Supercell

Supercell thunderstorms are the largest, most severe class of single cell thunderstorm. Supercells can evolve from a regular thunderstorm, or can be generated independently. Supercells usually produce copious amounts of hail, torrential rainfall, strong winds, substantial downdrafts, and can sometimes produce tornadoes.

They are primarily caused by low pressure, and warm humid air that is below a colder upper layer. The warm air rises and the cold air descends, creating powerful convection currents. This convection drives the storm and generates a mesocyclone, which can cause tornadoes.

Supercells are usually seen in the Midwestern United States, but they can occur anywhere.