Tornado Basics
A tornado is a
violent whirlwind--a rotating funnel of air that extends from a cloud to
the ground. Tornadoes can travel for many miles at speeds of 250 miles
per hour or more. These storms change direction without warning,
randomly destroying homes and power lines, uprooting trees, and even
hurling large objects--such as automobiles--over long distances.
Tornadoes usually
accompany severe thunderstorms. Occasionally, tornadoes occur during
tropical storms or hurricanes. The path of damage left behind by a
tornado averages 9 miles long by 200 yards wide, but a severe tornado
can damage an area up to 50 miles long and a mile wide.
Tornadoes that occur
over oceans and lakes are called waterspouts. Because they
rotate less vigorously and affect less-populated areas, waterspouts are
usually not as destructive as tornadoes; however, waterspouts can move
inland and become tornadoes. Waterspouts are more common in the
Southeast, particularly along the Gulf Coast, but can form over any body
of warm water.
The most destructive
force in a tornado is the updraft in the funnel. As this unstable air
moves upward at high speed, it can suction up houses and trees and move
them hundreds of feet.
How Tornadoes
are Formed
When unseasonably
warm humid air collides with a cold front, intense thunderstorm clouds
form and tornadoes may develop.
As warm air rises
within the storm clouds, cooler air rushes in from the sides, creating a
whirling wind that draws surrounding air toward its center.
An area of strong
rotation develops, 2 to 6 miles wide. Next to appear is a dark, low
cloud base called a rotating wall cloud.
Moments later, as
rotation becomes even stronger, a funnel develops.
|