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 A
tornado
is a violently rotating column of air extending from a thunderstorm,
and often (but not always) visible as a funnel cloud. For a vortex
to be classified as a tornado, the air mass must have contact with
the ground AND the cloud base. Tornado development occurs most often
in severe thunderstorms (which form at the point where cold
air masses and warm air masses meet, known as a dry line),
the most violent being the supercell. A supercell is a rotating
thunderstorm with a well-defined radar cirulation. They can also produce
damaging straight line winds, hail, frequent cloud-to-ground lightning,
and torrential rain, as well as tornadoes. Tornadoes can occur anywhere
in the United States, but most frequently develop over the Nation's
Great Plains Region. This region has gotten the nickname "Tornado
Alley" due to the fequency of tornadoes in this area.
How a Tornado Forms
Before thunderstorms develop, a change in wind direction and an increase
in wind speed with increasing height creates an invisible, horizontal
spinning
effect in the lower atmosphere.
Rising air within the thunderstorm updraft tilts the rotating air
from horizontal to vertical.
An area of rotation, 2-6 miles wide, now extends through much of the
storm. Most strong and violent tornadoes form within this area of
strong rotation.
(Pictures and explanations from:www.ci.fort-collins.co.us)
 Each
tornado is unique in its appearance, behavior, and strength.
It may range from being a very thin rope-like
structure to a wedge shaped twister with a width of over
a mile. It may have only one vortex reaching to the ground,
or it may consist of multiple vortices. It may only stay in
contact with the ground for only seconds, or they may travel
for more than an hour before dissipating. Tornadoes most often
move on a West to East, or a Southwest to Northeast direction,
but this is not always the rule. Many tornadoes have the tendency
to frequently change direction.
A tornado's strength also varies from
causing only light damage, to inflicting incredible amounts of destruction,
depending on a number of factors. A scale of tornado damage was devised
in 1971 by T. Theodore Fujita of the University of Chicago, to help
classify tornado strength levels (To
view F-scale click here), but its reliability has never been scientifically
tested and proven. Factors such as flying debris, wind speed and direction,
and how well structures are built may cause the amount of damage to
vary as well. Despite these flaws, the Fujita scale is the only tornado
rating method used in the United States.
No
matter what a tornado looks like, they are a dangerous, unpredictable,
and deadly entity that should be taken seriously in all situations.
When a tornado watch (this means conditions are favorable for
the development of a tornado) has been issued for your area, certain
steps should be taken to prepare you and your loved ones for a tornado
occurance. If a tornado warning (meaning a tornado has either
been physically spotted, or has been indicated on Doppler Radar) is
issued for your area, you need to take cover immediately. Please click
on the "Tornado Safety Tips" button below to see a list
of what you should and should not do when a tornado is imminent for
your area.
*All
tornado information collected from Storms Prediction Center of the
NOAA. For more
in-depth information on tornadoes, please see their web site,
www.spc.noaa.gov/faq/tornado
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