An F6 Tornado?

[Gabe Garfield]

Originally posted by Mike Smith
Chris,

I don't understand your point. The Lubbock tornado was rated F-5. I struck a skyscraper. The skyscraper stood, although heavily damaged.

If a tornado struck a well-engineered skyscraper and levelled it, why wouldn't that be evidence of F-6 damage?

Mike

This presupposes that the skyscraper was in a segment of F5 damage. Most F5 tornadoes do F5 damage in only a few places. Take the Bridge Creek/Moore tornado for example: the tornado tracked 38 miles and destroyed thousands of houses and yet only 17 locations along that entire path length were rated F5.

The Fujita scale assigns a rating of F5 to any tornado that levels well-constructed homes, tosses cars extreme distances, etc. As I understand it, Fujita did not include damage to industrial or commercial buildings (such as a skyscraper) in his rating system. Which begs the question, "If the skyscraper had been leveled, would the tornado have been rated an F6?" Nope.

First, because there is no way of knowing whether or not a skyscraper or high-rise building can withstand stronger winds than an ordinary dwelling space. Furthermore, it is logistically impossible to study the effects of wind speed on such heterogeneous structures. That is, there is (generally speaking) no national standard for building large structures. They come in all different sizes and shapes, are made with different materials, and are constructed differently.

Second, as has been said ad nauseum, there is no such thing as an F6 tornado in the real world. An F6 tornado is called "inconceivable" for a reason. Because the damage that an F5 tornado incurs is so complete, it leaves nothing further to damage. Fujita didn't leave room for it in his scale, and that's that. (Though I think a better damage scale could be created to better delineate between "weak" and "strong" F5 tornadoes...which is what I believe those working with the Enhanced Fujita Scale are trying to accomplish.)

Gabe

However,

 

[Chris Sokol]

Originally posted by Mike Smith
Chris,

I don't understand your point. The Lubbock tornado was rated F-5. I struck a skyscraper. The skyscraper stood, although heavily damaged.

If a tornado struck a well-engineered skyscraper and levelled it, why wouldn't that be evidence of F-6 damage?

Mike

Because there is no F6 rating.

 

[Michael Auker]

Another question would be: do F-5 tornadoes really occur? With engineers finding that F-5 damage occurs at lower windspeeds, are past F-5's really deserving of that destinction? Maybe there haven't been any F-5's yet?

 

[rdale]

"r question would be: do F-5 tornadoes really occur?"

Yes...

"With engineers finding that F-5 damage occurs at lower windspeeds"

Not to pick on you - but why are windspeeds STILL being mentioned? Wind speeds have nothing to do with rating tornado damage. The F-Scale is a damage scale.

"are past F-5's really deserving of that destinction?"

Do they meet Fujita's definition of F5? If so - they are considered F5.

"Maybe there haven't been any F-5's yet?"

Not sure I follow.

- Rob

 

[Mike Smith]

Sorry, folks. I am still not getting this discussion.

I went to Dr. Fujita's own discussion on page 31 of his book, "Mystery of Severe Storms" published in 1992 by the University of Chicago Press. The F-Scale chart clearly shows BOTH wind speeds and damage as F-Scale determinators.

If the F-Scale rating is made using damage then a lower case "f" is to be used before the numerical value.

If the F-Scale rating is made using wind speeds then an upper case "F" is to be used.

So, if one documented a tornado with 325 mph wind speeds, it would clearly be F-6. Fujita DID define the wind speeds associated with F-6 and even used an adjective, "inconceivable", to describe it. He just (at least at that time) didn't speculate how one would tell the difference.

I don't understand why this is being called "impossible." I don't think we know.

 

[Robert Dewey]

Originally posted by rdale
\"Maybe there haven't been any F-5's yet?\"

Not sure I follow.

- Rob

I think he was talking about F5 in terms of wind speed, NOT damage.

But again, as stated MANY, MANY times in this thread: The F scale is a damage scale... In the future, the wind speeds associated with each F scale rating might change, but the damage will still remain constant to each rating (so while the wind speed for a particular tornado might be "changed", it still produced F5 damage and will remain an F5).

