Bryan Mckay, age 10, of Merrillville, Ind., for his question:
HOW FAST DOES A TORNADO MOVE?
Scientists in the National Weather Service constantly gather weather information from all parts of the United States. They use radar and other equipment to forecast and locate tornadoes. If weather conditions indicate that a severe thunderstorm or a tornado may occur, bulletins are broadcast on radio and television to warn communities in the path of the storm.
A tornado is a powerful wind storm. The storm has winds that are the most violent that occur anyplace on earth. Many tornadoes have caused widespread death and destruction.
Winds in the center of a tornado move 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. Other funnels can strike the surface of the earth, withdraw into the dark cloud above, and then dip down and strike the earth again.
Most funnel clouds tend to travel toward the northeast in the United States. They can occur anyplace in the world but mostly they hit the United States and chiefly in the spring and early summer. About 700 tornadoes have been reported each year in the United States since the mid 1950s.
Most tornadoes measure several hundred yards in diameter. They last less than an hour and usually travel a distance of about 20 miles at a speed of 10 to 25 miles per hour.
Some tornadoes last several hours and measure up to a mile and a half in diameter. Others have been known to travel up to 200 miles or more at speeds up to 60 miles per hour. Those that travel great distances are especially destructive.
The greatest killer tornado on record is the one that sliced through Missouri, Illinois and Indiana on March 18, 1928. It killed 689 persons.
The roaring, rotating winds of a tornado blow down almost everything in its path. The explosive force on a building is caused by a difference in air pressure between the inside and outside. As the tornado passes over a house, it sucks up air from around the structure. As the air pressure drops, often the building will explode outward because it cannot equalize the pressure difference quickly enough.
The great lifting force of a tornado results from a powerful updraft of air inside the funnel. Tornadoes have uprooted large trees, overturned railroad cars, and have carried automobiles hundreds of feet.
Most tornadoes happen on a hot, humid spring day in the afternoon or early evening.