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

[Cincysnow]

Hopefully, in years to come, we can invest more tax $$ for radars, to fill in some of these holes

 

[ClicheVortex2014]

 

[Ingyball]

8 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

The upper jet orientation does support this. My only concern are lapse rate and warm temperatures around 700mb. Of course I just woke up and haven't looked at any soundings today. That's purely based on what I saw yesterday. 

[ClicheVortex2014]

One thing that’s throwing a red flag for me is the strong convection along the Gulf coast. If HRRR is right with the placement, it might not be a big deal. But if it slows down and gets in between the supercells and the Gulf, it’ll disrupt the flow of moisture return and the event will wildly underperform

Edited November 28, 2022 by ClicheVortex2014

[Ingyball]

2 minutes ago, ClicheVortex2014 said:

One thing that’s throwing a red flag for me is the strong convection along the Gulf coast. If HRRR is right with the placement, it might not be a big deal. But if it slows down and gets in between the supercells and the Gulf, it’ll disrupt the flow of moisture return and the event will wildly underperform

Yeah with it being late November that has a much greater impact than mid April where the Gulf is warming up and can effortlessly spread moisture northward. 

[ClicheVortex2014]

12 minutes ago, Ingyball said:

The upper jet orientation does support this. My only concern are lapse rate and warm temperatures around 700mb. Of course I just woke up and haven't looked at any soundings today. That's purely based on what I saw yesterday. 

Ah, mids. That’s gonna be me next week.

I agree, I see where low-level lapse rates look really weak but, from what I’ve seen, that’s mostly in the northern half of MS. Southern MS maintains respectable LLLR for a while after dark. Storm coverage seems more questionable down there… but there should be a solid corridor where LLLR are sufficient with storms. How big that corridor will be is the question. Especially if we’re considering a high risk
 

Of course, things will very likely look different tomorrow morning. There’s not much room for this to look nastier and a lot of room for it to look better. Unfortunately, I can still see it going either way… especially if HRRR is underdoing dew points

Edited November 29, 2022 by ClicheVortex2014

[Ingyball]

1 minute ago, ClicheVortex2014 said:

Ah, mids. That’s gonna be me next week.

I agree, I see where low-level lapse rates look really weak but, from what I’ve seen, that’s mostly in northern MS. Southern MS maintains respectable LLLR for a while after dark. 
 

Of course, things will very likely look different tomorrow morning. There’s not much room for this to look nastier and a lot of room for it to look better. Unfortunately, I can still see it going either way… especially if HRRR is underdoing dew points

HRRR underdoing dews isn't surprising, though that may be more of a Plains problem with the dryline (you'll experience it first hand in Amarillo). Typically I like to take something in between the NAM and HRRR unless one just looks way out of whack. 

[ClicheVortex2014]

12 minutes ago, Ingyball said:

HRRR underdoing dews isn't surprising, though that may be more of a Plains problem with the dryline (you'll experience it first hand in Amarillo). Typically I like to take something in between the NAM and HRRR unless one just looks way out of whack. 

I don't remember if it's as much of a problem anymore but I remember HRRR is really keen on overmixing in the warm season even in Ohio. Don't really know/remember if it is in the cool season. But if higher dew points do verify, yikes. That would probably erase the low-level instability concerns. Obviously would lower LCL even more which isn't necessary.

Finally have wifi at my apartment. So I can share this piece from Memphis this afternoon

Low LCLs (cloud bases) and
storm movement in excess of 60 mph will make for particularly
dangerous convective environment, where tornadic storms appear to
arrive suddenly, preceded by little if any visual or audible
notice. Definitely a time to keep a weather radio with battery
backup and a fully-charged cell phone nearby.

