Severe WX April 11-14th, 2022 Severe Weather Threat

[KevinH]

I know this may be a bit early but…. it IS April. I will delete if this thread ends up not being needed, but in the meantime… discuss.

I’ll go first:

SPC is highlighting the 11th and 12th days for severe weather. As usual (this far out), risk areas/levels will be modified in the coming days as data comes in. As such, I might modify the dates of this thread as well.

Also I keep seeing talk about the 13-15th, so I have included those dates here. I will post what I see about these dates later today if someone else does not already do so.

 

[CheeselandSkies]

Some pretty significant differences between the 06Z GFS and 00Z Euro which is to be expected at this range...Euro has a more favorable look overall regarding trough structure and orientation, although they both agree on a large trough coming through in the general mid-next week time frame with some degree of severe weather potential; hence SPC introducing long-range outlook areas.

 

[Fred Gossage]

Putting this also over here since there is a dedicated thread about this synoptic system now...

As expected, the 00Z EPS has decidedly trended away from a low-amplitude solution and now favours high-latitude blocking and split flow. The trough axis is also much narrower on Wednesday, despite still being negatively tilted. The trajectory of moisture return prior to the main event also looks to be less favourable than on earlier runs, hence greater CAD over portions of Dixie Alley (eastern extent of warm sector), especially AL/GA. One thing is clear: UL divergence is extremely robust on the latest run and ad verbatim the setup would imply a significant event for portions of OK/KS/MO. The main threat looks to remain north and west of Dixie Alley on the latest EPS.

The trough is a little more amplified and a little northwest on the overnight Euro ensembles, but there hasn't been a significant/major shift. GFS ensembles have been more northwest than either the Euro ensembles or Canadian ensembles though, and that can't be ignored. But to the Euro ensembles, 576dm at 500mb has been proven for decades to be a good delineator of the south/east edge of the more substantial risk of a severe weather event, and that is through northwest MS into middle TN as early as 18z Wednesday, and into northwest AL by 00z Thu. The face value dryline by 18z Wednesday is almost completely east of Oklahoma, and that doesn't account for mixing that would likely carry the dryline farther east than shown by the lower-res globals when keeping in mind the large-scale EML plume aloft that will advect out as well as the drought over the Plains. The low-level jet is also centered over the eastern 2/3 of Arkansas, through Louisiana, southeastern Missouri, and across the river into west TN/KY by 18z Wednesday, and it is centered completely east of the MS River over IL/IN/KY/TN/MS/AL by 00z Thursday.

There's been an undeniable trend in all the ensemble guidance for this to inch northwest, and if there is also any slowing trend added as we get closer, that would keep a dryline into eastern Oklahoma deeper into the afternoon. However, just using the EPS guidance you used at just face value alone, while the greatest threat is undeniably northwest of central MS and north/central AL, the threat definitely does extend (and is centered) a bit farther east than you outline as early as the afternoon and early evening, and a lower but still appreciable threat definitely extends eastward into the I-65 corridor as far east as Indiana, Kentucky, middle Tennessee, and north Alabama by the overnight. And with the wide and expansive warm sector and what would be a large-scale EML plume that would advect out overtop the warm sector (and has been modeled to do so in the operational models that have an even higher amplitude trough at times than the ensembles), this is not going to be a case where instability just goes away at sunset. This would be a situation where a threat would continue deep into the overnight hours Wednesday, if not the morning hours of Thursday before the wave pulls too far north and the low-level jet pulls away from the heart of the warm sector.

To give room for a slowing trend or wiggle room for any further northwest trend, I would say the elevated threat extends as far west as east OK, east KS, west MO, and northeast TX... but the main threat to me looks to be across the eastern half of Missouri, central and southern Illinois, and down through west Kentucky and Tennessee, through a large part of Arkansas, into northwest Mississippi, and into northern Louisiana... and then a sunset Wednesday to predawn Thursday (lower but appreciable) threat continues as far east as west/southwest Ohio, middle/east Kentucky and Tennessee, north Alabama, and maybe into central Alabama/northwest Georgia if height falls are okay enough. There will be height falls and cyclonic curvature aloft to help with large scale ascent.

There's large scale diffluence, appreciable height falls, and cyclonic curvature aloft way out ahead of the cold front/dryline out over the low-level jet axis and open warm sector. This would not be the type of threat where storms are restricted to be just ahead of the dryline/cold front. Unless there's a problem in the setup that's talked about next...

