Severe WX Severe Threat 25 March 2021

[CAL]

Based on radar?EF5?

This is a fascinating case. I have a tornado intensity forecasting index (the Vortex Value) which, even upon detailed reanalysis (e.g., VWP, sfc conditions etc.), failed to to indicate greater than minimal EF3 for the Newnan area. Must have been an extremely localized area of EF4 damage, perhaps enhanced by terrain flow or another oddity. Correlation coefficient data for the vortex value is over 0.9.

 

[TH2002]

I do have to wonder about this particular view from Greensboro, AL:


Are these empty foundations? If so, is there any way of getting a rough idea of the construction quality of these homes (Street View data, for example)?

 

[Shakespeare 2016]

I do have to wonder about this particular view from Greensboro, AL:

View attachment 7727
Are these empty foundations? If so, is there any way of getting a rough idea of the construction quality of these homes (Street View data, for example)?

It looks like there was some wind rowing of debris as well.

 

[TH2002]

It looks like there was some wind rowing of debris as well.

There was definitely some wind rowing along with debris granulation and tree debarking. Violent instances of damage.

 

[Equus]

The EF4 rating seems surprisingly liberal. Definitely not second guessing FFC as it probably deserves it but from damage I've seen I'd not be shocked if that would've peaked at high EF3 in some WFOs. Kind of like Hattiesburg 2013 and Dayton 2019.

 

[Shakespeare 2016]

The EF4 rating seems surprisingly liberal. Definitely not second guessing FFC as it probably deserves it but from damage I've seen I'd not be shocked if that would've peaked at high EF3 in some WFOs. Kind of like Hattiesburg 2013 and Dayton 2019.

Some of them photos you posted of those houses that were completely flattered to the slab foundation looks like low-end EF4 damage. That is if the houses were well-built. Yeah that rating did seem more liberal from the NWS in Peachtree.

 

[buckeye05]

We no way of definitively determining if those empty foundations were from houses, barns, or outbuildings without a closer view. I have yet to see anything along the Greensboro/Brent path that screams EF4 to me. It’s definitely possible, but let’s not get ahead of ourselves.

Also, don’t try to say there’s debris granulation based on aerial views. The only way to determine that is via up close inspection of the debris field.

 

[Equus]

It's definitely a proper precedent to rate tornadoes that leveled homes to the slab EF4, so I don't disagree with the rating, just saying that most WFOs have gotten extremely conservative and it's interesting to see violent rating used to rate violent damage for once.

 

[eric11]

The EF4 rating seems surprisingly liberal. Definitely not second guessing FFC as it probably deserves it but from damage I've seen I'd not be shocked if that would've peaked at high EF3 in some WFOs. Kind of like Hattiesburg 2013 and Dayton 2019.

Another weird feature is that there are tons of tors accompanied by nasty radar appearance entering big cities in recent years, Dayton 2019,Jefferson city 2019, Dallas 2019,Chattanooga 2020,Nashville 2020,and Newnan 2021, but yet none of them behaved what a solid EF4 should be like(Nashville and Dayton may be some borderline EF4 events).The big discrepancy between radar and damage confuses me a lot, and, why always nighttime? why always big cities? Is it some new climate trend or something else?

 

[TH2002]

We no way of definitively determining if those empty foundations were from houses, barns, or outbuildings without a closer view. I have yet to see anything along the Greensboro/Brent path that screams EF4 to me. It’s definitely possible, but let’s not get ahead of ourselves.

Also, don’t try to say there’s debris granulation based on aerial views. The only way to determine that is via up close inspection of the debris field.

Exactly why I said "an empty foundation isn't an obvious indicator of EF5 damage".

I believe earlier in this thread someone posted a video with a ground level view from Greensboro showing what appeared to be granulation of debris, unless I'm mistaken.

 

[pohnpei]

We no way of definitively determining if those empty foundations were from houses, barns, or outbuildings without a closer view. I have yet to see anything along the Greensboro/Brent path that screams EF4 to me. It’s definitely possible, but let’s not get ahead of ourselves.

Also, don’t try to say there’s debris granulation based on aerial views. The only way to determine that is via up close inspection of the debris field.

There was ground level footage to show these debris really churn into very Small peices and carried very long distance.

 

[Matthew70]

Honestly a lot of these ratings to me make no sense. I’m no expert but could some of these ratings be biased to make this a more severe outbreak than it was? I can find many from 4/27/11 that were rated much lower with more extreme damage. So what gives?

 

[TH2002]

There was ground level footage to show these debris really churn into very Small peices and carried very long distance.

