Government Revises Tornado Ratings Scale

http://www.washingtonpost.com/wp-dyn/content/article/2006/02/02/AR2006020201165.html ^

[lunarbicep]

ATLANTA -- 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.

[lunarbicep]

Sounds like it’s the “home construction” scale that needs amending

[GSlob]

"Sounds like it’s the “home construction” scale that needs amending"
Well, reinforced masonry with large interlocking blocks would do the job, but an average size house would then cost several million.

[UseYourHead]

They need a few more Fs on then since F3's are now F5's - how will we really know when a mile wide monster is about to hit?

[spetznaz]

Hmmmm .....then I guess under this new system the 1999 Oklahoma tornado must have been a what ....F8? After all, it was an extremely strong F5 (some say they should have given it a new rating of F6) ....thus with the new ratings it apparently got an enlargement.

[billorites]

[brothers4thID]

It's all just a label game anyway. The tornado that hit Marshall Co Kentucky last fall was classified as an F3 "or maybe an F4" by the weather service. It demolished houses and leveled everything in it's path- but in an isolated and fairly rural area around Kentucky Lake.

The tornado that hit Madisonville, just "down the road" as we say in KY, was classified an F5 but the damage was no worse there.

What I'm trying to say is, when there's a 200 year old oak tree where your bedroom used to be or a few cement blocks where the rest of your house used to be, it doesn't matter what the weather service classifies the tornado as.

[Right_Handed_Writer]

Here is the SPC official explanation. I figure by the time we hit June the media will be all over the global warming my god we've had soooo many more F-5's this year story.

"New Enhanced F-Scale"

[Disambiguator]

We use a modified "F" scale for dust devils here in New Mexico.

The "F" rating is determined by the number of blue Wal-mart bags swirling around in the vortex.

[UseYourHead]

I always wondered where she worked...

[GSlob]

"The "F" rating is determined by the number of blue Wal-mart bags swirling around in the vortex."
The F rating is determined from the length and complexity of audible expletive pronouncements by those on the scene at the time.

[lunarbicep]

I figure by the time we hit June the media will be all over the global warming my god we've had soooo many more F-5's this year story.

rest assured it's coming

[babaloo]

<"The "F" rating is determined by the number of blue Wal-mart bags swirling around in the vortex."
The F rating is determined from the length and complexity of audible expletive pronouncements by those on the scene at the time.>

Hilarious. I live in Iowa and I know of what you speak.
Thanks for the laughs.

[JTHomes]

More dumbing down of our rating systems.

[janetjanet998]

There will NOT be any more F5's then the old system..all they did was lower the wind scale for ALL of the old system..the old fugita scale was based on damage NOT wind Speed...the wind speed was estimated from the damage to structures at the time(1950's)

Now we know its doesn't take a 300 MPH wind to leave nothing but a foundation of a house(with all debris swepted away) it only takes a 200+ MPH wind...

That being said monsters like the OKC tornado with its high wind speed recorded or the even stronger xenia ohio tornado in 1974 would be "off the charts" under the new systems...

[Right_Handed_Writer]

"here will NOT be any more F5's then the old system..all they did was lower the wind scale for ALL of the old system..the old fugita scale was based on damage NOT wind Speed"

My point exactly. I've surveyed several tornado aftermath's. The difference between an F-4 and and F-5 on the FuJita scale was more than noticeable. And with DOW giving pretty precise measurements of these monster storms, numerous tornadoes that top 200 mph will now lump into one category. With the 28 level damage assessment scale, which is way too complex for the average media type to get into, all that will come across the tube is "It was another F-5!"

I think it is a good new system since it will give greater definition to the type of damage. But it will go over the head of 95% of the populous.

[houeto]

Hmmmm .....then I guess under this new system the 1999 Oklahoma tornado must have been a what ....F8? After all, it was an extremely strong F5 (some say they should have given it a new rating of F6) ....thus with the new ratings it apparently got an enlargement.

Agree. Same thing needs to happen with the Safhir/Simpson(sp) with regards to hurricanes. I have been through MANY. Katrina came ashore as a cat 3. I was in Camille in '69 and THIS storm dwarfed her. I learned many lessons living through Katrina.