TORNADO

violent cyclonic storm, relatively small in diameter but with rapidly rotating winds that form a funnel cloud, or vortex, and that moves over land. Whirlwinds are similar but smaller storms of less intensity. When a tornado forms or passes over a water surface, it is called a waterspout. Additional reading Joe R. Eagleman, Severe and Unusual Weather (1983), presents an overview of weather disturbances. Types of storms, their attendant phenomena, and their effects are treated in Edwin Kessler (ed.), ThunderstormsA Social, Scientific, & Technological Documentary, 3 vol. (198182), including studies of tornadoes; and Snowden D. Flora, Tornadoes of the United States, 2nd ed. (1954), a standard work. Nelson Raymond Williams The Editors of the Encyclopdia Britannica