Lois Windrem, age 12, of Orlando, FL for her question:
DOES A TORNADO LAST LONG?
A tornado is a powerful, twisting wind storm. Winds of a tornado are the most violent that occur on earth. Most tornadoes last less than an hour.
Most tornadoes measure several hundred yards in diameter and many have caused widespread death and destruction. They may whirl around the center of the storm at speeds of more than 300 miles per hour.
A tornado is actually a rotating funnel cloud that extends downward from a mass of dark clouds. Some funnels do not reach the earth while others may head for the surface, strike and then withdraw into the dark clouds above. They may then dip down and strike the earth again and again.
In the United States, most funnel clouds tend to travel toward the northeast. The winds whirl in a counterclockwise direction in the Northern Hemisphere and clockwise in the Southern Hemisphere.
People in some regions call a tornado a twister or a cyclone. A tornado that occurs over a lake or ocean is called a waterspout.
While most tornadoes last less than an hour, they may travel distances of about 20 miles at speeds of from 10 to 25 miles per hour. Some tornadoes may last several hours and measure up to a mile and a half in diameter.
Some tornadoes may travel 200 miles or more at speeds up to 60 miles per hour. Such tornadoes are especially destructive.
You'll find tornadoes throughout the world, but mostly in the United States where they hit chiefly in spring and early summer. No one knows exactly how many tornadoes occur yearly because many of the storms occur in thinly populated areas and many may not be reported. About 700 tornadoes have been reported annually in the United States since the mid 1950s.
Perhaps the worst tornado in history slashed through Missouri, Illinois and Indiana on March 18, 1928. It killed 689 persons. It was one of the largest and fastest tornadoes ever recorded. Its path measured about 220 miles long and up to a mile wide. The storm traveled at a speed of about 60 miles an hour.
Scientists do not know exactly why tornadoes develop. But most form along a front or boundary between cool, dry air from the north and warm, humid air from the Gulf of Mexico.
A narrow zone of cumulonimbus clouds, called thunderstorm clouds, develops along such a front. This zone of clouds, called a squall line, produces violent weather.
The violent weather produced by a squall line results when a mass of warm, humid air rises extremely rapidly. As this air rises, more warm air rushes in to replace it. The inrushing air also rises and, in some cases, begins to rotate. The rotating air then forms into a tornado.
The violent, rotating winds of a tornado blow down almost everything in its path.