Twin tornados. View of two EF4 rated tornados on the ground at the same time. A tornado is a violent rotating column of air characterised by a funnel-shaped cloud that forms within thunderstorms. They can measure up to 100 metres in diameter, contain winds moving at over 500 kilometres an hour, and cause widespread devastation. This was the first time in nearly 50 years that twin violent tornadoes occurred like this. Photographed in Pilger, Nebraska, USA.