There are four different kinds of thunderstorms: squall line, multi-cell, single-cell and supercell. The rarest and usually the most extreme of these four types of storms are supercell storms.
Supercell storms are storms that are characterized by a vortex of air known as a mesocyclone. The vortex is approximately two to ten kilometers in diameter. These vortexes are often cyclonic and can be accompanied by hail and strong winds as well as heavy downpours. In severe cases they can lead to tornadoes. While many associate supercell thunderstorms with tornadoes, only about 30% actually do cause tornadoes. Supercells can change the local climate of areas up to twenty miles away.
Supercells can be classified into two different types: low-precipitation and high-precipitation. Low precipitation supercells are often found in dry climates whereas high-precipitation supercells are more often found in moist climates. These storms can occur anywhere, though they most often occur in the high plains of the United States. Supercells are storms that have both updrafts and downdrafts that are almost balanced, which allows the storm to last for a long period of time, often several hours. Supercells also have a persistent and strong updrafts that rotate. They are considered the most intense kind of thunderstorm.
There are several features of a supercell thunderstorm including the overshooting top, anvil, precipitation-free base, wall cloud, mammatus clouds, precipitation area and flanking line.
The overshooting top is caused by a powerful updraft and can only be seen is the observer is not too close to the storm. The overshooting top is found directly above the anvil.
The anvil of a supercell storm is the cold, precipitation free area that is formed in the uppermost part of the storm. The clouds that form in this area come out in front of the storm like a shelf.
The precipitation-free base is usually found on the southern side of the storm and is also known as the main updraft area.
The wall cloud is between the precipitation and the precipitation free base and often forms near the interface of the downdraft and updraft. This is where tornadoes can be formed.
The mammatus clouds are clouds that are pillowy and rounded and extend from underneath the anvil portion of the storm.
The precipitation are is exactly as it is named.
The flanking line of the storm is a line of cumulus clouds that form in the air that is being pulled by the updraft of the storm.
For more information, please check www.ravenstorm.co.uk/stormchasing/stormfacts/terminology/index.htm, en.wikipedia.org/wiki/Supercell, en.wiktionary.org/wiki/supercell, http://en.wikipedia.org/wiki/Supercell and www.nssl.noaa.gov/projects/vortex2/learn/glossary.php. All the information gathered for this article was found in these sites.