2011-05-24 El Reno OK EF-5

[Mike Smith]

When Ted created the scale that bears his name, it was actually a dual scale that allowed for both ratings by damage (F) and wind (f). Because there were no good ways to measure the maximum winds (like DOWs), the damage part became standard.

Personally, I think the EF scale is a bust which is why I usually refer back to Ted's original scale. The maximum wind speeds in the EF scale are misleadingly low as indicated, to cite one example, here: http://www2.ljworld.com/news/2011/jun/03/department-homeland-security-strengthen-national-b/

 

[Jeff Duda]

I've also come to realize some inconsistencies in the EF-scale lately. I try to think of the scale as a relationship between an independent variable (damage, primarily, although the wind speed part could also be considered) and a dependent variable (EF-scale rating). The problem I see is that the rating is based off an estimated wind speed which is based off of a DOD to a DI. Thus, when someone evaluates tornado damage, they obtain an independent variable (a DOD to a DI) and use basic piecewise defined functions (i.e., the wind speed estimates based on the DOD for a given DI) to get a wind speed estimate. THEN that wind speed estimate determines EF-scale rating. While I understand the curiosity with estimating horizontal wind speeds in tornadoes (let's not even go into the idea that vertical accelerations near ground level may also create damage), why use the estimate to get an EF-scale rating? Why not just bypass it and go straight to the rating? Because now you have two outputs from one input running side-by-side, but one of the outputs can change with time according to the latest and greatest in technological developments (i.e., the wind speed value associated with a given EF-scale rating). This seems overly complicated and is leading to what others are calling a contamination of the database of tornadoes.

I liked the EF-scale when I first heard of it. However, it seems to me that the scale has caused just as many new problems as it has solved old problems. Allowing radar wind speed estimates to affect the tornado rating is simply not consistent with what I thought the EF-scale was supposed to be. I could be wrong, but if I am I would really like someone to explain it. Some previous posts have begun that explanation, but again, it just seems too convenient to me. It's like the EF-scale should use this rule: "we'll use whatever measurements or estimates we have to determine an EF-scale rating, whether they're based on damage, in-situ observed wind, or remotely sensed observed wind."

 

[Jeff Snyder]

I think most meteorologists use the EF-scale primarily to obtain an estimate of the intensity of a tornado. For most of us, we don't really use the EF-scale to assess the engineering ramifications of tornadoes -- we look at tornado ratings to get a feeling for the intensity of a tornado. Well should all know that one of the main problems with the EF-scale is that, 99.9% of the time, any assessment is based on damage (e.g. the DoDs for the DIs), which is problematic when a tornado does not hit any significant DIs (or completely destroys those that it does hit). These ratings are then used in climatology and correlation studies to examine meteorological characteristics that may help discriminate between environments that support high-end (and often high-impact) tornadoes from those that do not. There have been some very good publications from SPC mets focused on just this; we use 0-1 km SRH, LCL height, Significant Tornado Parameter, and other parameters because they've shown utility in the past in determining when certain environments may support high-end tornado risks.

As noted previously, the problem with lack of DIs for some tornadoes can be problematic. If a tornado with 250 mph winds at 10 m AGL spins in a field and hits absolutely nothing, there's a good chance that the tornado will be underrated in the eyes of most mets (again, I think many of us work on the premise that the EF scale is proxy for intensity ). This, in turn, certainly can cause issues with correlation studies (e.g. "look, this tornado occurred in an environment of 5000 j/kg MLCAPE and 400 m2/s2 0-1km SRH, yet it was only an EF1"). If we have high-quality measurements near the surface that are convincing, then I see little reason why those data cannot be used with non-traditional indicators to augment a rating. In the case of the El Reno tornado, there was a direct surface observation within the tornado. If that tornado hadn't hit anything in the way of high-end DIs, then should that surface ob be ignored? Ideally, the EF-scale may be based on damage, but isn't the practical use of it to use damage as a proxy for intensity? If so, then any data that can be corroborated with other, non-traditional indications should be included, IMO. Heck, even without ANY quantitative measurements, there can be a considerable amount of subjectivity in the ratings. For example, some of the homes that were "slabbed" were deemed to have substandard construction. However, the result is that one can only establish a lower bound to the winds (they were at least 1xx). In addition, the majority of the the winds associated with the different DoDs for each DI are subjective, based largely on the consensus of a group of wind damage and engineering experts. The original EF-scale document lists, if I recall correctly, the range of the wind speed estimates given by the different people involved in the development of the EF-scale for each DoD and DI, and you can see that some DoDs for some DIs have a very significant range.

In this case, the winds we sampled were not 205 mph. The winds measured (~65 m AGL) were well over the lower EF5 boundary. Even a very conservative estimate yielded a sfc-estimated wind above 200 mph, with the peak radial velocity, again, very much in excess of that speed. I'd agree with being more skeptical in the use of radar data if the data were farther above ground level or much nearer the EF4/EF5 threshold, though.

EDIT: This is entirely my personal opinion and does not represent the feelings of the group with which I work.

 

[Charles Kuster]

I am curious, were you guys the only ones sampling the storm with mobile radar? Also, the last time I was at OU ('07) Dr. Biggerstaff was building the dual polar, X-band (I think? or perhaps it was C-band) mobile radar. What type of radar was Howie's team using?

I don't have many specifics, but I do know that one of the SMART-R radars, SR-1 which is not dual-pol, was sampling the El Reno supercell from a position north of the storm. SR-2 which does have dual-pol capabilities did not collect data on May 24th thanks to technical problems.

Here are a couple archived radar images that I have from when the tornado was crossing I-40. I believe this is relatively close to the time when the oil rig was destroyed as well as when cars were thrown nine hundred yards.

http://i52.tinypic.com/33o1e84.jpg (reflectivity)
http://i51.tinypic.com/5x4n5t.jpg (SRV)

Here is a hodograph from the 21Z Purcell, OK profiler as well.

 

[Chad Ringley]

It does for a few days, and maybe a bit longer for those directly impacted, but that's it. I dare you to give me any MPH numbers from any tornado you chased in 2008 off the top of your head.

Easy, 0, was unable to chase in 2008 I understand your point.

 

[Adam Lucio]

I think an actual measured wind gust within the tornado holds more weight than someones best guess based on damage. I would much prefer that over using damage. Obviously its pretty difficult to get a measurement from every tornado, but when one is gotten, as long as those wind instruments are proven accurate they should definitely hold more weight.

We caught a glimpse of this tornado and then the damage afterward, it ended our chase day as we stopped to do search and rescue. The tornado was incredibly rain wrapped which for me made it harder to judge distance as it was coming straight at us, so I took the safe approach and made sure I got well south of it. I knew it was passing by the changing inflow winds as it passed just to our north.

 

[Bob Hartig]

Reading through this thread, I'm struck by just how problematic the F/EF Scale really is. Keep it simply a damage rating and you wind up with an unrealistic designation for strong to violent tornadoes that never impacted a DI; include in-situ measurements of wind speeds and you wind up skewing modern measurements in a way that doesn't easily and consistently correlate to the previous F Scale.

If meteorologists are going to take the latter approach, then I suppose that now, while the EF Scale is still in its infancy, is the time to do so. The new scale is the fruit of accumulated wind engineering knowledge, but it also comes at a time when radar measurements of wind speeds can be and are being taken. That's a new variable that the old F Scale didn't account for. Of course, if you take this approach, then it seems to me that it's pointless trying to harmonize modern EF ratings with historic F ratings. Realistically, we've got two different animals that don't hybridize well.

This leads me to another question: Practically speaking--not theoretically, but in actual use--is the EF Scale primarily for public or scientific use? The way tornado research is advancing, I don't think those two interests can be reconciled as easily as in the past. If the EF Scale is primarily a handy rating that can be disseminated to the media and has a certain amount of historical usefulness, then it needs to be simple. It's easy for people to wrap their minds around a single rating: this tornado was an EF-4; that one was an EF-2.

But if the scale's main use is scientific, then I note what Mike Smith has said about Ted Fujita's original concept of using dual ratings--F for damage and f for wind speed. It seems to me that if accuracy is the objective, and mobile radar and other in-situ measurements are now being thrown into the mix in order to achieve that accuracy, then a multiple-rating approach is far more realistic than a single number that can never satisfactorily address all of the variables. Wouldn't it be more useful, for research purposes, to have a scale that, besides the two existing categories of damage (F) and wind speed range (f), also included observed maximum wind speed and perhaps damage potential? That way you've got a more comprehensive rating tool that can utilize all available data with fewer limitations when some data is missing.

 

[rdale]

Wouldn't it be more useful, for research purposes, to have a scale that, besides the two existing categories of damage (F) and wind speed range (f), also included observed maximum wind speed and perhaps damage potential? That way you've got a more comprehensive rating tool that can utilize all available data with fewer limitations when some data is missing.

I'd say that sounds great in theory, but the little (f) is at best going to be 5 tornadoes per year maybe? I can't imagine there will ever be enough radars to reliably observe wind speeds in more than a handful of tornadoes. I guess "forcing" the DOW obs into the current F is good enough for now in my book.

 

[J Allen]

Unless the DODs applicable to EF-5 ratings are expanded the scale will remain a joke. The cases where a suitable DOD cannot be found nearby the swathe of maximum damage means that we will continue to see EF-4 where the damage is of the same degree as other EF-5s but its impossible to prove due to the lack of those very few indicators. This is reflected in the number of near EF-5 ratings in terms of wind speeds (195 mph EF-4, can we really be sure that that 5 miles an hour did not occur within that swathe). How we address this distribution skewing (which also occurs at the lower-mid range) will remain an issue for years to come. Are we just falling for the human trap of needing to categorise everything, including categories? Is it necessary?

 

[Greg Ansel]

Let's say, for the sake of argument, that we find a way to design buildings to withstand EF-5 wind damage, won't that cause tornadoes to be rated very low? It would make the EF scale obsolete and worst and skewed at best. I think wind speed should be included as an integral component of any tornado measuring scale, because the speed, although fluctuating, is less arbitrary than what the tornado does damage to. Most people in the path of a tornado want to know the damage it has the potential to cause, and wind speed is a good indicator of that.

 

[rdale]

Let's say, for the sake of argument, that we find a way to design buildings to withstand EF-5 wind damage, won't that cause tornadoes to be rated very low?

That's not a realistic argument, so while I understand your point - it's just not going to happen ever. We'll have dopplers on every corner LONG before EVERY building the US is ready to withstand 200+ mph winds.

Most people in the path of a tornado want to know the damage it has the potential to cause, and wind speed is a good indicator of that.

Zero people in the path of a tornado know how much damage it could potentially cause, since that's not known until after the tornado is past.

 

[Greg Ansel]

Zero people in the path of a tornado know how much damage it could potentially cause, since that's not known until after the tornado is past.

I think you could make the argument that a tornado with 70 mph winds is not going to do as much damage as one with 200+ mph winds given the same track/path. So I think that information could be somewhat important; I know it is to people like Sean Casey when he is trying to intercept. I see these local yahoos out trying to get close to tornadoes, and I think if they knew how strong the winds actually were, they might change their minds.

 

[rdale]

I think you could make the argument that a tornado with 70 mph winds is not going to do as much damage as one with 200+ mph winds given the same track/path.

No argument there...

I see these local yahoos out trying to get close to tornadoes, and I think if they knew how strong the winds actually were, they might change their minds.

Sure, but there's no way to tell them how strong the winds actually were. Notice it took a few days to get the numbers out for this event, and that was a storm with coverage. 99% of all tornadoes will not have a radar interrogating them with the ability to give speeds.

 

[Bob Hartig]

I'd say that sounds great in theory, but the little (f) is at best going to be 5 tornadoes per year maybe? I can't imagine there will ever be enough radars to reliably observe wind speeds in more than a handful of tornadoes. I guess "forcing" the DOW obs into the current F is good enough for now in my book.

I wouldn't argue that the full gamut of data will usually be missing. I had written, "That way you've got a more comprehensive rating tool that can utilize all available data with fewer limitations when some data is missing." My thinking is, maybe the rating system needs a plate that can accommodate the whole enchilada, even if most of the time all you get is a half-order. That way you've got a scale that is equipped conceptually to deal with
* damage only, and extrapolate wind speeds from it (how we normally conceive of the F/EF Scale, and what I understand the little "f" to actually reflect: not measured wind speeds, but derived ones).
* measured wind speeds only, and extrapolate a potential damage rating from them even when no DIs have been impacted.
* both damage and measured wind speeds: rare but ideal, the kind of information that has cropped up with the El Reno tornado and led to its being upgraded to EF-5 status.

My point isn't that you'd often be able to satisfy every category--because most of the time you wouldn't--but that you'd have allowed for every kind of iinput without requiring every kind of input, and you'd have a simple, convenient means of showing exactly what data was available for any given tornado incident. No more "is it a damage rating or a wind speed rating?" questions. The answer would be, it's both; it uses whatever information is available, and it clearly displays that information in a concise, useful format.

This, by the way, is just my editorial mind processing in writing. I acknowledge that far more knowledgeable heads than mine continue to wrestle with the knotty nuances of the EF Scale. But we amateurs just looooove to talk about this stuff.

 

[Greg Higgins]

I think that one of the things that has been overlooked in all of these discussions is; What was the "intent" of the author(s) (taking into consideration Dr. Fujita and the developers of the EF scale)? All anyone on here is doing is providing their own interests and interpretation, not necessarily what the authors envisioned or intended. Might be time to go to the “source” and see if one (or more) of the authors could provide their insight.

 

[rdale]

I think that one of the things that has been overlooked in all of these discussions is; What was the "intent" of the author(s) (taking into consideration Dr. Fujita and the developers of the EF scale)?

I've posted some of the lines from the original EF scale report about wind speeds... Here are their primary points:

• Identify additional damage indicators
• Correlate appearance of damage and wind speed
• Preserve the historical database
• Seek input from users

All anyone on here is doing is providing their own interests and interpretation, not necessarily what the authors envisioned or intended.

That's why I went to the source of it. I also hoped that someone on the "EF scale revival committee" would chime in with current plans to keep it alive, but not sure what the quiet means

http://www.spc.noaa.gov/faq/tornado/ef-ttu.pdf

 

[Greg Higgins]

"All anyone on here is doing is providing their own interests and interpretation, not necessarily what the authors envisioned or intended.

That's why I went to the source of it. I also hoped that someone on the "EF scale revival committee" would chime in with current plans to keep it alive, but not sure what the quiet mean"

Anytime someone injects a comment to the effect of, "I feel" or "I think", it usually is their own opionion, not neccessarily the intent of the authors. All anyone has to do is read through this thread and it should be obvious that several comments are what / how the commenter "wants" or "thinks" the EF scale should be, sometimes 180 degrees from what the document states. Posting the primary points should help.

 

[Hank Schyma]

Here is the Hinton tornado as its wiping out the small community East of town... also where my chase transitioned to search and assist. Amazingly, no deaths here
http://www.youtube.com/watch?v=DhZS9KIIx3Q

 

[Shawn Schuman]

This is something I've been wondering about, if I'm understanding your point correctly. I'm very much an amateur so I don't doubt there's something I'm missing, but wouldn't it be possible to add additional DIs? From what I understand, there are a few "unofficial" indicators that are often used, or at least considered, when determining EF4/EF5 damage. Among them are vehicles thrown long distances, extensive ground scouring and debarked or otherwise damaged low-lying shrubbery. I realize it would be difficult to base an EF5 rating on any of those things alone, but is there any particular reason they aren't officially included?

I do understand that there are probably difficulties with each of those, and I'm sure the ground scouring in particular would depend on the type and condition of the soil, hardiness of the grass, quality and condition of asphalt and so on. It would involve a fair bit of interpretation. But then, so do all the other official indicators. All of them are probably far more likely to be encountered by a tornado than a home of "superior construction" or other EF5-worthy indicator. I've wondered about it quite often. Would anyone like to alleviate my curiosity?

 

[Joshua Nall]

Just some thoughts here… I’m self taught, not trained or schooled in damage or rating, but I think this whole discussion shows how impossible it is to accurately and simply categorize something so varied and complex as tornadoes. Just read over some of this thread again and noticed there was no mention of how ground speed of the tornado effects the DOD to DIs. This was on my mind because I had just finished reading your blog on the Jarrel, TX tornado.

This is probably one of the more extreme examples…. 7 miles in 45 minutes, let’s say 10 mph. And perhaps at times it was moving more like 5 mph and at other times 15. Ground scouring and debarking of trees, any sort of damage to something in a fixed position, including allowable DIs I would assume, will be much greater than if it were moving at 50 mph. Concerning some of your examples, the peeling back of asphalt is a process that happens over time. Air is forced under one section and it lifts up, then air gets under the next small section and it lifts, etc… So is removal of top soil, so is debarking of trees. Perhaps a car is picked up and rethrown or rolled multiple times out in front of a slower moving tornado. But then so does the degree of damage to official DIs increase with duration, with few exceptions maybe. I've not read enough about it to know if this was all looked at closely with this particular tornado, but surely it's been hashed out many times.... I have read 260 was the estimated wind speed. Those additional DIs you mentioned would be more time dependent than say a beam bolted to concrete, I would think. Complications arise in that you are deriving a rating from a wind speed that is derived from DIs. And the DOD for most DIs, the way I understand it is dependent on many things…. speed, duration, direction, how much air born material, what the material is, etc…

 

[Mike Z]

Does anyone know why/how the El Reno tornado changed direction from SE to NE? Also, how rare is a change of direction like that?

 

[Alex Elmore]

Does anyone know why/how the El Reno tornado changed direction from SE to NE? Also, how rare is a change of direction like that?

I believe the tornado you are referring to isn't the tornado discussed here, but the May 31, 2013 El Reno tornado. While many maps that display tornado tracks have them moving in a straight line, it's fairly common for tornadoes to deviate from a straight path. This is essentially because tornadoes are formed by interactions between the outflow and inflow of the parent storm. Changes in intensity in either the outflow or inflow could cause a change in a tornado's path. The May 31, 2013 El Reno tornado is an exceptional case, but I believe the change in its path was due to the strong rear flank downdraft that was present in this storm, pushing it more to the NE. It's fairly common for tornadoes to curve to the left (relative to the motion of the storm) near the end of their life span. This tornado just happened to be a pretty dramatic example of that.

 

[Jeff Duda]

Trochoidal/cycloidal motion also probably explains a significant portion of any tornado's track. Imagine a tornado as a single point embedded within a circular mesocyclone that is both rotating and translating. The tornado's path would be defined by tracing the path of the point along the (mesocyclonic) circle as it rolls along in the environment. I believe that explains a lot of sudden and hard right turns such as the one the May 20 2013 Moore tornado took. Such a path also implies an overall leftward curve over the life cycle of any tornado.

I think that environmental influences such as rear-flank outflow or ambient inflow generally only impact a tornado's path during the dissipating or rope stages of a tornado. During the development and mature stages, the parent mesocyclone strongly controls the path of the tornado.

 

[Ethan Lang]

I would really like to see more ratings given due to Mobile Radar. One thing I haven't understood was that if we scan the tornado and see that it obviously is reaching EF-5 wind speeds but only does EF-3 damage (El Reno 2.6 mile wide) then why not actually rate it EF-5. Had the El Reno tornado struck more buildings and residential areas I truly believe we would have seen more significant damage.

 

[rdale]

That's called reviving a dead thread

The EF scale is based on damage. ONLY. I'm part of a group that is revising the EF-scale and mobile radar data will most likely be a part of the future process. But for now - rules is rules.