Atornado—also popularly known as a twister—is an atmospheric phenomenon associated with a supercell thunderstorm or hurricane. It consists of a small rapidly and violently rotating column of air—or vortex—extending continuously from a convective cumuliform cloud to the ground. When the vortex is spinning but not touching the ground, it is called a funnel cloud, which eventually may extend to the ground evolving into a tornado. It becomes clearly visible in daylight as a funnel or tube cloud when it carries water vapor and debris lifted from the ground. It may be thin and rope-shaped in the case of weak tornadoes with speeds below 175 kilometers per hour (110 miles per hour). Sometimes the funnel is not visible except by signs such as whirling debris on ...