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Severe Weather Threat 5/19-5/22/2024

jiharris0220 said:
Eh, I don’t really think it matters too much.

The structures within Greenfield didn’t look particularly sturdy, and the tree damage fits the bill with that wind speed designation.

This damage survey definitely took a lot of time and I’m confident they really did try to find higher DIs, but again, these Great Plain towns rarely have good construction.

Now if the contextuals were obviously high end this would more egregious, but other than that single vehicle that got chassied, I didn’t see any.

So far, I haven’t seen any surveys this year that were bad or underestimated the damage a tornado caused. I’m still a little unsure about the Celina rating but even that is splitting hairs.
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I also would add that aerial imagery to date has shown very little scouring over farmland, even in the areas where radar-derived velocities were highest. Fields around the turbines, for instance, showed little or no scouring. Scouring was actually most pronounced in Greenfield itself, after the tornado had weakened a bit. Yet even there the various DIs suggested no more than high-end EF3 or low-end EF4 (partial debarking at best with one or two exceptions, little real granulation or high-end vehicular damage, subpar quality of construction, etc.). Had the tornado been stronger at the very least scouring of farmland would likely have been more pronounced. Overall, at no point along the path do DIs, contextual or otherwise, convincingly suggest anything more than a fairly marginal EF4, at least in my view, notwithstanding radar-derived data suggesting near-EF5 winds just above the ground. This goes to show that radar by itself is far from adequate in determining peak intensity. (DOW notwithstanding, El Reno 2013 also produced less intense DIs than similarly slow-moving tornadoes over similar terrain.)
 
Casuarina Head said:
I also would add that aerial imagery to date has shown very little scouring over farmland, even in the areas where radar-derived velocities were highest. Fields around the turbines, for instance, showed little or no scouring. Scouring was actually most pronounced in Greenfield itself, after the tornado had weakened a bit. Yet even there the various DIs suggested no more than high-end EF3 or low-end EF4 (partial debarking at best with one or two exceptions, little real granulation or high-end vehicular damage, subpar quality of construction, etc.). Had the tornado been stronger at the very least scouring of farmland would likely have been more pronounced. Overall, at no point along the path do DIs, contextual or otherwise, convincingly suggest anything more than a fairly marginal EF4, at least in my view, notwithstanding radar-derived data suggesting near-EF5 winds just above the ground. This goes to show that radar by itself is far from adequate in determining peak intensity. (DOW notwithstanding, El Reno 2013 also produced less intense DIs than similarly slow-moving tornadoes over similar terrain.)
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Yeah, I'd have to respectfully disagree. This was nothing less than a mid-range EF4. Not "fairly marginal."
 
Lord here we go again.
 
I still believe the Greenfield tornado has the potential to be upgraded to a high end EF4. There is still a lot of DI’s that need to be added in the survey, including some slabbed homes in the southwest corner of town that appear (at least on a surface level) to be well constructed.
 
slenker said:
I still believe the Greenfield tornado has the potential to be upgraded to a high end EF4. There is still a lot of DI’s that need to be added in the survey, including some slabbed homes in the southwest corner of town that appear (at least on a surface level) to be well constructed.
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I am starting to get confused myself despite my frustrations on how tornadoes are rated.
 
jiharris0220 said:
To be honest, I wouldn’t call any tornado above Ef2 “fairly marginal”.

Just seems a bit off base, also along with the fact the objective description of ef3/ef4 is literally significant and violent.
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@jiharris0220 I meant that the DIs, including those on the DAT, so far do not really support much more than the lower bound (~170–175 mph or so). Even if, pending additional data, structural DIs can be debated, I think that my point about scouring still stands; in general I believe, as you do, that the survey has accurately appraised the case thus far. Even if some stronger structural indicators were located the contextual evidence might or might not support a higher wind.
 
jiharris0220 said:
Kinda confused by this post, the comments on here at least that I’ve seen haven’t been emotionally charged or too far in the deep end.

So far it seems it’s just respectable opinions regarding the Greenfield rating, unless there has been no no comments that have been deleted that I’ve missed, lol.
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I think he’s referring to you know who lol your comments were fine. Mr. Head’s usually have an agenda behind them
 
slenker said:
I still believe the Greenfield tornado has the potential to be upgraded to a high end EF4. There is still a lot of DI’s that need to be added in the survey, including some slabbed homes in the southwest corner of town that appear (at least on a surface level) to be well constructed.
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Yeah, I’m not sure why people are already jumping to the conclusion that it won’t get rated above 175 mph when there are still plenty of DIs to be added and the NWS said 175-185 mph.
 
SouthFLwx said:
Yeah, I’m not sure why people are already jumping to the conclusion that it won’t get rated above 175 mph when there are still plenty of DIs to be added and the NWS said 175-185 mph.
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I can kinda understand why. There are a couple of 170 MPH EF4s that were likely much stronger that come to my mind, like Cordova or Henryville, but at the same time, Rolling Fork took something like a month to get upgraded from 170 MPH to 195 MPH. It just needs some time and I’m sure the survey will be a very complete one.
 
