Interesting Comparison: Beaufort, Torro, and Fujita Scales

This article:
http://www.torro.org.uk/TORRO/ECSS_Slide_S...ide%20show.html

Is a Powerpoint slideshow explaining the origin of the F scale with it's roots in the Beaufort scale along with comparisions to the Torro scale. It tries to make an argument that the International Torro scale is a better scale and we'd be better off with it than the F scale, but I'm not sure it carries it.

It proposes a unified TF scale for 'Tornado Force'.

Not sure I agree that TF or T or Beaufort would be better than the F-Scale. I agree it would be more standardized to international usage and provide more data points covering the 98% F0-F3 tornadoes that we experience in the US. Would this truly be of benefit though? What does standardization buy us?

I think it is interesting that it points out that each F-scale number is a range around the average midpoint value so an F5 really ranges from an F5.0 to an F5.99. This makes that elusive F6 just F.01 away!
 
Speaking of the Fujita scale, wasn't the NWS working on an upgraded version of the Fujiat scale? I think that I've seen this somewhere?
 
I'm not going to claim to be real educated on this subject or on the details with any of the scales. I do know that this argument has been around for a long time, and scientists in the international community have been pushing the U.S. to change.

Personally, I'm not sure I buy it. Okay, so the T scale was created to match more closely and correspond with the Beaufort scale.

I find a fault in this argument, which I would be more than happy to have explained to me. Okay, an F0 tornado is rated as such because is produces no damage that can be found. The Harper, TX, storm in the presentation is rated a "T6 or TF6" and a F0 by the NWS. How do you know that this is the proper rating?

I don't understand how a rating can be applied if no damage can be found whether it hits a structure or not. Currently, we have no reliable way to regularly measure the surface winds of a tornado. Thus, the only thing we can estimate a tornado's intensity is on the damage it produces.

The F scale is a damage scale. Nothing more, nothing less. Yes, it could be used to estimate winds inside a tornado. But nothing more than that.

I do not know very much about conducting damage surveys. Maybe our techniques are good enough to make better determination of wind speeds. I think this is why the NWS was looking to revise the Fujita scale.[/b]
 
I find a fault in this argument, which I would be more than happy to have explained to me. Okay, an F0 tornado is rated as such because is produces no damage that can be found. The Harper, TX, storm in the presentation is rated a "T6 or TF6" and a F0 by the NWS. How do you know that this is the proper rating?

I don't understand how a rating can be applied if no damage can be found whether it hits a structure or not. Currently, we have no reliable way to regularly measure the surface winds of a tornado. Thus, the only thing we can estimate a tornado's intensity is on the damage it produces.

In the slideshow, it mentions that Doppler Radar estimates are one factor in determining the "T scale" rating. If this is true, it goes AGAINST radar meteorology principles. It is WELL KNOWN AND DOCUMENTED that we are not seeing the ground-level circulation on radar....so there is no real way of accurately using Doppler Radar for ground-based wind speeds from within the tornadic ground-level circulation. Also.......how many countless times have there been Armageddon-type mesocyclones on Doppler.....but not even a weak tornado touch down. It just doesn't make sense to use radar to try to assign a rating to a tornado, especially when damage is also a factor for the same scale.....which is probably how they rated that TX tornado.
 
In the slideshow, it mentions that Doppler Radar estimates are one factor in determining the "T scale" rating. If this is true, it goes AGAINST radar meteorology principles. It is WELL KNOWN AND DOCUMENTED that we are not seeing the ground-level circulation on radar....so there is no real way of accurately using Doppler Radar for ground-based wind speeds from within the tornadic ground-level circulation. Also.......how many countless times have there been Armageddon-type mesocyclones on Doppler.....but not even a weak tornado touch down. It just doesn't make sense to use radar to try to assign a rating to a tornado, especially when damage is also a factor for the same scale.....which is probably how they rated that TX tornado.

Right. That is the interesting part of the slideshow as it mentions the Torro scale is damage and also based on wind measurement. This is something that the F-scale isn't. In fact it is a totally different animal with who knows what implications. Perhaps Torro would use a local DOW vehicle to measure the winds. Then again there aren't any DOW's in Europe.

