Mesocyclone thunderstorm moving over farmland. A mesocyclone is a rotating column of air found in the centre of extreme thunderstorms, known as supercell thunderstorms. The mixing of warm updrafts and cold downdrafts in the mesocyclone results in hail, the presence of which generates lightning, and heavy rainfall. Powerful downdrafts can also occur, which can ultimately lead to the generation of tornadoes. This mesocyclone produced extremely large ('softball-sized') pieces of hail on 18th April, 1992. Photographed in Oklahoma, USA.