 

[Michael Auker]

 

[Michael Auker]

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

<!--QuoteBegin-rdale

\"Maybe there haven't been any F-5's yet?\"

Not sure I follow.

- Rob

I think he was talking about F5 in terms of wind speed, NOT damage.

But again, as stated MANY, MANY times in this thread: The F scale is a damage scale... In the future, the wind speeds associated with each F scale rating might change, but the damage will still remain constant to each rating (so while the wind speed for a particular tornado might be "changed", it still produced F5 damage and will remain an F5).[/b]

Yes, I meant an F-5 in terms of the original Fujita wind damage and wind speed scale, which, to my knowledge, hasn't been revised since Fujita created it...

 

[Robert Dewey]

Mike Smith's findings are pretty interesting...

But I think the current system uses F in terms of "damage". Why? Because it's easier to survey after the event than take real time readings of every tornado. This way, most tornadoes get "logged" and can be used in future case studies, climate data logs, etc..

About the whole F6 thing - with a pure damage scale, it's not possible. You can't get any more damage than complete destruction... It would be like trying to de-saturate an already white pixel - it can't get any more white! (LOL, stupid analogy - but whatever).

In terms of pure wind, if the question is asked "can a tornadoes wind speed ever reach >318MPH?", rather than asking "is an F6 possible?" - then the answer might be yes. But as far as a >318MPH tornado being an F6 on the damage scale? Nope.

 

[Bob Hartig]

Evidently the Fujita scale has been modified through time and application to focus on the question of damage. However, in the beginning, it clearly was conceived as scale that rated both wind speeds and damage, not just damage. Up to the F5 rating, the scale attempted to correlate those two concerns, but the fact that Fujita carried the rating well past F5 seems a pretty clear indication that he wasn't concerned with rating damage alone. Otherwise, why even postulate a rating of F6, let alone F12--ratings which, by Fujita's own definition, could not be determined from damage? What would have been the point if it was all about damage? For that matter, why bother listing ranges of wind speeds at all?

In practical application, the scale appears to have been modified to reflect a concern for rating storms according to the actual damage they produce. With all the variables that have got to go into assigning such ratings, I can only imagine how tough this must be. But don't the very complexities that make determining these ratings difficult run counter to the simplicity of the F scale? I mean, if a strong frame house is leveled off its foundation and swept away, isn't that by definition F5 damage, period, regardless of other concerns such as wind speed, duration of wind at one location, damage from flying debris, angle of roof, and so forth?

It seems to me that the F scale has evolved from its initial conception, and it needs to continue to do so. Until something exists that satisfies the concerns of rating both wind speed and damage, as Fujita at least set out to do, folks on both sides--and there are obviously some pretty strongly entrenched sides--will no doubt continue to argue and insist. As for me, heck, I'm just a layman, so having shared my opinion, I'll just shut up and watch how it all plays out. I just hope the result is one that is most useful to the broadest array of concerns.

 

[rdale]

"However, in the beginning, it clearly was conceived as scale that rated both wind speeds and damage, not just damage."

Where do you get that from? What part of his paper?

 

[mikegeukes]

Some articles, I have posted in the past

Enhanced F-Scale
A Recommendation for an ENHANCED FUJITA SCALE (EF-Scale)
Submitted to The National Weather Service
and Other Interested Users June 2004
http://www.wind.ttu.edu/f_scale/images/efsr.pdf

James R. McDonald* Texas Tech University, Lubbock, Texas
DEVELOPMENT OF AN ENHANCED FUJITA SCALE FOR ESTIMATING TORNADO INTENSITY
http://ams.confex.com/ams/SLS_WAF_NWP/21SL...racts/47974.htm
http://www.wind.ttu.edu/f_scale/images/AMS.pdf

James R. McDonald, Texas Tech University, Lubbock, TX 79409-1023., Kishor C. Mehta, and Sundarrajan Mani.
F-Scale Modification Process and Prosposed Revisions
http://ams.confex.com/ams/annual2003/FSCAL...racts/53999.htm

