Severe WX December 10 & 11, 2021 Severe Threat

[CalebRoutt]

The contextual damage at Cambridge Shores was most certainly EF5. Trees either completely debarked or shredded to near or at ground level, multiple homes swept in addition to severe debris granulation. Photo below.

The Bremen home wasn’t just a block home. There was a portion around the storm shelter that was a concrete foundation and was well bolted. That portion was swept to its slab. There is literally a home of similar structure that is still in the EF-Scale manual for EF5, thus a home (if well anchored) can be rated EF5

I do know at least 1 home at Cambridge Shores was well built, but as for the rest im actually not sure of. The DAT tool kit only has a couple of homes. Considering radar had pixels of 170-190 mph im not too upset about high-end EF4 for that area.

 

[CalebRoutt]

If only a small portion of the structure as bolted down to a concrete slab then that does not make it an EF5 candidate, the entire structure needs to be.

More aerials from Cambridge Shores note the severe granulation of the homes along the sides of the hill. All vegetation was stripped.

The Bremen home was well-built even better than most homes of typical construction. Now, if the CMU blocks weren’t filled with concrete then yes, they cannot rate it as EF5.

 

[pohnpei]

I do know at least 1 home at Cambridge Shores was well built, but as for the rest im actually not sure of. The DAT tool kit only has a couple of homes. Considering radar had pixels of 170-190 mph im not too upset about high-end EF4 for that area.

I don' think pixels of 170-190mph on radar had much relation to the rating issue even you consider the topography was relatively high because those pixels are not equivalent to actual winds in reality, let alone its distance between station and the tornado. I noticed you sometimes have a tendency to use velocity as actual winds Inside tornados which was absolutely wrong,even for mobile radars, let alone 88D. Smithville had velocity lower than this doesn't mean It should be rated anything lower than EF5 and Vilonia 2011/2014 had very similar performance on radar didn't mean they have similar intensity.

 

[xJownage]

I do know at least 1 home at Cambridge Shores was well built, but as for the rest im actually not sure of. The DAT tool kit only has a couple of homes. Considering radar had pixels of 170-190 mph im not too upset about high-end EF4 for that area.

The radar at the time was NOT 0m. Don't try to use radar wind speeds to determine tornado intensity. You're never truly at ground level, so those winds can never be truly accurate.

We already have evidence that wind speeds are different when taken from something like a DOW, that can get winds as low as 30m, vs what they actually are at the ground. Let's not talk about radar signatures from 88D to assume otherwise.

 

[CalebRoutt]

The radar at the time was NOT 0m. Don't try to use radar wind speeds to determine tornado intensity. You're never truly at ground level, so those winds can never be truly accurate.

We already have evidence that wind speeds are different when taken from something like a DOW, that can get winds as low as 30m, vs what they actually are at the ground. Let's not talk about radar signatures from 88D to assume otherwise.

There's actually some correlation between DOW data and 88D data if the quality of WSR-88D is good. See paper here: https://journals.ametsoc.org/view/journals/wefo/28/2/waf-d-12-00019_1.xml

 

[CalebRoutt]

I don' think pixels of 170-190mph on radar had much relation to the rating issue even you consider the topography was relatively high because those pixels are not equivalent to actual winds in reality, let alone its distance between station and the tornado. I noticed you sometimes have a tendency to use velocity as actual winds Inside tornados which was absolutely wrong,even for mobile radars, let alone 88D. Smithville had velocity lower than this doesn't mean It should be rated anything lower than EF5 and Vilonia 2011/2014 had very similar performance on radar didn't mean they have similar intensity.

Keep in mind the data from KGWX from Smithville wasn't super-res (at least it wasn't archived) so the actual winds on velocity aren't known. I do know there was well over 200+ mph pixels in the higher tilts of the Hackleburg tornado which is definitely likely. With that said, no 88D shouldn't be used to determine tornado winds right at the sfc, but there are cases where winds on 88D are somewhat similar to what's occurring at the sfc especially in violent tornadoes. The fastest winds are within sub-vortices which definitely cannot be resolved with WSR-88D.

 

[pohnpei]

Keep in mind the data from KGWX from Smithville wasn't super-res (at least it wasn't archived) so the actual winds on velocity aren't known. I do know there was well over 200+ mph pixels in the higher tilts of the Hackleburg tornado which is definitely likely. With that said, no 88D shouldn't be used to determine tornado winds right at the sfc, but there are cases where winds on 88D are somewhat similar to what's occurring at the sfc especially in violent tornadoes. The fastest winds are within sub-vortices which definitely cannot be resolved with WSR-88D.

