Tornado Definition

by Laurent Cousineau
(Montreal)

A tornado is a localized, violently destructive windstorm that occurs over land.

The powerful column of wind spirals around a center of low atmospheric pressure.

The long, funnel-shaped cloud extending toward the ground is made visible by both condensation and debris.

Furthermore, tornadoes often come with hailstorms and are considered the most dangerous storm known to mankind.

Also called twisters, they travel across the ground at high speeds and can kill in only a matter of seconds.

Rotation

Due to our planet's unique weather system, twisters rotate counter clockwise in the Northern Hemisphere. On the other hand, they rotate clockwise in the Southern Hemisphere.

Duration and Traveling Distance

Tornadoes can last anywhere from a few seconds a few hours. Incidentally, some may even disappear and reappear minutes later.

Tornadoes can possibly form in a minute or less and can disappear just as fast. In fact, many of these storms never actually come into contact with the ground, creating only harmless funnels in the thermosphere.

Usually, tornadoes travel less than 15 miles and will last less than twenty minutes.

However, super storms which can travel over 100 miles will sometimes occur. Despite their rare occurrence, they are responsible for as much as 20 % of all tornado casualties.

Diameter

The typical twister has a diameter ranging from around 200 to 300 yards, whereas some grow large enough to spawn smaller tornadoes known as satellite tornadoes.

Satellite tornadoes, the offspring of larger tornadoes, measure about 50 yards across but are quite fierce and can cause a lot of damage.

Moreover, they usually branch away from the parent funnel and will follow different paths.

The Fujita Scale

Introduced by Tetsuya Fujita of the University of Chicago in 1971, the Fujita Scale measures tornadoes in terms of the amount of damage they cause.

F0 - Gale

With winds ranging from 40-72 mph (64-116 km/h), gale tornadoes will cause light damage. Essentially, there will be some damage to chimneys, branches broken off trees, damaged sign boards, and shallow-rooted trees will be pushed over.

F1 - Moderate

With winds ranging from 73–112 mph (117–180 km/h), these tornadoes will cause moderate damage. In essence, the surface of roofs will be peeled, mobile homes will be pushed off foundations or overturned, moving autos will be pushed off roads, and attached garages may be destroyed.

F2 - Significant Damage

With winds ranging from 113–157 mph (181–253 km/h), these twisters will cause significant damage. Roofs will be torn off frame houses, mobile homes destroyed, boxcars overturned, large trees snapped or uprooted, high-rise windows broken and blown in, as well as light-object missiles generated.

F3 - Severe

With winds ranging from 158–206 mph (254–332 km/h), these tornadoes will cause severe damage. Under these tornadoes, the roofs and some walls of well-constructed homes are torn off, trains will be overturned, most trees in forests will be uprooted, and heavy cars will be lifted off the ground and thrown.

F4 - Devastating

With winds ranging from 207–260 mph (333–418 km/h), these tornadoes will cause devastating damage. In this situation, well-constructed houses will be leveled, structures with weak foundations will be blown away a small distance, cars will be thrown, and large missiles will be generated.

F5 - Incredible

With winds ranging from 261–318 mph (419–512 km/h), these tornadoes will cause incredible damage. In this very dire situation, strong frame houses will be lifted off foundations and carried considerable distances to disintegrate, automobile sized missiles will fly through the air in excess of 100m (109 yards), trees will be completely debarked, and even steel reinforced concrete structures will be badly damaged.

F6 - Inconceivable

Some will include an F6 tornado which is theoretically possible although no such wind speed over 318 mph have ever been recorded. However, it is possible that the 1999 Oklahoma City tornado, which caused 1.9 billion dollars in damages and lasted 72 hours, may have been an F6.

It should also be noted that some countries use the updated Enhanced Fujita Scale. Although it also measures tornado strength by damage caused, it takes into account the quality of construction and standardizes different types of structures in determining the degree of destruction.

Each year, 500 million dollars of damage is caused by tornadoes in the United States.

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