Assigning EF Scale Ratings Based on Radar Indicated Wind Speeds

[Ensō]

Wurman et al. 2013, which is the former. Sorry for the confusion. The other article is pretty interesting too, though, if you get a chance. If you look at the direct comparisons between radar and TIV, they're pretty similar (much more so than I ever would have guessed for sure). Ringing endorsements would obviously be nice, but we're dealing with the best, or probably least bad, of several choices in estimating tornado intensity. This is about as well as you're going to do, seeing as surveys are woefully inaccurate, particularly over open country. More obs are definitely necessary for rigorous comparisons, as I alluded to above. The available science supports the radar choice, in my opinion. You could reduce the radar obs by almost 50% (far far higher than any experimental results) in this case and still have EF5 winds. I believe this is much more defensible scientific evidence than that obtained by judging winds over an open field where there is essentially no way to judge wind speeds.

 

This is exactly why I don't understand eschewing radar data. I know we're all just going around in circles complaining about it, but when you consider how consistently inconsistent damage surveys are, it's hard to come up with a reason to pass on data that's almost certainly more representative of a tornado's true intensity (which is the whole idea anyway). As you said earlier, and as was the case with the first El Reno tornado, you could reduce the observed speeds by a massive factor and still be above EF5 threshold. The first El Reno obviously left extremely intense non-DI damage, but still.

[AtticaFanatica]

SMFR is a passive remote sensing instrument that makes several assumptions about the local environment to even get the measurement of winds in the first place (hurricane folks can comment more accurately). Weather radar is an active remote sensing instrument in which there's little to no argument that what's being measured, assuming adequate SNR, etc., are direct radial velocity measurements within the given resolution volume. The only issue that I think has scientific basis is the height issue, and the evidence so far points to that also being a relatively minor exercise. But let's, for the sake of argument, accept that premise. I don't see why one would be more comfortable with a damage survey done over open country, which has biases that everyone knows about and admits to, over actual scientific measurements.

I agree with this sentence. I'm just saying, at this point, I don't see the need to throw out either data or only choose to use one piece of data. I understand that obviously the NHC only has to analyze the intensity of 10-25 cyclones each season as compared to thousands of tornadoes, so they can afford to take months to compare all available data and come up with a best guess of intensity. That's not practical per se for forecast offices.... but the spirit behind it can still apply-- use all data, including building engineer surveys (like after Joplin), and weight some data more than others. I guess I don't see the point of, given that the research is still cutting edge on "the height issue," completely dismissing the work of the engineers either.

There's no doubt that, in a large majority of cases, the best proxy for tornado intensity is damage where there is something to damage. I'm guessing in such cases, the wind estimates are at least in the right neighborhood. In this particular case, there was very little to damage AND there were high quality radar obs near the ground. So there's unfortunately little that engineering could even tell us for this case, which I think is more than enough justification to use the radar data from both radars (RaXPol and DOW).

[Ground Scouring]

http://www.spc.noaa.gov/climo/torn/fatalmap.php

Hmm. So far, both OUN and the SPC elsewhere, such as on the F5 list, still list the tornado as an EF5. If a decision had truly been made, I would have expected the other pages to show the downgrade.

[Ensō]

Hmm. So far, both OUN and the SPC elsewhere, such as on the F5 list, still list the tornado as an EF5. If a decision had truly been made, I would have expected the other pages to show the downgrade.

 

It may have been something as simple as they haven't updated it until a final decision is made. I'm sure they'd have announced the decision in some form.

[AtticaFanatica]

OUN is not inclined to change it. It's probably just a matter of how much those above OUN want to force the issue.

[Ensō]

While we're on the topic, Attica, do you have any insight on why the Canton Lake tornado on 5/24/11 wasn't upgraded via radar? I read Wurman's paper and IIRC they (both DOW and NOXP) observed ~85 m/s velocities at something like 40 or 45m, which seems to suggest EF4, but the rating is based on the EF3 damage found near the lake.

[AtticaFanatica]

While we're on the topic, Attica, do you have any insight on why the Canton Lake tornado on 5/24/11 wasn't upgraded via radar? I read Wurman's paper and IIRC they (both DOW and NOXP) observed ~85 m/s velocities at something like 40 or 45m, which seems to suggest EF4, but the rating is based on the EF3 damage found near the lake.

