Severe WX March 21-23 2022

[Clancy]

Based on the discussion's wording, the SPC still seems really confident in the threat of some particularly nasty storms on the 22nd, even given the potential limiters. Seems like there's a lot of questions on this one, but they don't seem nearly as uncertain as I would expect.

As strong upper low/trough over the central and southern Plains
region shifts gradually eastward, a belt of very strong mid- and
upper-level southwesterlies will likely extend from east Texas
across the Tennessee Valley, atop a 60 kt southerly low-level jet.
The resulting/anticipated degree of veering and increasing flow with
height falls within high-end parameter space for significant
tornadoes.

In addition, the strong low-level southerlies will persistently
advect high theta-e Gulf air (dewpoints averaging in the upper 60s)
northward into the pre-frontal warm sector, which -- despite limited
heating due to cloud cover and potentially ongoing convection in
some areas -- will combine with modestly steep mid-level lapse rates
to yield what should prove to be ample CAPE at least as far north as
central Mississippi, and later central Alabama.

Overall, given very strong shear, the strength of the upper system,
and the Gulf warm sector expected inland, a high-end environment
appears likely to exist across a geographically-focused area
centered over the central Gulf Coast states, supporting potential
for a substantial outbreak of severe/supercell storms.

 

[Clancy]

Checking AFDs, BMX describes an all-hazards threat on Tuesday. They already have defined a tornado threat with a confidence level of 3/5 on their HWO graphic.

By Tuesday, the ridge axis is now to our east, and the Plains
trough/occluding storm system is now moving east. A region of upper-
level divergence should now near the mid/lower Mississippi Valley as
southerly low-level flow strengthens along the Gulf Coast toward the
Tennessee Valley. Warm, moist advection will occur across Central
Alabama as a 60-70 kt low-level jet moves across the Deep South,
establishing warm sector conditions. Height falls begin to occur
during the afternoon, and I expect showers and thunderstorms to
gradually increase in coverage from the west as a result. With the
presence of abundant wind shear and increasing instability, severe
weather appears to remain a distinct possibility in some fashion
Tuesday afternoon into Tuesday night.

Latest operational guidance is in agreement that kinematics will be
quite high on Tuesday. A strong low-level jet will be in place, as
well as broad hodographs and decent veering in deep-layer wind
profiles. This includes SSE to SE surface winds amidst ongoing
pressure falls toward the northwest. Effective bulk shear will
increase to 50-60 kts as a result, along with MLCAPE of 500-1,000
J/kg owing to dewpoints increasing into the low to mid 60s. This
parameter space will support supercell thunderstorms along/ahead of
an advancing synoptic cold front, across MS, on Tuesday
afternoon/evening. Convection will have additional support from
dynamics aloft, as a shortwave perturbation ejects from southeast
Texas toward the Ohio Valley. This is supported on medium-range
guidance, which also show evidence of an EML on their respective
forecast soundings. Nonetheless, severe convective weather should
approach our forecast area from the west Tuesday afternoon/evening.
We will maintain our HWO status, perhaps with an increase in
confidence. All modes of severe weather will be possible, and we
will work to refine & fine-tune forecast details in forthcoming
updates.

FFC anticipates a line of storms with attendant tornado risk late Tuesday night into Wednesday.

To the west, models in strong agreement on closed upper low
developing on Monday over NM and W TX. What happens here depends
greatly on when and where upper low will eject and lift NE. Some
differences on these details but overall, flow aloft appears to
be more south to north oriented by late Tues and assuming
sufficient low level moisture and associated instability arrives,
likely to see line of strong to severe convection move through
Tues Night and/or Wed with damaging winds and a few embedded
mesovortices and with tornadoes possible. Low level shear should
be much stronger than our most recent system yesterday. EC, GEFS
and CMC ensembles show at least ~75% of members with MLCAPE > 500
J/kg and a few (<10%) nearing 1500 J/kg. Will need to monitor
expected environment closely next few days.

