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do some thunderstorms produce violent tornadoes while most do not? The answer is related
to the wind. If the wind changes direction and gets stronger with
height, it can cause a column of air to rotate. Think of a rotating column of air about 2
miles high and half a mile wide. Suddenly a thunderstorm updraft pulls this column upward.
Now it's 3 miles high and a few hundred yards wide.
When this happens the air spins up. Sit in a swivel chair and hold your arms out. Now
have someone spin you around. As you spin bring your hands to your lap. Be careful doing
The scientific term for this spinning up is conservation of angular momentum. It is
this process that can take 50 mph winds and turn them into a tornado with 200 mph winds!
Everything has to come together just right for a tornado to occur.
More tornadoes occur in the United States than any other place in the world. Alabama
ranks 4th in the nation for the number of killer tornadoes, and the risk of tornadoes is
higher in the Tennessee Valley.
Texas and Oklahoma have many more tornadoes than we do, here in the
ours tend to be more deadly. The worst tornado disaster occurred on March 21, 1932. Over
300 people were killed in the state during 2 waves of tornadoes that day.
Is That A
You have probably asked yourself
that question at least once while watching an approaching storm. There are several
important clues that will help you tell the difference between a scary looking cloud and
a developing tornado.
Tornadoes form in the updraft region of a thunderstorm. The rain and hail fall out of
the downdraft. If a tornadic thunderstorm is moving Northeast, then the tornado would most
likely form on the Southwest end of the storm with the rain out ahead of it. If you are in
the path of the storm, then you would most likely not see the tornado approaching until it
was very close.
photograph tornadoes know that the safest way is to follow the storm. If a tornado
develops, it will be easier to see as it moves away.
This is Dan's favorite tornado picture, it is from the Storm
Spotter's Guide Slide series.
Since the tornado is forming in the updraft, there may be a low cloud slowly rotating
Rain Free Base
of the storm. This low cloud is called a Wall Cloud
and is the parent cloud to a tornado. Not all Wall
|Dan was in
Oklahoma a few years ago chasing and collecting video of
tornadic conditions for a News piece on Severe Weather, when a
Wall Cloud developed. He is explaining the event to his
Clouds produce tornadoes, but if you see a low
rotating cloud at the back edge of a storm, take no chances. Many times blue sky or
sunshine will be behind the wall cloud or tornado. Hail and lightning accompany many wall
along with high wind. Tornadoes are wind not clouds. Until they pick-up dust or
moisture, may not be visible. Many times all you can see is a large swirl of dust or
debris near the ground.
National Severe Storms Laboratory
Storm Spotters Guide
NWS Norman, OK Storm Spotters Guide
Terms for Storm Spotters
Tornado History & Historical Tornado Statistics
The Tornado Project -
give the subject a little different twist, with tornado myths, tornado oddities, personal
experiences, tornado chasing, tornado safety, and tornadoes in the past as well as more
Severe Weather Safety
NOAA Weather Radio
USA Today's Index of Tornado
Fujita Tornado Intensity Scale &
Enhanced Fujita Scale