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4/11/20 - 4/13/20 Severe Weather Outbreak

Hopefully, this case study dispels the defunct notion that the ECMWF is *always* going to drag its feet w/ troughs in the Desert SW, it was by far the slowest of all NWP models, but even it was not slow enough. I'd argue if anything that the GFS is still going to be more progressive to a greater degree & do so more frequently than the ECMWF is slow.
 
That looks nasty for NC on Monday. It is that time of year.
 
Webberweather53 said:
Pretty classic ? express event is going to contribute to much of the rainfall & deep-layer moisture we see this week.

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Damn you for stealing my post. I was about to say this is becoming almost like a winter event where the initial upper low drops into the SW and we get an excited jet extending across the SE with embedded low amplitude waves ahead of the main system. If you look at all the models they now suggest some form of heavy rain in association with the initial warm front and moisture surge. They also have some semblance of a weak shortwave ejecting from the parent in the SW and maybe some MCV development across Tx/La late Saturday that aids in enhancing things a bit.

Additionally the 0z really tried to develop a secondary sfc low in the immediate foothills in NW NC/SW VA
1586352743954.png
Given that this is 12z if we push this back 6-8 hours and are able to get temps into 75-80 range, no bueno
 
SD said:
Damn you for stealing my post. I was about to say this is becoming almost like a winter event where the initial upper low drops into the SW and we get an excited jet extending across the SE with embedded low amplitude waves ahead of the main system. If you look at all the models they now suggest some form of heavy rain in association with the initial warm front and moisture surge. They also have some semblance of a weak shortwave ejecting from the parent in the SW and maybe some MCV development across Tx/La late Saturday that aids in enhancing things a bit.

Additionally the 0z really tried to develop a secondary sfc low in the immediate foothills in NW NC/SW VA
View attachment 38653
Given that this is 12z if we push this back 6-8 hours and are able to get temps into 75-80 range, no bueno
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Oh jeez, I wonder where I've seen that before.

Screen Shot 2020-04-08 at 9.40.27 AM.png



Yeah if we slow down & see a mesolow form over the northern piedmont or SW Virginia, we're gonna be in really big trouble.
 
Man thats a nasty look. If mesoscale features are favorable itll be a long weekend. Disregard the halo youtube box? i need something to entertain me at workScreenshot_20200408-085102_Samsung Internet.jpgScreenshot_20200408-085055_Samsung Internet.jpgScreenshot_20200408-085048_Samsung Internet.jpg
 
Brick Tamland said:
I was worried about the same thing. Just something about severe threats in April and NC.
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I hate to seem so rash, but at this point, I only see 2 viable options on the table for us late Sunday into Monday, and one of them is very likely to verify. If the timing is verbatim as the Euro shows, option #1 is very heavily favored, if however we slow things down into Monday afternoon & there's cooperation with mesoscale features (like a mesolow for ex), then the door is wide open for option #2:

1) Really nasty QLCS &/or squall line with embedded tors and widespread straight line wind damage (bad)

2) Historic tornado outbreak (really bad)

Either scenario is bad and going to be very impactful & we're probably going to get hit pretty hard by something, it's really become more of a question of who, when, & how hard.
 
Webberweather53 said:
Oh jeez, I wonder where I've seen that before.

Yeah if we slow down & see a mesolow form over the northern piedmont or SW Virginia, we're gonna be in really big trouble.
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Well I believe this is why the GFS has the QPF bomb over our area, divergence much?
1586354556362.png

With this type of jet structure you would think as the primary did head northward into the OV/Lakes there would be some attempt to get a secondary circulation going in the deep convection along the prefrontal trough to the S/SSE of the primary.
 
SD said:
Well I believe this is why the GFS has the QPF bomb over our area, divergence much?
View attachment 38660

With this type of jet structure you would think as the primary did head northward into the OV/Lakes there would be some attempt to get a secondary circulation going in the deep convection along the prefrontal trough to the S/SSE of the primary.
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Yes, the upper level kinematics definitely support formation of an additional surface low over NC/VA in the midst of that coupled jet look which will favor large-scale ascent due to upper level divergence in the corresponding left exit region of the southern jet streak and right entrance of the northern one. The placement and implied occlusion of the primary low over the Ohio Valley and lower lakes certainly opens the door for another surface low to form further SE on the front.

There are 2 other pieces of information that also favor mesolow formation in NC/VA as the Euro shows in addition to the upper level jet streak, 1) diabatic heating within convection causing local pressure anomalies along the front & 2) stretching in the low-mid levels as deep layer flow moves up & over the south-central Apps, causing cyclonic vorticity on the leeward side. The intersection of these 3 heavily favors the formation of a secondary in VA or NC which would significantly increase the low-level shear and steepen the lapse rates due to isollobaric effects near the secondary low. The weak low level lapse rates due in part to the timing of the front is currently the primary inhibitor I see to tornadoes here.

The two remaining questions for me are where exactly this secondary &/or mesolow forms and the timing of the front. We'll probably have an answer to one of these within the next few days as the synoptic-scale details are refined, any more slowing by the Euro & EPS today and tomorrow w/ this upper low over the SW US would indeed be worrisome & favor the tornado outbreak scenario.
 
Webberweather53 said:
Fwiw, 12z GFS:

Really crappy thermos, but holy crap I've never seen that much SRH before when we didn't have CAD.

Just your every day 1300+ 0-3 SRH.

View attachment 38670
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Had a sounding just like that back in February and still managed to see a handful of tornadoes around CLT with that QLCS, just imagine what this can do... that’s a humongous low level hodo
 
Hate to ask a backyard question but I’m still learning, how do soundings etc look for north metro Atlanta on Sunday?


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