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 often referred to as a twister or a cyclone,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 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 tornadoes can attain |