Supercell thunderstorm and lightning over rural South Dakota, USA. Time-exposure image of lightning during a supercell thunderstorm. This storm lasted several hours, producing lots of lightning, six tornadoes, and baseball-sized hail. A supercell thunderstorm is a severe long-lived storm within which the wind speed and direction changes with height. This produces a strong rotating updraft of warm air, known as a mesocyclone, and a separate downdraft of cold air. Tornadoes may form in the mesocyclone, in which case the storm is classified as a tornadic supercell thunderstorm. The storms also produce torrential rain and hail. Photographed on 21 June 2015, in northern South Dakota, USA.