The word tornado came from the Spanish tronada ("thunderstorm").
Tornadoes are also popularly called twisters or cyclones.
They are rapidly rotating columns of air hanging from cumulonimbus clouds.
They are generally observed as tube- or funnel-shaped clouds.
At ground level they usually leave a path of destruction
around 170 ft. and travel an average of 5 to 15 mi.
Ground contact is often an intermittent nature
lasting usually less than a couple of minutes in any area, because the funnel skips.
Tornadoes exhibit a certain characteristic cycle
of behavior between formation and final disappearance.
The first sign of a tornado may be a strong whirlwind of dust
, often in conjunction with the appearance of a short funnel
growing from the storm cloud above it.
The funnel becomes more organized and descends further from the cloud,
sometimes touching the ground.
The winds in the funnel generally move counterclockwise in the Northern Hemisphere
and clockwise in the Southern Hemisphere, but exceptions are observed.
The funnel as a whole commonly moves forward slowly,
but can travel at speeds greater than 100 ft. per second.
The tornado eventually becomes fragmented and dissipates.
Tornadoes are the result of great instability
in the atmosphere and are often associated with severe Thunderstorms.
The full details of the formation of tornadoes are not known.
The existence of a strong updraft, which generated a severe thunderstorm,
and the conservation of
rotational momentum are fundamental considerations.
The falling of rain or hail drags air from aloft,
and the resultant inrush of air tightens the rotational motion.
The tornado proper is inside the tornado cyclone,
an area of low pressure about 5 to 15 mi in diameter
with wind speeds of approximately 150 mph or less.
The tornado center is an area of exceedingly low pressure.
This extreme pressure gradient causes buildings to explode
as the tornado effect is felt, if they are not sufficiently ventilated
for rapid adjustment to the change in pressure.
Wind speeds of approximately 500 mph have been inferred from the resultant damage.
In the United States, tornadoes are most often associated with conditions
in advance of cold fronts.
Weather forecasts include tornado alerts when these conditions arise.
Tornadoes can occur ahead of warm fronts or even behind cold fronts.
Tornadoes also occur frequently in association with hurricanes.
A tornado that begins on land and then crosses water is a waterspout.
That term is applied more commonly to a less intense form of tornado activity.
This originates over a body of water and is not necessarily associated with storm activity.
The water in the spout comes from condensation, not from the water below.
The greatest incidence of tornadoes is generally assumed
to be in North America, and especially in the Mississippi Valley.
Other countries, such as Italy, New Zealand, and the United Kingdom,
exceed or at least challenge the incidence rate of the United States.
In numbers observed, Australia ranks second to the United States.
The United States is notable for the incidence of severe tornadoes.
Tornadoes occurring in the tropics are usually extremely weak
and often begin as waterspouts.
The Stockholm (Sweden) and Saint Petersburg (Russia) areas
appear to be the northernmost regions that experience tornadoes.
Within the United States, Texas records the greatest number,
about 15 to 20 percent of the nation's annual total of about 1,000.
On an area basis, Texas ranks ninth, far behind Oklahoma, Kansas, and Massachusetts.
A rather steady increase in the annual total has been observed,
probably as a result of the improving reporting system.
The seasonal maximum occurs in the spring and early summer,
although tornadoes have been reported in all months.
The height of the tornado activity is in early spring
in the southern United States, later across the more northerly regions,
and in July in western Canada.
Tornadoes most frequently occur during the middle and late afternoon.
There is a large interannual variation, as well.
The worst tornado in US History cut through
Missouri, Illinois, and Indiana March 18, killing 689,
injuring thousands, and wreaking property damage in the millions.
Tornadoes usually last for a few minutes, and rarely last for more than an hour.
Tornadoes are cyclonic winds, and they rotate at very high speeds around a low-pressure center.
Tornadoes are smaller than hurricanes and are shorter lasting.
A tornado can be as little as 100 feet to as much as 1.5 miles wide.
The smallest tornadoes are called minis and the largest tornadoes are called maxis.
A mini will last no longer than a few minutes,
travel about a half a mile and have windspeeds up to 100 miles an hour.
Maxis may travel 200 miles or more, last up to 3 hours,
and have windspeeds of more than 250 miles per hour.
A tornado has a very irregular path.
When the funnel touches the ground, it moves in a straight line or may loop.
It may even double back on itself,
hop over places, or form multiple funnels.
Most tornadoes in the northern hemisphere travel
from southwest to northeast and spin counterclockwise.
