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.

Definition: a strong rotating funnel of air stretching from a thunderstorm cloud to the ground
Frequency: about 1,300 strike the U.S. every year
Wind Speeds: the most powerful ones can reach over 300 miles (480 km) per hour!
Measurement: the Enhanced Fujita (EF) Scale describes a tornado's wind speeds based on the damage it causes (ratings EF0-EF5)
Largest on Record: nearly 2.5 miles wide, near Hallam, Nebraska on May 22, 2004
Cool Fact: The 200-plus-mph winds can bend metal!

Image credits: main image, © AMNH.