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Severe
Weather Hits Midwest |
Posted:
3.15.06
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The Midwest is cleaning up after an unusually severe and deadly
start to tornado season.
Printer-friendly versions: PDF
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Violent weather, including hail as big as softballs, high winds
and lightening, caused flooding in Indiana, grass fires in Texas
and deadly tornadoes across five states last weekend. The storms
left at least 11 people dead and millions of dollars in damage.
The number of tornadoes -- over 110 -- was nearly twice the previous
record for March and over 10 times the average.
Missouri was particularly hard hit, prompting Governor Matt Blunt
to declare an emergency throughout the entire state. Parts of
Arkansas, Illinois and Indiana also were declared disaster areas,
making them eligible for money from Washington to help clean up.
Most of the twisters struck in tornado alley -- a flat region
in the southern and central plains between the Rocky and Appalachian
mountains.
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What is a
tornado? |
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A tornado is a violently rotating column of air that extends
from the base of a strong thunderstorm cloud to the ground.
The size, shape and severity of tornadoes vary widely. They can
appear as long thin ropes or a large rotating column a mile wide.
Some tornadoes don't even have a visible column.
The tornado column starts out white -- the color of the droplets
of moisture caught in the storm cloud. However, when it touches
land it often takes on the color of the dirt and debris that get
sucked into the tornado.
Most tornadoes have winds between 110 and 205 mph, but some have
had winds reported over 300 mph.
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Why so many
recent tornadoes? |
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Tornadoes occur when warm, moist air is trapped under cold, dry
air creating large rotating thunderstorms called supercells.
This phenomenon is most rampant in the plain states of tornado
alley where the warm, moist air from the Gulf of Mexico in the
South collides with cold air from the North and dry air from the
West.
Since the plains are open and flat, the storms can roll on for
miles without dissipating.
These unique land features mean the United States experiences
more tornadoes than any other country in the world. On average,
the United States has over 1,000 tornadoes per year which kill
an average of 60 people annually.
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Predicting
and measuring tornadoes |
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Scientists describe tornadoes with the F-scale, named for Dr.
Tetsuya Theodore Fujita. Fujita developed the scale in 1971 to
measure tornadoes by the damage left in their wake. The scale
ranges from F1 (weak) to F5 (incredible).
 Today,
the National Weather Service uses an Enhanced Fujita Scale which
measures tornadoes by damage indicators, wind speed, intensity
and area.
The National Weather Service's Storm Prediction Center issues
tornado forecasts and tornado watches. A tornado watch means weather
conditions are such that a tornado is possible. A tornado warning
means a tornado has been seen in your area and you should seek
shelter immediately.
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Tornado safety |
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Following the damage from last week's storms, several governors
have called for Severe Weather Awareness Weeks and drills in schools
and government buildings.
"Tornadoes can strike with little or no warning, leaving
only moments to make life-or-death decisions," North Carolina
Governor Mike Easley said. "I ask everyone to take the time
to put together and rehearse your family emergency plans, so that
when the National Weather Service issues a tornado warning in
your area, you can act quickly and take shelter."
Because most of the deaths from tornadoes are caused by flying
debris, experts say avoid windows, go to the lowest floor and
find a small room or hallway in the center of the house with no
windows, crouch as low to the floor as possible and cover your
head with your hands.
Cars are not safe during tornadoes. If possible, park and find
shelter in a building. If you are in open country, get out of
the car, find low ground away from any cars and lay flat, face-down
covering your head with your arms.
Tornadoes can occur any time of year, but they typically strike
in March, April and May with a secondary peak in November.
--
Compiled by Anne Bell for NewsHour Extra
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