Tornados are the most lethal atmospheric condition; they have caused 9000 deaths over the past 50 years in the USA. They come in varying shapes and sizes but are typically visible as funnels. Extreme tornados can be up to two miles wide, stay on the ground for dozens of miles, and have winds greater than 300 mph. About 700 tornados touch down in the USA each year. Fortunately, most tornadoes touch down in uninhabited areas. The Midwest is one of the few parts of the world where cold air masses converge with warm, humid air masses causing tornadoes. In other parts of the world, where the two air masses are known to collide, there is a natural obstruction, such as a small mountain range or a large body of water, preventing them from forming a tornado.