A thunderstorm characaterized by a rotating updraft (called a mesocyclone) that is persistent (~30 minutes or longer) and deep (~through at least 1/3 the depth of the storm. Supercell thunderstorms can be as small as 10 km across/5 km tall to as large as 100 km across/12 km tall and produce a disproportionate amount of the severe weather observed around the world in general, and US in particular. 15% of supercells can proceed through a cascade of phenomena ending with a tornado.