Severe WX April 11th-13th, 2020 Severe Weather Threat

[Equus]

Yeah CAMs did excellently with that. I'd suspected for a day or two in advance there would be a cluster practically overhead spitting tornadoes on that thermal boundary and that indeed happened to a grand scale. Very memorable event

 

[vanni9283]

Closer shot. This was indeed a house!
View attachment 2917

But again, what was the structural integrity of it?

 

[Equus]

I'm a little annoyed that the EF scale requires a massively overbuilt house before EF5 will be considered. Since literally no one builds houses massively above code, that practically eliminates the chance of an EF5 rating in 99% of violent tornadoes unless they strike a big city. I would MUCH rather see EF5 start at 'average' homes with decent anchoring being swept, rowed, and scoured (which currently rarely gets rated above 170-175) with mid-end EF5 (210) reserved for the overbuilt nuclear bunkers they currently want to see shredded for a low end EF5.

 

[vanni9283]

I'm a little annoyed that the EF scale requires a massively overbuilt house before EF5 will be considered. Since literally no one builds houses massively above code, that practically eliminates the chance of an EF5 rating in 99% of violent tornadoes unless they strike a big city. I would MUCH rather see EF5 start at 'average' homes with decent anchoring being swept, rowed, and scoured (which currently rarely gets rated above 170-175) with mid-end EF5 (210) reserved for the overbuilt nuclear bunkers they currently want to see shredded for a low end EF5.

They didn't finish the survey yet. I don't believe.

 

[Kory]

20 tornadoes in Alabama alone Sunday...that puts us at #5 in all-time tornado outbreaks for this state. Unless we add 3 more, we will remain at #5.

 

[Equus]

They haven't even gotten much past Bassfield yet as far as I know so there's a lot of survey to go; the EF complaint applies to all tornadoes though not just this one. Not that I'm jumping on the "BASSFIELD OBVIOUSLY EF5 REEEEE" bandwagon, but the EF scale is deliberately set up to make it very hard for house damage to be rated that high. That would be okay if F5 wasn't handed out like candy in 1970s-1990s for much lesser damage, rendering comparisons for EF5s vs F5s completely impossible.

 

[Shakespeare2016]

They haven't even gotten much past Bassfield yet as far as I know so there's a lot of survey to go; the EF complaint applies to all tornadoes though not just this one. Not that I'm jumping on the "BASSFIELD OBVIOUSLY EF5 REEEEE" bandwagon, but the EF scale is deliberately set up to make it very hard for house damage to be rated that high. That would be okay if F5 wasn't handed out like candy in 1970s-1990s for much lesser damage, rendering comparisons for EF5s vs F5s completely impossible.

NWS in New Orleans saw the house that was slabbed and had the anchor bolts ripped out. They said it will be considered in the final EF rating.

 

[vanni9283]

They haven't even gotten much past Bassfield yet as far as I know so there's a lot of survey to go; the EF complaint applies to all tornadoes though not just this one. Not that I'm jumping on the "BASSFIELD OBVIOUSLY EF5 REEEEE" bandwagon, but the EF scale is deliberately set up to make it very hard for house damage to be rated that high. That would be okay if F5 wasn't handed out like candy in 1970s-1990s for much lesser damage, rendering comparisons for EF5s vs F5s completely impossible.

My gripe about it is that I think the wind estimates at the high end of the scale are too low.

 

[Equus]

Honestly when they introduced the EF scale they figured the wind estimates would be a lot more accurate, but as time goes on I think the original F scale winds were far closer to accurate vs the damage caused than the EF scale. Maybe a touch too high, but at the higher end of the scale I think the EF scale underestimates violent tornado wind speeds. Plenty of DOW measured 200+mph not far from ~EF3 damage

 

[Shakespeare2016]

My gripe about it is that I think the wind estimates at the high end of the scale are too low.

I think maybe somewhat but they probably are lower than the 261 mph which started the F5 category on the F-scale.

 

[Equus]

Honestly it might turn out that the actual winds are right in between the F and EF scale estimates. But that's something we will probably never know with absolute confidence

 

[vanni9283]

I think maybe somewhat but they probably are lower than the 261 mph which started the F5 category on the F-scale.

Probably. What would be the ideal wind speed to start the EF-5 range in your view?

 

[Shakespeare2016]

Probably. What would be the ideal wind speed to start the EF-5 range in your view?

I would guess around 230 mph. Historically I believe most F5 and EF5 tornadoes had winds of 250+ mph.

 

[Equus]

I like the idea that was proposed that had overlapping speeds; somewhere in the 200-250 range seems a good place for EF5 to start, maybe in the 220 range or so if I had to pick something. But that comes with no wind engineering expertise, just opinion.

 

[vanni9283]

Honestly it might turn out that the actual winds are right in between the F and EF scale estimates. But that's something we will probably never know with absolute confidence

Well I think the range of the EF-4 category should exceed 200 mph for sure.

 

[vanni9283]

I would guess around 230 mph. Historically I believe most F5 and EF5 tornadoes had winds of 250+ mph.

230 mph is approximately 200 kts. I say change the mph values to kts, maybe that would be more accurate.

 

[andyhb]

Yet another EF3 in Columbia’s CWA.

 

[South AL Wx]

20 tornadoes in Alabama alone Sunday...that puts us at #5 in all-time tornado outbreaks for this state. Unless we add 3 more, we will remain at #5.

Looks like MOB has added 3 tornadoes to the Alabama total:

IEM :: PNS from NWS MOB

PNS issued by NWS MOB at 15 Apr 2020 00:06 UTC

mesonet.agron.iastate.edu

 

[Mike S]

I know some of you care about this stuff - ABC 33/40 has posted James Spann's wall to wall coverage from Sunday night on Youtube

 

[xJownage]

Has anybody figured out the failure mode in S AL? I've heard a few different reasons (veered winds, too much shear tearing apart updrafts, storms having already grown upscale while they were still elevated in LA) but nothing really substantial.