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TORNADOES
Although tornadoes
occur in many parts of the world, these destructive
forces of nature are found most frequently in the United
States east of the Rocky Mountains during the spring and
summer months. In an average year, 800 tornadoes are
reported nationwide, resulting in 80 deaths and over
1,500 injuries.
A tornado is defined
as a violently rotating column of air extending from a
thunderstorm to the ground. The most violent tornadoes
are capable of tremendous destruction with wind speeds
of 250 mph or more. Damage paths can be in excess of one
mile wide and 50 miles long.
HOW DO TORNADOES FORM?
Before thunderstorms
develop, a change in wind direction and an increase in
wind speed with increasing height create 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.
 
 
 
SHAPES AND SIZES
Weak Tornadoes:
69% of all tornadoes, less than 5% of
tornado deaths, lifetime 1 - 10+ minutes, winds less
than 110 mph.
Strong Tornadoes:
29% of all tornadoes, nearly 30% of all
tornado deaths, may last 20 minutes or longer, winds 110
- 205 mph.
Violent Tornadoes:
Only 2% of all tornadoes, 65% of all
tornado deaths, lifetime can exceed 1 hour, winds
greater than 205 mph.
WHAT TO LISTEN FOR
Tornado Watch:
Tornadoes are possible in your area. Remain alert for
approaching storms.
Tornado Warning:
A tornado has been sighted or indicated
by weather radar. If a tornado warning is issued for
your area and the sky becomes threatening, move to your
pre-designated place of safety.
Remember:
Tornadoes occasionally develop in areas in which a
severe thunderstorm watch or warning is in effect.
Remain alert to signs of an approaching tornado and seek
shelter if threatening conditions exist.
ENVIRONMENTAL CLUES
Look out for: dark
often greenish sky, large hail, wall cloud, loud roar
similar to a freight train, circular rotation in the
clouds.
CAUTION: Some
tornadoes appear as a visible funnel extending only
partially to the ground. Look for signs of debris below
the visible funnel. Some tornadoes are clearly visible
while others are obscured by rain or nearby low-hanging
clouds.
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