Tornado over plains and trees. Tornadoes are fast-spinning vortices of air that typically form beneath large cumulonimbus storm clouds. They become visible as a funnel-shaped cloud as the low pressure in the vortex causes water to condense into droplets, as in a cloud. Tornadoes feature the highest wind speeds on Earth, sometimes in excess of 400 kilometres per hour. As such, they can cause huge damage when they occur in to built up areas. They are particularly common in the central United States due to the geography of the region, particularly in the area known as Tornado Alley, which extends from northern Texas through Oklahoma, Kansas and Nebraska to South Dakota. This tornado was filmed in South Dakota on 18th June 2014.