Casuarina Head said:
I also would add that aerial imagery to date has shown very little scouring over farmland, even in the areas where radar-derived velocities were highest. Fields around the turbines, for instance, showed little or no scouring. Scouring was actually most pronounced in Greenfield itself, after the tornado had weakened a bit. Yet even there the various DIs suggested no more than high-end EF3 or low-end EF4 (partial debarking at best with one or two exceptions, little real granulation or high-end vehicular damage, subpar quality of construction, etc.). Had the tornado been stronger at the very least scouring of farmland would likely have been more pronounced. Overall, at no point along the path do DIs, contextual or otherwise, convincingly suggest anything more than a fairly marginal EF4, at least in my view, notwithstanding radar-derived data suggesting near-EF5 winds just above the ground. This goes to show that radar by itself is far from adequate in determining peak intensity. (DOW notwithstanding, El Reno 2013 also produced less intense DIs than similarly slow-moving tornadoes over similar terrain.)
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Please, just stop.
 
Got my chase footage (such as it is) from May 21 up. Got on the storm that was tornado-warned near Corydon/Albia and wild-goose chased it to Eddyville. Something was a little off about the environment east of I-35 in Iowa (perhaps weak lapse rates owing to not enough time for recovery behind earlier convection) and storms struggled to produce once past that corridor despite SPC's quite ominous MD No. 879.

 
SouthFLwx said:
Yeah, I’m not sure why people are already jumping to the conclusion that it won’t get rated above 175 mph when there are still plenty of DIs to be added and the NWS said 175-185 mph.
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Re: Greenfield: there are grounds to believe that the actual near-surface winds were (considerably?) lower than indicated by radar. A recent study suggests this:

Comparison of Tornado Damage Characteristics to Low-Altitude WSR-88D Radar Observations and Implications for Tornado Intensity Estimation​

Anthony W. Lyza,
Matthew D. Flournoy, and
A. Addison Alford

Online Publication: 19 Mar 2024
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Unfortunately, the body of the work itself is behind a paywall, but the critical portion is highlighted below (note that it is supposedly corroborated by other studies):
This study builds upon a recently proposed empirical relationship between radar-observed velocities in the lowest 150 m AGL and the theoretical peak 15-m AGL wind speed. We create and analyze a dataset of 194 velocity observations within tornadoes in the lowest 150 m AGL. These observations are drawn from 105 individual tornadoes that occurred across a diverse range of EF-scale ratings (EF0–4), convective modes (discrete supercell and quasi-linear convective system), geographical regions, and housing-unit densities (HUD). Comparing the radar-estimated and damage-estimated tornado wind speeds, and corresponding EF- and F-scale ratings, is the primary focus of the ensuing analysis. Consistent with recent work, damage-estimated tornado wind speeds tend to be lower than radar-estimated near-surface wind speeds, especially for stronger tornadoes.
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Now the study does suggest that, in cases where damage aligns with radar, the EF scale underestimates high-end wind speeds near ground level. By the same token, however, if damage suggests weaker winds, then the radar might also overestimate some events. The former would apply to the well-known events that have been discussed here. The latter might apply to events such as Greenfield. Once again, based on DIs, I still do not see much evidence to support considerably higher wind speeds than the survey and DAT currently indicate, unless I am missing something.
 
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Casuarina Head said:
Re: Greenfield: there are grounds to believe that the actual near-surface winds were (considerably?) lower than indicated by radar. A recent study suggests this:

Unfortunately, the body of the work itself is behind a paywall, but the critical portion is highlighted below (note that it is supposedly corroborated by other studies):

Now the study does suggest that, in cases where damage aligns with radar, the EF scale underestimates high-end wind speeds near ground level. By the same token, however, if damage suggests weaker winds, then the radar might also overestimate some events. The former would apply to the well-known events that have been discussed here. The latter might apply to events such as Greenfield. Once again, based on DIs, I still do not see much evidence to support considerably higher wind speeds than the survey and DAT currently indicate, unless I am missing something.
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I think the rest of the abstract gives better context to what Lyza's thinking is:
Damage- and radar-estimated wind speed differences are not strongly related to the availability of damage indicators (as measured by HUD). While some relationship exists—particularly underestimates of peak wind speeds for strong–violent tornadoes in low HUD areas—the tendency of radar-based strong/violent tornado intensity estimates to be meaningfully higher than EF-scale-based damage estimates exists across the HUD spectrum. The legacy F-scale wind speed ranges may ultimately provide a better estimate of peak tornado wind speeds at 10–15 m AGL for strong–violent tornadoes and a better damage-based intensity rating for all tornadoes. These results are contextualized with regards to ongoing community efforts to improve tornado intensity estimation.
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I personally think that whether an event is 'high' or 'low' end of a given rating in a relative sense and the murky relationship between what EF DIs allege and what radar shows aren't the same thing. Related, very much so, but not the same thing.
 
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