Severe Weather 2020

[Fred Gossage]

I'm feeling more uncertain about the idea of a complex of storms to our south as we get closer to this thing. Most of the guidance is solidly backing away from that. The more I look at the orientation of the trough and the mid/upper winds, I can understand why. Models have inched the trough itself a little farther northwest. Combine that with such southerly deep-layer flow that would be parallel to any line that would try to form down there, and I can easily see how this would be a case where we don't see a linear complex on the coast that sweeps eastward quickly. I'm still not yet sold on areas north of I-20 needing to sound the alarm for this, but we will have to watch it carefully. I do think, given the sharpness and meridional nature of the trough and the deep-layer winds being mostly parallel to the front, the convective mode will be mainly linear... however, like BMX mentioned, that could easily contain embedded supercells, and 2020 alone showed us multiple times that QLCS tornadoes aren't always brief low-end spin-ups.

 

[Richardjacks]

I'm feeling more uncertain about the idea of a complex of storms to our south as we get closer to this thing. Most of the guidance is solidly backing away from that. The more I look at the orientation of the trough and the mid/upper winds, I can understand why. Models have inched the trough itself a little farther northwest. Combine that with such southerly deep-layer flow that would be parallel to any line that would try to form down there, and I can easily see how this would be a case where we don't see a linear complex on the coast that sweeps eastward quickly. I'm still not yet sold on areas north of I-20 needing to sound the alarm for this, but we will have to watch it carefully. I do think, given the sharpness and meridional nature of the trough and the deep-layer winds being mostly parallel to the front, the convective mode will be mainly linear... however, like BMX mentioned, that could easily contain embedded supercells, and 2020 alone showed us multiple times that QLCS tornadoes aren't always brief low-end spin-ups.

Hi Fred!
Yep, this one concerns me. The only thing that gives me some some hope of a Forecasted Convective Amplification Deficiency here is the amount of rain ahead of the front and how it could limit instability from possibly moving north of Montgomery. I fear capes in the 400+/- range will be plenty for serious trouble.

 

[Fred Gossage]

Hi Fred!
Yep, this one concerns me. The only thing that gives me some some hope of a Forecasted Convective Amplification Deficiency here is the amount of rain ahead of the front and how it could limit instability from possibly moving north of Montgomery. I fear capes in the 400+/- range will be plenty for serious trouble.

The synoptic setup is strikingly reminiscent to Christmas Day 2012 and February 23, 2016. Both were full-blown outbreaks near the coast, worthy of High Risks and both almost got such from SPC. Both also had widespread rain north of the warm front that locked the big action from Montgomery south. Those troughs ejected more ENE out of the area though, while this trough ejects almost due N out to our west. That and the trough grabbing the elevated mixed layer and advecting it north may help to expand the warm sector north, but these deep troughs centered so far south almost never work out for areas north of Montgomery. Those two mentioned differences may be enough to have a much different outcome though.

 

[Richardjacks]

The due north trajectory will likely lead to some very fast changes in the instability. Tough forecast.

 

[Justin Hindman]

I can confidently say this will be the last event for 2020 or the first for 2021. I do think with things trending slower it will lesson the threat in central Alabama due to timing. Whether we see convection or not at the coast, looks likes a frustrating squall line with a few embedded tornadoes. Hopefully this system doesn’t speed up and it comes in the afternoon. Models should get more consistent in the next 24-36 hours

 

[Fred Gossage]

I can confidently say this will be the last event for 2020 or the first for 2021. I do think with things trending slower it will lesson the threat in central Alabama due to timing. Whether we see convection or not at the coast, looks likes a frustrating squall line with a few embedded tornadoes. Hopefully this system doesn’t speed up and it comes in the afternoon. Models should get more consistent in the next 24-36 hours

We're in the time of the year where daytime heating usually matters very little to severe weather threats in the overall scheme of things, especially one that would have a mainly cloudy warm sector. Destabilization would happen by advection instead of insolation, and that would occur to the same degree, whether it is day or night. A slower timing would actually allow for more moisture advection farther northward, increasing the degree of instability and how far north it extends. Very VERY few severe weather threats in the winter months are modulated much by daytime heating, despite how you may hear otherwise ahead of a system by people who apply anecdotal "classic" rules that are based on April-May systems in the Plains. Real, actual systems in Dixie repeatedly say differently. If that wasn't the case, a good 85-90% of our severe weather events here in the winter months wouldn't even happen at all. When we get to 70+ in a warm sector in December-February, it is usually because of strong warm air advection, not several hours of sun breaks. In the few times that is not the case and we have decent insolation too with a severe threat during this time of the year, we are usually slapped with a higher-end event... either a full-blown tornado outbreak or a "storm-of-the-day" event that produces a violent tornado.

Having said all that, I'm still leaning toward this being a case, with how sharply southeast the low-level winds are until right at the last minute... that this is another one of those events with widespread rain north of the warm front that falls into cooler, more stable air advecting in from Georgia... and that reinforces the warm front and keeps it locked down south. The current SLGT comes up almost to Tuscaloosa, but I see this being a situation where the higher threat may stay south of Demopolis, Selma, and Montgomery. The exact same thing happened with the Christmas Day 2012 and Feb. 23, 2016 systems, the two events that this setup almost carbon-copy analogs to. But those were also high-end outbreaks down south, at least by coastal standards. Both had multiple long-tracked, strong tornadoes, and both would've verified a High Risk. This may end up being a substantial supercell-flavored tornado threat for southeast Louisiana, south Mississippi, into southwest Alabama, and maybe the far western Florida panhandle. I think we eventually go ENH Risk down there, and I wouldn't be shocked if there's an eventual upgrade to MDT.

 

[andyhb]

I will say, if you’re looking for an upper jet configuration that would result in sig severe near the Gulf Coast, this would be a prime candidate to both suppress coastal convection and provide plenty of 0-8 km shear.

 

[Richardjacks]

Fred, it does concern me that the GFS has the Td in BHM getting into the mid 60's. I think this partly due to it having little rain, which could be underplayed. Rain into that drier air coming from the east would likely kill surface based instability for up here, but if sfc Td's got into the mid 60's, we could see an entirely different scenario.
EDIT: there is some slowing of the overall closed low...giving more time for higher instability to move in, but I am also beginning to wonder if the closed low just moves too slow and reduces severe threat to further west.

 

[Fred Gossage]

I also think the models may be underdoing the rain north of the warm front to a degree. By late in the day Thursday, we have a wide 50-60+ kt 850mb jet blasting north directly across that warm front, and north AL is directly on the nose of that intense 250mb jet, with strong diffluence directly overhead. There's no possible way the rain won't be more widespread and heavy than currently depicted. I honestly wouldn't be surprised if this starts to trend more toward looking like a flash flood threat north of Birmingham as we get closer.

 

[TCLwx]

An interesting end of year read from the Capital Weather Gang/WaPo. ZERO confirmed tornadoes in Wichita CWA in 2020.

The tornado drought of 2020: Plains lacked trademark twisters this past year​