Enhanced Fujita Ratings Debate Thread

[TH2002]

I’ve thought about this. Generally it’s thought that EF4+ wind speeds have to occur for this to happen but the current transmission tower DI tops out at 165 MPH, hence the EF3 rating in Kouts this year.

One issue though in terms of calculating it though may stem from the fact that it’s not a “solid” object (not the best description but you know what I’m getting at). Instead, it’s a latticework of interconnected metal bars with lots of space in between for the wind to pass through. I could be wrong, but it might be tough to calculate due to the wind passing through much of the tower during a tornado impact. Another problem is a transmission tower isn’t going to maintain the same shape and weight distribution when being hit by a tornado. It’s going to twist and crumple into different unpredictable shapes while being lofted.

The bridge support that was thrown up the canyon embankment at Hurricane Creek outside of Tuscaloosa also had a similar truss-type structural makeup. I think that one might also be tougher to calculate for that reason too, among others.

Wasn't Bowdle (at least partially) rated EF4 based on damage to transmission towers?

FWIW, Spann wrote in his 4/27 book that he believes the destruction of the railroad bridge over Hurricane Creek was indicative of EF5 intensity. I know he's not a damage survey expert, but he is a well-respected meteorologist in the field, and honestly, that (combined with the AMETSOC paper that rates the tornado EF5 based on treefall patterns near the bridge) is good enough for me.

 

[buckeye05]

Wasn't Bowdle (at least partially) rated EF4 based on damage to transmission towers?

FWIW, Spann wrote in his 4/27 book that he believes the destruction of the railroad bridge over Hurricane Creek was indicative of EF5 intensity. I know he's not a damage survey expert, but he is a well-respected meteorologist in the field, and honestly, that (combined with the AMETSOC paper that rates the tornado EF5 based on treefall patterns near the bridge) is good enough for me.

Oh yeah Bowdle absolutely was. But they had to “break the rules” and go beyond the assigned upper bound for transmission towers, which is something most WFOs are not going to. Hopefully the new upper bound for transmission towers will be extended into the EF4 range once the updated scale is rolled out.

Also I’m not at all doubting that EF5 winds were required to do that to the Hurricane Creek railroad bridge support. In fact, I’m highly confident that EF5 winds had to have occurred there, and the treefall data from that location backs it up even more. I’m just saying getting a precise calculation might be tough there due to the shape/design of the support, along with the fact that the calculation wouldn’t just be as simple as “what windspeed is needed to loft this bridge support?”. The calculation would be, “What windspeed is needed to roll this bridge support up an embankment with a slope of this specific degree, tumbling it uphill but without fully lofting it?” That’s very specific and tricky. But is it impossible? Probably not, but it would definitely take a lot more work and involve far more variables than a lofted fertilizer tank or train car.

The railroad bridge is one of the top two things I want to see calculated, but I’ve been really thinking about it lately, and it’s going to be a lot more complicated than I first thought it would be.

 

[Grand Poo Bah]

Oh yeah Bowdle absolutely was. But they had to “break the rules” and go beyond the assigned upper bound for transmission towers, which is something most WFOs are not going to. Hopefully the new upper bound for transmission towers will be extended into the EF4 range once the updated scale is rolled out.

Also I’m not at all doubting that EF5 winds were required to do that to the Hurricane Creek railroad bridge support. In fact, I’m highly confident that EF5 winds had to have occurred there, and the treefall data from that location backs it up even more. I’m just saying getting a precise calculation might be tough there due to the shape/design of the support, along with the fact that the calculation wouldn’t just be as simple as “what windspeed is needed to loft this bridge support?”. The calculation would be, “What windspeed is needed to roll this bridge support up an embankment with a slope of this specific degree, tumbling it uphill but without fully lofting it?” That’s very specific and tricky. But is it impossible? Probably not, but it would definitely take a lot more work and involve far more variables than a lofted fertilizer tank or train car.

The railroad bridge is one of the top two things I want to see calculated, but I’ve been really thinking about it lately, and it’s going to be a lot more complicated than I first thought it would be.

I'm currently at the realization that it's completely unreasonable to try and attach an exact wind speed to tornado damage. We really need to go back to more broad wind speed ranges for these classifications.

I'm sure the question "Is it probable sub-200 mph winds could cause this damage?" Is much easier to answer mathematically than "what exact wind speed caused this damage?"

 

[buckeye05]

I'm currently at the realization that it's completely unreasonable to try and attach an exact wind speed to tornado damage. We really need to go back to more broad wind speed ranges for these classifications.

I'm sure the question "Is it probable sub-200 mph winds could cause this damage?" Is much easier to answer mathematically than "what exact wind speed caused this damage?"

Yeah I’ve often thought about that. Maybe keeping things more broad and maybe assigning a range of possible wind speeds could solve some of the issues? It’s an interesting idea.