How many times have we had it hammered into our heads that F scale is a damage scale and not a wind speed? When you start thinking about this it could make your head spin....(like a tornado) - LOL.
 
I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes. If a tornado forms but doesn't have any substanial structures to destroy and gets rated F1 while the DOW measures near surface windspeeds of F3 force I think they should be able to take that into account. Of course since the F scale is damage based it would have to be changed/compromised in order to do so.
 
Speaking of the Fujita scale, wasn't the NWS working on an upgraded version of the Fujiat scale? I think that I've seen this somewhere?

There is a movement called the Enhanced Fujita Scale... There's a load of information on the EF scale (and a good report on it) at http://www.wind.ttu.edu/F_Scale/default.htm ... One of the primary aspects of the project is focused on accurately assessing the damage vs. wind speed relationship for a slew of different structures (trees, large warehouses, schools, antenna towers, etc.). It's a very interesting read, IMO.
 
I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes.

That's a good idea in theory, but we all know how hard it is to storm chase. I don't think we could get a DOW on every single tornadic storm, even though I wish we could. Imagine how much more we could learn both in real-time and in later analysis. But I digress.... Even the DOWs succomb to the limitation of Doppler radar. Their measurements, although closer to the ground, are still not necessarily at the surface.

A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.
 
Originally posted by Chris Nuttall
A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.

Would that mean that the Bridge Creek/Moore tornado reached F6? Because if the winds mesured (318mph) were not at ground level, that means that AT ground level the winds were higher, am I right on this?
 
Originally posted by Gaetan Cormier

Would that mean that the Bridge Creek/Moore tornado reached F6? Because if the winds mesured (318mph) were not at ground level, that means that AT ground level the winds were higher, am I right on this?

No. Friction plays a large role on near-surface winds. So, the winds at the surface were likely less than those measured... FWIW, in this case, Dr. Wurman has seemed to have restated the max wind measurement, as he mentioned this past spring in on online chat. I'm don't remember exactly what he said, but it was something like "301mph +/- 17mph" or somehting like that.

Even IF the DOWs had measured 320mph, this DOES NOT mean that the tornado would have been assigned an F6 rating! The F-scale is a damage scale, so a wind measurement should not affect F-scale rating. That said, I'm not sure if a direct wind measurement wouldn't be used in a tornado rating assessment. I mean, I think there's a good chance that, for example, a tornado that produces F0 damage but for which there is an anemometer measurement of 130mph winds IN the tornado would be rated not at F0. Of course, the odds of an anemometer sampling a tornado is pretty small, even when mobile (TOTO project).
 
Originally posted by Chris Nuttall+--><div class='quotetop'>QUOTE(Chris Nuttall)</div>
<!--QuoteBegin-Scott Olson
I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes.

That's a good idea in theory, but we all know how hard it is to storm chase. I don't think we could get a DOW on every single tornadic storm, even though I wish we could. Imagine how much more we could learn both in real-time and in later analysis. But I digress.... Even the DOWs succomb to the limitation of Doppler radar. Their measurements, although closer to the ground, are still not necessarily at the surface.

A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.[/b]

Just to clarify, I didn't mean to actual build a fleet of DOWS and have them chase after tornadoes. I just meant for tornadoes that the DOW scans and when it contradicts with the damage assessment by a good degree. I think it is more accurate than a scale that is built on damage assessment. Verification of ground speeds using Samaras probes will be used and then they can come up with a formula to bring the normal low-level scan mode to represent a best guess ground speed.
 
Thanks Jeff for clarifying this for me! It's much clearer now. I always tought that the winds at surface were higher than higher up, I did not think about friction!

Thanks again
 
Originally posted by Scott Olson+--><div class='quotetop'>QUOTE(Scott Olson)</div>
Originally posted by Chris Nuttall@
<!--QuoteBegin-Scott Olson

I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes.


That's a good idea in theory, but we all know how hard it is to storm chase. I don't think we could get a DOW on every single tornadic storm, even though I wish we could. Imagine how much more we could learn both in real-time and in later analysis. But I digress.... Even the DOWs succomb to the limitation of Doppler radar. Their measurements, although closer to the ground, are still not necessarily at the surface.

