Scientists speculate that mesocyclones form when strong horizontal upper air winds interact with normally occurring updrafts. The shearing effect of this interaction forces the horizontal wind to flow upward intensifying the updraft. Tornadoes that travel across lakes or oceans are called waterspouts . Winds within the tornado funnel may exceed 500 kilometers per hour. High velocity winds cause most of the damage associated with these weather events.
Tornadoes also cause damage through air pressure reductions.
The destructive path of a tornado is usually about half a kilometer wide, and usually no more than 25 kilometers long. However, a spring tornado in 1917 traveled 570 kilometers across Illinois and Indiana lasting well over 7 hours. Damage from these tornadoes varies from broken windows and tree branches to shingles blowing off roofs and moving cars pushed from roads. Weak tornadoes have a path that is about 1.5 kilometers long and 100 meters wide, and they generally last for only 1 to 3 minutes. According to the Fujita scale, strong tornadoes can have wind speeds between 182 and 332 kilometers per hour.