These pixels are NOT winds! These are just outbound and inbound velocity towards radar. So the vrot of the tornado+translation speed is the real velocity of the tornado rather than one pixel on one side of the tornado. If you think these are true winds inside tornados then tornados like Dalton EF4 may only had wind speed like 40 or 50kt. The KGWX wasn's super res enough but even RaxPol isn't super res enough for tornados. You actually don't know the true wind speed inside tornados but you can't say in which case It matched quite well.

 

[CalebRoutt]

These pixels are NOT winds! These are just outbound and inbound velocity towards radar. So the vrot of the tornado+translation speed is the real velocity of the tornado rather than one pixel on one side of the tornado. If you think these are true winds inside tornados then tornados like Dalton EF4 may only had wind speed like 40 or 50kt. The KGWX wasn's super res enough but even RaxPol isn't super res enough for tornados. You actually don't know the true wind speed inside tornados but you can't say in which case It matched quite well

Correct! Not what I was trying to hint at.

What I was saying was that 170-190 mph winds matched quite well over Cambridge Shores, the damage there certainly supports it. Of course the winds may of been higher.

RaxPol, DOW, TTUKA etc all sample violent tornado's fairly decently especially when they are within the "tornado boundary layer". A good example of what I was meaning occurred on May 3rd 1999. The peak Delta-V on KTLX was ∼77 m/s (172mph) and DOW was recording a very large area of 170-180 mph winds (with the exception of the core). So in that case there was some correlation with radar derived wind speeds and low-level winds. I will say at the core the winds were MUCH higher.

 

[xJownage]

There's actually some correlation between DOW data and 88D data if the quality of WSR-88D is good. See paper here: https://journals.ametsoc.org/view/journals/wefo/28/2/waf-d-12-00019_1.xml

This is absolutely true, but not my point. My point is that if even DOW data isn't good enough for 0m, 88D is probably worse. There's a correlation, sure, but to suggest that the wind speed on radar has any significance in determining precise windspeed at the ground is simply irresponsible.

 

[CalebRoutt]

This is absolutely true, but not my point. My point is that if even DOW data isn't good enough for 0m, 88D is probably worse. There's a correlation, sure, but to suggest that the wind speed on radar has any significance in determining precise windspeed at the ground is simply irresponsible.

The winds do not have to be at 0m, in a lot of cases winds at roof top height can be the same as right near the sfc due to cyclostrophic upsets. I wasn't saying 170-190 mph winds was occurring at the sfc at Cambridge, but they more than likely did given the damage.

 

[pohnpei]

Correct! Not what I was trying to hint at.

What I was saying was that 170-190 mph winds matched quite well over Cambridge Shores, the damage there certainly supports it. Of course the winds may of been higher.

RaxPol, DOW, TTUKA etc all sample violent tornado's fairly decently especially when they are within the "tornado boundary layer". A good example of what I was meaning occurred on May 3rd 1999. The peak Delta-V on KTLX was ∼77 m/s (172mph) and DOW was recording a very large area of 170-180 mph winds (with the exception of the core). So in that case there was some correlation with radar derived wind speeds and low-level winds. I will say at the core the winds were MUCH higher.

One thing here is those data were just raw velocity and you have to justify to get Vgamx.

https://www.pnas.org/doi/10.1073/pnas.2021535118

Following standardized procedures, our analysis adjusts Vd for the effects of coarse spatial sampling and inferred unobserved Vgmax due to Vp. Vd are corrected for aspect ratio sampling error, (39, 41, 51, 72) by multiplying by 1/(1−0.48(B/Xd)). This adjustment is capped at 1.086, equivalent to what would be applied for B/Xd > 6, to arrive at a temporary product, adjusted velocity, Vda. Vd is a measure of only the toward/away component of the full wind-velocity vector since Doppler radars do not sample the component of motion perpendicular to radar beams. For tornadoes propagating at any appreciable angle to the radar beams, the unobserved component of the wind velocity vector, Vp sin(θ) where θ is the angle between Vp and the radar-beam pointing angle, is significant. To account for this, Vgmax = Vda + Vp sin(θ). The median Vp is 10 m⋅s−1 at the time of maximum intensity, with an extreme of 25 m⋅s−1 consistent with that found in individual case studies. The corrections applied to Vd through this process are usually substantially less than Vp due to multiplication by sin(θ). As stated above, no correction is applied to data collected while the DOWs are mobile unless precise navigation is available, or if Vp or sin(θ) are not known with confidence, due to uncertain DOW angular navigation or limited duration of observations.

That's part of the reason why "winds" of Bridge Creek mentioned in this article was 144m/s rather than 170-180mph raw velocity from GR2.

 

[CalebRoutt]

One thing here is those data were just raw velocity and you have to justify to get Vgamx.

https://www.pnas.org/doi/10.1073/pnas.2021535118

That's part of the reason why "winds" of Bridge Creek mentioned in this article was 144m/s rather than 170-180mph raw velocity from GR2.