Fujita Scale Enhancement Project
http://www.wind.ttu.edu/f_scale/f-scale.htm

James R. McDonald, Ph.D., P.E. Kishor C. Mehta, Ph.D., P.
Summary Report: FUJITA-SCALE FORUM
http://ams.confex.com/ams/pdfpapers/53999....scale_forum.htm
http://www.wind.ttu.edu/f_scale/images/Fuj...ita%20forum.pdf

Symposium on the F-Scale and Severe-Weather Damage Assessment
http://ams.confex.com/ams/annual2003/FSCALE/index.html

James R. McDonald, Texas Tech University, Lubbock, TX 79409-1023., Kishor C. Mehta, and Sundarrajan Mani.
F-Scale Modification Process and Prosposed Revisions
http://ams.confex.com/ams/annual2003/FSCAL...racts/53999.htm
http://ams.confex.com/ams/pdfpapers/53999.pdf

Harold E. Brooks, NOAA/NSSL, Norman, OK 73069.
A CLIMATOLOGY OF THE FUJITA SCALE IN SPACE AND TIME
http://ams.confex.com/ams/annual2003/FSCAL...racts/53119.htm
Donald W. Burgess, NOAA/NSSL, Norman, OK 73072., G. Stumpf, J. Wurman, D.C. Dowell, Y. Richardson, and M.A. Magsig.

Donald W. Burgess, NOAA/NSSL, Norman, OK 73072., G. Stumpf, J. Wurman, D.C. Dowell, Y. Richardson, and M.A. Magsig.
RADAR WIND SPEED AND HOUSING DAMAGE DURING THE F-5 TORNADO AT MOORE, OKLAHOMA
http://ams.confex.com/ams/annual2003/FSCAL...racts/56622.htm

Roger Edwards, NOAA/NWS/NCEP/SPC, Norman, OK 73069.
RATING TORNADO DAMAGE: AN EXERCISE IN SUBJECTIVITY
http://ams.confex.com/ams/annual2003/FSCAL...racts/55307.htm
http://ams.confex.com/ams/pdfview.cgi?username=55307

Elaine S. Godfrey, Univ. of Oklahoma, Norman, OK 73019., Robert J. Trapp, Harold E. Brooks, and Sarah A. Tessendorf.
A DISCUSSION OF THE F-SCALE OF TORNADOES FROM QUASI-LINEAR CONVECTIVE SYSTEMS
http://ams.confex.com/ams/annual2003/FSCAL...racts/52518.htm
http://ams.confex.com/ams/pdfview.cgi?username=52518

Jared L. Guyer, NOAA/NWS, Hastings, NE 68901. and Todd J. Shea.
AN ASSESSMENT OF THE VARIABILITY IN OPERATIONAL ASSIGNMENT OF F-SCALE DAMAGE
http://ams.confex.com/ams/annual2003/FSCAL...racts/56411.htm
http://ams.confex.com/ams/pdfview.cgi?username=56411

Jared L. Guyer, NOAA/NWS, Hastings, NE 68901. and Michael L. Moritz.
ON ISSUES OF TORNADO DAMAGE ASSESSMENT AND F-SCALE ASSIGNMENT IN AGRICULTURAL AREAS
http://ams.confex.com/ams/annual2003/FSCAL...racts/57495.htm
http://ams.confex.com/ams/pdfview.cgi?username=57495

Timothy P. Marshall, Haag Engineering Co., Carrollton, TX; and W. F. Bunting and J. D. Weithorn
PROCEDURE FOR ASSESSING WIND DAMAGE TO WOOD-FRAMED RESIDENCES
http://ams.confex.com/ams/annual2003/FSCAL...racts/52226.htm
http://ams.confex.com/ams/pdfview.cgi?username=52226

Timothy P. Marshall, Haag Engineering Co., Carrolloton, TX 75006.
THE LAPLATA, MD TORNADO: ISSUES REGARDING THE F-SCALE
http://ams.confex.com/ams/annual2003/FSCAL...racts/53280.htm
http://ams.confex.com/ams/pdfview.cgi?username=53280

