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Severe WX Severe Weather Threat 3/14-3/16

Well, a lot has changed in the past 24 hours. Friday still looks not as significant as originally expected. Of course still a risk of significant severe weather as per the SPC's 30% area. One of the main issues is of course the poor moisture quality. You might think by the fact 60F dps are already along the coast by as early as 00z Thursday there would be plenty of time for northward moisture advection, but the depth of the moisture is extremely poor. The moist layer is less than a km deep in places and subsequently daytime heating will mix the dry air to the surface both during the day Thursday and Friday, meaning on Friday its harder to overcome the slightly warmer mid-levels and instability is low in areas with the best wind profiles.

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Certainly not a write off though, and if later uptrends in the boundary layer moisture become apparent just 1-1.5kj/kg of surface based CAPE could be sufficient for an EF2+ tornado threat given wind profiles. That's the UKMET kind of scenario, currently supported by ICON. GFS and NAM would most likely be a limited threat and the ECM is somewhere in between. That's just referencing the supercellular tornado threat, however. A QLCS tornado and wind threat are much more of a given further north, which will bring a widespread severe thunderstorm risk anyway and is probably driving that SPC 30%. Even the GFS scenario could easily be a wind-driven MDT for MO into IL with a strongly forced line coinciding with a dry boundary layer and 90-100kt jet core, could get some very powerful downdrafts - not that exact outlook categories hugely matter.

Saturday though having looked less impressive yesterday as now swung back to being more volatile, as was always a possibility.
trend-gfs-2025031112-f108.300wh.conus.gif

General trend for the upper level pattern is for a slightly more amplified, stronger but still broad based trough - a notoriously dangerous setup atop a moist warm sector. Couple things to note in the jet pattern from the GIF above is the stronger flow on the backside of the trough, not any sort of official forecasting technique but a sort of eyeball method to gauge that the trough will be approaching peak strength/maturity on Saturday afternoon.

Also most importantly notice the coupled jet pattern which has become increasingly apparent in the last couple runs. That's the segment of stronger flow branching from C IL up into southern Ontario. The area in between which current models have to be around KY/TN have very strong divergence (decreasing wind gradient) and diffluence (spreading apart wind barbs) which together provide an extremely strong signal for a secondary low to develop in that region.

Moisture of course won't be an issue with Friday's system essentially acting as the new lead wave. Super tall and thick instability profiles, unusual for this time of year. All together current models have a setup strongly supportive of severe weather across Dixie alley on Saturday afternoon. 12z UKMET probably the highest end output with an insane low level jet and near 70f dps fairly widely.

1741713948391.png

Still, its Day 5 and plenty can and will change. So I'm uneager to jump massively into the hype, even if current output deserves it. What needs to be focused on are trends, and broad themes. This setup is in some ways quite 'fragile' in the sense it wouldn't take much to shift this into your normal severe weather event, as yesterday's set of model runs showed where the trough ejection is not quite as favorable so the low level wind response isn't as impressive. I do think moisture will be almost a given as it will be the second day of large scale moisture return, though we will start getting a good idea of the true extent tomorrow as a smaller wave passes through.

Main trends to be look for will be:
- The emergence of a more prominent shortwave. Often that's something that can become apparent in these longer wavelength troughs at shorter ranges, I recall this happening in the 12/10 outbreak. An embedded shortwave or speed max would strengthen the low level wind fields which pretty much improves the environment all round.
-The sub-tropical jet nosing too much to the north, which may limit thermodynamics especially with the low-level lapse rates
-Trough either de-amplifying or becoming too amplified both of which could reduce the severe threat
-Trough trending a little north which could expand the extent of the warm sector northwards

As we get into the D1-D3 range is obviously when the smaller scale details which could make or break the setup become apparent. Still think its a wait and see game because who knows the parameter space and synoptics will be the same by the time we get to Saturday, though for a local forecaster perspective increasing awareness early is obviously important.
 
I was planning to drive through Tennessee and stay in the Atlanta area on Saturday, going on to Florida panhandle on Sunday.

