Severe Weather 2021

[mdberry]

Fred,

Thanks for the update. I know that we are eight days out from next weekend; however, in your opinion what type of severe threat are we talking about? The reason I am concerned, is that our church (in Madison County), has our Shop with A Hero event next Saturday. Several hundred people involved in that event.

Your thoughts are greatly appreciated.

 

[CheeselandSkies]

Fred,

Thanks for the update. I know that we are eight days out from next weekend; however, in your opinion what type of severe threat are we talking about? The reason I am concerned, is that our church (in Madison County), has our Shop with A Hero event next Saturday. Several hundred people involved in that event.

Your thoughts are greatly appreciated.

Slightly OT but your avatar looks like the Stoughton, WI tornado of 2005. Are you from around here?

 

[mdberry]

Slightly OT but your avatar looks like the Stoughton, WI tornado of 2005. Are you from around here?

No, just saw that one day and picked it… I am an old Alabama boy.

 

[Fred Gossage]

Fred,

Thanks for the update. I know that we are eight days out from next weekend; however, in your opinion what type of severe threat are we talking about? The reason I am concerned, is that our church (in Madison County), has our Shop with A Hero event next Saturday. Several hundred people involved in that event.

Your thoughts are greatly appreciated.

It being this far out means it's not really possible to have that conversation yet. Let's get through the weekend, let's data continue to come in, and let's have a conversation again Monday. We still want know small scale details, but we'll have a decent idea of consistency on a large scale setup by then.

 

[mdberry]

It being this far out means it's not really possible to have that conversation yet. Let's get through the weekend, let data continue to come in, and let's have a conversation again Monday. We still want know small scale details, but we'll have a decent idea of consistency on a large scale setup by then.

Thank you Fred

 

[CheeselandSkies]

No, just saw that one day and picked it… I am an old Alabama boy.

I see. That tornado nearly hit the house where I was living at the time (and my parents still do).

 

[mdberry]

I see. That tornado nearly hit the house where I was living at the time (and my parents still do).

Wow….glad it missed you guys.

I have had way too many close calls with tornadoes here in the Huntsville area.

 

[Fred Gossage]

Tonight's Euro run is a worse caliber setup for next Saturday than both the 12z Euro was and what last night's Canadian (that spooked everybody) had. There's still a lot of model disagreement about the exact evolution of the system next weekend, but even the weakest solutions lead to a tornado risk of some caliber in Dixie. What's important is that this front that comes through Sunday night into Monday morning does not scour the Gulf. It hovers between the coast and the Tennessee Valley all week. The Gulf will be primed all week long. I think, regardless of how the shortwave and surface low/fronts ultimate evolve, this will be a case where thermos will not be in question... and during the cool season, that is automatically a red flag. Lots of time to watch for changes though.

 

[Austin Dawg]

Winter has left the building (for now).

View attachment 10786

I'm really hoping it doesn't show back up like last year because that just might break us here in South Central Texas if we had another unreal cold snap coupled with the economic and supply chain issues we have now.

 

[Clancy]

SPC made mention of next weekend in their Day 4-8 outlook today.

 

[Fred Gossage]

12z Euro is the third one in a row with an outbreak type setup. 12z Canadian is an example of how you get a significant tornado event with a positive tilt trough. 12z GFS is most strung out and the weakest scenario, and it still results in a supercell tornado environment of some magnitude. It's just that uncertainty in the exact setup, like that SPC outlook mentioned. However, this is beginning to look like it's a situation where "all roads lead to tornadoes" type ordeal, and that is usually a red flag.

 

[Fred Gossage]

The 18z GFS went in the direction of the Euro, Canadian, and some of the more volatile previous GFS runs. It's still a full week away. There will be changes in the models. There is uncertainty. We're able to sit and talk and explain things on here, but on our channel, we may introduce the "strong storm" verbiage in our weathercasts and on social media on Sunday, but it is too soon to do much more than that to the overall general public.

Even though there's inherent uncertainty just because of how far out this is, and there is uncertainty because of models waffling as they lock toward a common solution with time, there are some larger-scale things we can infer now... and that's what it's really about at this stage in the game.

1. We know that the front tomorrow night into Monday morning stalls near the coast going into Monday, and then it waffles between the coastline and the Tennessee Valley through at least Thursday. It never scours the Gulf of Mexico. That is critically important because it means that quality low-level moisture will be down there waiting, readily available to be advected northward as a system ejects out.

2. We are getting a steadily increasing signal that the warm front moves north into the Tennessee and Ohio Valleys during the day on Friday. That puts a quality warm sector in place across Dixie Alley a full 24 hours or more in advance.

3. Because of the complete lack of a subtropical jet and the WSW mid/upper flow across the developing warm sector before the main wave ever ejects out, with that mid/upper flow originating from the northern Mexican plateau and the Southwestern U.S., we know that a large scale elevated mixed layer will be advected overtop the warm sector Friday going into Saturday morning. That provides steep mid-level lapse rates and it also caps the warm sector.

Regardless of how the models try to depict the wave ultimately evolving, which will determine the ultimate magnitude of the risk, we can use those few things above to know that a quality low-level air mass will be available, that a large warm sector will be in place a full day in advance, and that unlike most systems the past several years, that warm sector may be largely quiet, clean, and capped as we head through Friday night and Saturday morning. All that put together suggests that the thermodynamics will not be in question, regardless of the eventual exact system evolution. In the winter months, winning the battle with the thermos is winning 70% of the overall entire battle.

