Tornado Outbreak Aftermath: April 26th-30th, 2014

[JC-CT]

Regrading these bolded points, if a home isn't built to withstand high winds how can you rate the winds any higher than what is required to completely destroy it? This is the point I'm making, eventually there is an upper limit to the wind required to do the damage, and you can't go any higher than that without further information.

 

And how do you know many of the 2003 F3s would be EF4s today? Are you just making that up, or is there some source out there that confirms this?

 

All I'm arguing is that there was likely no ulterior motive involved here keeping this tornado an EF4. The team did the best job they could with available information.

 

At this point there are far more expert opinions in this thread than I can offer, I'm not going to convince anyone that there wasn't something nefarious or incompetent going on at LZK.

 

 

The question that seems to naturally arise from this is, why would mobile radar data be completely thrown out as further information?

 

Is the radar really that far off, technologically, from being useful? I can certainly understand why we wouldn't want to use only radar data, but I don't understand (and maybe I just don't understand) why it is not considered as additional evidence within the context of the damage assessment.

[AtticaFanatica]

The question that seems to naturally arise from this is, why would mobile radar data be completely thrown out as further information?

 

Is the radar really that far off, technologically, from being useful? I can certainly understand why we wouldn't want to use only radar data, but I don't understand (and maybe I just don't understand) why it is not considered as additional evidence within the context of the damage assessment.

There's some unanswered questions, such as a. how radar estimated winds at 50 or 100 m height or higher compare to tornado winds where damage is occurring, b. how nearly instantaneous radial wind estimates compare to 3 s gusts used for the EF scale, c. how air velocity (what we're interested in) differs from scatterer velocity, d. the effects of complicated scatterer distributions within a resolution volume on the velocity estimate, and e. the impacts that asymmetric flow and large vertical velocities in tornadoes have on the velocity estimate.

However, in all of the above issues except b., the effect is for the radar estimate to be less than the true wind speed. Accounting for all of the above, the radar estimate is very likely to be a lower bound on the true tornado wind speed. Therefore, it should be a reasonable tool to upgrade tornado intensity ratings, but not to downgrade them.

That being said, mobile radar data are not a panacea for the intensity climatology. Very few tornadoes get observed by mobile radars, and not nearly enough to even begin to correct for the chronic and severe underrate bias that far surpasses in importance the comparatively minor differences of opinion expressed in this thread.

[Ensō]

However, in all of the above issues except b., the effect is for the radar estimate to be less than the true wind speed. Accounting for all of the above, the radar estimate is very likely to be a lower bound on the true tornado wind speed. Therefore, it should be a reasonable tool to upgrade tornado intensity ratings, but not to downgrade them.

 

This (among other things actually) is what doesn't make sense to me. I could certainly understand not rating EF5 based on, say, 94 m/s observed at a couple hundred meters AGL for a few seconds. There would be too many questions to feel comfortable in using data like that. But in cases where you have velocities well above the threshold for a given rating observed at a reasonable height for an extended period of time, there doesn't seem to be any scientifically valid reason to discard it. Of course, as was suggested earlier in this thread, the objections largely don't seem to be based in science anyway. Apparently it's a moot point after last year, but I really hope that radar-based ratings (or at least incorporating radar data in the survey process) is reconsidered in the near future.

 

Although, on the subject of inconsistency, even radar data didn't seem to be used consistently. The 5/24/11 El Reno tornado was rated EF5 on the basis of ~125 m/s velocities observed by RaXPol at fairly low elevation (despite the fact that it produced some extraordinary damage that should easily have been EF5 in its own right - but that's a whole different ball o' wax), but the Canton Lake tornado on the same day was rated EF3 despite both DOW7 and NOXP observing high-end EF4 velocities (~85 m/s) at an even lower elevation than at El Reno, something like 40 or 45 meters. The Canton Lake tornado also produced ground scouring and pretty high-end tree damage, so it's not like there was no support for potentially violent-level intensity.

 

Anyhow, I suppose we'll still be dealing with inconsistencies like that regardless of our methodologies, I just think a lot more could be done to reduce them, and I think we have good reason for wanting to do so.

[Ensō]

Regrading these bolded points, if a home isn't built to withstand high winds how can you rate the winds any higher than what is required to completely destroy it? This is the point I'm making, eventually there is an upper limit to the wind required to do the damage, and you can't go any higher than that without further information.

 

And how do you know many of the 2003 F3s would be EF4s today? Are you just making that up, or is there some source out there that confirms this?