I do not. It's strange since RaXPol data were used for the El Reno tornado rating that same day. Maybe the office was not aware of the ob at the time of the rating?

[OceanStWx]

There are no DIs for ground scouring or vegetative damage, so there is no such thing as evidence of EF5 winds using those fields, at least scientifically. All past evidence is anecdotal. The reason for that is ground scouring and vegetative damage likely are influenced by a whole host of factors, including vertical winds in the tornado, moisture content, wind residence time, the type of vegetation, dirt, asphalt, etc. and probably a lot of others.

It's one thing to compare actual measured velocities to DIs that are based on wind science engineering studies. It's another to compare them with a vague idea of what we perceive tornadoes of a certain intensity *should* do.

 

 

Speaking of vegetative damage, isn't the theory on debarking that debris is what is causing the damage and not the wind itself? It is really around EF3 that significant material is lofted from say a typical single family home. This is part of the reason why debarking of trees can neither prove nor disprove winds higher than EF3. In this situation, it's just continued negative feedback. No DIs to hit means no debris to potentially scour or debark.

 

Even when there are DIs to hit sometimes the surveys leave something to be desired. We had one a couple weeks ago where a brief tornado snapped or uprooted a small patch of pine trees. It was rated EF0 with winds 50-60 mph. No place on the EF scale does it say that snapped or uprooted softwood trees have expected winds 50-60 mph. Was it subjective because it was such a small damage swath, visually less impressive than the macroburst just to the west, etc?

[Buckeye05]

 I would also think that granulated material (dirt/sand/ect) may play a role to some extent as well, as there have also been many cases of total debarking/scouring taking place in vast, rural areas devoid of large structures or potential projectiles. (Harper, KS 2004 and Kellerville, TX 1995 are great examples of this).

 

When it comes to ground/grass scouring, there aren't any formal studies on it as far as I know (though I really would love to see one). I personally don't think that large debris impacts are what causes it. Larger pieces of debris such as 2x4s will leave noticeable and distinct pock-marks and gouges in the ground as they bounce and slice into the soil, rather than an even, consistent removal of grass and topsoil over a large swath. 

[Ensō]

 I would also think that granulated material (dirt/sand/ect) may play a role to some extent as well, as there have also been many cases of total debarking/scouring taking place in vast, rural areas devoid of large structures or potential projectiles. (Harper, KS 2004 and Kellerville, TX 1995 are great examples of this).

 

Probably the clearest example of this "sandblasting" type of effect is Jarrell. After it scoured out a massive amount of sandy soil it just completely sandblasted everything. There's one photo of a tree that's probably as stripped bare as you'll ever see, and it's immediately downstream of where the extreme scouring began. I think I have the photo somewhere, I'll look. And of course that's also where the complete destruction, sweeping away and granulation of homes, mangling of vehicles and farm equipment, etc.. took place. Picking up that much grainy debris has got to add an extraordinary amount of force to the wind. The same thing happened in the 2011 El Reno tornado, where there was extraordinary debarking/denuding of everything from large trees to small trees and even small shrubs just downstream of substantial scouring. There was also very heavy structural damage in that area (near Cactus 117), but I suspect the scoured dirt/sand was probably a big factor in the stripping action. For example:

 

[Buckeye05]

Yeah Jarrell is a perfect example of that kind of thing. The second picture illustrates it quite well, as you can see that even the tiniest twigs have been stripped of bark. As for the electrical cord, I have a hard time wrapping mind around that. I guess it could have been "whipped" into the tree at a high speed, for lack of a better term.

[AtticaFanatica]

Probably the clearest example of this "sandblasting" type of effect is Jarrell. After it scoured out a massive amount of sandy soil it just completely sandblasted everything. There's one photo of a tree that's probably as stripped bare as you'll ever see, and it's immediately downstream of where the extreme scouring began. I think I have the photo somewhere, I'll look. And of course that's also where the complete destruction, sweeping away and granulation of homes, mangling of vehicles and farm equipment, etc.. took place. Picking up that much grainy debris has got to add an extraordinary amount of force to the wind. The same thing happened in the 2011 El Reno tornado, where there was extraordinary debarking/denuding of everything from large trees to small trees and even small shrubs just downstream of substantial scouring. There was also very heavy structural damage in that area (near Cactus 117), but I suspect the scoured dirt/sand was probably a big factor in the stripping action. For example:

 

 

Yeah Jarrell is a perfect example of that kind of thing. The second picture illustrates it quite well, as you can see that even the tiniest twigs have been stripped of bark. As for the electrical cord, I have a hard time wrapping mind around that. I guess it could have been "whipped" into the tree at a high speed, for lack of a better term.

