November 29th-30th, 2022 | Severe Weather | Lengthy Dixie Alley Tornado Outbreak on the 29th

[CentralLA_Wx]

Pretty big 60 sigtor over Louisiana Tuesday afternoon. Somewhat nervous about this event locally. Seems like late fall/early winter events are more likely to overachieve in my area than spring severe threats. 

[Neoncyclone]

Just realized that we're within HRRR range of the beginning of the event. It's not pretty, I'm pretty much set on this being a significant severe day probably worthy of a day 2 moderate. The subtropical jet will have no problem transporting moisture into the warm sector while interacting with the jet streak associated with trough.  I feel it's also important to note that amongst most CAM's it seems like the moisture transport just keeps pushing further north creating a larger warm sector. The only question I wondered about was forcing but as we get closer to the event all the CAM's within range agree on discrete mode convection and plenty of it too. 

Edited November 28, 2022 by Neoncyclone

[Grace]

I'm getting concerned now. I disregarded it 2 days ago thinking this was a much further south risk. Us Mayfield folk getting a little edgy as risk area creeps close to us. 

I tell yall something spooky. Meteorologist Trent Okerson from WPSD in Paducah visited the elementary school my wife teaches at the day before last DEC tornado. Well, he's visiting her elementary school again tomorrow.

Silly i know, but after what our town went through everything sticks out like a sore thumb.

[Chinook]

Here is the NAM STP, which shows very high values for Day-3 time frame, at nighttime, that is, 06z. 

Edit: the new 00z NAM from tonight has values of 3.0 or better in some of the same areas. The 18z GFS had weaker winds at 850mb, so it has lower 0-3km SRH, but still the parameters are decent in the overall region.

Edited November 28, 2022 by Chinook

[ClicheVortex2014]

The environment is unquestionably very favorable for tornadoes, but CAMs still aren’t as convincing about warm sector convection as I’d like to see from a forecasting point of view. Tough call for SPC in that regard but if they feel confident about warm sector convection, then the instability/shear profiles make their job easier because there’s no question about that. So it’ll be interesting to see what they do

[Ingyball]

Haven't been able to look at this storm too much due to being sick, but I can tell you that this is a very favorable upper jet orientation that happens to be bisecting the warm sector. This would favor discrete storms and a potentially significant tornado threat. Lapse rates could be better but I think we're probably going to see a pretty decent outbreak out of this assuming a failure mode doesn't creep in on the day of. If the upper jet was either removed from the warm sector or more meridional I'd be more concerned about linear convection and less forcing out ahead of the front.  

[ClicheVortex2014]

Good thread about this event

Good example of what needs to verify in order to make this event: subtle warm sector forcing

 

[Neoncyclone]

 

[ClicheVortex2014]

Day 2 moderate introduced on the first outlook. Yikes

[Neoncyclone]

Quote

SPC AC 280703 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0103 AM CST Mon Nov 28 2022 Valid 291200Z - 301200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF FAR NORTHEAST LOUISIANA...FAR SOUTHEAST ARKANSAS...NORTHWEST MISSISSIPPI AND FAR SOUTHWEST TENNESSEE...

...SUMMARY... Severe thunderstorms with tornadoes and wind damage, along with some hail, will be likely on Tuesday afternoon and evening, extending into the overnight period across parts of the lower to mid Mississippi Valley. Significant and/or long-track tornadoes will be possible. ...Regional Tornado Outbreak Possible Tuesday Afternoon and Evening Across Parts of the Lower to Mid Mississippi Valley...

