What is a tornado?
A tornado is a violent, whirling windstorm that crosses land in
a narrow path. It can result from wind shear and updrafts inside a
thunderstorm. The usual form is a funnel-shaped cloud with
destructive spinning winds, that descends from a cloud to the
ground over a relatively short period of time.
Powerful tornadoes create the highest wind speeds on the surface of the Earth, which may be in excess of 200 mph (320 kph). The winds and debris will destroy houses and similar structures, and may cause numerous fatalities. Tornadoes are spawned by mesocyclones, and also form as tropical cyclones come ashore.
According to the Glossary of Meteorology (AMS 2000), a tornado is "A violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud." Literally, in order for a vortex to be classified as a Tornado, it must be in contact with the ground and the cloud base. Weather scientists haven't found it so simple in practice, however, to classify and define Tornadoes.
Tornado is sometimes referred to as "twister". A tornado is a rotating column of air in contact with the ground and looks like a funnel cloud.