An F6 Tornado?

[rdale]

Every scientific study that correlates wind speeds to F-scale shows that the speeds are too high... I.E. F5 could come with winds that are not as strong as listed, Dr F did not use any real research when he came up with the splits.

- Rob

 

[Robert Dewey]

Originally posted by rdale
Every scientific study that correlates wind speeds to F-scale shows that the speeds are too high... I.E. F5 could come with winds that are not as strong as listed, Dr F did not use any real research when he came up with the splits.

- Rob

I wonder what the actual numbers are closer to... Any research, or ideas?

 

[Andrew Khan]

Cattle were Skinned, and there lungs were sucks out.....? It seems very odd, and unlikely for cows to actually have there lungs and skin ripped off...but anything is possible, that's sad, however. I thought in order for your flesh to be ripped of winds would need to exceed 500 mph....

 

[Mike Smith]

There could be an F-6 tornado. On the rare occasions when tornadoes have struck downtown areas (Lubbock, Topeka, Ft. Worth, etc.) most engineered buildings have little (in relative terms) damage. If a skyscraper was knocked down or an engineered building completely blown away it would be F-6 or higher.

 

[David Brookshier]

If they look at rating tornados based on damage then they should seriously consider doing away with the exact wind speed classification system for example 261-318=F5 now curious people like myself will only end up asking ...so what happens at 319 if it's only damage they are looking for in rating tornados why use the current precise wind ratings for the respective F scale at all? Who knows maybe this is why many of the textbooks I've seen have done away with F6 but on the other hand shouldn't they also extend F5 tornado speeds beyond 318 to avoid confusion:?:

 

[Andrew Pritchard]

Originally posted by David Brookshier
If they look at rating tornados based on damage then they should seriously consider doing away with the exact wind speed classification system for example 261-318=F5 now curious people like myself will only end up asking ...so what happens at 319 if it's only damage they are looking for in rating tornados why use the current precise wind ratings for the respective F scale at all? Who knows maybe this is why many of the textbooks I've seen have done away with F6 but on the other hand shouldn't they also extend F5 tornado speeds beyond 318 to avoid confusion:?:

Basically, the wind speeds are complete crap. Every bit of damage done by a tornado is within a certain category on the scale.. The windspeeds generally are just a push for real wind speeds, as well as a way to seperate lower-middle-higher ends in the categories. But the rating is certainly determined by the damage caused.. and is usually explained in the NWS's surveys which are usually posted online after the tornado.

 

[Justin Turcotte]

The Fujita Scale was designed as a wind speed scale but it is generally utilized as a damage scale. Fujita himself recognized that modern housing faltered at lower windspeeds. Tim Marshall has also shown this in numerous conference and professional papers. It is probably best to think of an F-rating in terms of damage rather than wind speed. As far as an F6 is concerned, the damage would not be easily distingished from an F5 as an F5 already cleans the plate. The only real way to distiguish an F6 from an F5 would be an actual wind measurement. Fujita stated an F6 is inconceivable but nobody said it was impossible. We only have about 50 years of video and 30 years of doppler data of a select few tornadoes within these time frames... But when you get right down to it, is there any real difference between 300 mph winds versus 320 mph winds?

 

[rdale]

"There could be an F-6 tornado."

No there cannot, at least with the F-Scale, because Dr F defined F5 as total cleansing...

"The only real way to distiguish an F6 from an F5 would be an actual wind measurement."

No, because the F-Scale is a damage scale.

 

[Justin Turcotte]

Originally posted by rdale
\"There could be an F-6 tornado.\"

No, because the F-Scale is a damage scale.

Fujita imperically derived F-scale wind speeds by connecting the Beaufort scale to the Mach scale (see above chart), therefore, I will take the side that it was designed as a wind scale that in application only is a damage scale... I agree that for application purposes (rating damage), the highest rating will be F5.