A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.

Just to clarify, I didn't mean to actual build a fleet of DOWS and have them chase after tornadoes. I just meant for tornadoes that the DOW scans and when it contradicts with the damage assessment by a good degree. I think it is more accurate than a scale that is built on damage assessment. Verification of ground speeds using Samaras probes will be used and then they can come up with a formula to bring the normal low-level scan mode to represent a best guess ground speed.[/b]

I think consistency is desired for any scale... What to do if the damage assessment indicates higher wind speeds than a DOW measurement? What do you do if there is a small-scale eddy not sampled by a radar that has winds >30mph above the "ambient" tornado winds. Do you take radar-sampled winds when the tornado is in a field and does no damage? That means that a tornado may be given an F3 rating when there is no damage to support it. Overall, this may not be too bad, but it leads to inconsistency that can cause disruptions with climo IMO
 
Originally posted by Scott Olson
Just to clarify, I didn't mean to actual build a fleet of DOWS and have them chase after tornadoes. I just meant for tornadoes that the DOW scans and when it contradicts with the damage assessment by a good degree. I think it is more accurate than a scale that is built on damage assessment. Verification of ground speeds using Samaras probes will be used and then they can come up with a formula to bring the normal low-level scan mode to represent a best guess ground speed.

Scott, I know that's not what you meant. My bad. I just phrased things wrong. I tried to go back and edit my post, but it wouldn't let me...weird.

I've read in several places that it is believed that the in the strongest F5 tornadoes, particularly multi-vortex tornadoes, that F6 damage has likely been produced. However, with the debris leftover and the fact that an F5 pretty much wipes out everything, F6 damage is not descernible from F5.
 
Originally posted by Chris Nuttall
The F scale is a damage scale. Nothing more, nothing less. Yes, it could be used to estimate winds inside a tornado. But nothing more than that.

I do not know very much about conducting damage surveys. Maybe our techniques are good enough to make better determination of wind speeds. I think this is why the NWS was looking to revise the Fujita scale.
[/b]

Ok, Fujita devised his scale on the basis of wind speed. The F-scale is really just a mathematical equation that connects the Beaufort scale to the Mach scale with an F12 being Mach 1.

fscale.jpg


Since we usually arn't able to directly measure wind speed within a tornado we are forced to infer it through observed damage. So yes, the F-scale is being utilized as a damage scale but it was mathematically devised as a wind speed scale.
 
Originally posted by Chris Nuttall
I've read in several places that it is believed that the in the strongest F5 tornadoes, particularly multi-vortex tornadoes, that F6 damage has likely been produced. However, with the debris leftover and the fact that an F5 pretty much wipes out everything, F6 damage is not descernible from F5.

I've heard and read that from different sources as well. IMO though I think you could potentially determine F6 if there was a structure strong enough for F6 that could be measured afterwards. This is just a guess of course. F scale goes all the way up to Mach 1 at F12 I believe.

I would like to add the footnote that (from what I understand) it is true that winds above ground are typically higher than those at ground level due to frictional effects however obstacles (such as overpasses) can focus tornadic winds and using the Bournoulli Effect accelerate winds to higher speeds perhaps matching or surpassing those above ground level.
 
I will chip in briefly here.. While the F scale is adequate for rating big tanking USA tornados.. The finer resolution of the T-Scale is more suited for world wide tornadoes as almost all of them are less than F2.

While I don’t want to get in brawled in a F/T scale debate (perhaps I already have?) we need to look at a scale that can be applied to tornados world wide.

Over all, and not wishing to stir up a flame war. How long is Fahrenheit going to be used for USA surface Obs when the rest of the world uses Celsius. An international scale is required – an one that fits all locations. So are we looking at a change here (Also might be time to go to M/S wind speed!) – International Athletics already do it during there running events.

BTW I have to declare that I am a member of TORRO and they are the body that devised the T- Scale back in Early 1970’s so I guess that I am some what biased on this subject but still I keep a very open mind on the way forward).

