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

EV_WS said:
Has anyone seen tweets or posts from @Webberweather53 ?
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No major changes (yet) in my overall thinking for tomorrow here. Strong damaging winds and isolated tornadoes will be the main threat(s) over the Carolinas and this is liable to be a respectable severe event here.

Although many are assuming that storm mode will be linear here based on climo, it doesn't look super clear cut to me once you get east of Greensboro-Charlotte into the eastern piedmont and coastal plain. I definitely lean in the direction of linear modes but there are several possible failure points in maintaining a bonafide QLCS the whole day tomorrow.

Large cyclonically curved hodographs basically the whole way thru the troposphere that’s being modeled consistently across the board inhibits neighboring storm collisions and thus cold pool mergers.

We honestly still don't know how strong diabatically forced rear inflow jet (from mainly stratiform precip) will be in addition to how much the cold pools will be advected by the deep layer shear vector, if it's closer to // wrt the line orientation (doesn't look superb here verbatim atm) that encourages break up into discretes (this is how Apr 16 2011 happened) in addition to the potential for the mountains to disrupt the segment of the QLCS & low level cold pool that enters the Carolinas. The synoptic scale forcing will become less impressive (relatively speaking) after tomorrow morning, as the parent surface low occluded and becomes further removed from the Carolinas & this EML is no joke (& verifying stronger than forecast). It's actually possible some of the storms deteriorate a lot or just die as they enter the piedmont around sunrise, which if some places like RDU & Fayetteville, are sufficiently unstable downstream, could encourage new, discrete cells in the warm sector. Also, many cams are trying to break up the line once it gets to about the US HWY 1 corridor.

The other red flag I see for qlcs maintenance beyond the western piedmont of N.C. is the fact that these storms don't appear to be directly attached to the cold front, rather it's a pre frontal trough.


Even though we'll have respectable DCAPE that will encourage stronger cold pools, this suggests that the downdrafts associated with these storms will be warmer as they literally mix warmer air ahead of the front into the wake of the storms, which doesn't favor continuation of a purely linear mode. Along with other aforementioned variables, warmer downdrafts due to the synoptic-mesoscale character of the storm environment is also a primary contributor to April 16, 2011’s very, very unique storm mode evolution from purely linear to discretes in a matter of a few hours which rarely if ever happens. Almost always it’s going to be the other way around. I think this may be linked to something fundamental about the Carolinas, where the Appalachian mountains block the low level cold air on the leading edge of cold fronts, encouraging disentanglement between the front and storms, and thus being more favorable to discrete supercells.

All this being said, I'm certainly in favor of the qlcs idea over discretes for now, albeit not by much. I personally think the most likely scenario regarding storm mode in the Carolinas is we see a qlcs w/ embedded supercells roll thru at least Charlotte and Greensboro, but we see it devolve into an rather obfuscate semi-discrete mode, with respectable completely broken line segments and multiple clusters of embedded supercells, or basically a linear-discrete hybrid mode.
 
What are yalls thoughts for central and southern SC now? Less of a threat? Have been super busy, and not paid much attention to weather today. Although I have seen some tweets from Mississippi earlier :oops:
 
NorthGaWinter4 said:
So Cantore said Georgia won’t see the type of violence that Mississippi saw. So, are we busting on the tornado threat here?
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Can we please not call getting less severe weather and tornadoes a “bust”...no rules against and I don’t want to start any kind of argument. Just a pet peeve of mine I guess. I understand the sentiment when the weather doesn’t turn out as models predict. Maybe someone can come up with a more appropriate term considering the potential damage and injuries that would be averted?
 
packfan98 said:
Can we please not call getting less severe weather and tornadoes a “bust”...no rules against and I don’t want to start any kind of argument. Just a pet peeve of mine I guess. I understand the sentiment when the weather doesn’t turn out as models predict. Maybe someone can come up with a more appropriate term considering the potential damage and injuries that would be averted?
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My bad. I couldn’t think of a better word. Just was curious why he said it wasn’t going to be as bad here
 
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Sleet City USA said:
Probably because the environment is not nearly as favorable in GA than it was in MS
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But why isn't the environment as favorable ? This is an historic severe weather event as FFC has mentioned. I would think the environment would be very favorable for all modes of severe weather.
 