Jarrell is a tough tornado to gauge because of its slow movement, which likely influenced the damage it left behind in some manner not well understood.

[tornadotony]

 

 

Jarrell is a tough tornado to gauge because of its slow movement, which likely influenced the damage it left behind in some manner not well understood.

Have you heard anything about whether or not SRH is forcing the issue of changing the rating back?  I ask because I noticed SPC's fatal tornadoes log was updated today, and it updates the rating on the El Reno tornado to EF5 (had been EF3 up to the last update which was 3 July).

 

http://www.spc.noaa.gov/climo/torn/fatalmap.php

[AtticaFanatica]

Have you heard anything about whether or not SRH is forcing the issue of changing the rating back?  I ask because I noticed SPC's fatal tornadoes log was updated today, and it updates the rating on the El Reno tornado to EF5 (had been EF3 up to the last update which was 3 July).

 

http://www.spc.noaa.gov/climo/torn/fatalmap.php

Nice catch, but no I haven't heard anything. Last I heard, nobody at OUN was interested in changing much. I have heard that at least some of those that were skeptical of the radar data became much less skeptical after viewing the data. In other words, I think there's a lot more evidence of EF-5 winds than the one measurement that was released in the statement.

[tornadotony]

Nice catch, but no I haven't heard anything. Last I heard, nobody at OUN was interested in changing much. I have heard that at least some of those that were skeptical of the radar data became much less skeptical after viewing the data. In other words, I think there's a lot more evidence of EF-5 winds than the one measurement that was released in the statement.

I'm not real familiar with the damage associated with El Reno other than the vehicles destroyed/fatalities.  Were there any non-traditional DIs (ground scouring, crop damage) that maybe build support for keeping the rating?  You know my thoughts on this, but I was just wondering since such a forceful push seemed to be coming from up-top to change it back w/o damage evidence.

[AtticaFanatica]

I'm not real familiar with the damage associated with El Reno other than the vehicles destroyed/fatalities.  Were there any non-traditional DIs (ground scouring, crop damage) that maybe build support for keeping the rating?  You know my thoughts on this, but I was just wondering since such a forceful push seemed to be coming from up-top to change it back w/o damage evidence.

My understanding is no, there was not. This is probably the reason there was so much hand-wringing at calling it an EF-5. Doing so really is based on the radar data and little else.

[JoMo]

I didn't know where to stick this and didn't really want to make a new thread about it.

 

Is this accurate or just 'lazy science'? (it does make sense that higher elevations or with the tornado moving uphill, there would be more damage as the winds are stronger the higher you go up... but I doubt the conclusion that they tend to want to go to higher elevations)

 

New Study Shows Tornadoes Tend Toward Higher Elevations and Cause Greater Damage Moving Uphill

 

http://newswire.uark.edu/articles/21786/new-study-shows-tornadoes-tend-toward-higher-elevations-and-cause-greater-damage-moving-uphill

[AtticaFanatica]

I didn't know where to stick this and didn't really want to make a new thread about it.

 

Is this accurate or just 'lazy science'? (it does make sense that higher elevations or with the tornado moving uphill, there would be more damage as the winds are stronger the higher you go up... but I doubt the conclusion that they tend to want to go to higher elevations)

 

New Study Shows Tornadoes Tend Toward Higher Elevations and Cause Greater Damage Moving Uphill

 

http://newswire.uark.edu/articles/21786/new-study-shows-tornadoes-tend-toward-higher-elevations-and-cause-greater-damage-moving-uphill

1. I'd wait until (if) it's published in peer review. Until then, it's very difficult to evaluate.

2. That being said, these types of studies are often prone to causal problems. There are a great many factors that influence how a tornado travels and its strength. To claim such relationships with terrain, a variety of other dynamical effects need to be accounted for and controlled for in the study. If not, then a pretty large sample of data is needed to make generalizations.