 

While I'm at it... Jackson's AFD

Tuesday-Tuesday night: At the start, significant upper level jet &
strong cold frontal system will be taking shape over the central
Plains. Sfc cyclone of 995mb will be deepening over the central
Plains, quickly ejecting E-NE through the mid-MS Valley by midday
Tues & gaining latitude into the N Great Lakes by Tues evening to
Tues night. Sfc frontal system will be diving SE towards the area by
Tues aftn in the ArkLaTex through the Ozarks & Mid-MS Valley by Tues
evening & sweeping through the area by Wed morning. Strong synoptic
jet of 75-85kts @ 500mb & +125kts @ 300mb downstream jet streak
intensifying into the central Plains Tues in advance of mean trough
ejecting out of the Pacific NW with favorable jet
placement/diffluence in the area. Subtropical ridge will deepen over
the W Carribean, keeping the bulk of the trough/forcing & height
falls well off to the NW. However, significant WAA & moisture
advection will bring boundary layer moisture with dewpoints climbing
into the upper 60s-low 70s across the region. With anomalous warmth
& dewpoints, combination of moderate to significant destabilization
& anomalous mean bulk shear aloft will favor significant severe
weather event. This will lead to combination of significant
kinematics & thermo profiles, some values not seen per SPC sounding
climatology (i.e. MLCAPE around 1000-1500 J/kg) & long clockwise
curved hodographs with +300-400 m2/s2 effective SRH & mean layer
bulk shear around 30-45kts in the 0-1km/0-3km & 50-60kts in the 0-
6km layer. This will continue to support all modes of significant
severe weather, including tornadoes, some strong & long track
tornadoes, damaging winds up to 80mph & large hail of golf ball size
or potentially larger. Highest threat looks to be along & NW of the
Natchez Trace corridor. Storm mode looks to be a combination of mid-
morning warm advection showers growing upscale & developing into
supercell mode into the afternoon hours. There are some challenges
on initial development timing & any southern storms developing
across the region, which could limit some inflow of most efficient
moisture. However, this area in SE MS could have better mid-level
capping & 700mb heights which could suppress some convection into
the Pine Belt. After collaboration with SPC earlier today, the
"Moderate" & "Enhanced" risk areas were expanded to the E & SE into
the Hwy 82/Hwy 45 corridors & along I-20 corridors, while the Slight
was also expanded to include the most S & E extreme portions of the
region. Timing for the most significant severe weather looks to be
in the 6PM to midnight timeframe, with some lingering after midnight
through 4AM. The earlier development is tricky & some severe &
tornado potential are possible as early as mid-morning to early aftn
hours. Kept timing as is for now but confidence beginning of the
warm sector supercells is lower while increased confidence of
decreasing severe potential in the Delta around 8PM-11PM in the NW
Delta, the I-55 corridor around midnight or 1AM & most potential
moved out by just before daybreak in E-SE MS.

In addition, some potential for some localized to areas of flash
flooding will be possible. Added an "Elevated" for S into SE MS &
the Pine Belt where some increased QPF totals & some training could
occur over some areas that have received decent rain totals
recently. Left the rest of the area the same with a "Limited" for
localized flash flooding. Strong gradient winds are possible, with
some gusts up to or exceeding 30mph. For now, no mention was added
in the HWO but may be needed as we get closer. Strong WAA will help
highs warm near-above normal into low-mid 70s Tues, while above
normal into low to upper 40s in the Delta to low-mid 60s in SE MS
for the frontal passage Tues night. Expect the front to quickly move
through Wed, ushering in dry air, sfc ridging & helping clearing
rain & storms/clouds out of the area into Wed aftn with highs cooler
in the Delta into mid-upper 50s while closer to 70 degrees in the
Pine Belt. /DC/

 

Edited November 29, 2022 by ClicheVortex2014

[ClicheVortex2014]

These hodographs are crazy. Nearly textbook for long-lived supercells. Only critique I could even think of is the weak speed shear from 1km to ~4km. That's nitpicky though.

 

[Neoncyclone]

The 00z HRRR is still loading but i'm really impatient, thought i'd share that on this run there's a mature supercell by 19z.