 

This is the whole point though. There are very, very, very few homes that are of such superior construction that they provide incontrovertible evidence for an EF5 rating all by themselves, and if that were all that mattered then I'd wager we would probably only see an EF5 maybe two or three times a decade. That obviously isn't the case though, and it isn't the case because some surveys rightly look beyond strictly construction quality and consider the surrounding context as well.

 

I know I've harped on this over and over, but bear with me for one more example. Let's say you have two identical homes, both of them constructed exactly the same as the home on E Wicker St. (properly spaced anchor bolts, nuts and washers, but some uncertainty regarding the stud/sill plate connections), and both of them are swept away. In the area around one of the homes, trees are moderately damaged (leaves and small limbs removed, maybe a few limbs broken, small trees snapped and/or shallow-rooted trees uprooted, that sort of thing). There's no clear ground scouring or wind rowing evident, nor is there any immediately upstream or downstream from the home. You'd probably be inclined to go with the expected wind speed, if not even lower, since the surrounding environment doesn't give you any reason to be confident in a higher estimate.

 

Now in the area surrounding the second identical home, trees show debarking/denuding and other high-end damage. There's pronounced ground scouring and wind rowing both immediately surrounding the homesite and upstream/downstream, and other homes in the same area - though not as well-built - were also completely swept away and scattered hundreds of yards. There's also a Chevy Suburban that was thrown a long distance from the home (1/4 mile according to the homeowner) and very badly damaged. Maybe the destruction of the home itself would suggest a wind speed of 185 or 190 mph if you adhere strictly to the build quality, but all of the evidence surrounding that home ought to give you greater than normal confidence in going above what the construction alone would tell you. That's generally where EF5 ratings come from, not from perfectly built homes. All of those things I mentioned are precisely what Jim LaDue, Tim Marshall and some of the other foremost experts in damage surveys advise using when trying to discriminate between EF4 and EF5 ratings.

[AtticaFanatica]

This (among other things actually) is what doesn't make sense to me. I could certainly understand not rating EF5 based on, say, 94 m/s observed at a couple hundred meters AGL for a few seconds. There would be too many questions to feel comfortable in using data like that. But in cases where you have velocities well above the threshold for a given rating observed at a reasonable height for an extended period of time, there doesn't seem to be any scientifically valid reason to discard it. Of course, as was suggested earlier in this thread, the objections largely don't seem to be based in science anyway. Apparently it's a moot point after last year, but I really hope that radar-based ratings (or at least incorporating radar data in the survey process) is reconsidered in the near future.

Although, on the subject of inconsistency, even radar data didn't seem to be used consistently. The 5/24/11 El Reno tornado was rated EF5 on the basis of ~125 m/s velocities observed by RaXPol at fairly low elevation (despite the fact that it produced some extraordinary damage that should easily have been EF5 in its own right - but that's a whole different ball o' wax), but the Canton Lake tornado on the same day was rated EF3 despite both DOW7 and NOXP observing high-end EF4 velocities (~85 m/s) at an even lower elevation than at El Reno, something like 40 or 45 meters. The Canton Lake tornado also produced ground scouring and pretty high-end tree damage, so it's not like there was no support for potentially violent-level intensity.

Anyhow, I suppose we'll still be dealing with inconsistencies like that regardless of our methodologies, I just think a lot more could be done to reduce them, and I think we have good reason for wanting to do so.

Sometimes local offices aren't aware of mobile radar data because, admittedly, often that radar data isn't looked at for several days or weeks after it's collected.

Regardless, I think these debates about select cases and whether they're EF4 or EF5 really lose the forest for the trees. At least on these cases, the rating is right to within 1 EF scale, which is probably good enough for most scientific endeavors (most studies lump all violent tornadoes together anyway). The much bigger problem is the very large number of tornadoes rated EF0 that are off by multiple EF scales.

[Ensō]

Sometimes local offices aren't aware of mobile radar data because, admittedly, often that radar data isn't looked at for several days or weeks after it's collected.

Regardless, I think these debates about select cases and whether they're EF4 or EF5 really lose the forest for the trees. At least on these cases, the rating is right to within 1 EF scale, which is probably good enough for most scientific endeavors (most studies lump all violent tornadoes together anyway). The much bigger problem is the very large number of tornadoes rated EF0 that are off by multiple EF scales.

