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 110 miles per hour (177 km/h),are about 250 feet (76 m) across,and travel a few miles (several kilometers) before dissipating.The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (483 km/h),stretch more than two miles (3.2 km) across,and stay on the ground for dozens of miles (more than 100 km).