[Iceresistance]

4 minutes ago, Neoncyclone said:

The 00z HRRR is still loading but i'm really impatient, thought i'd share that on this run there's a mature supercell by 19z.

Nasty HPS near Alexandria, LA on the HRRR

EDIT: The 0z HRRR also has semi-discrete Supercells in NE Mississippi and NW Alabama!

Edited November 29, 2022 by Iceresistance
Updated

[Iceresistance]

1 hour ago, ClicheVortex2014 said:

I don't remember if it's as much of a problem anymore but I remember HRRR is really keen on overmixing in the warm season even in Ohio. Don't really know/remember if it is in the cool season. But if higher dew points do verify, yikes. That would probably erase the low-level instability concerns. Obviously would lower LCL even more which isn't necessary.

Finally have wifi at my apartment. So I can share this piece from Memphis this afternoon

Low LCLs (cloud bases) and
storm movement in excess of 60 mph will make for particularly
dangerous convective environment, where tornadic storms appear to
arrive suddenly, preceded by little if any visual or audible
notice. Definitely a time to keep a weather radio with battery
backup and a fully-charged cell phone nearby.

 

While I'm at it... Jackson's AFD

Tuesday-Tuesday night: At the start, significant upper level jet &
strong cold frontal system will be taking shape over the central
Plains. Sfc cyclone of 995mb will be deepening over the central
Plains, quickly ejecting E-NE through the mid-MS Valley by midday
Tues & gaining latitude into the N Great Lakes by Tues evening to
Tues night. Sfc frontal system will be diving SE towards the area by
Tues aftn in the ArkLaTex through the Ozarks & Mid-MS Valley by Tues
evening & sweeping through the area by Wed morning. Strong synoptic
jet of 75-85kts @ 500mb & +125kts @ 300mb downstream jet streak
intensifying into the central Plains Tues in advance of mean trough
ejecting out of the Pacific NW with favorable jet
placement/diffluence in the area. Subtropical ridge will deepen over
the W Carribean, keeping the bulk of the trough/forcing & height
falls well off to the NW. However, significant WAA & moisture
advection will bring boundary layer moisture with dewpoints climbing
into the upper 60s-low 70s across the region. With anomalous warmth
& dewpoints, combination of moderate to significant destabilization
& anomalous mean bulk shear aloft will favor significant severe
weather event. This will lead to combination of significant
kinematics & thermo profiles, some values not seen per SPC sounding
climatology (i.e. MLCAPE around 1000-1500 J/kg) & long clockwise
curved hodographs with +300-400 m2/s2 effective SRH & mean layer
bulk shear around 30-45kts in the 0-1km/0-3km & 50-60kts in the 0-
6km layer. This will continue to support all modes of significant
severe weather, including tornadoes, some strong & long track
tornadoes, damaging winds up to 80mph & large hail of golf ball size
or potentially larger. Highest threat looks to be along & NW of the
Natchez Trace corridor. Storm mode looks to be a combination of mid-
morning warm advection showers growing upscale & developing into
supercell mode into the afternoon hours. There are some challenges
on initial development timing & any southern storms developing
across the region, which could limit some inflow of most efficient
moisture. However, this area in SE MS could have better mid-level
capping & 700mb heights which could suppress some convection into
the Pine Belt. After collaboration with SPC earlier today, the
"Moderate" & "Enhanced" risk areas were expanded to the E & SE into
the Hwy 82/Hwy 45 corridors & along I-20 corridors, while the Slight
was also expanded to include the most S & E extreme portions of the
region. Timing for the most significant severe weather looks to be
in the 6PM to midnight timeframe, with some lingering after midnight
through 4AM. The earlier development is tricky & some severe &
tornado potential are possible as early as mid-morning to early aftn
hours. Kept timing as is for now but confidence beginning of the
warm sector supercells is lower while increased confidence of
decreasing severe potential in the Delta around 8PM-11PM in the NW
Delta, the I-55 corridor around midnight or 1AM & most potential
moved out by just before daybreak in E-SE MS.

