An F6 Tornado?

[Greg Stumpf]

A number of people posting on this thread have stated unequivocally that a f- or F- 6 is "impossible." Please reference where Fujita explictly states that it cannot occur. Opinions don't count.

It is generally accepted in the modern "community" of storm damage experts that F5 is the highest rating given, and that the Fujita scale is a damage scale and not a wind scale, regardless of what Fujita initially desired. Chuck Doswell's comments sum that up very well.

But, certainly, it is possible that a tornado could exceed the the 318 mph speed limit that Fujita arbritrarily applied to the rating scale. But recall that those numbers are quickly becoming moot in light of present day engineering analyses and research. Furthermore, if and when the Enhanced Fujita Scale is applied, there will no longer be any designation above EF5.

Yes, the F5 designation is for complete destruction to well-built single-family residences. But if an engineered steel and concrete structure (like an office high rise) were to be swept clean someday, I'm sure the engineers will study that profusely and might consider a higher rating. But for now, I wouldn't expect any F6+ or EF6+ ratings from official survey teams.


greg

 

[Mike Smith]

Greg,

Thank you. At last, we get to the crux of the matter.

I don't dispute your statement about what the "community" might think or believe regarding wind speeds in tornadoes. I also don't dispute that Fujita's wind speed estimates may be high.

But, my point is that the Fujita Scale is the Fujita Scale. The "community" has no standing to change Ted's scale and still call it the Fujita Scale.

So, if the "community" wants to create an "Enhanced Fujita Scale" and redefine damage and wind speeds, knock yourselves out. I am confident it will be an improvement. But, it should be called the "Enhanced Fujita Scale" (or whatever), not the Fujita Scale.

Ted allowed for F-6 and f-6. That is a fact. Whether we will ever be able to detect a tornado of this intensity is another matter... if and when one should occur.

 

[Saul Trabal]

^

For winds higher than 318 mph, you'll have to go to other planets in our solar system.

 

[David Draun]

Originally posted by Saul Trabal
^

For winds higher than 318 mph, you'll have to go to other planets in our solar system.

or be in the vicinity of a nuke explosion, lol. :roll:

I read that that was the reson for f6+.

 

[Chris Sokol]

Fujita's wind speeds associated with the damage were a guess. Given that it was a scientifically researched guess, but still, a guess. There were no methods to use to actually measure wind speed associated within a tornado during the creation of the F scale.

Tim Marshall has shown through his research that damage to structures that appear to be from the F-0 to F3 range can actually occur without the tornado actually striking the structure. So...just how do we accurately rate a tornadoes strength?

 

[Chris Lott]

www.earthscape.org/r2/ams/vol82_01/ams82_01_05.pdf+author:%22McDonald%22+intitle:%22T.+Theodore+Fujita:+His+contribution+to+tornado+...%22]Click Here[/url]

Interesting. Sounds like Dr. Fujita intended for it to be a damage scale all along. " The Fujita Scale is the primary instrument for for indirect estimates of tornado wind speeds used today."

 

[Michael Auker]

I'm somewhat puzzled by the many adamant proclamations that the Fujita scale is just purely a damage scale? The Fujita scale, even if it's wind speed estimates are off, still correlates damage and strength... a tornado that levels and sweeps away a well-anchored and well-built home is still stronger than a tornado that just tears some shingles off. If Fujita had intended it to be purely a damage scale, why did he ascribe wind speeds to each category? He actually began the scale with the wind categories, and then assigned a damage level to each...

Fujita established categories, each representing arange of wind speed. He then described damage thatwould likely be observed for each range of wind speed.

 

[Aaron Kennedy]

Michael: in your case it is straight forward, but lets consider a tornado that takes a roof off a home. Whether the house had tornado/hurricane straps or not can make a big difference. Did the tornado hit a lumber yard before? Debris in a torando can also induce different severities of damage. How long was the tornado over the location of the house? Lots of factors go into damage. That's why it is so hard (operationally) to determine a tornado's true strength (in wind speed) and relate it to the damage scale.

Aaron

 

[Chris Sokol]

Fujita created a scale which groups tornadoes into categories based on how much damage the caused. He came up with categories by connecting the Beaufort wind scale with the speed of sound in twelve steps. For each category he estimated how strong the wind must have been to cause the damage.

Estimated. Now again...estimated. Not measured. Not calculated using photogrammetry. Not using scientific methodology in the study of damage patterns and computer modeling. Estimated.

Before 1971, there was no way for scientists to rank tornadoes by their strength. The visual size really had no bearing on how strong it was. Because they're so intense, you can't measure the wind speed or pressure in a tornado like you can in a hurricane. T. Theodore Fujita, a professor at the University of Chicago, came up with a system to rank tornadoes according to how much damage they cause.

The above quotes and image are courtesy of UCAR: http://www.windows.ucar.edu/tour/link=/ear...ado/fujita.html

Now this from the National Climatic Data Center:

The Fujita scale bridges the gap between the Beaufort Wind Speed Scale and Mach numbers (ratio of the speed of an object to the speed of sound) by connecting Beaufort Force 12 with Mach 1 in twelve steps. The equation relating the wind velocities (V in mph) with the F scale (F) is V = 14.1 * ((F+2) to the 1.5 power).

