F6 Tornadoes-What's the Closest We've Come?

[Shane Adams]

Yeah, DOW did measure 318 mph winds, I was going to bring that up, however the winds were measured higher up in altitude, so the surface winds were likely less than this.

Andrew Pritchard

Interestingly though, one particular instance that was used as an example of "evidence" that F-scale winds are too high was this same day, where the DOWs measured windspeeds of only 200mph in the same areas where survey teams labled F5 damage.

So why is a 318mph measurement taken with a grain (and widely, generally scoffed at in the science world) while the lesser, more "tame" 200mph measurement is used as evidence against the current suggested speeds associated with the F-scale? Are DOW measurements taken seriously or not? Depends :wink:

It's all politics. Some time back, scientists decided the winds were too high, so now every "finding" will point to exactly that.

 

[Jeff Snyder]

One of the most important things to remember in considering the 318mph DOW measurement is elevation! Since that radar was scanning at an elevation >0 (it was ~0.5degrees I think), the farther from the radar one gets, the higher the radar beam is (relative to the ground). Because of this, the DOWs measured the wind (by radar) a couple of hundred feet above the surface. Since friction reduces surface wind speeds, the actual wind at the surface was likely a little less than 318. Whatever the case, it was still in the F5 range by wind estimation, which doesn't officially matter anyways...

From a FAQ on the NWS OUN website:

"Q: Was the Bridge Creek/OKC area tornado on May 3, 1999, rated F6?

A: No. The tornado has been rated F5 (minimal F5, in fact), and will not be "upgraded" to F6. There was some speculation in the media of an F6 rating after "Doppler on Wheels" (DOW) researchers from the University of Oklahoma announced that their radar measured 318-mph winds in the tornado while it was near Bridge Creek. However, the jump in reasoning to rating this tornado F6 can not be made, for many reasons:

F-scale ratings are assigned based on the severity of the damage caused, *not* on wind speed. Although some of the damage was incredible (as it is with any F5 tornado), the most severe damage from the May 3 tornado was comparable to, but not worse than, other documented F5 tornadoes.

Wind speeds used in the F scale have not been scientifically calibrated to the severity of damage that defines each F scale level. They are, essentially, only estimates.

Even if the F-scale wind speed ranges were reliable estimates, the DOW measurement of 318 mph is still in the F5 range (261-318 mph) as defined by Dr. Fujita.

The data obtained by the DOW team are still in the process of being reviewed scientifically, and so the validity of the 318-mph wind measurement is still open to some question at this point. Early results of this review process suggest that the maximum speed actually may be less than 318 mph (although it likely will remain above 300 mph).

The 318-mph wind measurement was obtained at a height of about 50 to 100 meters (160 to 320 feet) above the ground. Since winds typically decrease as you get closer to the ground, wind speeds at the ground (where the damage was done) would have been less.

In reality, there is no such thing as an F6 tornado. When Dr. Fujita developed the F scale, he created a scale that ranges from F0 to F12, with estimated F12 winds up to mach 1 (the speed of sound). But he added that "tornadoes are not expected to reach F6 wind speeds." This leaves only the F0 to F5 range as the actual tornado F scale. For a tornado to be given an unprecedented F6 rating, it would have to produce damage more severe than has ever been observed. As stated above, there was nothing unusual or unprecedented in the damage from the May 3 tornado as compared with other F5 tornadoes in the past."

---> http://www.srh.noaa.gov/oun/storms/1999050...3/may3faqs.html

{I'm posting this in an extended form since it was public information, available to the general public on a government website. As such, there should be no "3rd Party" issues to deal with here}

 

[Glen Romine]

Shane,

I'm actually not aware of a DOW velocity to damage survey having been done for the May 3 case (do you have a link?) - though one was done for the Spencer, SD 1998 storm. Since the measurements are taken well off the ground, with a very short in time sampling interval, taking into account much of the signal is from flying debris and vertical alignment issues - a lot of modification is required to infer what wind speeds might be at ground level. Nevertheless, the Spencer study actually had relatively good agreement between the 'measured' and observed damage - at least by scientist standards.

Yes, there is a growing audience of engineers and meteorologists that stress the difficulty in damage assessment - as the structural integrity of one home within a community is only as good as the weakest home - as that home becomes flying debris that impacts the neighbor and weakens the structure. If the intensity of the May 3 tornado as it moved through Moore had been in an area with fewer structures - there may have been fewer missles, and perhaps the level of damage inflicted would have been less. It is a very difficult problem to estimate the winds that will cause a particular structure to fail - but even harder to know how it will hold up to being bombarded with debris at the same time. Home construction differences opens a real can of worms regarding the home's vulnerabilities - as well as the orientation of the home to the strongest winds - duration of strongest winds - rate of wind acceleration - did the winds peak once or twice, if twice the difference in angle, etc.... So yes - lots of concerns about the current rating system - but I think it is shy of a conspiracy theory. There is, however, a lot of pressure on assessment teams to rate damage 'higher' when personal injury/loss enters the picture - so maybe some politics there.

Glen

 

[Kiel Ortega]

I think there is too much focus on the wrong part of the story here. Who cares about the scale? The scale is relative, because when damage assesments are done, how buildings were built comes into play. It's pretty relative: "F5" damage to a house built in 1910 would probably be "F3" or "F4" damage to a house today.

On a separate note, I don't see why people are always in a fuss to get a rating on the tornado (and try to get the highest rating possbile at that). Wake up, the thing destroyed property and possibly injured or killed people...who cares what the rating is then?

 

[nickgrillo]

I think people want to see the Moore, OK be rated higher than F5 since it has happened in such a modern age... with such better equipment.

Like that story said above, their is NOTHING different about the 5-3-99 tornado from all other "strong" F5 tornadoes. But, if it happened 75 years ago... probley 200+ people would have been killed.