...Lower to Mid Mississippi Valley/Sabine River Valley/Western Ohio and Tennessee Valleys... A progressive upper-level trough will move quickly eastward across the Rockies Tuesday and into the Great Plains. Ahead of the system, a moist airmass, with surface dewpoints in the lower to mid 60s F, will advect northward across the lower and mid Mississippi Valleys. Thunderstorm development will be likely during the day on the eastern edge of the most airmass, from the central Gulf Coast states northward into the western Ohio Valley. While elevated, an isolated severe threat will be possible with some of this convection. Further to the southwest, an axis of moderate instability is forecast to develop by mid to late afternoon from northwest Louisiana northeastward into far eastern Arkansas. This airmass should continue to destabilize during the evening, as rich low-level moisture streams north-northeastward, with MLCAPE reaching the 1500 to 2000 J/kg range by 03Z Wednesday across parts of northern Louisiana, southeast Arkansas and northwest Mississippi. Surface-based convective initiation appears likely to occur during the late afternoon and early evening in northern Louisiana, with these storms tracking northeastward across far southeast Arkansas and into northwest Mississippi.

Throughout the day on Tuesday, deep-layer shear will steadily increase across the region as a 70 to 90 knot mid-level jet translates quickly eastward across the south-central U.S. This jet is forecast to move through the base of the trough at around 55 knots, which will help sustain a 40 to 60 knot low-level jet ahead of the system. NAM forecast soundings along the most favorable corridor from far northeast of Monroe, Louisiana to near Memphis, Tennessee at 03Z Wednesday, have MLCAPE in the 1500 to 2000 J/kg range, with 0-6 km shear near 70 knots, and 0-3 km storm-relative helicities around 400 m2/s2. Hodographs are forecast to be long and curved, suggesting the environment will be favorable for tornadic supercells. A long-track and/or significant tornadoes will be possible, with the most favorable corridor located from far northeast Louisiana northeastward across northwest Mississippi. An earlier and further southwest convective initiation would be most favorable for a tornado outbreak, which would give the storms more time to move northeastward through the most unstable air. Supercells will also have potential for wind damage and isolated large hail. During the mid to late evening, a strengthening low-level jet should help maintain the severe threat across the region. A threat for tornadoes, wind-damage and hail will be possible with supercells and with organized bowing line segments from mid evening into the early overnight period. Further northeast into north-central Tennessee, western Kentucky and far southern Illinois, moisture advection during the early to mid evening, will likely increase dewpoints into the lower 60s F. As a cold front approaches from the west, scattered thunderstorms are expected to develop across the moist sector. Although instability is forecast to be weak ahead of the front, large-scale ascent should be very focused due to the approaching trough. This combined with strong deep-layer shear should support a severe threat, with wind damage and a few tornadoes possible.

..Broyles.. 11/28/2022

 

[Neoncyclone]

06z HRRR, I've got to say it's pretty damn impressive how well the warm sector holds up, still a large area with over 1000 CAPE at 06z.

 

 

Edited November 28, 2022 by Neoncyclone

[StormfanaticInd]

KIND

Long Term...(Tuesday through Sunday) Issued at 259 AM EST Mon Nov 28 2022 *

Gusty winds likely Tuesday and Wednesday * Strong to possibly severe storms possible Tuesday night * Warming trend by late week with rain possible by the weekend

