Tornadoes form when warm, humid air collides with cold, dry air. The denser cold air is pushed over the warm air, usually producing thunderstorms. The warm air rises through the colder air, causing an updraft. The updraft will begin to rotate if winds vary sharply in speed or direction.

Where do twisters form?

Most tornadoes are found in the Great Plains of the central United States – an ideal environment for the formation of severe thunderstorms. In this area, known as Tornado Alley, storms are caused when dry cold air moving south from Canada meets warm moist air traveling north from the Gulf of Mexico.

How often do twisters occur?

The US has more tornadoes than anywhere else in the world, on average, around 1,200 tornadoes a year.