So basically, he divided by 12 to get estimated wind speeds. An estimation. Granted, a scientifically thought out estimation, but still an estimation.

Now..from Texas Tech, and their research on the Fujita Scale Enhancement Project:

http://www.wind.ttu.edu/F_Scale/default.htm

Dr. Theodore T. Fujita invented the Fujita Scale in 1971. The purpose of the scale was to classify tornadoes by intensity, i.e. to distinguish between weak ones and strong (intense) ones. He defined six categories F0 to F5, with F0 being weak and F5 being the most intense expected. Fujita then envisioned the type of damage he would expect in each of the six categories.

Fujita also assigned wind speed ranges to each category, which are non-overlapping and increase in magnitude from F0 to F5. The ranges also are shown in \"Original Fujita Scale\". The wind speeds in the table have been converted to three-second gust speeds at 10 m height in flat open terrain. There were no attempts at a definitive correlation between appearance of damage and wind speed. Fujita used his best judgment as the world’s leading expert on tornadoes at the time. Both the meteorological and engineering communities immediately accepted the Fujita Scale because in 1971 there was a critical need for it. Among other needs, a growing nuclear power industry was struggling to design tornado-resistant facilities.

This information is from the team attempting to re-design the F-Scale into an enhanced version. I would venture to guess that they most likely have pretty accurate information about the origons of the Fujita scale, and the processes that were used to define it. The members of the research team include:



1. Timothy P. Marshall, P.E. (18 years experience conducting wind damage surveys; has conducted approximately 65 surveys.)
2. Timothy A. Reinhold, PhD (Associate Professor of Civil Engineering Clemson University)
3. Douglas A. Smith, PhD, P.E (Associate Professor of Civil Engineering, Texas Tech University)
4. Greg Forbes, PhD (PhD from the University of Chicago; Studied under Dr. Ted Fujita)
5. Thomas Lee Smith, AIA, RRC (Author of a number of papers on performance of roof systems in high wind.)
6. Don Burgess, Chief: Warning Research & DevelopmentDivision, National Severe Storm Laboratory



Hmmm...sorry, but I have to go with these guys.

Several studies indicate that the Fujita Scale overestimates wind speeds in categories F3, F4 and F5.

So..if this is true, then the theory of "319=F6" is history.

And lastly, from the storm prediction center:

*** IMPORTANT NOTE ABOUT F-SCALE WINDS: Do not use F-scale winds literally. These precise wind speed numbers are actually guesses and have never been scientifically verified. Different wind speeds may cause similar-looking damage from place to place -- even from building to building. Without a thorough engineering analysis of tornado damage in any event, the actual wind speeds needed to cause that damage are unknown.

So there it is...feel free to believe whatever you choose to believe, but personally I am more likely to go with that the scientist and engineers (including one that studied under Fujita) that have worked on this subject for years have to say on the subject. They didn't just read his book...they lived it.

 

[Robert Dewey]

...... And he said an F6 might be identifiable by a ground swirl pattern. So if it's possible that it could be identifiable, then it's possible that it could exist - or at least that would be the first logical thought.

I'm not arguing that the Fujita scale isn't based primarily on damage, I'm just arguing that an F6 would be possible based on what Fujita said (as Mike Smith quoted).

I think the only way an F6 rating would be assigned is if the following occured:

1) Widespread extensive F5 damage
2) DOW wind speed in excess of the current known F5 wind rating
3) An extensive ground swirl pattern (perhaps the tornado created a trench in the ground) is evident, unlike any seen before

Obviously it's all hypothetical, but that's how it'd probably go down.

 

[Karen Politte]

A big part of this is that we're - again - trying to classify the unclassifiable. It is human nature to classify and have everything in nice, neat categories.

Supercells don't care whether they are wet or dry and tornadoes don't care if they're 170mph or 316 mph. These beasts will defy our explanation for a lot longer than the next few years.

I think that one of the nicest ways to describe a tornado is visually. Did it look violent, or lazy? Did it look solid, or transparent?? I know that is not a sure fire way of classifying anything - but it helps to be honest with what you've seen, too.

KR

 

[nickgrillo]

There will never be an F6 tornado... The fujita scale is based upon the damage a tornado causes, and you can't get any more powerful then total destruction.

Okay, case closed... When is this thread gonna die?!!

 

[Michael Auker]

An F-5 won't blow away a skyscraper... :lol:

 

[Robert Dewey]

Originally posted by nickgrillo
There will never be an F6 tornado... The fujita scale is based upon the damage a tornado causes, and you can't get any more powerful then total destruction.

..

Yeah you can... As Fujita himself said: ground swirls. :lol:

I agree though, science doesn't support an F6. I don't care if we had a 10 mile wide wedge with a measured wind of 400MPH by several mesonets - scientists are too stubborn to deviate from the norm.

 

[Jeff Snyder]

If we had ground-truth of winds >320mph, then there'd be more rigorous scientific discussion I think. Just remember that you shouldn't use radar data as absolute ground truth, either, since there are still approximations/estimations/averaging that occurs (pulse averaging, range sampling, etc).

We haven't had an F5 for more than six years, just as a reminder.