Tornadoes need particularly intense or unseasonable heat to develop. As the ground temperature increases, moist air heats and starts to rise.
When this moist, warm air meets dry, cold air above, a thunder cloud begins to build.
This cloud can develop quickly, bringing with it rain, thunder and lightning.
Winds blowing from different directions cause the air to rotate, after which a visible cone or funnel drops out of the cloud towards the ground.
Tornadoes can be hundreds of metres wide. They can last anywhere from several seconds to more than an hour, and can travel dozens of miles.
The Fujita scale is used to determine how powerful a tornado is. The highest on the scale – an F5 – is used to categorise tornadoes travelling at up to 318mph (511km/h).
These tornadoes can cause incredible damage, with the power to throw away vehicles and sweep away strong buildings.
