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Severe WX Severe Weather 4/24-4/26

CheeselandSkies said:
I will say, the GFS evolution has become a little less negatively tilted with the shortwave over the last day or so. On the 06Z run the axis looks neutral to slightly positively tilted at 00Z Tuesday. However that just the operational output of one model. It did previously look more negatively tilted though for example on the 00Z Thursday (Wednesday evening) run.
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FWIW, 12Z NAM now goes out to 00 Tuesday (7 PM CDT Monday) and it has a solid negative tilt at that time (just looking at the 500mb pattern, ignoring details like soundings, thermodynamics at this point).
 
While the Middle Mississippi Valley portion of Monday's threat seems pretty robust, I have a lot of questions about the southern extent of the threat, and many of these same factors probably have to do with why the SPC has pulled that D4 highlight is moved so far north. There will definitely be a severe threat with any convection that happens in the Deep South, to be sure, but how exactly that plays out is still a little bit of a head-scratcher to me. GFS has been pretty consistent with a line of convection moving from northwest to southeast across the Gulf Coast states early Tuesday morning, and then an additional wave of storms Tuesday afternoon. It's also consistently depicted basically no instability accompanying these late night/early morning storms, which I find a little hard to believe. Kinematics still look good from 00Z to 12Z Tuesday, but after that, dynamics pull away and there's relatively meager shear for the Tuesday afternoon storms to work with.

Again, I do think the threat is still there, and folks in the Southeast should definitely still be watching it closely, but it's a much bigger question mark that's leaving me with much less forecast confidence than the situation further north. I do think in terms of the actual threat geography, CSU's model is doing a good job at depicting it properly. I'm most concerned about Tennessee, northern Mississippi and northwestern Alabama for the overnight activity in the Southeast. If convection remains robust overnight, then the kinematics definitely support a strong tornado threat in the MS/AL/TN/GA area. Tuesday afternoon into the evening, most of the Gulf states are in play for what I'd have to imagine becomes much more of a wind and hail threat, though small, curved hodographs could support some limited tornado threat.

Late tonight through Sunday morning could also be an active period for strong storms, with multiple waves of convection forecast. I wouldn't be surprised to see the introduction of wind and hail probabilities across the Southeast for the D2 forecast. Regardless of the exact outcome, it seems pretty clear that we're in for a pretty unsettled and stormy period, that will continue even after this system passes through. It'll bring some much-needed rain, that's for sure.
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jackhutwx said:
12z rrfs is now barley in range, can't make out if anything is discrete, but def looks big for monday.
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Looks like it implies a couple of discrete cells across IL between 21-00Z (FH081-84). Ahead of the monster QLCS. Of course RRFS simref should be considered pure entertainment.
 
I noticed something interesting and potentially ominous while look at the 0z through 12z CAMs

The NAM 3k, HRRR and RRFS are all depicting a single, massive updraft helicity streak across eastern Oklahoma, moving NW to SE.

The NAM has been showing this consistently for 3 consecutive runs. The HRRR is also onboard with the 12z run, as is the RRFS.

Unusual and concerning to see such consistency in that type of output, for such an intense supercell. Not sure if it's just a surface-based mega-hailer triggering that, or a real tornado. But something to watch closely.
 
lake.effect said:
I noticed something interesting and potentially ominous while look at the 0z through 12z CAMs

The NAM 3k, HRRR and RRFS are all depicting a single, massive updraft helicity streak across eastern Oklahoma, moving NW to SE.

The NAM has been showing this consistently for 3 consecutive runs. The HRRR is also onboard with the 12z run, as is the RRFS.

Unusual and concerning to see such consistency in that type of output, for such an intense supercell. Not sure if it's just a surface-based mega-hailer triggering that, or a real tornado. But something to watch closely.
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What date/time is this valid for? Sunday afternoon/evening?
 
lake.effect said:
I noticed something interesting and potentially ominous while look at the 0z through 12z CAMs

The NAM 3k, HRRR and RRFS are all depicting a single, massive updraft helicity streak across eastern Oklahoma, moving NW to SE.

The NAM has been showing this consistently for 3 consecutive runs. The HRRR is also onboard with the 12z run, as is the RRFS.

Unusual and concerning to see such consistency in that type of output, for such an intense supercell. Not sure if it's just a surface-based mega-hailer triggering that, or a real tornado. But something to watch closely.
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Ive mentioned it a couple times and I think the CAM's are latching on a supercell riding the OFB left over from tonight convection, they are showing very high localized shear around that boundary.
 
hurricaneguy said:
Most of the more widespread looking severe weather outbreaks this year have really scaled back in the last 48 hrs leading up the event. Will be interesting what tomorrow starts to bring especially when hi res models kick in.
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To be fair, none of them have really had "the look" at 500mb the way Monday does (possible headfake downtrend from the GFS that I mentioned aside).
 
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