While the violence and damage from tornadoes are well known, the actual mechanics of these storms are complex and not completely understood.
They can occur in a variety of situations but are generated most often in severe thunderstorms that occur when warm air and cold air collide.
The collision forces warm air upward, and that creates a low-pressure area at the ground. Surrounding air moves in to fill the vacuum.
In severe storms, cloud tops can rise high into the air, reaching the level of strong horizontal winds that blow the tops into the classic anvil shape often reported around tornadoes. When this happens, more air is pulled upward in something like a chimney effect.
The air moving in toward the "chimney" begins to turn counterclockwise and then rises in a twisting column of extreme violence.
Winds in a tornado are believed to reach more than 200 to 300 mph.
Normally tornadoes form in the rear portion of severe storms that move toward the east or northeast and are separate from the heavy rains that occur in these storms.