Looks like I'm going to be revising that plan from Saturday/Sunday morning to Friday/Saturday morning.
 
Atlantic said:
So they have really uptrended?
Click to expand...
I think more so, that there's more confidence in the original solution that models had been hinting at off and on and portraying the past 3 days or so with the secondary low. Moisture has up ticked that's for sure (at least across Alabama) and so has shear, and still may uptick more, given the proximity to the secondary low as we get into mesoscale models.
 
1741718127622.png

CAPE not looking good. Helicity and Sheer getting into big time uh oh territory. I managed to pull some soundings that were closer to 600 0-3km helicity, but I didn't save them and can't find it again. I think between Saturday 18z and 0z is when we'll see peak values across the board.

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Mike S said:
You're welcome to start your own weather forum.

An overmoderated forum sucks.

Now, back to your regularly schedule Spring severe season.
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Not asking for over moderation - but a lot of posts seem to be young guys rooting for bad weather who don’t know what they are talking about, but speaking with an air of authority that is troubling given that this isn’t a sports forum. The number of barely severe events with people constantly saying certain storms are about to be warned, or there’s a tornado on the ground, or there’s a near certainty of X is high. That isn’t helpful to a forum. People should feel free to ask questions and learn, but just imho, people who speak with authority who have no idea what they are talking about need to be corrected and encouraged to learn more.
 
I've been lurking here for a while but just officially joined because this seems like a good meeting place of actual, knowledgeable people and amateur weenies like myself. A breath of fresh air compared to the click-driven overhyping on other forms of social media. Appreciate the back and forth here and the no-nonsense reading of models rather than overhyping a model run for 9 days from now (I've already seen people hyping up the Sunday 3/23 solution from GFS :rolleyes:)
 
UpperLevelLOL said:
I've been lurking here for a while but just officially joined because this seems like a good meeting place of actual, knowledgeable people and amateur weenies like myself. A breath of fresh air compared to the click-driven overhyping on other forms of social media. Appreciate the back and forth here and the no-nonsense reading of models rather than overhyping a model run for 9 days from now (I've already seen people hyping up the Sunday 3/23 solution from GFS :rolleyes:)
Click to expand...
Welcome!
 
UpperLevelLOL said:
I've been lurking here for a while but just officially joined because this seems like a good meeting place of actual, knowledgeable people and amateur weenies like myself. A breath of fresh air compared to the click-driven overhyping on other forms of social media. Appreciate the back and forth here and the no-nonsense reading of models rather than overhyping a model run for 9 days from now (I've already seen people hyping up the Sunday 3/23 solution from GFS :rolleyes:)
Click to expand...
Welcome, I’ll admit this place certainly has its ups and downs as well, but compared to other places this is an upper class mall while most other social media sites are the shady drugstores that may or may not be selling illegal merchandise.
 
UpperLevelLOL said:
I've been lurking here for a while but just officially joined because this seems like a good meeting place of actual, knowledgeable people and amateur weenies like myself. A breath of fresh air compared to the click-driven overhyping on other forms of social media. Appreciate the back and forth here and the no-nonsense reading of models rather than overhyping a model run for 9 days from now (I've already seen people hyping up the Sunday 3/23 solution from GFS :rolleyes:)
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Welcome! I hope you enjoy this place!
 
jiharris0220 said:
Welcome, I’ll admit this place certainly has its ups and downs as well, but compared to other places this is an upper class mall while most other social media sites are the shady drugstores that may or may not be selling illegal merchandise.
Click to expand...
Hey now, we all love a little illegal merchandise every once in a while /s
 
UK_EF4 said:
Main trends to be look for will be:
- The emergence of a more prominent shortwave. Often that's something that can become apparent in these longer wavelength troughs at shorter ranges, I recall this happening in the 12/10 outbreak. An embedded shortwave or speed max would strengthen the low level wind fields which pretty much improves the environment all round.
-The sub-tropical jet nosing too much to the north, which may limit thermodynamics especially with the low-level lapse rates
-Trough either de-amplifying or becoming too amplified both of which could reduce the severe threat
-Trough trending a little north which could expand the extent of the warm sector northwards

