The Tornado

CORE DEFINITION

A tornado, also known as a twister or whirlwind, is a violent weather phenomenon consisting of a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. Tornadoes often occur in association with cumulonimbus clouds or beneath them, typically forming a funnel shape that is wider at the top and narrower at the bottom, extending to the ground, and often surrounded by dust and debris. In very rare cases, tornadoes may also originate from cumulus clouds. Whether on land (landspout) or over water (waterspout), the conditions for their formation generally require extremely unstable air disturbances, or the intense convergence of hot, humid air with cold air. Therefore, tornadoes often occur near mid-latitude extratropical cyclones and severe convective thunderstorms. The funnel-shaped cloud of a tornado is called a 'funnel cloud' or 'tubular cloud'. It typically forms from a supercell, when the thunderstorm is cut off from its updraft by cold air at the base. Typically, a tornado's diameter is about 75 meters (246 feet), with wind speeds usually ranging from 64 kilometers per hour (18 meters per second) to 177 kilometers per hour (49 meters per second), and a total travel distance of about several kilometers. Some large tornadoes can have wind speeds exceeding 480 kilometers per hour (130 meters per second), diameters up to 1.6 kilometers (1.0 mile), and paths over 100 kilometers.