In addition, some potential for some localized to areas of flash
flooding will be possible. Added an "Elevated" for S into SE MS &
the Pine Belt where some increased QPF totals & some training could
occur over some areas that have received decent rain totals
recently. Left the rest of the area the same with a "Limited" for
localized flash flooding. Strong gradient winds are possible, with
some gusts up to or exceeding 30mph. For now, no mention was added
in the HWO but may be needed as we get closer. Strong WAA will help
highs warm near-above normal into low-mid 70s Tues, while above
normal into low to upper 40s in the Delta to low-mid 60s in SE MS
for the frontal passage Tues night. Expect the front to quickly move
through Wed, ushering in dry air, sfc ridging & helping clearing
rain & storms/clouds out of the area into Wed aftn with highs cooler
in the Delta into mid-upper 50s while closer to 70 degrees in the
Pine Belt. /DC/

 

The wifi part was also me when I got the fiber optics, I forgot how slow the previous one was!

[Neoncyclone]

0z HRRR EDIT: Sidenote i'm watching the FV3 come in and I gotta say, how can we take a model seriously when everything it convects goes supercellular lol

Edited November 29, 2022 by Neoncyclone

[Ingyball]

47 minutes ago, Neoncyclone said:

0z HRRR EDIT: Sidenote i'm watching the FV3 come in and I gotta say, how can we take a model seriously when everything it convects goes supercellular lol

It's a known issue they're hoping to fix

[Neoncyclone]

I was hoping the 0z CAMS would start coming together somewhat but still seeing a lot of uncertainty.

[ClicheVortex2014]

At least NSSL and ARW agree on a robust supercell in central Mississippi

[Chinook]

2 hours ago, Neoncyclone said:

0z HRRR EDIT: Sidenote i'm watching the FV3 come in and I gotta say, how can we take a model seriously when everything it convects goes supercellular lol

The FV3 probably has too many high-precipitation cells south of Jackson MS. Otherwise I think there's a somewhat large range of possibilities. As mentioned before, the CAMs don't have super good agreement.

[Neoncyclone]

Just to add to the ridiculous amount of confusion trying to piece together a forecast for this event lol. Nadocast going crazy with values you only see on very high end days. I'm really not convinced, there's a lot of ways tomorrow could underperform the way I see it right now, I hope it does at least. obviously it also has a pretty high ceiling so who knows, models have been having some pretty crazy cold bias I guess.

 

Edited November 29, 2022 by Neoncyclone

[ClicheVortex2014]

oof

 

[Neoncyclone]

Day 1

Quote

SPC AC 290509 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1109 PM CST Mon Nov 28 2022 Valid 291200Z - 301200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS FAR EAST-CENTRAL LOUISIANA INTO CENTRAL MISSISSIPPI...

...SUMMARY... Severe thunderstorms capable of producing tornadoes, very large hail, and a few severe wind gusts are expected this afternoon into the overnight period across parts of the lower to mid Mississippi Valley and parts of the Southeast. A few strong tornadoes will be possible.