 

[Taylor Campbell]

The EURO is more messy, but there remains presentable shear and instability for a significant severe risk.

 

[andyhb]

The EURO is more messy, but there remains presentable shear and instability for a significant severe risk.

The Euro barely has any instability north of the Gulf Coast, this is underselling how bearish it is.

 

[Equus]

I never trust models explicitly with moisture return/advection as they tend to underestimate it at least here, but definitely does seem like a very saturated column with little capping, probably will be strong tornadoes somewhere but also can certainly see messy modes and lots of junk convection especially this far east. That said, we tend to get dozens of tornadoes with said messy modes and junk with those dynamics so...

 

[kcyalater]

Based on the discussion's wording, the SPC still seems really confident in the threat of some particularly nasty storms on the 22nd, even given the potential limiters. Seems like there's a lot of questions on this one, but they don't seem nearly as uncertain as I would expect.

i find this very curious as it seems the potential mitigating factors are increasing and the models are backing off instability making it north of far southern MS and AL on the 22nd.

 

[Equus]

Instability is something models really struggle with, would wait for surface obs picking up downstream before assuming they got a handle on the recovery; lack of instability could definitely be an issue but with the insane LLJ being shown I'd think we get better advection than some of the models show at least in the southern ⅔ of the risk

 

[Fred Gossage]

Limited moisture return with this setup, especially northeast of a line from Greenville MS to Dothan AL, is because of the sharp southeast component to the surface winds. This is not Oklahoma. When you have southeast surface winds there, your air mass is originating from the western 2/3 of the Gulf of Mexico. When we have surface winds sharply from the southeast here, we are not advecting in low-level air from the warmer parts of the Gulf of Mexico. Our trajectories are originating from Georgia, sometimes the Carolinas, and from the western Atlantic... that has cooler water temperatures than the Gulf and has dewpoints in the 50s. This is not a smaller-scale problem. This is a synoptic level problem originating from the position of the subtropical high in the low-levels and the troughing off the East Coast. Seeing the models that have been most aggressive the whole time with moisture recovery inland for this thing now trend toward the least aggressive moisture solution as we get closer should be telling to you. It's not just models underdoing moisture and instability. It's an air mass origin problem at a size scale too large to accommodate sudden changes and "fixes" this close in. The things that are in play on the East Coast to facilitate this more truncated moisture return are already in motion right now in real-world time, not model future land. This may not limit the threat much at all for southwest Alabama and areas of Mississippi along and south of about a Yazoo City latitude, but we're certainly getting a clear signal that we have very unfavorable low-level trajectories for significant destabilization north and northeast of there.

 

[Equus]

Very interesting, lots of synoptic complexities on the larger scale at work here haha. Neat information to know.

 

[CheeselandSkies]

Limited moisture return with this setup, especially northeast of a line from Greenville MS to Dothan AL, is because of the sharp southeast component to the surface winds. This is not Oklahoma. When you have southeast surface winds there, your air mass is originating from the western 2/3 of the Gulf of Mexico. When we have surface winds sharply from the southeast here, we are not advecting in low-level air from the warmer parts of the Gulf of Mexico. Our trajectories are originating from Georgia, sometimes the Carolinas, and from the western Atlantic... that has cooler water temperatures than the Gulf and has dewpoints in the 50s. This is not a smaller-scale problem. This is a synoptic level problem originating from the position of the subtropical high in the low-levels and the troughing off the East Coast. Seeing the models that have been most aggressive the whole time with moisture recovery inland for this thing now trend toward the least aggressive moisture solution as we get closer should be telling to you. It's not just models underdoing moisture and instability. It's an air mass origin problem at a size scale too large to accommodate sudden changes and "fixes" this close in. The things that are in play on the East Coast to facilitate this more truncated moisture return are already in motion right now in real-world time, not model future land. This may not limit the threat much at all for southwest Alabama and areas of Mississippi along and south of about a Yazoo City latitude, but we're certainly getting a clear signal that we have very unfavorable low-level trajectories for significant destabilization north and northeast of there.

