Tornadoes usually form from large thunderstorms. When the winds beneath a storm are unstable, they blow at different speeds. These unstable winds underneath the thunderstorm can begin to rotate. If that rotating air gets pushed up into the storm, it can gain strength and speed. A dark cone of air may swirl down from the storm. This is called a funnel cloud. If the funnel touches the ground, it becomes a tornado.
Tornadoes can form very quickly. They create the strongest winds on the planet, with speeds that can top 200 miles per hour. In 1967, a powerful tornado struck Oak Lawn, Illinois. Patti Ernst lived through that tornado as a child. "Our garage blew away. Our car was crunched," she remembered in an interview with Chicago television station, WGN. Still, she knew it could have been much worse. A powerful twister can rip houses from their concrete foundations and flatten whole neighborhoods. "My family was so lucky," Ernst said.
The Oak Lawn tornado destroyed over 100 homes, and it killed dozens of people. But survivors of 2011's Joplin, Missouri tornado know that tornadoes can be much worse. Rance Junge described the tornado to ABC News.

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