As synoptically evident as the system is on the large scale, the magnitude of this threat definitely is not still set in stone. That subtle little wave that's being modeled to run out ahead of the trough Tuesday night into Wednesday morning will have to be monitored. Those type of things can often disrupt the low-level jet and low-level convergence from where the large-scale setup would typically have it placed, and can take the convective focus away from the main upper forcing. Usually it centers it east... similar to how it does in these situations in the Southeast where we see a lead subtle wave focus the low-level jet across Georgia and into the Carolinas when the placement of the approaching main upper trough would otherwise have the low-level jet back over MS/TN/AL. If that subtle wave trends more pronounced in the data, that could not only cause LLJ/convergence displacement and disruption for the main event, but possibly cause contamination in the warm sector, and also move the convective focus away from the upper-level support. While those things may make a threat setup farther east/southeast than the synoptics would suggest, they would also likely lower the ceiling of the event as a whole. A lot to work out in the coming days...

 

[CheeselandSkies]

Something is odd about the GFS output, particularly for Tuesday afternoon/evening over the Plains. Despite the extremely deep surface low and what looks like great directional shear just by looking at the 850/500mb wind barbs, the hodographs/SRH numbers on the forecast soundings are not that impressive. Any ideas why this might be?

 

[Fred Gossage]

Something is odd about the GFS output, particularly for Tuesday afternoon/evening over the Plains. Despite the extremely deep surface low and what looks like great directional shear just by looking at the 850/500mb wind barbs, the hodographs/SRH numbers on the forecast sounding are not that impressive. Any ideas why this might be?

It's a combination of the GFS keeping the mid/upper jet pulled back west of the warm sector Tuesday afternoon and evening and also lead impulse disrupting flow over TX/OK. There's a distinct and substantial weakness in the wind fields across the dryline on the latest GFS. It had been there on the 00z run as well, but didn't extend farther north than northern Oklahoma. This new 6z run has the weakness extend well north through Kansas as well because it is keeping the upper jet pulled back more.

 

[Fred Gossage]

It's a combination of the GFS keeping the mid/upper jet pulled back west of the warm sector Tuesday afternoon and evening and also lead impulse disrupting flow over TX/OK. There's a distinct and substantial weakness in the wind fields across the dryline on the latest GFS. It had been there on the 00z run as well, but didn't extend farther north than northern Oklahoma. This new 6z run has the weakness extend well north through Kansas as well because it is keeping the upper jet pulled back more.

I'd be careful reading too much into it just yet though. Just the 00z run had a stronger low-level jet over Kansas, although there was still the weakness in the flow over Oklahoma, and there was widespread 0-1 km SRH of 400+ (heavy emphasis on the +) over central/east Kansas and up to double digit 3 km EHI values there when throwing in the modeled 2500-3000+ CAPE. The operational GFS continues to be a drunken donkey when trying to figure out how this is all going to evolve. Earlier yesterday, it shifted the trough from the Four Corners to the MS Valley for Wednesday from just the 12z to 18z runs... and the 12z run had slowed the MS/AL/TN threat all the way down to Friday afternoon and evening. Somebody needs to lay hands on and get the anointing oil and prayer cloths after the operational GFS...

 

[CheeselandSkies]

Thanks, Fred!

 

[KevinH]

The new D4-8 (April 10-14th) outlook issued this morning.

I do not think I can ever recall seeing the risk area move so slowly over a few days. Will be interesting to see how this evolves leading up to the event(s?) in question.

 

[Fred Gossage]

View attachment 13305
The new D4-8 (April 10-14th) outlook issued this morning.

I do not think I can ever recall seeing the risk area move so slowly over a few days. Will be interesting to see how this evolves leading up to the event(s?) in question.

That's primarily because the main system doesn't actually bodily eject out until Wednesday, and the Monday/Tuesday threat is primarily driven just by southwest flow aloft helping initiate return flow ahead of the dryline and lee cyclogenesis over the High Plains. And of the sequence, I think those two have the highest bust potential... especially Monday because of questions about moisture depth and quality. The Gulf gets wiped by a Mr. Clean Magic Eraser over the weekend. High octane boundary layer moisture will be available to come well inland Wednesday, and probably even Tuesday, but Monday may be stretching it outside of Texas.