That's interesting. I always thought of surface winds as more of a shear issue (less SE=less backed/less SRH) and/or a convergence issue.

 

[Fred Gossage]

That's interesting. I always thought of surface winds as more of a shear issue (less SE=less backed/less SRH) and/or a convergence issue.

It's very telling that out of all of our F5 days in Alabama history, 4/27/11 was the only one of them with surface winds at the synoptic level any degree east of due south. All the others had synoptic surface winds ranging from due south to due southwest, and then any backing was near/ahead of the storms on the smaller scale. In Dixie Alley, history has proven repeatedly that we need just enough turning to curve the lowest 1km of the hodograph, and speed shear takes care of the rest. You can't expect to advect in unstable air if the source region of your low-level winds is coming from a cooler air mass.

 

[Fred Gossage]

The analog I mentioned yesterday, April 13 2019, did not have the East Coast troughing leading up to it. There was actually a big upper low over the Northern Plains a day or two before, and the eventual shortwave rotated in on the south side of it as the Northern Plains ULL weakened and filled in. Not having that East Coast troughing leading in to the 2019 event is a critical difference between it and the coming system, because that allowed 60-65 dewpoints to be sitting over southern Georgia and off the Southeast Coast. That allowed us to "get away" with having the sharp southeast winds leading into that event. Far and away not the case this time.

 

[Equus]

Now that it's in range NAM definitely has a long period of SE/ESE flow coming out of lingering drier air from E GOM/FL before veering south out of a better quality moisture region not far ahead of the storms so that certainly tracks, if we had a longer recovery time for E GOM it might be different; watching the source region is pretty important I guess

 

[Fred Gossage]

Having said all of this, I still think areas south/west of a line from Greenville to Meridian end up as a sigtor-driven Moderate Risk, if not something higher than that... as long as things don't line out or get too messy too fast. There's still the meridional flow and line-parallel deep-layer shear vectors that are an issue.

 

[MattW]

I know everyone is focused on what seem to be big-time events to the west, but I find it interesting that the SPC has a D5 out for Georgia centered pretty much on Eufala-Columbus-Augusta-Columbia. Looking at some historical maps, it looks like Georgia's "southern tornado alley" is just south of that exact line so well within the outlined area.

 

[Fred Gossage]

Based on data I've seen the past 12-24 hrs, the most potent/possibly violent looking day of this whole ordeal may end up being Wednesday from south/east Georgia up through the Carolinas...

I think it would be highly prudent to add 3/23 to the date in the thread title here.

 

[Austin Dawg]

The analog I mentioned yesterday, April 13 2019, did not have the East Coast troughing leading up to it. There was actually a big upper low over the Northern Plains a day or two before, and the eventual shortwave rotated in on the south side of it as the Northern Plains ULL weakened and filled in. Not having that East Coast troughing leading in to the 2019 event is a critical difference between it and the coming system, because that allowed 60-65 dewpoints to be sitting over southern Georgia and off the Southeast Coast. That allowed us to "get away" with having the sharp

The GFS and NAM are not as bullish with dewpoints getting very far north as the EURO and keep the inflow of moisture out of the SE as you point out. However, Texas does not have that problem with any of the models. They did move our greatest risk just to my east but it still looks like the firing line will be right over my head. I would love to shoot some pics for you but I am regulated to my chair with my foot up snd a continuous IV antibiotic flow so I will keep an eye out for others shooting pics and video and posting them online.

I hope the NAM SigTor has had too many margaritas.

 

[Taylor Campbell]

I find there to be fair resemblance to the convective schema as April 11th, 2005 for Tuesday.

 

[Taylor Campbell]

I see that interstate 20 could be the divider of the best wind threat north in MS and of the best tornado threat south.

 

[Taylor Campbell]

Looks like the new Day 3 is a moderate risk.