Yep, that's the video.

 

[Matthew70]

There was ground level footage to show these debris really churn into very Small peices and carried very long distance.

What was the construction of the houses? Vinyl or brick? Plus debarking? I see trees still with bark on them.

 

[pohnpei]

Another weird feature is that there are tons of tors accompanied by nasty radar appearance entering big cities in recent years, Dayton 2019,Jefferson city 2019, Dallas 2019,Chattanooga 2020,Nashville 2020,and Newnan 2021, but yet none of them behaved what a solid EF4 should be like(Nashville and Dayton may be some borderline EF4 events).The big discrepancy between radar and damage confuses me a lot, and, why always nighttime? why always big cities? Is it some new climate trend or something else?

I think many people tend to overreact about the damage after these big city tornados like house all gone or vanish, something like this. Actually none of these tornados's radar couplet reached well above EF4 level so the rating of them may not be that surprising. And the limited thermodynamics in the evening can work as a factor to hinder these tornados went stronger.

 

[pohnpei]

What was the construction of the houses? Vinyl or brick? Plus debarking? I see trees still with bark on them.

I think trees were obviously debarked if you look closely. Not largely debarked for sure, but that is actually a matter of the amount of debris factor which can't be so many in such rural areas.

 

[Equus]

There were two tornadoes with probable violent damage including one which was likely down for over an hour, and both tornadoes in the Bham metro to Ohatchee family (assuming it lifted) were likely of EF3 intensity; that's a very high end outbreak for this area. I'm baffled as to why we would want to downplay what was a rather high end outbreak. The initial outlook over NE MS and NW AL largely busted but given the parameters that risk was 100% entirely justified with absolutely incredible parameters. Why it did not come to pass over the NW part but instead occurred on the SE edge of it can be discussed and studied but that level of risk was clearly necessary for the parameters. Those that were spared should count themselves extremely fortunate as yesterday had devastating potential over more areas than actually verified.

And I don't think we should compare ANY aspect of April 27 to the events of yesterday, damage ratings/level or otherwise, as 4/27 was a whole different order of magnitude to any outbreak since 1974 and probably any for many years to come; it is, however, still clearly skewing what the idea of a very significant outbreak actually is in the southeast.

 

[pohnpei]

There were two tornadoes with probable violent damage including one which was likely down for over an hour, and both tornadoes in the Bham metro to Ohatchee family (assuming it lifted) were likely of EF3 intensity; that's a very high end outbreak for this area. I'm baffled as to why we would want to downplay what was a rather high end outbreak. The initial outlook over NE MS and NW AL largely busted but given the parameters that risk was 100% entirely justified with absolutely incredible parameters. Why it did not come to pass over the NW part but instead occurred on the SE edge of it can be discussed and studied but that level of risk was clearly necessary for the parameters. Those that were spared should count themselves extremely fortunate as yesterday had devastating potential over more areas than actually verified.

And I don't think we should compare ANY aspect of April 27 to the events of yesterday as 4/27 was a whole different order of magnitude; it is, however, still clearly skewing what the idea of a very significant outbreak actually is in the southeast.

The fact that yesterday had numerous supercells(actually 3) walked very long distance and all being very prolific at prodcing long track EF3-4 level tornados was quite impressive. These types of event was rare in at least past 5-6 years, not just in Dixie, but in entire US. Easter had one paticularly impressive supercell family in MS but rest of them were QLCS event at night. And I think years like 2016 or 2018 don't have this types of event at all.

 

[Equus]

Absolutely. Having three discrete, long-tracked, sustained supercells maintaining themselves for that long and dropping multiple strong tornadoes is VERY rare and high end in Dixie. Whole years do go by without events that can do that, and yesterday did so despite the weaker shortwave and rain mass.

 

[Equus]

I do think it's problematic that two straight highs in Mississippi produced virtually nothing there and it would be nice to get some research into why modeling was a swing and a miss both times; there will certainly be some big time complacency across MS and parts of north AL next time because two straight events passed without significant severe in either place.

With yesterday's event, it's looking like a much weaker shortwave than expected (leading to SW surface winds parallel to storm motion and thus rapid upscale growth until late in the afternoon) was one of the big issues; in AL, that massive rain shield really killed the instability since the very strong EML that moved in behind the mass could not be overcome with the much lower level of instability that resulted, capping off the second round. The open warm sector wherever storms weren't blobbed up together clearly produced violent sustained cells, but the ingredients just didn't come together across N MS and most of NW AL, again.