As we get into the D1-D3 range is obviously when the smaller scale details which could make or break the setup become apparent. Still think its a wait and see game because who knows the parameter space and synoptics will be the same by the time we get to Saturday, though for a local forecaster perspective increasing awareness early is obviously important.
Click to expand...
Correct me if I'm wrong, but doesn't the longwave broad nature of this trough make it more difficult for it to become de-amplified or too amplified since any changes would have to occur within the larger structure of the trough? I could see where the shortwave on Friday becomes too amplified, but I'm having a more difficult time seeing how that could happen on Saturday.
 
OK, I am just now having the time to dig into the models to look at this. All I can say is WOW, especially the Saturday timeframe. What impresses me most here is how the stacked upper low pulls northeast while another s/w digs into a large open trough with plenty of difluence....also confluence near the coast- probably keeping coastal convection at a min...all while the shear maxes out as instability overspreads the area. Still open enough and broad based to provide shear for extended time with some long trackers. The stacked upper low is a great priimer...but it doens't move too fast north/east...allowing the instability to be readily available for the new s/w. Quite impressive...but still several days away/plenty of time for changes....but for now at least, very impressive in both time period and spatial coverage.
 
FFC's discussion has a good but simple breakdown of our possible hazards on Saturday.
.LONG TERM...
(Friday morning through next Monday)
Issued at 152 PM EDT Tue Mar 11 2025

- Severe thunderstorm concerns remain in place from Saturday
into Sunday with all modes of severe weather possible.

- A heavy rainfall and flash flooding threat could also
accompany this weekend system.

Moisture will be advecting northward into the area at the start of
the forecast period Friday as a low pressure system deepens over
and begins to lift northeastward across the Central Plains. By
Saturday morning, this increasingly stacked system will be situated
over the Upper Midwest/Great Lakes region, with the associated
surface cold front draped across the Mississippi Valley. By Saturday
afternoon and evening, an additional surface low looks to initiate
and lift northward across the Tennessee Valley. While some showers
and embedded thunderstorms may be ongoing in portions of north
Georgia Saturday morning amid isentropic lift, additional convective
development will develop to our west on Saturday as the surface cold
front approaches.

The severe risk then looks to be highest from late Saturday into
Sunday as these storms push into the state. While the most favorable
parameter space may exist to our west where afternoon instability
will be highest, a very strong LLJ (45-55+ kts at 850 mb) and
resultant impressive 0-1 km SRH would maintain an ongoing
(potentially significant) severe threat. As mentioned in earlier
discussions, some uncertainty remains at this juncture regarding the
thermodynamic environment, particularly given the potential local
timing being Saturday night into early Sunday being some degree of a
limiting factor. Even so, NBM mean SBCAPE in excess of 500 J/kg
Saturday evening and still on the order of 200-500 J/kg overnight
would still be supportive of a tornado and damaging wind threat
given aforementioned very favorable shear parameters. If higher
instability is realized, then this threat would be further
maximized. All this is to say, the potential for a significant
severe event remains in play from Saturday evening into at least
early Sunday before the front shifts eastward on Sunday. This threat
remains highlighted by the continued Day 5 (Saturday) 30% risk area
from SPC and lingering 15% risk area for Day 6 (Sunday).

Additionally, alongside the severe risk, hydrologic concerns will
also be on the increase with this system. Multiple rounds of
convection would lead to training potential, particularly across
north Georgia from Saturday through early Sunday. A Day 5 "Slight"
risk for excessive rainfall is already in place by WPC across north
Georgia to highlight this risk.
Click to expand...
 
Do these soundings indicate Kentucky and Ohio could get in on the action Saturday as well, or am I missing something? Forgive me, I've been trying to get my head wrapped around soundings for a while now, and this system seems like the perfect one to help with it.

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