Daniel W. McCarthy, NOAA/NWS/NCEP/SPC, Norman, OK 73069
NWS TORNADO SURVEYS AND THE IMPACT ON THE NATIONAL TORNADO DATABASE
http://ams.confex.com/ams/annual2003/FSCAL...racts/55718.htm
http://ams.confex.com/ams/pdfview.cgi?username=55718
http://www.spc.noaa.gov/publications/mccar...thy/f-scale.pdf

Chris J. Peterson, University of Georgia, Athens, GA 30602.
FACTORS INFLUENCING TREEFALL RISK IN TORNADOES IN NATURAL FORESTS
http://ams.confex.com/ams/annual2003/FSCAL...racts/53292.htm
http://ams.confex.com/ams/pdfview.cgi?username=50675

Joseph T. Schaefer, NOAA/NWS/NCEP/SPC, Norman, OK 73069. and Richard L. Livingston
THE CONSISTENCY OF F-SCALE RATINGS
http://ams.confex.com/ams/annual2003/FSCAL...racts/52293.htm
http://ams.confex.com/ams/pdfview.cgi?username=52293

Thomas W. Schmidlin, Kent State University, Kent, OH 44242., Barbara O. Hammer, Paul S. King, and L. Scott Miller
WIND SPEEDS REQUIRED TO UPSET VEHICLES
http://ams.confex.com/ams/annual2003/FSCAL...racts/50675.htm
http://ams.confex.com/ams/pdfview.cgi?username=50675

Joshua Wurman, University of Oklahoma, Norman, OK 73019. and Curtis Alexander.
DOW RADAR MEASUREMENTS OF DOPPLER VELOCITIES IN TORNADOES AND COMPARISONS WITH DAMAGE
http://ams.confex.com/ams/annual2003/FSCAL...racts/58862.htm

Joshua Wurman, University of Oklahoma, Norman, OK 73019., Don Burgess, David C. Dowell, Yvette Richardson, Michael A. Magsig, and Curtis R. Alexander
RADAR MEASUREMENTS OF EXTREME WINDS IN TORNADOES AND COMPARISONS WITH OBSERVED DAMAGE
http://ams.confex.com/ams/annual2003/FSCAL...racts/58864.htm

Other Readings on F-5
Edwards, R. and D.G. Harmon, 1999:
Lubbock F-Scale Exercise on Spencer, SD Tornado Damage
http://www.spc.noaa.gov/misc/spencer/spenf_ex.htm

National Weather Service
A Guide to F-Scale Damage Assessment
http://meted.ucar.edu/resource/wcm/ftp/Fin...ssmentGuide.pdf

McCarthy, D.W., and J.T. Schaefer, 2004:
Tornado Trends over the Past 30 Years
http://www.spc.noaa.gov/publications/mccar...hy/tor30yrs.pdf

Storm Prediction Center
F5 Tornadoes of the United States: 1950-Present
http://www.spc.noaa.gov/faq/tornado/f5torns.html

Mike
http://mgweather.com
There are very few jobs in meteorology. I keep looking,

 

[Chris Lott]

I guess if they ever clock a wind speed of 320+ mph in a tornado they can just say, " We don't know what the F it was!" Sorry guys, I couldn't resist that one.

 

[Jeff Snyder]

One of the links Mike posted was a good read... In particular, http://meted.ucar.edu/resource/wcm/ftp/Fin...ssmentGuide.pdf brings up some issues regarding F4 vs. F5 ... Check it out... The discussion of the issues involved in the high-end of the F-scale starts about page 35 of the PDF, or page 28 on the document (page number on the bottom of the page), and ends around page 43 (PDF) or page 36 (on the bottom of the page).

 

[Chris Nuttall]

I guess I'm a little confused. There seems to be multiple debates going on here, so I don't really know what points we are specifically discussing. But, since I'm confused, let me throw this out.

It's my understanding that the Fujita scale is NOT defined by damage and/or wind speed. The F rating is ONLY defined by damage. Then, it is possible to INFER a range of possible wind speeds.