There are three general types of thunderstorms:
These develop in weak wind shear summer atmospheres. They typically do not tend to have any severe weather associated with them. However you can occasionally get severe single cell or pulse storms in more unstable atmospheres with weak wind shear. They can produce hail, downbursts or more rarely weak tornadoes.
Groups of storm cells moving together as one. These storms are more potent than single cell storms and form in clusters or lines (squall lines). In multicell clusters the strongest storms are found at the center of the cluster with developing cells towards the front and dissipating cells towards the rear. Squall lines move together as a line with one continuous gust front along the line. Severe weather produced by multicell storms however is similar to that of pulse severe thunderstorms. That is because each updraft is competing for the fuel warm moist inflow air and therefore updrafts are often not able to strengthen enough to produce very severe weather.
Schematic of a multicell thunderstorm (left) and accompanying labeled photograph (right)
The strongest and most deadly of thunderstorms. They consist of one huge, intense rotating updraft and can last for many hours. A rotating updraft is known as a mesocyclone. They develop in highly unstable strongly sheared environments. Wind shear occurs when the winds are changing direction and increasing with height. The most ideal conditions for supercells occurs when the winds are veering or turning clockwise with height. Supercell storms are most common in the plains states. Supercells bring very severe weather conditions including large hail stones, often up to baseball size, flash floods, strong downburst winds and anything from weak to extremely violent tornadoes.
Supercell storms are characterized by a rotating updraft (usually cyclonic - above left) which results from a storm growing in an environment of significant vertical wind shear.