Tornadoes, or twisters, are long funnels of violently spiraling winds beneath thunderclouds.
Tornadoes roar past in just a few minutes, but they can cause severe damage.
Wind speeds inside tornadoes are difficult to measure, but they are believed to be over 400 km/h.
Tornadoes develop beneath huge thunderclouds, called supercells, which occur along cold fronts.
England has more tornadoes per square kilometer than any other country, but they are usually mild.
Tornado Alley in Kansas, USA, has 1000 tornadoes a year. Some of them are immensely powerful.
Cloud base Tornadoes are especially destructive in central USA but they can occur wherever there are thunderstorms.
Supercell cloud Funnel touches down in a whirling cloud of dust.
A tornado starts deep inside a thundercloud, where a column of strongly rising warm air is set spinning by high winds roaring through the cloud’s top. As air is sucked into this column, or mesocyclone, it corkscrews down to the ground.
A tornado may be rated on the Fujita scale, from FO (gale tornado) to F6 (inconceivable tornado).
An F5 tornado (incredible tornado) can lift a house and carry a bus hundreds of meters.
In 1990 a Kansas tornado lifted an 88-car train from the track and then dropped it in piles four cars high.
In 1879, a Kansas tornado destroyed an iron bridge and sucked up a river beneath it.