 

[Casuarina Head]

That subtle little wave that's being modeled to run out ahead of the trough Tuesday night into Wednesday morning will have to be monitored. Those type of things can often disrupt the low-level jet and low-level convergence from where the large-scale setup would typically have it placed, and can take the convective focus away from the main upper forcing.

The most recent three runs of the EPS have definitely trended toward a more pronounced wave during this timeframe, owing to a more amplified upper-air pattern overall. I think that this will substantially negate the extent and degree of the threat on Wednesday over a wide area. As I have mentioned previously, we are still not seeing the kind of broad-based, low-amplitude pattern that one would expect during a robust -PDO/-ENSO/+TNI. As we draw nearer to the event, models trend back toward a higher-amplitude, blockier, split-flow pattern. This is a recurring theme.

 

[Fred Gossage]

The most recent three runs of the EPS have definitely trended toward a more pronounced wave during this timeframe, owing to a more amplified upper-air pattern overall. I think that this will substantially negate the extent and degree of the threat on Wednesday over a wide area. As I have mentioned previously, we are still not seeing the kind of broad-based, low-amplitude pattern that one would expect during a robust -PDO/-ENSO/+TNI. As we draw nearer to the event, models trend back toward a higher-amplitude, blockier, split-flow pattern. This is a recurring theme.

That is still a broad-based, low amplitude trough, especially when compared to any of the systems so far this year that have caused full-on tornado outbreaks. But you are correct that there are issues with blocking and subtropical influence. I also think that will mitigate this from being what it otherwise could be, but I'm not sure how much, especially given what we have already seen happen repeatedly with every single system... systems that have had much less favorable synoptic setups for the type of tornado activity they have all produced. But the -NAO is just in the process of relaxing as this system comes out, and that is at least some of the reason for the downstream blocking being there.

As far as the whole thing with expecting clean, low amplitude, polar-jet-only troughs just because there's a La Nina, -PDO, and +TNI... yes, you're more likely to see that type of trough geometry when those things are in place than when they are not, but there are many times it does not happen. Other factors drive the large-scale pattern also. If that wasn't the case, we'd have top-tier widespread tornado outbreaks just about every single time there is a La Nina, and that has NEVER been the case. Those types of things happen a lot less frequently in history, dating back over a century, than you have ever accepted as fact... despite weather records... since you made your very first post on this forum over a year ago.

 

[Fred Gossage]

Let's not forget that we have had two separate tornado outbreaks, each with 70+ confirmed separate tornado tracks and multiple strong tornadoes, with trough geometry in each that never should've supported anything more than a messy, line-parallel flow driven QLCS. And then we turn around just this week and squeeze out another tornado outbreak with multiple wedges and significant structural damage from a system that trended completely disjointed and sheared apart. We need to stop pretending that we need a 4/3/74 or 4/27/11 looking trough in order to have a significant tornado event. Even with multiple "problems" from the synoptic level down, this year has proven that it is built differently, and nothing is underperforming.

 

[Casuarina Head]

As far as the whole thing with expecting clean, low amplitude, polar-jet-only troughs just because there's a La Nina, -PDO, and +TNI... yes, you're more likely to see that type of trough geometry when those things are in place than when they are not, but there are many times it does not happen. ... Those types of things happen a lot less frequently in history, dating back over a century, than you have ever accepted as fact... despite weather records... since you made your very first post on this forum over a year ago.

To clarify: I meant that so far 2022 has not featured at least one “clean, low-amplitude, polar-jet-only” system, despite having generated several outbreaks. (The winter of 2021 did feature at least one system that met this description: the major outbreak on 10–11 December.) My point is that I would expect a robust winter-/springtime -PDO/-ENSO/+TNI to yield at least one “clean, low-amplitude, polar-jet-only” system to date in 2022—a large-scale synoptic system that is unaffected by blocking and subtropical interference.

 

[Fred Gossage]

To clarify: I meant that so far 2022 has not featured at least one “clean, low-amplitude, polar-jet-only” system, despite having generated several outbreaks. (The winter of 2021 did feature at least one system that met this description: the major outbreak on 10–11 December.) My point is that I would expect a robust winter-/springtime -PDO/-ENSO/+TNI to yield at least one “clean, low-amplitude, polar-jet-only” system to date in 2022—a large-scale synoptic system that is unaffected by blocking and subtropical interference.