Doesn't everybody agree that it will almost be impossible for a tornado to take 100+ lives in such a modern age? I forgot the total count... how many fatalities came from the 5-3-99 tornado?

 

[Jeff Snyder]

Doesn't everybody agree that it will almost be impossible for a tornado to take 100+ lives in such a modern age? I forgot the total count... how many fatalities came from the 5-3-99 tornado?

Absolutely not! I think it would be quite easy to kill, oh, 2000 folks. Put the Bridgecreek / Moore OK F5 through the heart of Dallas/Fort Worth Metroplex... More even if it were during rush hour... I think a signficant tornado hitting any urban, downtown area could potentially cause a ton of fatalities. Of course, this isn't a guarentee, seeing how Moore and southern OKC survived an F4 last year without a single death! However, it's generally agreed that a signficant tornado, through downtown D/FW, and it's a bad bad thing...

 

[nickgrillo]

Even with all the warning time for most significant tornadoes?

DTX did a little graph showing what if a F5 went through modern-day Detroit...



If that were to happen... a F5 would destroy my house! :shock:

 

[Robert Dewey]

Even with all the warning time for most significant tornadoes?

DTX did a little graph showing what if a F5 went through modern-day Detroit...



If that were to happen... a F5 would destroy my house! :shock:

Yep, thats the 1953 Flint F5 (the last deadliest tornado in US history), superimposed over Detroit.

 

[Jamie Lahowetz]

I think the amount of tornado related deaths is determined by the area the tornado strikes. If a tornado were to strike Metro Dallas during rush hour, I dont believe those people would just sit in there cars and watch the twister barrel straight through the city. They will find shelter cause i believe in a way, we here in the cenral and southern plains have been "conditioned" to know what to do during a tornado warning. We know that we must seek shelter. The public is being better informed about weather and information moves much quicker allowing for a faster response. Something must be working since the amounts of deaths are declining (http://www.nssl.noaa.gov/users/brooks/publ...ml/deathtrivia/). But when we look at the southeast states particularly we see a less prepared community (http://www.disasterrelief.org/Disasters/02...22tornadostudy/) and a larger chance for massive tornado related deaths. I have also heard of a diference in how the public takes the appearance of a tornado in the southeast states, but have nothing to cite on it (as stated by my Professor). Of coarse i may be giving to much credit.
I do believe an F6 could occur but , since the Fujita Scale is a damage scale and the suggested wind speeds should not be set in stone, after an F5 there really isnt anything left for the tornado to damage I dont believe we can ever officially classify a tornado as an F6.

 

[Jeff Snyder]

Even with all the warning time for most significant tornadoes?

If that were to happen... a F5 would destroy my house! :shock:

Yes, simply because there is no physical, realistic way to tell a couple million people to get below ground. This would be especially catastrophic if it occurred near rush-hour, when stopped-traffic would be sitting duck for a signficant tornado... For those interested, the NCTCOG did a rather extensive modeling study of what would happen should the Moore F5 trek through the DFW area... You can view it at http://www.nctcog.org/weather/study/index.asp ...

 

[rdale]

"I've been asking that question for years"

...and it's been answered... There is not a F6 classification for tornadoes.

From Dr Fujita's memoirs:

===
2.4 The Fujita Tornado Scale

In scaling the intensity of tornadoes, I connected the upper end of the Beaufort Scale (B12) or 73mph with the lower end of Mach Number (M1) or 738mph into 12 non-linear steps. Taking into consideration the recorded peak winds and corresponding damage, I assume that tornado windspeeds can be expressed by the 6-point scale, F0 to F5. The Fujita Tornado Scale was thus devised, Fujita (1971b.)

===

1971b: Proposed characterization of tornadoes and hurricanes by area and intensity. SMRP Res. Paper 91, Univ of Chicago, 42pp #91

I have boxes of his papers that his son gave me - I'll see if the original is in there and get in scanned.

- Rob

 

[Joe Zemek]

Southern tornado peril

Also, IIRC the South experiences tornadoes a) much earlier in the year, before the severe wx public awareness machine cranks up, and B) more often overnight, when almost everyone is a sleeping duck. The idea of a strong, maybe fast moving urban tornado at 3am is pretty sobering, even with the best efforts of local police/fire to rouse the populace.

 

[Jared Mysko]

Clearly as technology develops, and chasers become more sophisticated, we will have to update the ratings system. Personally, I think I should where a suit and tie today and I will be rating our storms on the "Cowasaki Scale"

mo= Kicks some dust up, disorganised funnel action
moo= decent looking funnel, kicking lots of dust and maybe some grass
mooo= clearly a tornado, breaking up some trees and bushes
moooo= at this point cows begin to get concerned and start to move to the other end of the field
mooooo= this would be a huge tornado that could really break a lot of stuff and knocks the cows over
moooooo= this one makes the cows airborne
mooooooo= I heard the natives talk about this one, you only see it once.

That's the Canadian Cowasaki Scale for rating tornadoes,

Jared Mysko

 

[Michael P. Morris]

The Fujita scale is all well and good, but it is a little too subjective. I prefer the M-Scale as defined below:

http://operations.ocs.ou.edu/~nebain/weath...mor/moojita.htm

 

[Charles Kuster]

F6

With the Fujita Scale it would be very hard to have an F6. An F5 causes such massive damage that it would be almost impossible to prove that there was a short section of F6 damage in between all of the F5 damage. Maybe in the future we will get new technology that can measure winds of a tornado at the surface. Then if it measures winds over 318mph maybe the tornado would be classified as an F6. As of now the closest we have come to an F6 is the strong F5's. The May 3, 1999 Oklahoma City tornado or the Tri State tornado, or the Andover tornado could have come close. :?: