Enhanced Fujita Ratings Debate Thread

[buckeye05]

All of this debate about the Vilonia rating -> what about the non-existent surveys for literally dozens of structures that were swept away in the path? That's the biggest issue by far that I have with that survey; the fact that we don't have even have at least half of the evidence that we should have to be able to decide one way or another between EF4 and EF5.

I was vague but that’s what I meant in my earlier post when I said “all the troubling facts” surrounding Vilonia. It’s not like it just comes down to the one Wicker Street home and that’s it. We know there was at least one other properly bolted home slabbed on Coker Road, and not to mention other gaps in the DAT/survey where EF5 candidate damage occurred.

This includes but isn’t necessary limited to:

-Beryl Road
-Cemetery Road
-Fish Hooks Restaurant
-The fertilizer tank
-Various slabbed homes within Vilonia itself

I’d bet there are other properly anchored homes in these “gaps” we simply don’t know about. To “debunk” Vilonia as an EF5 candidate, you’d have to debunk all these locations, not just that one house on Wicker Street.

 

[Grand Poo Bah]

In my opinion:

If you have a completely swept home but a softwood/hardwood tree either directly in front or to the side of the home (I don't say behind, because debris loading will almost 100% exaggerate tree damage) is untouched, that is an extremely important indicator that either the home's construction was worse than it seems, or debris impacts were involved. That, of course, shouldn't be ignored when evaluating tornadic intensity. I used to be on the "contextuals don't matter" boat, but I've changed my mind. If the intensity was enough to sweep a home, it would also be enough to snap or maybe even debark that tree. Marion's tree damage was also directly behind the home, and thus could be accentuated by debris from the home itself.

Structural-wise, I don't really see the issue with nitpicking homes - if we are trying to get an accurate wind speed number, factoring in issues with the home seems reasonable. Maybe EF-scale wise, sure, but every quality issue is a thing that may have led it to be swept at lower windspeeds.

In response to your first paragraph, I almost entirely agree. The only difference is I believe those factors are the barrier between EF4 and EF5, rather than EF4 and EF3. That's it. I also believe there's a good amount of empirical evidence to support my view. The main argument the EF3 camp has is precedent from the last 10 years or so.

About Marion specifically, there was far more debarking than just around the EF4 house. Almost all the trees in the tornadoes path were nubbed, and several were partially or completely debarked. Here's a good video showing it. A good clip is my timestamp (7:48) until about 8:30.



In regards to your second paragraph, the problem is we don't KNOW how those structural "flaws"/details affect wind resistance. It's pointless speculation. What we DO have is a scale that took the average home, and had a panel of experts give their estimated wind speeds to destroy it. Then we took the average of those opinions for the final number. All we have is a vague idea, and pretending we have any inckling of precision outside of that is kinda silly and self-important in my opinion.

 

[Grand Poo Bah]

All of this debate about the Vilonia rating -> what about the non-existent surveys for literally dozens of structures that were swept away in the path? That's the biggest issue by far that I have with that survey; the fact that we don't have even have at least half of the evidence that we should have to be able to decide one way or another between EF4 and EF5.

This is also true for Mayfield. Especially in Cambridge shores and the areas before and after the famous Bremen picture. Dozens of homes were either surveyed by way of pictures taken from the passenger seat of a moving vehicle or drones. And several weren't even looked at.

Tuscaloosa and Greenfield have a similar story to a lesser extent, and probably some others I'm not thinking of. There's an argument to be made that, with limited resources, it's impossible for surveyors to get to everything after such extreme long track tornadoes, but with Vilonia they didn't need to. They already had all the EF5 evidence they needed. It's so much more more egregious when you add the "only one structure" quote to it. More evidence was surely available if they really needed it.

 

[Central Ohio Wx]

I'm noticing that a lot of those debarked trees are directly within debris paths and rowing (a heap of debris at the base of damaged trees is also a tell-tale sign of this). I'm not saying it's a completely invalid indicator, but a lot of that could be exaggerated by debris-loading.

 

[Grand Poo Bah]

I'm noticing that a lot of those debarked trees are directly within debris paths and rowing (a heap of debris at the base of damaged trees is also a tell-tale sign of this). I'm not saying it's a completely invalid indicator, but a lot of that could be exaggerated by debris-loading.

The large forested area at 8:27 has no visible debris or structures downwind.

The type of debarking we're talking about, where no debris is required, is exceptionally rare and achieved by only the top .1% of tornadoes. It shouldn't even be the EF5 threshold, let alone the EF4 one. This is what I meant earlier by context moving the needle to the extreme.

EF5 shouldn't be an impossible threshold to cross, and tornadoes shouldn't have to "impress" people who are completely desensitized to the damage they're capable of to be accurately categorized.

 

[Grand Poo Bah]

Regardless, I think we can all agree there's a huge imbalance currently, and if context can be used for extreme downgrades, it should also be used for extreme upgrades. It can't just go one way.

Edit:
This is definitely what makes the Enderlin rating so exciting. It was the total opposite of what we're used to.

 

[buckeye05]

Debris loading is only valid as a factor for reducing a wind speed estimate or giving less weight to impressive contextual damage if it can be conclusively be linked to a a specific airborne object or material. I cannot stress that enough.

Examples where it would be valid:
—————
-Destruction of a home or building being clearly exacerbated by a heavy object (vehicle, grain bin, mobile home frame, neighboring house, etc) impacting the house. It would have to be very obvious that the specific object or airborne material in question absolutely struck the building.

-Debarking being exacerbated by airborne debris immediately downwind of a specific structure. This is particularly true when sheet metal is in play, because over the years I’ve noticed that airborne metal tends to have a noticeable “vegetable peeler” effect on trees, even at intensities as low as EF2.


Example where it would NOT be valid
———
-A home being vaguely downwind of an area where heavy objects were thrown, and some may be laying within the general vicinity, but there is nothing to directly suggest that the objects have come in contact with the structure in question.

-A home or building being destroyed with collateral damage from flying material or objects cited as a factor for a lower-bound wind speed estimate, but the survey is unable to specify which specific material or object is to blame, or the distance between the two areas is so significant that the reasoning becomes a stretch. This applies to contextual/vegetation damage too.

Basically, unless a specific object or airborne material is identified as a clear, direct contributor to collateral damage, the debris loading argument is usually a total nothing burger statement. When you hear things like the potential for higher-end ratings being dismissed or downplayed via statements like “Well, the tornado was hitting a lot of buildings…so there was a lot of stuff flying around” it’s like well yeah….duh? Isn’t that what happens literally any time an EF2+ tornado impacts multiple structures? When I hear about high-end structural or contextual damage in a town directly impacted by a tornado being dismissed via a non-specific, general, vague “well the air was full of debris” excuse I always reply with this:

“Well if this had just been one of those violent tornadoes that magically don’t become debris-loaded while directly impacting a populated area, you would have had a shot at a high-end rating! Dang, so close! ”

See how silly that argument becomes when you really think about it? ALL high-end tornadoes become debris loaded unless they remain in rural areas. Therefore, it’s a nothing-burger point to bring up any time a violent tornado strikes a town, such as Vilonia. Occam’s razor says the reason the contextual and structural damage in Vilonia was exceptionally intense, is because the tornado was exceptionally intense, not because “yeah well there was debris and stuff”. There’s a reason why you don’t see grass-covered ground scoured to bare soil and wooded areas obliterated to completely bare, 100% barkless clusters of trees and shrubs every year: because it takes an exceptionally rare, extraordinarily violent caliber of tornado to do that.

 

[Grand Poo Bah]

An interesting Reddit post

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TL;DR basically he emailed a detailed analysis of the Greenfield parking stops and referenced a couple studies saying it required EF5 winds.

NWS Des Moines replied,

"Thank you for your email and damage analysis. The NWS will consider the concrete parking barriers should a re-evaluation of the May 21, 2024 Greenfield, IA tornado be conducted.

NWS Des Moines"

Two conclusions I'm drawing from this:

1. Re-rating past tornadoes is a serious discussion happening within the NWS right now.
2. Des Moines has finalized the Greenfield rating and won't budge on it unless specifically requested by the NWS.

 

[Grand Poo Bah]

Another great post about the Chapman EF4.

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"While I understand that ratings are based on Damage Indicators (DIs), the structural failures documented in this event—specifically the Concrete Breakout Failure and Railroad Track Deformation—are physically impossible at the wind speeds cited in your survey.

1. The Rebar Math (Tensile and Breakout Strength) At the farmstead southwest of Chapman, photos and survey notes show rebar ripped directly out of the poured concrete foundation.

The Physics: Standard Grade 60 #5 rebar has a yield strength of 60,000 PSI. A single anchor requires approximately 18,400 lbs of vertical tension to snap.

The Wind Gap: To generate 18,400 lbs of lift on a standard 40 sq ft wall section, wind speeds must exceed 300 mph.

Concrete Breakout: To "rip" the rebar out and crater the concrete, ACI 318 calculations for breakout strength require a force of roughly 28,000 lbs. This equates to wind speeds in the 370 mph range.

Conclusion: Your rating of 180 mph provides only 82 PSF (pounds per square foot) of pressure. This is nearly seven times less than the force required to fail these anchors.

1. The Railroad Track Proof The tornado bent and warped heavy-duty 136 lb RE rail. A 136 lb rail is designed to support hundreds of tons of moving weight. Bending this industrial steel laterally requires forces that do not exist in a 180 mph wind field. Even accounting for the slow forward speed of the storm, steel does not "fatigue" into a permanent warp from sub-yield wind loads. It requires an instantaneous peak pressure only found in EF5 vortices exceeding 200 mph.
2. Request for Re-evaluation If physics dictates that 300 to 370 mph is required to fail these specific materials, how can the NWS justify a 180 mph rating? If the Enhanced Fujita Scale is meant to be a proxy for wind speed, it should not ignore the literal breaking points of industrial steel and concrete. Recent 2025 precedents, such as the upgrade of the Enderlin, ND tornado based on the math of moving heavy objects, suggest that forensic engineering should be used to correct these discrepancies.

I look forward to your technical response regarding how 180 mph winds can overcome the 60,000 PSI yield strength of Grade 60 rebar."

 

[Central Ohio Wx]

Another great post

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"While I understand that ratings are based on Damage Indicators (DIs), the structural failures documented in this event—specifically the Concrete Breakout Failure and Railroad Track Deformation—are physically impossible at the wind speeds cited in your survey.

1. The Rebar Math (Tensile and Breakout Strength) At the farmstead southwest of Chapman, photos and survey notes show rebar ripped directly out of the poured concrete foundation.

The Physics: Standard Grade 60 #5 rebar has a yield strength of 60,000 PSI. A single anchor requires approximately 18,400 lbs of vertical tension to snap.

The Wind Gap: To generate 18,400 lbs of lift on a standard 40 sq ft wall section, wind speeds must exceed 300 mph.

Concrete Breakout: To "rip" the rebar out and crater the concrete, ACI 318 calculations for breakout strength require a force of roughly 28,000 lbs. This equates to wind speeds in the 370 mph range.

Conclusion: Your rating of 180 mph provides only 82 PSF (pounds per square foot) of pressure. This is nearly seven times less than the force required to fail these anchors.

1. The Railroad Track Proof The tornado bent and warped heavy-duty 136 lb RE rail. A 136 lb rail is designed to support hundreds of tons of moving weight. Bending this industrial steel laterally requires forces that do not exist in a 180 mph wind field. Even accounting for the slow forward speed of the storm, steel does not "fatigue" into a permanent warp from sub-yield wind loads. It requires an instantaneous peak pressure only found in EF5 vortices exceeding 200 mph.
2. Request for Re-evaluation If physics dictates that 300 to 370 mph is required to fail these specific materials, how can the NWS justify a 180 mph rating? If the Enhanced Fujita Scale is meant to be a proxy for wind speed, it should not ignore the literal breaking points of industrial steel and concrete. Recent 2025 precedents, such as the upgrade of the Enderlin, ND tornado based on the math of moving heavy objects, suggest that forensic engineering should be used to correct these discrepancies.

I look forward to your technical response regarding how 180 mph winds can overcome the 60,000 PSI yield strength of Grade 60 rebar."

He sent this to the wrong office (NWS ICT), funny enough. I highly doubt anything will come of this, although a re-analysis would be interesting.

 

[Central Ohio Wx]

An interesting Reddit post

Reddit - Please wait for verification

www.reddit.com

TL;DR basically he emailed a detailed analysis of the Greenfield parking stops and referenced a couple studies saying it required EF5 winds.

NWS Des Moines replied,

"Thank you for your email and damage analysis. The NWS will consider the concrete parking barriers should a re-evaluation of the May 21, 2024 Greenfield, IA tornado be conducted.

NWS Des Moines"

Two conclusions I'm drawing from this:

1. Re-rating past tornadoes is a serious discussion happening within the NWS right now.
2. Des Moines has finalized the Greenfield rating and won't budge on it unless specifically requested by the NWS.

His analysis is assuming every parking stop is built the same, which they objectively aren't. His "283 mph" claim is just a number and isn't backed up by any math (the June First video is assuming every condition is idealized and was solely caused by wind, which I believe he’s stated himself is unlikely); even if it was re-evaluated I doubt it would be re-rated.

 

[HAwkmoon]

Another great post

Reddit - Please wait for verification

www.reddit.com

"While I understand that ratings are based on Damage Indicators (DIs), the structural failures documented in this event—specifically the Concrete Breakout Failure and Railroad Track Deformation—are physically impossible at the wind speeds cited in your survey.

1. The Rebar Math (Tensile and Breakout Strength) At the farmstead southwest of Chapman, photos and survey notes show rebar ripped directly out of the poured concrete foundation.

The Physics: Standard Grade 60 #5 rebar has a yield strength of 60,000 PSI. A single anchor requires approximately 18,400 lbs of vertical tension to snap.

The Wind Gap: To generate 18,400 lbs of lift on a standard 40 sq ft wall section, wind speeds must exceed 300 mph.

Concrete Breakout: To "rip" the rebar out and crater the concrete, ACI 318 calculations for breakout strength require a force of roughly 28,000 lbs. This equates to wind speeds in the 370 mph range.

Conclusion: Your rating of 180 mph provides only 82 PSF (pounds per square foot) of pressure. This is nearly seven times less than the force required to fail these anchors.

1. The Railroad Track Proof The tornado bent and warped heavy-duty 136 lb RE rail. A 136 lb rail is designed to support hundreds of tons of moving weight. Bending this industrial steel laterally requires forces that do not exist in a 180 mph wind field. Even accounting for the slow forward speed of the storm, steel does not "fatigue" into a permanent warp from sub-yield wind loads. It requires an instantaneous peak pressure only found in EF5 vortices exceeding 200 mph.
2. Request for Re-evaluation If physics dictates that 300 to 370 mph is required to fail these specific materials, how can the NWS justify a 180 mph rating? If the Enhanced Fujita Scale is meant to be a proxy for wind speed, it should not ignore the literal breaking points of industrial steel and concrete. Recent 2025 precedents, such as the upgrade of the Enderlin, ND tornado based on the math of moving heavy objects, suggest that forensic engineering should be used to correct these discrepancies.

I look forward to your technical response regarding how 180 mph winds can overcome the 60,000 PSI yield strength of Grade 60 rebar."

It is not just the wind though that is the thing, its more complicated than that especially when it comes to the failure of the home as a whole.

 

[Grand Poo Bah]

His analysis is assuming every parking stop is built the same, which they objectively aren't. His "283 mph" claim is just a number and isn't backed up by any math (the June First video is assuming every condition is idealized and was solely caused by wind, which I believe he’s stated himself is unlikely); even if it was re-evaluated I doubt it would be re-rated.

It is not just the wind though that is the thing, its more complicated than that especially when it comes to the failure of the home as a whole.

Both your points would make a lot more sense if these were damage indicators we've seen several times before, and if they were in a vacuum by themselves where other incredible contextual damage wasn't present. We're talking about DIs that have been recorded an amount of times you could probably count on two hands.

The Greenfield parking stops were anchored. The Chapman house foundation was rebar reinforced. Both of these required INCREDIBLE force to break. Whether it was caused by wind or windborne debris doesn't change that fact. I know you're just playing devil's advocate, but to say "debris was probably a factor" is such a nothing statement. We don't know exactly what forces make this damage physically possible. That's kind of the whole point.

 

[Grand Poo Bah]

For all we know, the wind speeds required to throw a car through a house, could be close to the windspeeds required to blow a house away. The wind speeds required to granulate houses into projectiles that can debark entire trees in seconds, might be similar to the wind speeds required to debark trees. Until there is a quantitative study that goes in depth into those differences, speculating about it is presumptuous. It's just conjecture with no current value for extrapolating wind speeds. In fact it is continuously sabotaging every good faith attempt at extrapolating even remotely accurate wind speeds using arithmetic we actually understand.

Why lean on established science and math when you can just shrug and say "meh, beats me, it was probably just debris"? Right now surveyors are just attaching the absolute lowest common denominator with zero basis in reality because that's what some other surveyors did in years past. And those surveyors did the same thing! We've gone completely off the rails, and now even the basic math itself is scoffed at like it's the guesswork, and the increasingly outlandish, detached precedent is what's considered "concrete and reliable".

 

[Grand Poo Bah]

The other funny thing about Vilonia is it really cemented the "airborne debris" argument as justification for a ratings downgrade. Even when no evidence of airborne debris is present. Now it's commonly being used to downgrade EF4s to EF3s (violent category to strong) There's been a snowball effect where DIs that were easily in the F5/EF5 range in the past are commonly being rated EF3 now. And there's never been a shred of scientific evidence to justify the change.

 

[Central Ohio Wx]

Both your points would make a lot more sense if these were damage indicators we've seen several times before, and if they were in a vacuum by themselves where other incredible contextual damage wasn't present. We're talking about DIs that have been recorded an amount of times you could probably count on two hands.

The Greenfield parking stops were anchored. The Chapman house foundation was rebar reinforced. Both of these required INCREDIBLE force to break. Whether it was caused by wind or windborne debris doesn't change that fact. I know you're just playing devil's advocate, but to say "debris was probably a factor" is such a nothing statement. We don't know exactly what forces make this damage physically possible. That's kind of the whole point.

We have no actual idea of what it takes to shift the Greenfield parking stops, because the one person who’s done calculations on them has even stated his calculations are unrealistic in a real-world sense. You can say it takes a lot of wind, but putting a bunch of numbers in a passive-aggressive email (at least the Chapman one) and sending it to the wrong NWS office (again, the Chapman one) is just stupid. No offense to the poster. Until there is a number that has been deemed realistic for the parking stops, I’m not going to believe it took EF5 winds to shift them. Something being anchored doesn’t automatically make it EF5 damage, and it’s so non-standard that I’d like to see a more in-depth study.

And since the parking stops were in a populated area, it is 100% a possibility that debris was involved, and that’s worth a thought regardless of EF rating.

 

[slenker]

Ethan’s math on the parking stops in Greenfield assumes some things: One, that debris impacts were not involved - which actually makes sense with his logic. From the imagery of the parking stops, there is four to five in a row with a similar “look” to them with the damage. It’s also likely that if a major debris impact was involved with this damage, it would have likely been limited to only one or maybe two of the parking stops, and the damage would have been more catastrophic to said parking stops. Two, perpendicular and uniform wind load, which is almost always going to be a part of the calculations because doing it any other way is probably extremely nontrivial, so it isn’t a problem because this is the type of calculation that goes into pretty much any other DI.

I’m very trusting of the numbers he got here. Sure, only him getting these numbers from his analysis alone isn’t going to constitute as full on scientific analysis. However, he’s clearly shown that his analysis is worth something, because he’s a true mechanical engineer and also the numbers he got for Enderlin’s train throw were the same numbers Marshall and LaDue got, and he did that analysis months before the official upgrade took place. Not only that, I’m pretty sure Ethan’s math is very similar to, or maybe even the exact same logic used in the Joplin case, where Iowa State wind engineer Partha Sarkar concluded that parking stop throws were indicative of winds well into the EF5 range and NWS Springfield used the parking stop throws as a reason to keep Joplin’s EF5 rating alongside other contextual oddities and extremes. Also, consider the fact that parking stops are extremely low to the ground and we’re still getting numbers into the EF5 range. The assumption that pretty much needs to be made is that the winds further up are stronger. I’m not saying Greenfield was as impressive as Joplin because that’s not true, but it’s not hard to see a world where Greenfield is an EF5 because of this damage. It would be enough for me honestly.

The bottom line to me is that the assumptions made in the Greenfield tornado were the same assumptions made in Joplin’s case, and precedent says that we should stay consistent and rate Greenfield EF5 - it would probably be the weakest of the EF5s, but contextually just looking at the damage it just manages to have “the look” to it in some areas. And we have radar data that is very indicative of an EF5 strength tornado as well.

 

[Central Ohio Wx]

And we have radar data that is very indicative of an EF5 strength tornado as well.

The DOW readings were instantaneous and the EF scale is 3-second sustained (plus, those readings were over EF2 and EF3-rated damage). NEXRAD is, as always, unreliable for accurate tornado intensity (as seen with tornadoes like Essex, Hollister, etc.) I guess my issue with citing the Joplin study is that the stops could be a completely different model with different anchoring depths for all we know. It would be like citing the Marshall Greensburg study for the Marion home and going “well, the homes look like they have the same damage, so they must be the same windspeed” without factoring in construction or anything surrounding. My mind is open to changing, though.

 

[slenker]

The DOW readings were instantaneous and the EF scale is 3-second sustained (plus, those readings were over EF2 and EF3-rated damage). NEXRAD is, as always, unreliable for accurate tornado intensity (as seen with tornadoes like Essex, Hollister, etc.) I guess my issue with citing the Joplin study is that the stops could be a completely different model with different anchoring depths for all we know. It would be like citing the Marshall Greensburg study for the Marion home and going “well, the homes look like they have the same damage, so they must be the same windspeed” without factoring in construction or anything surrounding. My mind is open to changing, though.

I agree with radar data being unreliable on its own, but a 300 mph wind gust is certainly something that can be taken into account because it’s extremely rare to get that by itself, and it’s clearly coincident with very high end damage that possibly could justify an EF5 rating. Enderlin took radar data into account in its rating as well. However, it’s a completely different method of analysis and definitely better than NEXRAD because it utilized Vrot calculations with (I believe) WSR 88-D data, which have been shown to be pretty well correlated to higher tornadic intensities for higher Vrot values in some studies. I’d like to see that methodology applied to the Greenfield tornado to see what it reveals.

I used to be firmly in the “Greenfield isn’t an EF5” camp, but I’ve since stepped away from that viewpoint and it’s mostly due to the same contextual indicators that kept Joplin’s EF5 rating. Pretty sure Greenfield had a manhole cover that was sucked up as well, but I never saw any imagery of that damage, so I don’t know its validity.

EDIT: I also do want to add that if they keep Greenfield’s 185 EF4, I wouldn’t mind either. It’s a fine rating. But the parking stops in my eyes are very valid EF5 indicators if other experts come to the same conclusion, and if more detailed analysis is done on it that supports these findings, I fully support an upgrade to EF5.

 

[Central Ohio Wx]

I agree with radar data being unreliable on its own, but a 300 mph wind gust is certainly something that can be taken into account because it’s extremely rare to get that by itself, and it’s clearly coincident with very high end damage that possibly could justify an EF5 rating.

Interestingly, the 300+ mph (I don’t remember the exact number) reading that was captured was actually, if I remember correctly, over pretty standard EF2 and EF3 damage southwest of town. That could be just because they stopped taking scans as it went northeast into town (I haven’t read the study fully) but it’s interesting nonetheless.

Edit: NASA has a webpage on it and apparently DOW7 did continue scanning it in town; specific numbers aren’t attached to each pixel so it’s impossible to see where the highest winds were.