And because of the timing of NAO blocks, MJO propagation, etc., it doesn't always line up exactly, even when the La Nina, PDO, and TNI are favorable. That's why really bad days are pretty infrequent.

 

[UK_EF4]

And because of the timing of NAO blocks, MJO propagation, etc., it doesn't always line up exactly, even when the La Nina, PDO, and TNI are favorable. That's why really bad days are pretty infrequent.

As someone who doesn't particularly understand long-term global weather factors and teleconnections influences on tornadic activity like MJO and La Nina , does it seem like the current favourable pattern for these large troughs etc will continue after this big one coming up, and we will continue to see severe weather, or will most areas see a much needed severe wx break?

 

[tennessee storm chaser]

As someone who doesn't particularly understand long-term global weather factors and teleconnections influences on tornadic activity like MJO and La Nina , does it seem like the current favourable pattern for these large troughs etc will continue after this big one coming up, and we will continue to see severe weather, or will most areas see a much needed severe wx break?

I can certainly see a active pattern going into early May very least …

 

[Fred Gossage]

One "problem" so far is that the switch back to +NAO that was originally projected for right around now has gotten delayed. It's very usual to see extended range pattern changes get delayed by a week or even two. There's rarely a pattern change in the cool season months that doesn't get delayed. I think how this coming system next week on its exit determines a lot going forward for the rest of the month and whether this shift toward a slightly positive NAO is actually going to come about. Most guidance is suggesting that the MJO cycles around out of the "circle of death" toward Phases 8->1->2 as we head over the next 10-14 days, between now and the 20th and just beyond. Those are favorable MJO phases to have a more classic severe weather pattern, and it often takes MJO amplification like that to get the North Atlantic to shake itself out of a stagnant/blocked pattern. But given the delay we've seen, I'm in a wait and see mentality with that. I want to see the -NAO breakdown get within 120-168 hrs on modeling before I have higher confidence in it not just getting punted down the line. This coming system and how it exits the area will tell a lot about the rest of April. And beyond that, yes you CAN still get significant severe weather in the Southeast in May, but it gets progressively harder no matter what teleconnections are in place... and even more so when you're in a La Nina spring.

 

[Fred Gossage]

12z GFS, Canadian, and GFS ensembles have trended toward the system being a bit deeper and heights being lower east of the MS River overnight Wednesday night. There is significantly more cyclonic curvature aloft with the trough Wednesday night on the 12Z GEFS compared to previous runs too. The overall look of the data today would increase the overall Wednesday afternoon to Thursday morning risk and also elevate the chances of it extending east of the MS River Wednesday night into Thursday morning.

 

[Fred Gossage]

I know this may be a bit early but…. it IS April. I will delete if this thread ends up not being needed, but in the meantime… discuss.

I’ll go first:

SPC is highlighting the 11th and 12th days for severe weather. As usual (this far out), risk areas/levels will be modified in the coming days as data comes in. As such, I might modify the dates of this thread as well.

Also I keep seeing talk about the 13-15th, so I have included those dates here. I will post what I see about these dates later today if someone else does not already do so.

I think it's probably safe for you to cut the timeframe for this thread off at the 14th. I don't think a threat with this wave would extend beyond Thursday/Thursday night unless things were to radically slow down. You may also want to do a cutoff like that since there is a potentially increasing signal for another system behind this one over the weekend if this one lifts out correctly.

 

[Fred Gossage]

12z GFS, Canadian, and GFS ensembles have trended toward the system being a bit deeper and heights being lower east of the MS River overnight Wednesday night. There is significantly more cyclonic curvature aloft with the trough Wednesday night on the 12Z GEFS compared to previous runs too. The overall look of the data today would increase the overall Wednesday afternoon to Thursday morning risk and also elevate the chances of it extending east of the MS River Wednesday night into Thursday morning.

There remains the question of how the little lead subtropical impulse may or may not change the layout of the low-level jet, forcing, and deep-layer shear... but other than that, every single 12z operational model and every 12z ensemble suite said "northwest trend deez nuts" and ALL trended stronger, deeper, farther south/east, and more cyclonically curved aloft. Not a single piece of data didn't.