What is a tornado?

A tornado is a rapidly rotating column of air that extends from the base of a thunderstorm down to the ground. They form when warm, moist air meets cold, dry air and strong changes in wind speed and direction with height set the air spinning, which can then tilt vertical and tighten into a funnel. The most violent tornadoes can pack winds of over 480 kilometres per hour, strong enough to level buildings and hurl vehicles. Their strength is rated on the Enhanced Fujita scale from EF0 to EF5 based on the damage they cause. The central United States sees so many that a region there is nicknamed Tornado Alley.