Tornados
A TORNADO, or a twister, is a destructive storm with whirling winds. The winds make their way to earth as a spinning, funnel-shaped cloud. The path of destruction is very narrow, compared to other storms such as hurricanes, but the winds of a tornado are the most violent of any storm. Its winds can blow up to 400 miles per hour.
A tornado can destroy everything in its path, flattening homes and stripping the ground of vegetation.
Tornados can appear in isolation or travel in large groups. In the 1974 "Super Outbreak", 148 individual tornados devastated an area from Alabama to Michigan.
The conditions that create a tornado involve the three following different air masses meeting at the same place: warm, humid air, dry air, and cool, humid air. A tornado is "born" out of an intense storm. Its spinning shape usually develops as the winds at a high altitude blow faster and in a different direction than the winds traveling at a lower altitude. This causes the whole storm system to begin rotating.
The winds spins very fast with the air gaining speed as it spins inward. This creates a VORTEX, or spinning center, that acts as a vacuum, sucking in air near the ground and carrying it upward. The vortex is a low pressure area that draws in more and more winds that rotate faster and faster. The center grows bigger and bigger and begins extending to the ground. As it forms it is called a funnel cloud. When it actually reaches the ground, it is labeled a tornado. Tornados that occur over water are called water spouts.
Tornados move with the storm system at about 35 m.p.h.. Some tornados, however, have been recorded traveling at speeds up to 65 m.p.h. Not only the speed but also the width of a tornado can differ greatly from storm to storm. They can be anywhere from 300 feet to over a half mile in diameter and can cause destruction in an area of only a few yards to a path hundreds of miles long.
Although an occasional tornado may last more than an hour, the average life span is about fifteen minutes. One tornado in 1917, however, covered 293 miles in just under seven and 1/2 hours.
Tornados can occur anywhere, even in Europe, which reports about 30 - 60 tornados a year. Because of the directions in which the world's air currents blow, however, tornados are primarily a weather condition that only occurs in North America. There are approximately 800 tornados reported annually in the United States. They occur in every part of the country every year, but happen much less frequently west of the Rocky Mountains and north of North Dakota. The more severe tornados and heaviest concentration is in the Midwest and South.
The area of heaviest concentration of tornados across the United States is called "Tornado Alley". The states that make-up this area are Alabama, Arkansas, Florida, Iowa, Kansas, Mississippi, Missouri, Nebraska, Oklahoma, and Texas. Oklahoma has the dubious pleasure of having more tornados per year than anywhere else on earth.
The peak time for tornados in the United States depends on where you are. The Gulf of Mexico area can expect tornados in the late winter months, the Great Plains areas tend to get tornados in May and June, while the Southern states see tornados more often in the fall.
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The FUJITA TORNADO SCALE is a scientific classification system used to categorize the strength of a tornado. The scale assigns the tornado a number form 1 to 5, with a category 5 tornado being the most destructive.
Fujita Tornado Scale
number
wind speed
damage
F-0
up to 72 mph
light
F-1
73-112 mph
moderate
F-2
113-157 mph
considerable
F-3
158-206 mph
severe
F-4
207-260 mph
devastating
F-5
over 261 mph
incredible
Waterspouts resemble tornados and are basically rapidly rotating columns of air that form over lakes and oceans. There are two types of waterspouts: tornadic and non-tornadic.
Tornadic waterspouts form under the same conditions as tornados on land and are rare. Non-tornadic waterspouts are formed by the rotation of the water and updrafts. Water in the waterspouts extends FROM the water TO the cloud, which is the reverse of a tornado, which forms from the cloud to the land.
Waterspouts draw only a small amount of surface water that stays at the base of the spout. The water in the funnel is caused by the condensation resulting from the very low pressure within the spiraling air mass.
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