13K views · 347 reactions | Tornadoes occur on nearly every continent on Earth. Tornadoes form during thunderstorms, when warm moist air collides with cool dry air but will only form when the atmospheric conditions are just right. One of the great mysteries of science is why one storm will produce tornadoes and another won't. Watch Mutant Weather on Sundays at 7pm on National Geographic UK. | National Geographic UK | Facebook