Regarding severe potential on Tuesday... A highly progressive and modestly amplified jet pattern will set the stage for the primary weather concern through the long range. A longwave trough, currently located over the Pacific Northwest, will gradually amplify and move eastward. As a result, lee cyclogenesis will kick off in eastern Colorado on Monday. The subsequent surface low will race northeastward merging with a pre-existing surface low over central Canada. As it heads northward, it is expected to deepen significantly. The intensifying surface cyclone will tighten surrounding MSLP gradients, promoting the development of a strong LLJ in the system`s warm sector. With 850mb flow around 60 to 65 kts, warm moist air will rapidly advect northward on Tuesday. Surface winds may become quite strong late Tuesday as well, with gusts near 40 kts possible as the gradient and LLJ strengthens. Divergence aloft, combined with pre-frontal low level convergence, along with stronger forcing from the system`s cold front itself, should lead to sufficient lift for the generation of numerous showers. Guidance is generally in consensus on a 06Z-09Z arrival time for the front. However, in such progressive large scale flow regimes, synoptic systems similar to this tend to end up faster/earlier than progged. When assessing potential buoyancy production in late-season severe events, it is important to note that diurnal heating is not as critical for convective instability. In dynamically driven events such as this, instability is primarily driven by advective processes. Therefore, the limiting factor will be how far north can warm moist air advect northward into our CWA. As of right now, it appears that a fairly narrow corridor of modest instability may make it into our southwestern counties. The nocturnal timing of this event will not be a mitigating factor in determining severe potential. In terms of parameter space, deep layer shear is expected to be high, in the order of 55 to 65 kts, with long looping hodographs. Warm moist advection will rapidly saturate the column, with surface dew points rising to between 50 and 60 degrees. MLCAPE between 100- 400 J/kg shows up on the bulk of guidance during a brief window between 00Z-09Z (just ahead and along the approaching front). Given the narrow axis of forcing primarily focused along the front, a QLCS type event currently appears to be favored. A few showers or elevated thunderstorms may develop ahead of the boundary, however. Severe potential exists with a strong LLJ ahead of the front, low but sufficient instability, and strong shear. Damaging wind gusts appear to be the primary threat as of now. However, given the orientation and magnitude of the low-level shear, will need to keep an eye out for the potential development of isolated mesovorticies within the line.

Edited November 28, 2022 by StormfanaticInd

[Iceresistance]

You can use the DOT Cameras to find and confirm tornadoes for this setup that may happen, I have the links here 

Arkansas: https://idrivearkansas.com/

Louisiana: https://www.511la.org/

Mississippi: https://www.mdottraffic.com/default.aspx?showMain=true

Edited November 28, 2022 by Iceresistance

[Grace]

I'm not a severe weather expert but I see some big bust potential with this. Also threat certainly appears to be shifting further south & east. 

[Iceresistance]

3 minutes ago, Grace said:

I'm not a severe weather expert but I see some big bust potential with this. Also threat certainly appears to be shifting further south & east. 

It's a Glass Cannon setup! High potential, but could bust badly.

[ClicheVortex2014]

CAMs are looking very not good. Pretty strong signal for discrete supercells. I don’t think I’ve seen a case like this. There’s just discrete, long-lived warm sector supercells with no frontal squall. 
 

I mean, 4/27 was like that but I’m against comparing 99.99999% of events to that day. Very unlikely that this is the 0.00001% event. We saw what happened with 5/20/19 the day of the event.

But tomorrow could be a very nasty, very long day if the models keep this up

Edited November 28, 2022 by ClicheVortex2014

[Cincysnow]

Good move

 

[Iceresistance]

12 minutes ago, Cincysnow said:

Good move

 

I would keep it up unless there is an absolute emergency on the radar tower.

 

Tomorrow looks nasty, the Moderate Risk is in an area that is less affected by the drought.

Edited November 28, 2022 by Iceresistance

[Cincysnow]

45 minutes ago, Iceresistance said:

I would keep it up unless there is an absolute emergency on the radar tower.

 

Tomorrow looks nasty, the Moderate Risk is in an area that is less affected by the drought.

Pretty sure that’s what the tweet stated…

[Cincysnow]

Moderate maintained on new day 2, well i thought it was updated, let’s try this again: 