Again, those winds were at the core which is what the DOW had on the screenshot I had above. However those winds were surrounded by a widespread area of 170-180 mph.

 

[pohnpei]

Correct! Not what I was trying to hint at.

What I was saying was that 170-190 mph winds matched quite well over Cambridge Shores, the damage there certainly supports it. Of course the winds may of been higher.

RaxPol, DOW, TTUKA etc all sample violent tornado's fairly decently especially when they are within the "tornado boundary layer". A good example of what I was meaning occurred on May 3rd 1999. The peak Delta-V on KTLX was ∼77 m/s (172mph) and DOW was recording a very large area of 170-180 mph winds (with the exception of the core). So in that case there was some correlation with radar derived wind speeds and low-level winds. I will say at the core the winds were MUCH higher.

One thing need to add here is even DOW got fairly well data within "tornado boundary layer", It's still far away from actual wind speed. This paper had good explanation and caculation about this

Tornado vortex structure, intensity, and surface wind gusts in large-eddy simulations with fully developed turbulence | OpenSky

opensky.ucar.edu

 

[CalebRoutt]

The TBL is more in the vertical than horizontal. I was meaning there's a certain depth where wind speeds are pretty close to the same as the surface with the exception of within sub-vortices. The TBL can extend a decent way up depending on a number of factors. In no way did I say mobile radar gets the sfc winds correct.

 

[pohnpei]

Again, those winds were at the core which is what the DOW had on the screenshot I had above. However those winds were surrounded by a widespread area of 170-180 mph.

Yes and what I said was you can't really read velocity as high as 300mph on that 2354z scan. Some kinds of justification is needed and is also needed for another tornados.

 

[CalebRoutt]

I dont think I said winds were over 300 mph there, I said "overall" winds were consistent within the large outer core region of the tornado. The intense F5 damage was extremely small compared to the overall tornado.

 

[pohnpei]

The TBL is more in the vertical than horizontal. I was meaning there's a certain depth where wind speeds are pretty close to the same as the surface with the exception of within sub-vortices. The TBL can extend a decent way up depending on a number of factors. In no way did I say mobile radar gets the sfc winds correct.

Yes, other than subvortex, for most violent tornados, the gradient whithin the minimum range solution would still be considerablely large and result in disproportional wind speed whithin the pixel.

 

[buckeye05]

The contextual damage at Cambridge Shores was most certainly EF5. Trees either completely debarked or shredded to near or at ground level, multiple homes swept in addition to severe debris granulation. Photo below.

The Bremen home wasn’t just a block home. There was a portion around the storm shelter that was a concrete foundation and was well bolted. That portion was swept to its slab. There is literally a home of similar structure that is still in the EF-Scale manual for EF5, thus a home (if well anchored) can be rated EF5.

Wrong. The Bremen home was a CMU perimeter with a gravel fill inside of it, which had an apparently unanchored slab layered on top, which the house was built on. That is weird, weird construction and not equivalent to a poured concrete foundation. Having just a portion of the foundation being slab does not make it EF5 worthy either. It has to be the whole slab.

Regarding the context in Cambridge Shores, you’re seeing things at this point. That tree damage does not stack up to past EF5s, and there was no significant debris granulation. Significant granulation reduced the pieces smaller than the palm of your hand. It does not cut it for EF5, period. There WAS legit granulation in Bremen though.

You’re confident and mostly on the right track, but still getting quite a bit wrong. I’d suggest that you take a step back and ask yourself if you’d rather dig your heels in, or rethink your stance when presented with new info, and I can tell which of those two is best for people who are willing to learn, but the rest is up to you.

 

[buckeye05]

Also, the Dalton, MN EF4 tornado was immediately ruled out as an EF5 candidate when the survey team found the CMU foundation, even though bolt cells were mortared properly and everything stayed together. That establishes that what you’re saying isn’t true. This was stated during a visual presentation by the NWS surveyors, and is viewable on YouTube. Go watch it, I’m not making this stuff up.

 

[Sawmaster]

Also, the Dalton, MN EF4 tornado was immediately ruled out as an EF5 candidate when the survey team found the CMU foundation, even though bolt cells were mortared properly and everything stayed together. That establishes that what you’re saying isn’t true. This was stated during a visual presentation by the NWS surveyors, and is viewable on YouTube. Go watch it, I’m not making this stuff up.

The systemic problem exemplified. It's not only a question of if CMU's are involved; it's also a question of whether they acted as a slab would or whether they rolled/ shifted/ moved/ broke thus removing the solid support from under the house or wall sitting on them. They can be made nearly as strong as homogeneous concrete although in residential construction you'll never see that- the best you'll get is filled cells and that's only a part of the process.

The question needs to be changed from whether CMU's were used to whether or not the foundation failed; only then will you have a chance at finding the truth.

Phil