Dewpoint Dan said:
But why isn't the environment as favorable ?
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I mean I'm nowhere close to an expert, seems to me that the parameters in MS were just plain better for tornadic development.
Also I would imagine that Cantore was referencing the large tornado in southern MS, saying there likely wouldn't be anything like that in Georgia
 
GSP specifically mentioning tornadoes in the most recent disco
As of 755 pm...Strong low level warm advection is steadily
displacing the in-situ cold air damming that developed near the Blue
Ridge earlier today. E.g., the surface temp has warmed a whopping 12
degrees at KGSP in the past three hours. Surface-based instability
remains confined to areas along the I-20 corridor in AL/GA, but will
continue to be drawn northward in response to the very strong warm
air and moisture advection...and as lapse rates increase in response
to very strong forcing. A guidance consensus suggests an axis of
sbCAPE of up to 1000 J/kg will develop into the Upstate and northeast
GA zones by 06Z...just as QLCS is expected to be moving across the
area. Shear parameters will go through the roof after about 03Z as
60-70 kt LLJ translates across the area...supporting outrageous (>
500) values of 0-1 km SRH. Considering the expected degree of
instability, this is looking more like a "QLCS with embedded
supercell structures" type of event, rather than the "low-topped
QLCS with mesovortex" events that we`re used to. That being the
case, the SRH parameters are downright scary, and portend the
potential for a strong/damaging tornado or two. Swaths of downburst
damage also appear likely...if based on nothing else than good old-
fashioned convective mixing.

Speaking of which, gradient winds will also be an issue overnight
and into the daytime period Mon. With the lowering jet core, shallow
mixing will allow stg wind gusts to reach the sfc. With moist soils
these winds could down isol weak or dead trees. A Wind Advisory is
in effect for much of the forecast area.

Rainfall amounts have thus far been relatively tame in the
stratiform/showery upglide/warm front regime that`s been in place
across the area. However, intense rainfall rates within the QLCS
will nevertheless pose a threat for localized flash flooding,
especially across southwest NC and the GA mountains.
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packfan98 said:
Can we please not call getting less severe weather and tornadoes a “bust”...no rules against and I don’t want to start any kind of argument. Just a pet peeve of mine I guess. I understand the sentiment when the weather doesn’t turn out as models predict. Maybe someone can come up with a more appropriate term considering the potential damage and injuries that would be averted?
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Let me ask a serious question: We have a moderate risk area outlined by the SPC. We've had numerous tornado warnings, confirmed strong tornadoes, wind and hail reports, etc. Was/is this a bust? No high risk was issued. Was the SPC calling for some mega/historic outbreak? I mean, we've heard a lot of exceptional language describing this event and the parameters from posts here, but from an official standpoint, has this been a bust? Really?
 
Rah NWS: "powerful, long tracked tornadoes" is not something they say often..... kinda gives you that queasy feeling
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Mesoscale Discussion 0368
NWS Storm Prediction Center Norman OK
0736 PM CDT Sun Apr 12 2020

Areas affected...southeast Mississippi/central and southern Alabama

Concerning...Tornado Watch 110...

Valid 130036Z - 130200Z

The severe weather threat for Tornado Watch 110 continues.

SUMMARY...Severe/tornado risk continues across WW 110.

DISCUSSION...Latest radar loop shows a couple of rotating cells
moving east-northeastward across the northwestern corner of the WW
at this time -- i.e. Greene/Sumter County area in Alabama. The
broader band of convection that includes these storms extends
south-southwestward into eastern Louisiana, where a few
well-organized storms are occurring. This convection will spread
into western portions of WW 110 over the next hour -- sustained by
an axis of 1500 to 2000 J/kg mixed-layer CAPE over the southwestern
corner of Alabama. Given the background kinematic environment that
remains strongly supportive of supercells, severe risk -- including
potential for tornadoes -- continues.

..Goss.. 04/13/2020

...Please see www.spc.noaa.gov for graphic product...
 
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