How do tornadoes form?

Most strong tornadoes form in a type of severe thunderstorm called a supercell. They begin when warm, moist air near the ground rises rapidly beneath cooler, drier air above, and winds that change speed and direction with height set this rising air rotating. This creates a spinning column of air that can tilt upright and tighten into a fast, narrow vortex reaching down from the cloud to the ground. Wind speeds inside the most violent tornadoes can exceed 400 kilometres per hour. Tornadoes are often short-lived but can cause tremendous destruction along their path.