What are tornadoes?
They are powerful swirling winds which can strike suddenly and cause lots of damage. Sometimes, they are strong enough to pull houses and trees out of the ground, and sweep cars off the ground.
What causes them?
It's all about the weather. A tornado is formed when a warm wind meets a cold one. Thunderstorms play a big part in triggering them.
The way they are created has been compared to the force which makes water swirl down a plughole.
Where do they happen?
The fiercest tornadoes can often be found in America because of the cold and warm winds that are formed there. They occasionally happen in the UK, but they are much weaker.
How fast do they go?
They can reach up to 300mph at their worst - and can measure several miles across.
How long do they last?
Usually for a few minutes, during which time they travel one to three miles across the land.