As air rises from the ground in the tornado's vortex, a low pressure area is created near the ground. Air rushes to fill this area, causing additional damage to areas not directly hit by the tornado. As air rushes into the vortex, its pressure lowers, cooling the air. This cooling condenses water vapor in the air into the tornado's familiar funnel-shaped cloud. As the swirling winds pick up dust, dirt, and debris from the ground, the funnel turns even darker.
Tornadoes are also relatively small.
An average tornado will be 400 to 500 feet wide and travel four or five miles on the ground, lasting only a few minutes. A mile-wide tornado is extremely large, and tornadoes this big are rare. Many tornadoes are small, less than 100 feet wide, and last only a few minutes. A few monster tornadoes are a mile or more wide and can last for an hour or more. As the parent thunderstorm travels along, tornadoes can come down from the cloud, run along the ground and lift back up to be followed by other tornadoes.