...Synopsis...  A surface low will deepen while tracking from Kansas to the Great Lakes today, accompanied by an eastward advancing upper trough. A strong mid-level jet stream will overspread an intense low-level jet across the OH/TN Valleys into the Southeast. As such, strong deep-layer flow and shear will overlap with a moistening, destabilizing airmass from late morning to early evening from the lower MS Valley east-northeastward. Several strong to intense thunderstorms are expected to organize and promote a relatively robust severe threat, particularly across the Southeast, where regionally higher instability should reside. ...Portions of the Lower MS Valley today into early tonight... Strong warm-air advection should be underway across the Lower MS Valley at the start of the period (12Z), with rich boundary-layer moisture being transported northward by a 40-50 kt southwesterly low-level jet. Through the day, at least modest surface heating should support surface temperatures rising into the lower 70s F amid upper 60s F dewpoints within the warm-air advection regime, where an increase in thunderstorms is also expected. 50-70 kts of west-southwesterly 500 mb flow and 6.5+ C/km lapse rates will overspread the lower MS Valley and the warm-air advection regime by early afternoon, contributing up to 1500 J/kg MLCAPE, which is adequate in supporting a severe threat. Storms should eventually root into a gradually deepening boundary layer during the afternoon, taking advantage of the strong deep-layer and low-level speed/directional shear provided by the overlapping southwesterly low-level and westerly mid-level jets. Large, curved low-level hodographs with mid/upper-level elongation will support well over 50 kts of effective bulk shear, and 300-400 m2/s2 effective SRH. Supercell structures are expected initially, with large hail, tornadoes, and a few severe gusts all likely. A few instances of 2+ inch diameter hail and/or strong tornadoes are possible with the more robust supercells. Should a more dominant supercell develop, remain discrete, and traverse an axis of locally stronger surface heating/buoyancy, a long-tracked and intense tornado may occur. The latest high-resolution guidance consensus suggests this scenario would be most likely across central MS, where a Category 4/Moderate risk is in place. Later at night, storms should grow upscale into more linear segments as the surface cold front and greater low-level convergence approaches. Damaging gusts should then become the main threat, though a few tornadoes remain possible. ...Parts of the OH/TN Valley into early evening... A strong surface cold front should sweep across the OH/TN Valleys through the late afternoon and evening hours as the deepening surface low tracks across the Great Lakes. Strong convergence along the cold front should force a low-topped band of convection. Ambient tropospheric wind fields will be strong, with 55+ kts of flow likely just 1 km AGL. Downward momentum transport within this line may foster strong, occasionally damaging gusts, with a couple of severe gusts also possible, warranting the introduction of Category 1/Marginal probabilities this outlook. ..Squitieri/Darrow.. 11/29/2022

 

Edited November 29, 2022 by Neoncyclone

[ClicheVortex2014]

That day 1 definitely makes sense to me. CAMs absolutely nail that corridor. Pretty broad region outside of there where strong tornadoes could happen with any sustained supercell.

Unfortunately, there are 1.3 million people in that corridor.

As far as a high risk is concerned (since that inevitably comes to mind in any day 2 moderate), it comes down to 4 points to me. 1) environment? 2) long-duration event? 3) storm mode favorable? 4) confidence (in 1-3 and location)?

Parameters, long-duration event, favorable storm mode are all checked off. Certainly some questions about low-level instability right now. As it stands now, I don't see a high risk. But if moisture is stronger than expected, the chances bump up. 

Edited November 29, 2022 by ClicheVortex2014

[Neoncyclone]

FWIW on the 04z, 05z HRRR the LLLR's are looking better and more capable of sustaining updrafts in the low levels. These soundings are valid for 19z tomorrow in central LA. important to note on the 05z it looks like dewpoints are coming in a bit slower and surface temperature is a bit higher, if we get more surface heating like this naturally you'll get higher LLLR's.

 

 

Edited November 29, 2022 by Neoncyclone

[ClicheVortex2014]

The duration and discrete nature, as well as the upper 60/lower 70 dew points, feels like a Spring event.... not a late November one. 

 

[Neoncyclone]

3 minutes ago, ClicheVortex2014 said:

The duration and discrete nature, as well as the upper 60/lower 70 dew points, feels like a Spring event.... not a late November one. 

 

The 06z HRRR is truly nasty.... Numerous supercells in the warm sector from 19z-06z and then it looks like the tornado threat could shift south to southern LA, MS, AL around 05-09z, moisture is still being transported into S LA, MS, AL into the morning hours, crazy... 

Edited November 29, 2022 by Neoncyclone

[Neoncyclone]

08z HRRR