A tornado
(often referred to as a twister or, erroneously, a cyclone) 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. Tornadoes come in many shapes and sizes, but
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 110 miles per hour (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), stretch more than two miles
(3 km) across, and stay on the ground for dozens of miles (more than
100 km). There are several different scales for rating the strength of
tornadoes. The Fujita scale rates tornadoes by damage caused, and has
been replaced in some countries 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 their foundations and can deform large skyscrapers.
The similar TORRO scale ranges from a T0 for extremely weak tornadoes to
T11 for the most powerful known tornadoes. (source: wikipedia)
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