 

[Ryan McGinnis]

Originally posted by APritchard+--><div class='quotetop'>QUOTE(APritchard)</div>

<!--QuoteBegin-David Brookshier

Ah ha so we are only 1 mph off, that means we're getting closer to an F6. I have never seen the F scale go all the way to 12 wow Is this true? If so forget about an F6 I think I'll start looking for an F12 :shock: (you've just got to shoot for high goals no matter how unrealistic they really are)

Well, still.. as Fred stated.. how are we going to identify F12 damage. If an F5, or even F6 wipes everything clean.. what more can be done?[/b]

I think I'd put one caveat here: while the Fujita scale is generally determined by damage, not wind guesstimates, it IS a scale directly linked to windspeeds. i.e., this windspeed causes this damage, therefore, this damage must correspond to this windspeed. If we had a very reliable way to directly measure windspeeds within the lower fifteen feet of a torndao, I would have no problem at all with using that data to determine where that tornado falls on the Fujita scale. We only use damage because that's the best we can do right now with current technology (i.e., most windmeters are destroyed by tornadoes and can't register speeds of 200+ anyway), and most of the time tornadoes don't pass overwindmeters. And doppler can't scan the very bottom of a tube.

Just as we look at damage and try to ascertain windspeed, I'd have no problem with directly measuring windspeed (if we could) and then correlating it with the kind of damage that could have occured, had the tornado hit something that could have registered that damage. Thus, if someone WERE able to directly measure a ground circulation of, say, 340mph, I'd be all for calling that an F6, even if that twister didn't hit Fort Knox to prove it.

 

[Greg Stumpf]

The wind speeds assigned to the F-scale by Fujita were mostly abritrary, and were never calibrated. More recently, research by the Texas Tech wind engineering folks, and a committee of other damage experts (including Tim Marshall) are finding that the actual wind speeds that cause the described damage in the Fujita descriptions might be as much as 30-40% lower than what Fujita guessed. Also add to the fact that Fujita's descriptions were for well-built single-family residential homes only. Unfortunately, as we are discovering on almost every damage survey, very few homes hit by tornadoes are "well-built".

Regarding the comment about direct measurement of tornadoes by the Doppler On Wheels (DOW). This is not possible, because even at very close ranges (1-2 miles), there are still some horizon/clutter effects blocking any beam aimed near the ground. I think the closest to the ground that the measurements have been estimated is still 50-100 feet above ground level, which is still above the roofs of most single-family residential structures. There are rapid changes in vortex wind speed and acceleration in that lowest "skin" layer within 100 feet of the ground.

And yes - those like me who do damage surveys as part of our job are trained to know that the F-scale is a *damage intensity* scale, and that the distribution of wind speeds capabile of producing said damage actually have distributions that ovelap each scale category. There are many other factors to consider, such as exposure, angle to the wind, building construction, secondary damage caused by debris impacts, etc., such that a wind speed of a constant xxx mph could cause a range of damage to similar structures.


greg

 

[Chris Geelhart]

There are efforts ongoing to come up with an "Enhanced Fujita Scale", in order to eliminate some of the ambiguities that have been mentioned here. I found a good paper on the subject:

http://ams.confex.com/ams/pdfpapers/81090.pdf

This was part of the 2004 AMS severe storms conference. More information is also available at
http://www.wind.ttu.edu/F_Scale/default.htm

Chris G.

 

[rdale]

"I will take the side that it was designed as a wind scale "

Let me check on copyright issues, but if it's okay I've got plenty of his early papers that I would love to scan and put online. His son is a prof at Michigan State Univ, and called me one day saying his wife wanted to clean out the basement so either I take boxes of Dr F's stuff or it went to the landfill... Easy decision, now they are sitting in my basement though ;>

- Rob

 

[Joe Nield]

Originally posted by rdale
\"I will take the side that it was designed as a wind scale \"

Let me check on copyright issues, but if it's okay I've got plenty of his early papers that I would love to scan and put online. His son is a prof at Michigan State Univ, and called me one day saying his wife wanted to clean out the basement so either I take boxes of Dr F's stuff or it went to the landfill... Easy decision, now they are sitting in my basement though ;>

- Rob

He also brought boxes of old books and papers to the central Illinois AMS conference last month. I got a copy of his book on the DFW microburst and some other pamphlets/papers. Pretty cool stuff.

 

[Chris Lott]

According to this, there will never be an F-6. This also shows wind speeds for each category, but clearly the F scale is a damage scale.

http://www.disastercenter.com/tornado/fujipear.htm