The four stages of a tornado include: the organization stage, mature stage, shrinking stage and decaying stage. These stages begin because of atmospheric conditions during a thunderstorm.
A tornado begins in the organization stage, when it forms through a series of updrafts among cold and warm air systems. When the swirling air touches the ground, it is officially a tornado. In the mature stage, a tornado reaches its full development in terms of base size and wind speed. As the tornado wanes, it shrinks to a smaller tornado with a smaller base. In the decaying stage, a tornado is unstable, and it starts to dissipate until the funnel cloud stops its rotation completely.