 

I'd certainly agree with that. Alexander & Wurman's paper drove that point home, and I suspect it's probably just the tip of the iceberg with respect to underrating tornadoes due to lack of sufficient DIs.

[on_wx]

Sometimes local offices aren't aware of mobile radar data because, admittedly, often that radar data isn't looked at for several days or weeks after it's collected.

Regardless, I think these debates about select cases and whether they're EF4 or EF5 really lose the forest for the trees. At least on these cases, the rating is right to within 1 EF scale, which is probably good enough for most scientific endeavors (most studies lump all violent tornadoes together anyway). The much bigger problem is the very large number of tornadoes rated EF0 that are off by multiple EF scales.

 

Has there ever been discussion to try to patch this issue? Eg. rating based on video evidence of violent motion leading to a standard say EF2 rating, or lumping those 1/2-1 mile wide EF0's to EF1 just for closer rating accuracy?

[Ensō]

Has there ever been discussion to try to patch this issue? Eg. rating based on video evidence of violent motion leading to a standard say EF2 rating, or lumping those 1/2-1 mile wide EF0's to EF1 just for closer rating accuracy?

 

I know there's been a lot of talk about adding an "EF-unknown" category, which would at least remove some of that uncertainty from the data. It's far from an ideal solution but I think it might be a good start unless or until something more can be done to address those clearly violent tornadoes that don't strike much of anything. There was also a paper recently addressing the possibility of adding additional DIs that would help to cover those tornadoes that occur in very rural areas (farm equipment and assorted structures, gas/oil drilling equipment, more detailed and thorough accounting for trees and possibly grass scouring at some point in the future, vehicles, etc.) It's likely that a lot of strong/violent tornadoes would still go underrated, but at least it'd be a start.

 

I think photogrammetry might be an interesting possibility as well, though it's also less than ideal and may not be deemed accurate enough. It's intriguing though given the proliferation of chasers with HD video, precise GPS tracking, etc. You're a lot more likely to get several high-quality videos of a large tornado out in the middle of nowhere than for that same tornado to strike some substantial structures.

[gymengineer]

I just picked that span to point out that EF5s aren't necessarily a yearly occurrence. It is possible to have violent tornadoes that do a lot of damage that aren't EF5 in intensity. And plenty of people have mentioned in this thread that recent tornadoes would easily garner an EF5 rating in years past. That to me sounds like people think we're being too conservative now.

 

As far as consistency from WFO to WFO, do you think that there isn't consultation going on with experts? It's not like LZK goes out and gets to assign a rating without talking to experts (in many cases the same experts who assist on other large damage surveys).

Not EF5--- they're talking about F5 ratings using the "old" indicators before the EF scale came out. For example, the tornado pictured earlier in the thread (Belmond, IA) was rated F5 but certainly would not be rated EF5 nowadays-- the foundation was swept clean at one plot, but the house was deposited in a tidy pile a bit away from the foundation, and neighboring houses were barely damaged.

[AtticaFanatica]

Has there ever been discussion to try to patch this issue? Eg. rating based on video evidence of violent motion leading to a standard say EF2 rating, or lumping those 1/2-1 mile wide EF0's to EF1 just for closer rating accuracy?

You could, but then you'll just reverse the problem by overrating a lot of EF0s.

Photogrammetry requires a lot of additional information and for the equipment to be set up properly. EF unknown and EFx+ are options being discussed.

[mfgmfg]

Are there any databases being started/maintained that will use DOW *and* damage indicators to have a good record going forward for ground wind speed+damage indicator measurements?

[Ensō]

Are there any databases being started/maintained that will use DOW *and* damage indicators to have a good record going forward for ground wind speed+damage indicator measurements?

 

My understanding is that, when available, there will be a note on the mobile radar observations in the tornado's listing in Storm Data. For instance, the listing for the El Reno tornado includes this paragraph:

 

This tornado was well sampled by two separate mobile research radar teams: the University of Oklahoma RaXPol radar, and the Center for Severe Weather Researchs Doppler on Wheels. Both radars captured high temporal and spatial resolution data relatively close to the large tornado. Both radars measured winds in the tornado of more than 200 mph. The RaXPol radar data shows winds of at least 295 mph very close to the surface. These intense winds were present in very small sub-vortices within the larger tornado circulation. An analysis of the high resolution radar data combined with the results of the ground damage survey indicates that none of these intense sub-vortices impacted any structures in rural Canadian County. So despite the measured wind speeds, surveyors could not find any damage that would support a rating higher than EF3 based solely on the damage indicators used with the EF scale.

