A tornado undergoes considerable changes in size, shape, and behavior during its
life cycle. The tornado usually develops within a cumulonimbus cloud and subsequently
extends toward the ground. We see this stage as a rotating funnel cloud that descends
from the cloud base. When the rotating column of air reaches the ground, it becomes a tornado by definition. Sometimes dust and debris begin whirling on the ground before the
funnel actually touches down. In weak tornadoes, particularly in dry climates, this
ground-level dust whirl may be visible before the funnel cloud.
During the tornado’s mature stage, the funnel reaches its greatest width. It is
usually nearly vertical, and most of the time is touching the ground, though skipping may occur along a lengthy path. At this time, the tornado causes severe damage to whatever it
encounters.
During the tornado’s shrinking stage, the funnel narrows and tilts away from its
vertical position. Now the path of damage becomes smaller. As the tornado decays, the
funnel stretches into a rope shape, and the visible portion becomes contorted and finally dissipates. This stage is often called the rope stage because of its appearance.