Tornadoes are nature's most powerful storms. These swirling funnels of wind can rip cars, trees, and even houses from the ground. Tornadoes get their start from thunderstorms, when fast winds high in the atmosphere set a storm cloud spinning. As a tornado forms, the sky fills with low, dark clouds. As it approaches, there may be a loud "roar" like an oncoming train. People in some parts of the U.S. know these warning signs all too well.

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