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TORNADO.TXT
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1994-01-04
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TORNADOES
Tornadoes are not the largest of storms, but they are definitely the
most violent. There is no other weather occurrence that produces more
destructive power as it passes by. It sweeps the ground clear of all
moveable objects. It is a violently circulating column of air, small in
diameter, and reaches from a thundercloud to the ground. A tornado starts
as a funnel cloud which is a rotating column of air inside a cumulonimbus
cloud and begins to reach for the ground. When this rotating air reaches
the ground, it is an official tornado. As the tornado matures, the funnel
reaches its greatest diameter. It is usually vertical, most of the time
it is touching the ground, although many times skipping occurs along its
path. This is when the worst damage occurs, and many large pieces of
debris can be seen within its circular motions. As a tornado starts
to shrink, the funnel becomes smaller and tilts from its vertical angle.
As the tornado decays, it becomes long, distorted, and rope-shaped. The
end is near for this wind of destruction.
In the Northern Hemisphere, tornadoes nearly always turn counterclockwise,
although officially documented instances of clockwise tornadoes are on
record. Most tornadoes occur when temperatures are above 65 degrees F.,
(18 degrees C.), and the dew point temperature is at 50 degrees F.,
(10 degrees C.) or higher. The vast majority of tornadoes travel from
southwest to northeast, travel an average of 35 MPH, is an average width
of 121 yards, and has an average life of 14 minutes. Thus, this average
tornado would travel about 8.5 miles. It is interesting to note that even
though professionals know what type of clouds typically create tornadoes,
exact time and location is difficult, if not impossible, to predict with
absolute accuracy. There has never been any wind speed measuring
device created that can withstand the tortures of a tornado. However,
it is possible to estimate the wind speeds using less direct methods.
There have been many films and videos of the large debris flying around
in tornadoes. Engineers have determined the force required to move these
pieces of debris; thus, finding the approximate wind speed. More
recently Dopler radar has created more accurate findings.
Some definitions: A 'funnel cloud' is a potential tornado which never
touches the ground. 'Dust devils' and 'sand devils' are common in dry
desert areas, and are circulating columns of dust or sand. These can extend
up several hundred feet, and last but a few minutes. These are not to be
confused with tornadoes as they are caused by local heating of the earth's
surface, while tornadoes are created in large thunderclouds.