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Tornadoes

Accompanied by lightning, a tornado causes immense damage over a narrow strip of land. The most destructive storms on the planet, tornadoes are twisting columns of air, swirling at up to 400 km/h (250 mph). A tornado is even more powerful than a hurricane, although the damage it causes usually only affects a narrow strip of land. Its base may be only 100 metres (about 300 feet) across, but the winds are so strong it destroys nearly everything in its path. Most tornadoes occur in the US Midwest, but they are also quite common elsewhere—including the UK.



A tornado travelling across the border between Colorado and Oklahoma
The anticlockwise flow of air spiralling up through a tornado

Formation

A tornado usually forms at the rear of a thundercloud as the winds swirl at 400 km/h (250 mph) or more. A twisting column of air grows downwards from the cloud like an upside-down funnel. When it reaches the ground, its base may be only 100 metres (about 300 feet) or less across. But the winds are so powerful that animals, people, cars and even houses are plucked up into the clouds and then thrown outwards.
As the main storm moves at between 40 and 80 km/h (25–50 mph), the base may “skip” along the ground, touching down here and there to do most damage. Most tornadoes occur in the Midwestern states of the USA, although they have been observed on every continent, especially east of the Andes in South America and in eastern India.

Tornadoes are made visible by water vapour condensing into cloud droplets. They are often white, blue or grey, but may take on different colours if the winds suck up sands that are red or yellow.

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