Severe WX Severe Weather Threat - February 15-16, 2023

[xJownage]

Funny that a meteorologist friend of mine said the following yesterday about the formula for all these winter setups:

1. Models trend up on dews
2. As it closes in on 3-4 days models this themselves, everyone is like "its over, no severe, wrap it up"
3. models get back into business within CAMs range
4. surge in moisture unmodeled prior within 24 hours.
5. outbreak

This also goes with what we know about global models in particular being way too cold/dry on a lot of these setups. I don't see a "not much happens" scenario playing out here. Model disagreement is higher than its ever been with this system though, and the question is why. That being said, the overall synoptic pattern still points to a big event, even if the moisture/warm air return doesn't show to be robust; usually those details work themselves out anyways in these big winter events.

 

[MichelleH]

Funny that a meteorologist friend of mine said the following yesterday about the formula for all these winter setups:

1. Models trend up on dews
2. As it closes in on 3-4 days models this themselves, everyone is like "its over, no severe, wrap it up"
3. models get back into business within CAMs range
4. surge in moisture unmodeled prior within 24 hours.
5. outbreak

This also goes with what we know about global models in particular being way too cold/dry on a lot of these setups. I don't see a "not much happens" scenario playing out here. Model disagreement is higher than its ever been with this system though, and the question is why. That being said, the overall synoptic pattern still points to a big event, even if the moisture/warm air return doesn't show to be robust; usually those details work themselves out anyways in these big winter events.

^^ This

 

[UK_EF4]

Funny that a meteorologist friend of mine said the following yesterday about the formula for all these winter setups:

1. Models trend up on dews
2. As it closes in on 3-4 days models this themselves, everyone is like "its over, no severe, wrap it up"
3. models get back into business within CAMs range
4. surge in moisture unmodeled prior within 24 hours.
5. outbreak

This also goes with what we know about global models in particular being way too cold/dry on a lot of these setups. I don't see a "not much happens" scenario playing out here. Model disagreement is higher than its ever been with this system though, and the question is why. That being said, the overall synoptic pattern still points to a big event, even if the moisture/warm air return doesn't show to be robust; usually those details work themselves out anyways in these big winter events.

Yes, 100%. And this particularly relevant here where if we get increasing thermodynamics overlapping with where the best kinematics currently then the paramater space has the potential to become more volatile.

 

[UK_EF4]

This is what I mean: UKMET sounding taken somewhere near the Mississippi river at 06z on Thursday. The shear profile is very favourable, yet the low levels are a bit stable and instability isn't the best. Yet, if we see an increase in the thermodynamics this could easily become a crazy sounding.

 

[UncleJuJu98]

Funny that a meteorologist friend of mine said the following yesterday about the formula for all these winter setups:

1. Models trend up on dews
2. As it closes in on 3-4 days models this themselves, everyone is like "its over, no severe, wrap it up"
3. models get back into business within CAMs range
4. surge in moisture unmodeled prior within 24 hours.
5. outbreak

This also goes with what we know about global models in particular being way too cold/dry on a lot of these setups. I don't see a "not much happens" scenario playing out here. Model disagreement is higher than its ever been with this system though, and the question is why. That being said, the overall synoptic pattern still points to a big event, even if the moisture/warm air return doesn't show to be robust; usually those details work themselves out anyways in these big winter events.

Lol same sympathies from me; my post yesterday

Maybe its in my head but it seems like lately when threats get in the day 5/6 range it's a bit wonky. and then starts to go back to what it was in the beginning at the 3/4 day range.

 

[warneagle]

Funny that a meteorologist friend of mine said the following yesterday about the formula for all these winter setups:

1. Models trend up on dews
2. As it closes in on 3-4 days models this themselves, everyone is like "its over, no severe, wrap it up"
3. models get back into business within CAMs range
4. surge in moisture unmodeled prior within 24 hours.
5. outbreak

This also goes with what we know about global models in particular being way too cold/dry on a lot of these setups. I don't see a "not much happens" scenario playing out here. Model disagreement is higher than its ever been with this system though, and the question is why. That being said, the overall synoptic pattern still points to a big event, even if the moisture/warm air return doesn't show to be robust; usually those details work themselves out anyways in these big winter events.