3. That is not to say that terrain does not influence tornado strength or translational direction. I'd be surprised if it doesn't play a role. The best evidence I've seen yet that it does is the LES work done by Dave Lewellen (https://ams.confex.com/ams/26SLS/webprogram/Manuscript/Paper211460/SLS12_pap_submit.pdf)*. The nice part of the LES approach is that the storm-scale dynamical effects (except for turbulence) are accounted for and the effects of terrain are isolated. What he found is that intensity and direction were affected by terrain, but in very complicated ways due to a myriad of competing effects:

The simulated vortices are sometimes deflected by slopes, sometimes attracted to slopes, sometimes stalled for a time over topographic features, sometimes detached from the surface. The vortices sometimes weaken, sometimes strengthen, heading either up or down slopes, often exhibiting large changes in corner-flow structure during their evolution.

How the vortex was affected depended on its initial size, strength, and movement as well as the exact configuration of the topography. So, I tend to believe this is a really complicated problem that is difficult to generalize with two cases, which makes the article statement "The findings likely apply to all tornadoes" a little disconcerting.

It's a fascinating topic, though.

*Note that the Lewellen work is still ongoing and also has not been published yet.

[tornadotony]

1. I'd wait until (if) it's published in peer review. Until then, it's very difficult to evaluate.

2. That being said, these types of studies are often prone to causal problems. There are a great many factors that influence how a tornado travels and its strength. To claim such relationships with terrain, a variety of other dynamical effects need to be accounted for and controlled for in the study. If not, then a pretty large sample of data is needed to make generalizations.

3. That is not to say that terrain does not influence tornado strength or translational direction. I'd be surprised if it doesn't play a role. The best evidence I've seen yet that it does is the LES work done by Dave Lewellen (https://ams.confex.com/ams/26SLS/webprogram/Manuscript/Paper211460/SLS12_pap_submit.pdf)*. The nice part of the LES approach is that the storm-scale dynamical effects (except for turbulence) are accounted for and the effects of terrain are isolated. What he found is that intensity and direction were affected by terrain, but in very complicated ways due to a myriad of competing effects:

How the vortex was affected depended on its initial size, strength, and movement as well as the exact configuration of the topography. So, I tend to believe this is a really complicated problem that is difficult to generalize with two cases, which makes the article statement "The findings likely apply to all tornadoes" a little disconcerting.

It's a fascinating topic, though.

*Note that the Lewellen work is still ongoing and also has not been published yet.

It's more than disconcerting...it's wrong.  We have had tornadoes here that unequivocally show this to not be the case, my thesis work being one of them.

[AtticaFanatica]

Downgraded to EF3.

The climatology is safe.

[tornadotony]

Downgraded to EF3. The climatology is safe.

Yippie! Do we get a new set of blinders to celebrate the rescue?

[Chicago Storm]

Rozel should be downgraded then too.

Might as well stay consistent.

[thewxmann]

What about Rozel, Bennington, and SW Wichita (all of which were also upgraded based on Doppler)?

[andyhb]

Some serious lols on this whole thing.

[Natester]

What about Rozel, Bennington, and SW Wichita (all of which were also upgraded based on Doppler)?

 

Don't forget the El Reno EF5 back on May 24, 2011. >_>

 

And while they're at it, how about they rate any tornado that hits no structure as an EF0.

[andyhb]

Don't forget the El Reno EF5 back on May 24, 2011. >_>

 

And while they're at it, how about they rate any tornado that hits no structure as an EF0.

 

That would be a complete crock if they downgraded that one, it likely should've been an EF5 without radar evidence given the damage around the Cactus Rig 117 site.

[Natester]

I'm calling it.  The El Reno EF5 tornado on May 24, 2011 will be downgraded to an EF4.  If they don't downgrade it, I'm eating my shoe.

[f2tornado]

The NWS might as well just make a new EF3+ category and drop the EF4 and EF5. There isn't a hole heck of a lot of difference between 4 and 5 anyway. The original proposal for the EF-scale suggested the use of radar data where available. They obviously decided not to do that now. Now we're back to the what are we measuring debate. Is it damage or is it wind? It's wind, IMO, based on the damage, With that in mind, if you already have the wind measurement then why not use it?

[Stebo]

I think this whole ignoring of radar data when available is a terrible standard to go by. Especially when it is very strong data from multiple sources in this case.

[thewxmann]

Did they ever determine whether the Doppler-indicate EF5 wind swath passed over structures?

 

Maybe the standard should be that Doppler can only shift the EF rating by one level.