What is a tornado?

A tornado is a violently rotating column or air in contact with the ground.  When the column of air is not in contact with the ground, it is called a funnel cloud.  A tornado in contact with a water surface is called a water spout.  Tornadoes can vary greatly in size, intensity and appearance.  Wind speeds in a tornado can range from just less that 100 miles per hour to over 200 miles per hour.  The intensity of a tornado is classified using the Fujita scale.