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4/19/20-4/20/20 Severe Weather

Webberweather53

Webberweather53

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Desert Southwest ?
Definitely think it's time to go ahead & pull the trigger on this one given the overall support this has inside day 4 & I expect the SPC to denote this pretty soon in their convective outlooks. While a large proportion of this board may not see anything severe wx wise whatsoever, and this threat will be considerably more tame overall than this past weekend, definitely looks like a respectable event is coming up for the portions of the Arklatex, Gulf coast, and those well south of I-20.

A pair of closed lows off the coast of California will eject out of the Desert southwest this weekend, resulting in cyclogenesis over the southern plains and deep south, coupled with warm, moist southerly return flow off the Gulf of Mexico and modest-moderate destabilization, especially across the Arklatex and Gulf coast.

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Deep layer shear of 40-60 knots across the warm sector coupled with strong forcing for ascent & long cyclonically curved hodographs through the lowest 1-2km w/ some mid-level backing (especially later on in the evolution) favors supercell clusters and some upscale growth into a QLCS with primary hazards of damaging straight line winds and isolated tornadoes. Low-level shear across the warm sector & low-level lapse rates and instability appear to be the primary limiting factors to tornadoes but values somewhere in the ballpark of 200-250 m2/s2 & ~750-1000 j/kg respectively, are generally sufficient to produce tornadoes w/ some potential for a few to be strong, especially if more shear &/or CAPE is realized.

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CIPS severe weather analog guidance really picking up on this too.

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Pretty large area of the southeastern US has legitimately non-zero surface based CAPE, certainly going to be a lot of elevated convection along & north of the I-20 corridor in AL/GA/SC but many of these storms may actually be surface-based which is concerning given how much low-level shear there will be for tornadoes (not as much as last weekend but enough)

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This doesn't have the insane parameter space last weekend had, but as SPC notes, the low-level shear will increase dramatically as this system comes east and 200-300 0-1 SRH coupled with 250-400 j/kg CAPE is sufficient to produce plenty of tornadoes, and more in line w/ what we typically see during an "outbreak" in the SE US. Could be another overnight QLCS tornado threat, however probably not as bad as last weekend overall and low-level lapse rates are also going to be a limiting factor.

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I feel like the day 4 outlooked areas above look extremely close to the same areas the last outbreak started out like.
 
The NAM is smoking something rather strong.... Near BHM and north central MS. Can you say loaded gun soundings?! Stronger and more backed low level winds and there is a serious problem.

Edit: The NAM actually flags what would be true PDS sounding as the band of Supercells fire over MS and move into AL at 0z Sunday. This is how you get an April 8 1998 situation.

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Northern MS

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UKMet just south of Tuscaloosa. Any backing of low level winds and we have big problems.

Edit: UKMet is flagging 5/18/95 which was a powerhouse outbreak across TN/KY.

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QPF.


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I don't know if I should start getting worried about this next round, quite yet. Some of the modeling wants to keep this south of CLT/GSP/ATL area's, But we all know how that turned out last time... maybe @Webberweather53 can provide some sage advice or his opinion on this setup.
 
SD said:
That warm sector across Central/ South Ga, southern SC and parts of Fl is popping solid soundings. I do wonder how much sun the warm sector can get or if its locked into clouds
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I agree. Some CAPES over 2500 showing up. Shear not nearly as impressive, but more than ample for tornadoes.
 
This is what I think, during the day, supercells/organized multicellular clusters will develop with all hazards, although there will be capping in place, and LLvL LRs are questionable although they may be better than the last event, but given solid low level hodos with decent critical angles (50-80) with decent low level shear and moderate-high instability, some tornadoes will be possible, along with large hail/damaging winds 8F34672B-7D69-439C-BB17-D2767AC578B3.png7AA2C753-4D8B-44C1-93A3-713392FC5FBC.png27EC7269-4DD5-4A0D-AD0E-45BD3DB5688F.png
As it gets late at night, storm modes will shift towards a MCS/QLCS, low level jet will likely pick up as well with over 35-45kts of 1km shear, some QLCS tornadoes are possible with a wind damage threat, what gets my attention is the cyclonic flow on hodos from the low levels to the upper levels, that can help increase the chance of supercells getting going embedded in the QLCS just like the last event, this is something that has to be watched, I would say tho that parameters with the last event were scarier, but yet again, you can have scary parameters and have messy storms modes, but you can have less favorable parameters and have storm modes that are more favorable for isolated supercells so they end up producing, just something to keep in mind F5233E85-89B8-4E75-AF74-6184C2843141.pngB68AC6CE-0826-4802-A769-057F4CC756DA.png
 
When you pull a Southern SC sounding from the NAM, you get this...

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Crap...now isn't that delightful (not, and I looked at more than the possible hazard type). I hope it's the NAM going nuts but we'll see, because to me the short range actually did a really good job in SC with last time.
 
0z Euro backs surface winds to the south and yields 0-1km helicity 350-450 across AL, MS and 998mb over the far NW corner of AL. Keeps lots of precip in the warm sector which hampers instability though. However if you get the NAMs clean warm sector with this helicity numbers watch out.
 
From what I can tell, the 12z NAM was a bit further north yet than the 00z run.
 
Well, unless we see some major changes, this event looks doesn't appear to be as significant as last Sundays. And it looks to affect a smaller geographical area. So, that's good! Not that places in MS and LA won't get hit hard again, but it doesn't appear as dire.
 
ryan1234 said:
Well, unless we see some major changes, this event looks doesn't appear to be as significant as last Sundays. And it looks to affect a smaller geographical area. So, that's good! Not that places in MS and LA won't get hit hard again, but it doesn't appear as dire.
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A lot can change from now and then. Mesoscale details will ultimately determine the risk.
 
Zander98al said:
A lot can change from now and then. Mesoscale details will ultimately determine the risk.
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True, and a lot changed with last week's events as we approached it. But the overall setup isn't the same. Just got to wait and see.
 
ryan1234 said:
Well, unless we see some major changes, this event looks doesn't appear to be as significant as last Sundays. And it looks to affect a smaller geographical area. So, that's good! Not that places in MS and LA won't get hit hard again, but it doesn't appear as dire.
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In area size wise, no, locally absolutely if not higher. The question right now is how far does the warm front go north and how contaminated is the warm sector.
 
SD said:
Am I broken or is the 12z Euro worlds apart from other models and way slower
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I don't know, but the timing is fairly similar between the models, but the EURO puts a lot of NC back into play. Looks extremely similar to last Sunday/Monday. I haven't looked specifically at the soundings yet, though. Either way, many of the same areas that got hit last week will get hit again.
 
WxGSO said:
I don't know, but the timing is fairly similar between the models, but the EURO puts a lot of NC back into play. Looks extremely similar to last Sunday/Monday. I haven't looked specifically at the soundings yet, though. Either way, many of the same areas that got hit last week will get hit again.
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Soundings don't look like much of anything here in NC. Just a rainy mess.

Of course that can always change, but it seems like things up here would need to change really really drastically in order to even approach last week and none of the models are showing that.
 
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