They can be highly destructive but fortunately are relatively small in comparison to other extreme weather phenomena such as thunderstorms and hurricanes . The tornado can be seen by the rapid rotation of cloud caught up within it. Tornadoes are particularly common in the central United States. Rotating wind speeds are no greater than about 110 mph. Rotating wind speeds vary from 110 to 200 mph.
Most tornadoes form in the presence of thunderstorms .
All thunderstorms are characterised by rising or convecting air, called updrafts. These updrafts supply the warm, humid air that fuels thunderstorms. In some cases, the column of rising air becomes a vortex - a funnel cloud or tornado. Often, a tornado is located on the edge of the updraft, adjacent to the thunderstorm downdraft that accompanies the falling rain or precipitation . Meteorologists however, still do not fully understand why updrafts in some thunderstorms become tornadoes while those in apparently similar thunderstorms do not.