimes manifests as strong winds, severe lightning, and even Tornado es. If there is little Wind Shear , the storm will rapidly 'rain itself out', but if there is sufficient change in wind speed and/or direction the downdraft will be separated from the updraft, and the storm may become a supercell. Finally, in the ''dissipation stage'', updraft conditions no longer exist, and the storm is characterized largely by weak downdrafts. Because most of the moisture has precipitated out, there is not sufficient moisture in the lower air to sustain the cycle and the thunderstorm dissipates. LIGHTNING Lightning is an electrical discharge that occurs in a thunderstorm. It can be seen in the form of a bright streak (or bolt) from the sky. Lightning occurs when a charge is built up within a cloud. When a large enough charge is built up, a large discharge will occur and can be seen as lightning. The temperature of a lightning bolt can be hotter than the surface of the sun. Although the lightning is extremely hot, the short duration makes it not necessarily fatal. Contrary to the popular idea that lightning doesn’t strike twice, some people have been struck by lightning over three times. There are several kinds of lightning.
SEE ALSO EXTERNAL LINKS
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