 

[Clancy]

The 18z GFS went in the direction of the Euro, Canadian, and some of the more volatile previous GFS runs. It's still a full week away. There will be changes in the models. There is uncertainty. We're able to sit and talk and explain things on here, but on our channel, we may introduce the "strong storm" verbiage in our weathercasts and on social media on Sunday, but it is too soon to do much more than that to the overall general public.

Even though there's inherent uncertainty just because of how far out this is, and there is uncertainty because of models waffling as they lock toward a common solution with time, there are some larger-scale things we can infer now... and that's what it's really about at this stage in the game.

1. We know that the front tomorrow night into Monday morning stalls near the coast going into Monday, and then it waffles between the coastline and the Tennessee Valley through at least Thursday. It never scours the Gulf of Mexico. That is critically important because it means that quality low-level moisture will be down there waiting, readily available to be advected northward as a system ejects out.

2. We are getting a steadily increasing signal that the warm front moves north into the Tennessee and Ohio Valleys during the day on Friday. That puts a quality warm sector in place across Dixie Alley a full 24 hours or more in advance.

3. Because of the complete lack of a subtropical jet and the WSW mid/upper flow across the developing warm sector before the main wave ever ejects out, with that mid/upper flow originating from the northern Mexican plateau and the Southwestern U.S., we know that a large scale elevated mixed layer will be advected overtop the warm sector Friday going into Saturday morning. That provides steep mid-level lapse rates and it also caps the warm sector.

Regardless of how the models try to depict the wave ultimately evolving, which will determine the ultimate magnitude of the risk, we can use those few things above to know that a quality low-level air mass will be available, that a large warm sector will be in place a full day in advance, and that unlike most systems the past several years, that warm sector may be largely quiet, clean, and capped as we head through Friday night and Saturday morning. All that put together suggests that the thermodynamics will not be in question, regardless of the eventual exact system evolution. In the winter months, winning the battle with the thermos is winning 70% of the overall entire battle.

I have recently learned I will be travelling out of town next Saturday. What timing

 

[akt1985]

Although it’s never a good time for bad weather, at least the potential severe threat is next weekend and not this weekend. Imagine having to go wall to wall during the SEC Championship Game for tornado warnings.

 

[CheeselandSkies]

In the shorter term, slight risk tomorrow for parts of AR/W TN/NW MS.

 

[Fred Gossage]

A lot of the inconsistencies in the modeling related to the trough evolution next weekend stems from an upper low of the Baja coast, as early on in the evolution of the pattern as Thursday morning as the jet streak we're watching digs southeastward out of the Gulf of Alaska. Model runs tonight are stronger with that upper low and closer to the CONUS than previous runs. That is causing disruption with the incoming jet streak, and it ends up helping the wave get sheared through the large-scale longwave trough over the CONUS. Previous model runs, especially in the Euro and Canadian, had the upper low a bit weaker and a bit more westward. Back on Thursday morning's Euro and Canadian runs, the upper low didn't even exist. What's interesting is that the GFS did have it back then. However, the GFS is farther west and weaker with the upper low but still comes to the conclusion. This becomes a question of whether the GFS may have been right first compared to the Euro, similar to how it had done with both tropical and mid-latitude systems over the summer, or if the GFS is just showing its decades-long known bias of shearing apart systems, and this just happens to be short-lived waffling within the other models. I don't think we'll know for sure for a couple more days, and this is the kind of inconsistency that makes it prudent to control and reign in the tone used with the general public at this stage.

 

[Fred Gossage]

I think we start to get an idea of how this evolves over the next 24-48 hours, because that's when the little shortwave crests the Hawaiian ridge and then retrogrades and cuts off into an upper low off the Baja coast. What's interesting is that the GFS is weaker with that wave too but still ultimately shears apart the weekend system. I'm getting the idea more that the GFS is just showing its classic bias of shearing systems just for the sake of it, and it either end up that the Euro followed along this run because of short-term flux with the upper low, or the GFS is just the blind squirrel that accidentally found an acorn.

 

[Fred Gossage]

In the shorter term, slight risk tomorrow for parts of AR/W TN/NW MS.

Definitely can't forget about this short-term threat. It may even be a good little litmus test to see if we're still in a regime where systems overperform. 300mb temps sitting in the -42C range and 500mb temps below -15C concern me, because it means you can do more with less boundary layer warmth than you usually could. Very steep mid-level lapse rates as well in the 700-500mb layer.

 

[Fred Gossage]

Baron 3k model is onboard with the HRRR, WRFs, etc., with the idea of multiple lower-end updraft helicity streaks with these storms during the predawn to mid morning hours of Monday. Given the mid/upper level temperatures and lapse rates and the likelihood of lower 60 dewpoints and a few hundred j/kg of CAPE even as late as 5-8am, I certainly wouldn't be shocked at a tornado warning or two as far east as I-65 in middle Tennessee and north Alabama, and a slightly more organized threat from the afternoon into the late night back across the SPC SLGT area.

 

[Fred Gossage]

Still questions in the modeling with how the Baja area upper low will affect the late week evolution. I think we may have these questions another day or so. I'm starting to get the vibe though that regardless of how Saturday evolves, we need to watch Friday into Friday night with the lead impulse that comes out. There won't be a lot of forcing, but shear will be there over the warm sector, and the thermos will be there... since the warm sector gets into place Thursday night into Friday morning.