There are four main stages in a tornado's life. These are the organization stage , the mature stage , the shrinking stage , and the decaying stage . In the organization stage, a funnel appears and touches down. The tornado is at its largest in the mature stage. The funnel then decreases to a thin column in the shrinking stage, and becomes fragmented and very disorganized in the decaying stage, although it is still a destructive funnel.
Tornadoes require an almost perfect atmosphere to form.
Warm moist air must collide with cooler, drier air to form massive storms known as super cells. Despite all the neccesities needed, tornadoes form in great numbers across a stretch of the United States know as Tornado Alley. In this area, warm, moist Gulf air meets with cool, dry Canadian air during the Spring and early Summer months. This results in a large number of storms during this part of the year. When the warm air meets the cooler air, the warm air rises, and then condenses to form clouds.