Spoiler

Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CST Mon Nov 28 2022 Valid 291200Z - 301200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR CENTRAL/NORTHERN MISSISSIPPI...NORTHEAST LOUISIANA...SOUTHEAST ARKANSAS...EXTREME SOUTHWEST TENNESSEE... ...SUMMARY... Severe thunderstorms capable of producing tornadoes and wind damage, along with some hail, are expected Tuesday afternoon and evening, extending into the overnight period across parts of the lower to mid Mississippi Valley and parts of the Southeast. A few strong/long-track tornadoes will be possible. ...Synopsis... A deep and progressive mid/upper-level trough is forecast to move from the central/southern Rockies eastward Tuesday morning to parts of the Mississippi Valley region by early Wednesday. A surface cyclone initially over central KS will move quickly northeastward toward the Upper Great Lakes by Tuesday evening, as an attendant cold front sweeps through the Great Plains and eventually into the Midwest. ...Lower/mid MS Valley into the Southeast... The potential for several long-track supercells remains evident across parts of the lower/mid MS Valley late Tuesday afternoon into Tuesday night, with a threat of strong tornadoes, scattered wind damage, and hail. Seasonably rich low-level moisture will quickly stream northward across the lower/mid MS Valley region ahead of the cold front on Tuesday, aided by a strong southwesterly low-level jet. Meanwhile, modestly steep midlevel lapse rates will overspread the region, in advance of the deep/progressive mid/upper-level trough. This will result in the development of moderate buoyancy (MLCAPE in excess of 1500 J/kg) across the warm sector. This destabilization will be occurring within a strongly sheared environment supportive of organized storms, including supercells. Initially elevated convection is expected to gradually increase in coverage through the morning across the ArkLaTex region within a low-level warm advection regime, with additional development possible farther south across southern LA/MS where somewhat stronger heating is expected. A few surface-based supercells are expected to evolve by afternoon, which could potentially be longer-lived as they move northeastward through a moistening and strongly sheared environment. Favorable 0-1 km shear/SRH will support a tornado threat, though some uncertainty remains regarding the impact of potentially weak low-level lapse rates on the tornado potential. Any sustained supercells within the warm sector could pose a strong tornado threat, in addition to a risk of hail and damaging gusts. Storm coverage will continue to increase through the evening and overnight hours, with favorable low-level moisture and strong low-level and deep-layer shear continuing to support a threat of all severe hazards. Some tornado potential is likely to continue overnight across parts of MS into western/central AL. ...Parts of the OH Valley/Midwest... Weaker low-level moisture return is expected farther north into parts of the Midwest and Ohio Valley in advance of the cold front. Despite weak buoyancy, favorable large-scale ascent and strong deep-layer flow could support a threat of locally damaging gusts with any sustained low-topped convection. There is some potential for a damaging wind threat to spread farther north than currently indicated, and some northward expansion of wind probabilities is possible depending on shorter-term observational and guidance trends.

 

Edited November 28, 2022 by Cincysnow

[ClicheVortex2014]

Interesting bit about low level lapse rates introduces some uncertainty for tornado potential. I’d imagine that’ll be more valid for northern Mississippi than the southern part of the moderate risk. We’ll see 

[Neoncyclone]

3 hours ago, ClicheVortex2014 said:

CAMs are looking very not good. Pretty strong signal for discrete supercells. I don’t think I’ve seen a case like this. There’s just discrete, long-lived warm sector supercells with no frontal squall. 
 

I mean, 4/27 was like that but I’m against comparing 99.99999% of events to that day. Very unlikely that this is the 0.00001% event. We saw what happened with 5/20/19 the day of the event.

But tomorrow could be a very nasty, very long day if the models keep this up

This discussion is pretty important for the forecast on Tues. If we don't have the lapse-rates to sustain widening updrafts then it will be a lot more difficult to sustain right-moving supercells with the ability to access the 400-600 SRH. 

The thread talks about storm mergers as a way for supercells to reach maturity and take full advantage of the environment. Pretty neat because we're usually relying on storm interaction to limit tornado threat. 

 

Edited November 28, 2022 by Neoncyclone

[Neoncyclone]

18z HRRR

 

[ClicheVortex2014]

Fwiw

 

[Neoncyclone]

Good to see so much discussion about the event, a lot of really informative discussion going around on twitter. Definitely a tough forecast, but at the end of the day the ingredients are there so expect the worst hope for the best.

Edited November 28, 2022 by Neoncyclone