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A tornado is a violent, dangerous, 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. They are oftenreferred to as a twister or a cyclone, although the word cyclone is used in meteorology in a narrower sense, only to name hurricanes or typhoons. Tornadoes come in many shapes and sizes, but aretypically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust. Most tornadoes have wind speeds less than 110 miles perhour (177 km/h), are approximately 250 feet (80 m) across, and travel a few miles (several kilometers) before dissipating. The most extreme can attain wind speeds of more than 300 mph (480 km/h), stretchmore than two miles (3 km) across, and stay on the ground for dozens of miles (more than 100 km).

Waterspouts are characterized by a spiraling funnel-shaped wind current, connecting to a largecumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornadoes that develop over bodies of water.These spiraling columns of air frequently develop in tropical areas close tothe equator, and are less common at high latitudes.

Tornadoes have been observed on every continent except Antarctica. However, the vast majority of tornadoes in the world occur in the TornadoAlley region of the United States, although they can occur nearly anywhere in North America. Tornadoes can be detected before or as they occur through the use of Pulse-Doppler radar by recognizingpatterns in velocity and reflectivity data.

There are several different scales for rating the strength of tornadoes. The Fujita scale rates tornadoes by damage caused, and has been replaced in somecountries by the updated Enhanced Fujita Scale. An F0 or EF0 tornado, the weakest category, damages trees, but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off...