A
tornado is 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. They are often referred to as
twisters or
cyclones, although the word
cyclone is used in meteorology, in a wider sense, to name any closed
low pressure circulation. Tornadoes come in many shapes and sizes, but they are typically 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 , are about across, and travel a few miles (several kilometers) before dissipating. The most extreme tornadoes can attain wind speeds of more than , stretch more than across, and stay on the ground for dozens of miles (more than 100 km).