In the southern hemisphere, tornadoes spin clockwise.
Rating a Tornado
Much like the richter scale is used to measure earthquake intensity,
the Fujita-Pearson Tornado Intensity Scale is used by meteorologists,
to measure tornado wind speeds.
The scale was named after the two men
Dr. Theodore Fujita, and Allan Pearson, head of the Forecast Center in Kansas City.
The Fujita-Pearson Tornado Intensity Scale
Is: Classification, Wind Speed , and Damage.
F0 is 72 MPH. & Light
F1 is 73-112 MPH & Moderate
F2 113-157 MPH & Considerable
F3 is 158-206 MPH & Severe
F4 is 207-260 MPH & Devastating
F5 is 260-319 MPH & Unbelievable
F6 is 319-379 MPH & Out of this World!
The year of 1992 had very many tornadoes.
7 states broke or tied their record for most tornadoes in a year,
California (19), Delaware (6), Louisiana (77), Maryland (13), Colorado (81) and New York (25).
Ohio set a record of 61, which is over 4 times the state average.
Tornadoes By Intensity
For 1992 Scale, Number of Tornadoes, Percentage of Total Tornadoes.
F0 696 & 54%
F1 411 & 32%
F2 129 & 10%
F3 43 & 3%
F4 13 & 1%
F5 1 & 1%
F6 Anyone know???
Specific Tornadoes
One of the most notable tornadoes was 1992's only F5.
The tornado struck June 16, in Chandler, MN at 4:00 p.m., CST.
The tornado had a 16-mile path, 1 death, and 35 injuries.
The tornado leveled the town and cost $27 million in damages.
An extremely costly tornado struck Houston, Texas
November 21, 1992, at 3:27 p.m., CST.
The F4 force tornado grew to over a mile wide and traveled along a 30-mile path.
It caused $50 million in damage, and injured 16 people, killing none.
In 1992, 12 people were killed, and 122 injured when an F4 struck Brandon, Mississippi November 21, at 12:14 a.m., CST.
The tornado had a 128-mile track.
On March 18, 1925, at 3:35 p.m. , Howard Rawlinson was in his classroom
on the third floor of the Crossville, Illinios Community High School.
That afternoon, the school's janitor came rushing in and told Howard's class
that if they had never seen a tornado, they were about to see one.
Howard watched as one of the dark clouds put two fingers down to earth.
The tornado then came to a barn and the two funnels merged, picking up a barnhouse.
Some pieces of the barnhouse fell to the ground,
and the others started swirling around the outside of the tornado.
After the tornado had left, the damage was assessed.
A missing woman had been wedged into a sycamore tree.
A live chicken was found in a rolled-up ball of barbed wire,
still living, but plucked as clean as if it had been ready to go into the pot.
There was also the usual things like straws driven into trees .
Can you be safe?
If there is a chance of a Tornado, a Tornado Watch will be issued.
If a Tornado has been sighted, a Tornado Warning will be issued.
If you are home alone in a severe thunderstorm
you should take cover.
If you see or hear a severe thunderstorm approaching,
use a weather radio or battery-powered radio to listen to the local forcast.
Go to an inside wall on lowest floor,
and kneel on the floor facing the wall, and put your hands over your head.
When in school, stay away from rooms with wide roofs
that could collapse easily, such as gyms and auditoriums.
Don't use your phone, as it may conduct electricity to you.
If you are at your home, go to the basement
and get under the stairs or a piece of heavy furniture.
If you don't have a basement,
get in a closet in the middle of the house.
If advance warning of a Tornado is given:
If you are outside, go to a ditch, etc.
If you are in a car, get out.
Cars cannot outrun a tornado.
You should keep disaster supplies like flashlights, candles, matches, etc.
Storm Chasers
What storm chasers do is travel after any storm that has potential to produce tornadoes
or other severe weather phenomena.
At any given day a storm chaser can travel hundreds of miles in search of severe weather,
and only rarely do they get to see a tornado.
To be a storm chaser you have to be extremely patient.
It may take days to find a strong storm and even then it may not turn out to be very strong at all.
Storm chasing is also a dangerous profession,
because Mother Nature is quite unpredictable,
and you never know when or where a tornado might appear,
or where it might change direction and head right for you! Please watch the weather and be very careful. 
Don't get curious and not take cover to protect yourself!
Listen to the radio, TV, or weather radio!
I would like to thank Trina for some of the text.
Please visit her site
http://www.oocities.org/Heartland/Valley/6871
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