 

And the Bennington, KS tornado includes this very interesting bit:

 

This tornado was nearly 1 mile wide at times and NWS damage survey found EF3 damage indicators suggesting winds to around 150 mph.  2 mobile doppler radars were within 5-6km of this tornado and did sample winds around and above 100m well in excess of 166 mph. In fact they measured winds of 247 mph at 100m! Nothing close to EF5 damage was revealed on the survey.  However, given the lack of damage indicators available within the track of the tornado we have incorporated the mobile doppler wind data into our assessment of the tornado strength and we believe that this tornado contained at least EF4 winds in excess of 166 mph.  We acknowledge the current directive which states that one cannot rate tornado intensity by non-damage data sources so we will enter this in as EF3 however we are stating in the comments that this was a violent tornado with most likely EF4 intensity at some point during its life. 

[klw]

Sorry if this has been posted before.  It is security camera footage from Tupelo.

http://thevane.gawker.com/this-security-camera-footage-captured-the-moment-a-torn-1573007643/+sarah-hedgecock

 

 

[Ground Scouring]

Does anyone have ground-level images of the vegetative damage in the Bennington tornado?

 

I would also like to hear some explanations as to why the vegetative damage was less than expected in the 2013 El Reno tornado.

[AtticaFanatica]

It's easy to determine the strength of constructed materials in wind tunnel experiments. It's not easy to test the strength of vegetation of different species in varying soils with varying moisture contents, particularly when the impact of surface-level vertical velocities in the tornado are basically unknown.

[mfgmfg]

Sorry if this has been posted before.  It is security camera footage from Tupelo.

http://thevane.gawker.com/this-security-camera-footage-captured-the-moment-a-torn-1573007643/+sarah-hedgecock

That's some Wizard of Oz vibes I'm getting there with the shifts between color and B&W. I'd also like to hire whomever installed that camera to do some installations for me - it was like a rock.

[Torchageddon]

Has there ever been discussion to try to patch this issue? Eg. rating based on video evidence of violent motion leading to a standard say EF2 rating, or lumping those 1/2-1 mile wide EF0's to EF1 just for closer rating accuracy?

This is something I really dislike about the tornado scale, is rural strong tornadoes can get rated EF0 and junk. Violent motion gives it away a lot of the time.

 

Does anyone have ground-level images of the vegetative damage in the Bennington tornado?

 

I would also like to hear some explanations as to why the vegetative damage was less than expected in the 2013 El Reno tornado.

I often wonder when these very powerful tornadoes hit nothing why there isn't ground scouring observations and some debarking...like there were a bunch of those but we never hear of anything of significance afterwards. The supercell that was long-tracked on April 14, 2012 that went into Wichita KS had velocity scans that were indicating something above an EF4 for a good distance.

[TropicalAnalystwx13]

To reopen this can of worms, I was bored and decided to revisit the Vilonia tornado on the damage assessment toolkit. Apparently one home was constructed well enough for a potential EF5 rating. Here's their new reasoning for why it wasn't:

 

"An EF5 rating was not assigned because: Ratings are not normally assigned based on one only structure, the house was hit by the debris from the downtown buildings so there was uncertainty as to how much damage was done by the tornado itself vs. flying debris, and some trees (tall and skinny) were still standing along a ditch about 100 yards away."

 

[andyhb]

"An EF5 rating was not assigned because: Ratings are not normally assigned based on one only structure, the house was hit by the debris from the downtown buildings so there was uncertainty as to how much damage was done by the tornado itself vs. flying debris, and some trees (tall and skinny) were still standing along a ditch about 100 yards away."

 

Apparently these were the trees in question:

 

[blackjack123]

Apparently these were the trees in question:

 

Wikipedia also added the Vilonia tornado to its possible/probable F5/EF5 list. It mentions that a large metal fertilizer tank that weighed almost 30,000 lbs was found 3/4 mile away from where it originated.

[andyhb]

Wikipedia also added the Vilonia tornado to its possible/probable F5/EF5 list. It mentions that a large metal fertilizer tank that weighed almost 30,000 lbs was found 3/4 mile away from where it originated.

 

I'm pretty sure I know who added that to Wikipedia, and let's just say I wouldn't take his word for everything. The fertilizer tank part is true though.

 

I realize the controversy with the Vilonia tornado, but for this particular individual it has gone beyond that several times.