Twister! Have you ever wondered where tornadoes come from or why they can cause so much damage? In this lesson, you’ll learn all about these powerful storms.

Tornado Basics

In The Wizard of Oz, a tornado picks up Dorothy and Toto and puts them down safe and sound in Oz. But that’s in a story. In real life, Dorothy and Toto would have been in danger, because real tornadoes are strong, violent storms. In this lesson, you’ll learn where tornadoes come from and why they can be so dangerous.

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What Is a Tornado?

A tornado is a rotating column of air that stretches from the clouds of a thunderstorm down to the ground. The air in a tornado is spinning around and around very fast. Air is invisible, but you can see tornadoes because the spinning air picks up dust, water, and other things from the ground.

A tornado. Notice how the tornado is stirring up dust as it moves along the ground.

The United States has the most tornadoes of any country in the world. Over 1,000 tornadoes strike the US every year, and tornadoes have hit all 50 states. The part of the US where tornadoes are most common is called Tornado Alley. Tornado Alley includes parts of Texas, Oklahoma, Kansas, and Nebraska. The Wizard of Oz got that one thing right. Dorothy’s home was right in Tornado Alley.

Where do Tornadoes Come From?

Scientists still don’t understand exactly how tornadoes form. Tornadoes occur most often in the late spring and early summer, but they can strike at any time of year. Tornadoes form during thunderstorms, but because it takes special conditions for one to form, most thunderstorms never make a tornado.

Tornadoes start in thunderstorms. Look at the storm clouds above the tornado.

Scientists think that tornadoes form when cold air meets warm air. When this happens, the cold air pushes the warm air up. Imagine how when you go swimming the warm water is on the top while the cold water is deeper, or how when you take a shower the steam rises and the cold air hits your feet, making you cold.

If there’s a constant stream of cold and warm air coming together, then there’s a constant push for warm air to move upward. This movement of air is what helps to get the tornado winds going. But we also need to throw something else in the mix; there have to be winds that make the air spin around in a circle. When all these winds combine in just the right way, watch out because here comes a tornado.

The winds of a tornado can spin around at over 300 miles per hour, and the fastest tornado ever measured was 318 miles per hour. That’s five times as fast as a car drives on a highway, and almost as fast as an airplane flies. Wow, that’s fast!

Tornadoes don’t just spin around in a circle. They also move back and forth across the ground. Tornadoes usually move across the ground at just under 30 miles per hour.

This tornado was strong enough to knock down some big trees.
Trees uprooted by a tornado

Tornado winds are strong enough to destroy buildings. They can also pick up very heavy things, like trees and cars, and carry them through the air before dropping them back down. The good news is that tornadoes are short. Most tornadoes only touch the ground for a few minutes.

Lesson Summary

In this lesson, you learned about tornadoes. A tornado is a spinning column of air that stretches from a thunderstorm to the ground. Tornado winds are very strong, which makes them dangerous. A tornado forms in a thunderstorm when an area of warm air meets an area of cold air and the winds are blowing in just the right way.