[SMCARA] Fujita tornado scale revised

[J D Delancy]

Friend in South Texas came across this article; emergency coordinators
probably should be aware

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>From article on http://www. mysanantonio.com

Government revises tornado ratings scale
02/02/2006
By DANIEL YEE  / Associated Press

The government is changing how it categorizes tornadoes after finding that
it doesn't take 300 mph winds to disintegrate homes and turn cars into
missiles ­ a 200 mph twister can do just as much damage.

The National Weather Service said Thursday it had changed the Fujita Scale,
a three-decade-old system of ranking a tornado's strength, to align wind
speeds more closely with actual damage.

"It was apparent that many of the speeds used in the estimates were too
large, said Joe Schaefer, director of the service's Storm Prediction Center.
"The scale guiding wind speeds wasn't in tune with reality."

The change was introduced at the American Meteorological Society meeting in
Atlanta. However, the new system will not fully go into effect until
February 2007, giving weather scientists time to adjust to it.

Under the old system, created in 1971, an F-5 tornado ­ considered the most
powerful of tornadoes ­ was capable of destroying a typical frame house,
with wind speeds estimated at 261 mph to 318 mph. Since then, engineering
studies have shown that much slower winds could cause the same damage.

"It doesn't take 300 mph winds to totally destroy an ordinary frame house,"
said Greg Forbes, a former member of Penn State's meteorology department who
studied tornadoes under Theodore Fujita, the University of Chicago professor
who created the scale. Forbes now works for The Weather Channel.

Under the new system, an F-5 tornado ­ which can disintegrate a strong frame
house after lifting it off its foundation or badly damage reinforced
concrete buildings ­ has wind speeds of at least 200 mph.

Because the new system still uses actual tornado damage to estimate wind
speeds, officials said it is not likely that the new system's lower wind
speed rating for the F-5 tornado will result in more tornadoes being
classified with the nation's top tornado rating.
The old system rated tornadoes only based on damage to homes. The new system
classifies tornadoes based on damage to 18 other types of structures,
including trees, mobile homes and other types of buildings.

"If a tornado went over a row of trees and didn't hit a house, there was no
way to estimate the scale," Schaefer said.

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