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Severe WX April 1-2 (overnight) Severe Weather Event

18z NAM is absolutely nasty on Wednesday across a large area, particularly in the Mid South and Lower Ohio Valley from 21z through 03z (and probably longer).
 
andyhb said:
18z NAM is absolutely nasty on Wednesday across a large area, particularly in the Mid South and Lower Ohio Valley from 21z through 03z (and probably longer).
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Andy, are you seeing any failure modes for Wednesday? Capping looks pretty decent until storms initiate and I don't see crapvection being an issue. Forcing looks pretty decent as well, should support supercells with some a few pockets of linear development but not enough to turn it into a derecho. Lapse rate look more than sufficient and quite robust.
 
lake.effect said:
Andy, are you seeing any failure modes for Wednesday? Capping looks pretty decent until storms initiate and I don't see crapvection being an issue. Forcing looks pretty decent as well, should support supercells with some a few pockets of linear development but not enough to turn it into a derecho. Lapse rate look more than sufficient and quite robust.
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I second this…
 
lake.effect said:
Andy, are you seeing any failure modes for Wednesday? Capping looks pretty decent until storms initiate and I don't see crapvection being an issue. Forcing looks pretty decent as well, should support supercells with some a few pockets of linear development but not enough to turn it into a derecho. Lapse rate look more than sufficient and quite robust.
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There's a number of potential failure modes. The biggest one is early convection and outflow overrunning the warm sector. Another may be boundary orientation (which would be mitigated if a pre-frontal trough is present) and the fact that the primary wave is leaving the warm sector behind in the afternoon (which could be mitigated if there are any embedded shortwaves in the jet). A third may be a larger degree of mixing of the boundary layer that could create unfavorable LCL heights further south for a time.
 
andyhb said:
There's a number of potential failure modes. The biggest one is early convection and outflow overrunning the warm sector. Another may be boundary orientation (which would be mitigated if a pre-frontal trough is present) and the fact that the primary wave is leaving the warm sector behind in the afternoon (which could be mitigated if there are any embedded shortwaves in the jet). A third may be a larger degree of mixing of the boundary layer that could create unfavorable LCL heights further south for a time.
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What are your thoughts on tomorrow? It is certainly starting to get some serious hype.
 
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First look at the severe weather reflectivity for Tuesday and Wednesday courtesy of the 18z NAMNST. It clearly does not buy the notion of it being a super-cellular event, but instead a QLCS type event. However, in my opinion, rarely does it ever put all chips in the super-cellular table. Interesting nonetheless.
 
Muwx said:
What are your thoughts on tomorrow? It is certainly starting to get some serious hype.
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Tomorrow is trouble. The wind fields are incredible near the dryline in KS/OK, shear vectors off the boundary are ideal for discrete storms, and it's starting to seem like there will be enough moisture for pre-nocturnal convective initiation (notably, the wind fields fairly early on support right moving supercells dominating). Should that happen, we could be looking at a pretty substantial tornado outbreak across the area, as hinted at in the 12z MPAS runs. Timing of the shortwave will play a large role in deciding whether that happens.
 
I will say that it's definitely pushing forward significant STP and 0-1km SRH numbers, as well as enough CAPE for a severe weather outbreak.

P.S.: The numbers for KS/OK are unreal. Definitely an all or nothing type day.

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andyhb said:
Tomorrow is trouble. The wind fields are incredible near the dryline in KS/OK, shear vectors off the boundary are ideal for discrete storms, and it's starting to seem like there will be enough moisture for pre-nocturnal convective initiation (notably, the wind fields fairly early on support right moving supercells dominating). Should that happen, we could be looking at a pretty substantial tornado outbreak across the area, as hinted at in the 12z MPAS runs. Timing of the shortwave will play a large role in deciding whether that happens.
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We've seen it before with nocturnal violent tornadoes in Kansas (Udall, Hoisington, Greensburg to name a few), but it's all so conditional on everything coming together at the last minute. We've also seen plenty of similar setups that didn't produce (such as last year April 15th).
 
CheeselandSkies said:
We've seen it before with nocturnal violent tornadoes in Kansas (Udall, Hoisington, Greensburg to name a few), but it's all so conditional on everything coming together at the last minute. We've also seen plenty of similar setups that didn't produce (such as last year April 15th).
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It'll be fascinating to see how the SPC approaches tomorrow from an outlook basis, especially with it being an "all or nothing" day.
 
CheeselandSkies said:
We've seen it before with nocturnal violent tornadoes in Kansas (Udall, Hoisington, Greensburg to name a few), but it's all so conditional on everything coming together at the last minute. We've also seen plenty of similar setups that didn't produce (such as last year April 15th).
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This setup is not very analogous to that particular one. The shear profiles tomorrow from like 4-5 PM onwards are the type where if you give them an inch, they'll take a country mile.
 
18Z NAM was a notable uptrend for the northern extent of the risk area, after 12Z's downtrend from 0Z. A frustrating amount of flip-flopping for so close to the event, but the most significant development IMO is that it's a bit slower and further south with the surface low, allowing northern Illinois to remain in the warm sector with somewhat backed (southerly) surface winds as late 21Z (4 PM CDT), instead of veering to southwesterly after 18Z as the front pushes off to the east.

I still think there are some limitations to a more widespread high-end tornado threat, such as the axis of the LLJ being displaced off to the east of the stronger instability, at least for points north of about I-70 or 74 in Indiana at 21Z.

@andyhb I keep looking for a setup like Palm Sunday 1965, that can produce significant tornadoes all the way from Iowa to the western tip of Lake Erie. I've yet to see anything quite like that but I think Wednesday is close to the kind of setup that could do it, if only there were a little bit more instability with northeastward extent.
 
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