Any way great debate. :D
 
Originally posted by Jeff Snyder+--><div class='quotetop'>QUOTE(Jeff Snyder)</div>
Originally posted by Scott Olson+--><div class='quotetop'>QUOTE(Scott Olson)
<!--QuoteBegin-Chris Nuttall
@
<!--QuoteBegin-Scott Olson

I would like to see the DOW measurements be taken into account as part of our scale to rate tornadoes.


That's a good idea in theory, but we all know how hard it is to storm chase. I don't think we could get a DOW on every single tornadic storm, even though I wish we could. Imagine how much more we could learn both in real-time and in later analysis. But I digress.... Even the DOWs succomb to the limitation of Doppler radar. Their measurements, although closer to the ground, are still not necessarily at the surface.

A perfect example is the 5/3/1999 measurement of 318mph in the Bridge Creek/Moore tornado. Contrary to popular belief among the public, that wind speed was not at ground level.

Just to clarify, I didn't mean to actual build a fleet of DOWS and have them chase after tornadoes. I just meant for tornadoes that the DOW scans and when it contradicts with the damage assessment by a good degree. I think it is more accurate than a scale that is built on damage assessment. Verification of ground speeds using Samaras probes will be used and then they can come up with a formula to bring the normal low-level scan mode to represent a best guess ground speed.[/b]

I think consistency is desired for any scale... What to do if the damage assessment indicates higher wind speeds than a DOW measurement? What do you do if there is a small-scale eddy not sampled by a radar that has winds >30mph above the "ambient" tornado winds. Do you take radar-sampled winds when the tornado is in a field and does no damage? That means that a tornado may be given an F3 rating when there is no damage to support it. Overall, this may not be too bad, but it leads to inconsistency that can cause disruptions with climo IMO[/b][/quote]

I would tend to say to go with the higher of the two. With a greater emphasis on the DOW measurement when less reliable damage indicators are present. The idea I was presenting actually was to take both into account not to nearly throw away the damage assessment and base it only on the DOW. I definately see your point though regarding inconsistency as DOW assisted ratings would likely skew the ratings system since it is not across the board on all tornadoes. But the Fujita scale doesn't seem terribly consistent to me, in some cases there isn't resources to have lengthy investigations into the quality/building codes of a structure and If not done throughly one could overlook details that would greatly affect the rating.Dr. Rasmussen presented an example of this in one of his papers. Perhaps based on the resources we have the way it is now is the best we can hope to do.

But with the DOW's and a much better understanding of damage/wind speed coreleation I think the new scale could be valueable. In the least I would hope that Doppler measurements could be used as a indication. For instance, if I go out and do a damage survey in an open field and can only find indicated damage to support F1 but the DOW measured a 50m windspeed that when computed to 10m supports a F3 windspeed range. It seems just as silly to me to ignore the DOW measurements as it would be to ignore the fact that their is only F1 damage.
 
Originally posted by Stuart Robinson
Over all, and not wishing to stir up a flame war. How long is Fahrenheit going to be used for USA surface Obs when the rest of the world uses Celsius.

Probably the same time that the U.S. switches to S.I. units. There's been a movement ongoing for sometime. As easier as it would be, I just don't see it realistically happening. It may be the best thing to do scientifically, but until there is a real pressing need, it probably won't happen.

A lot of people have that "...when you pry it from my cold, dead fingers" attitude about it I think. :roll:
 
Chris I agree - these days I also have become quite good at mentally converting F to C or MPH to Knots or M/S - so much so that it is no longer an issue for me - but still a pain.

However we are going off the point here...

As far a tornado scale rating goes - then I believe that the time is right to go to a F point scale or the T scale - I already see reports written of a weak F2 or a strong F3 so already the scale can be sub divided.

Over all my gripe is that there is some difference between a weak F2 and a strong F2 - perhaps F2.25 or F2.75 that would be T3 or T4. But and the major point is world wide the F scale currently is too course for tornado rating.

Way off topic here .. Does anyone care to guess the number of tornadoes world wide that we gat a year?? 3000 perhaps?? I really dont know
 
Back
Top