Yeah this definitely sounds like a familiar pattern. Is it just a product of the biases in the models during the cold season?

 

[xJownage]

Yeah this definitely sounds like a familiar pattern. Is it just a product of the biases in the models during the cold season?

Honestly, I think that's exactly what it is. Cool/Dry bias in models during winter is well documented.

 

[UncleJuJu98]

 

[Timhsv]

I thought this was an insightful AFD from KBMX this morning and to some of the finer details and analysis as to the upcoming threat on Thursday.
Of coarse I've edited parts of it for emphasis.

AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
328 AM CST Sun Feb 12 2023

LONG TERM...
(Monday through Saturday)
Issued at 327 AM CST SUN FEB 12 2023

A southern stream shortwave trough will eject out over the Southern
High Plains Monday night, and then lift northeastward with a
negative tilt from the Southern Plains to the Mid Mississippi Valley
on Tuesday. Meanwhile a double barrel deep surface low will move
eastward from the Central Plains to the Mid Missouri Valley.
Strong southerly flow ahead of this system will result in another
spring-like day with temperatures out-performing guidance. With
925mb winds at or above 40 kts, mixing may allow wind gusts to
once again be near wind advisory criteria in our northwest
counties and will add this potential to the HWO. The forcing/height
falls will be out-running the low-level moisture return by late
Tuesday afternoon, and the front will stall near the Mississippi
River. Therefore only light to moderate showers are expected
Tuesday night as a pre-frontal axis of 1.3 to 1.4 inch PWATs moves
into the forecast area. Continued southerly winds will result in
mild overnight lows Tuesday night especially west of I-65. Height
rises are expected by Wednesday as the next shortwave/upper low
consolidates near and east of the Four Corners and a subtropical
ridge strengthens between Cuba and the Bahamas. The remnant
moisture axis from the Tuesday system will remain over the area,
with PWATs increasing to 1.5 inches. This axis will act as an
effective warm front and move northward Wednesday afternoon and
Wednesday night ahead of the next system, serving as a continued
focus for shower and thunderstorm activity. Steep mid-level lapse
rates will be present associated with an elevated mixed layer
(EML), and combined with strengthening bulk shear this could allow
for some strong storms with hail Wednesday afternoon/Wednesday
night. However, the lack of forcing and only modest MUCAPE values
suggest the probability of an isolated severe storm is too low to
mention in the HWO at this time.

The Four Corners upper low will lift northeastward to the Mid-
Missouri Valley Wednesday night and shear out as the associated
trough starts to phase with a northern stream trough. The net result
will be a fairly amplified positively tilted trough with an
elongated strong shear vorticity axis on its eastern side moving
into the Mid-South region. The southern end of height falls will
move into Alabama during the afternoon and evening hours, along with
of broad area of upper-level divergence. At the surface, low
pressure will deepen as it moves northeastward from Missouri to
Michigan Wednesday night and Thursday, while the associated cold
front moves into West Alabama Thursday afternoon. Mid 60s dew
points and decent mid-level lapse rates associated with the
remnant EML will contribute to CAPE values of at least 500 to 1000
J/kg, potentially higher as temperatures will probably be a bit
warmer than raw model output, and if dew points trend any higher.
0-6km bulk shear vectors around 65 kts with a large component
normal to the front will favor supercells with 0-1km SRH generally
around 250-350 m2/s2. These parameters certainly check a lot of
boxes when it comes to assessing tornado potential in Alabama. Of
some concern would be the broad warm sector and positively tilted
trough orientation allowing for supercells to remain sustained
for a while ahead of the front. Of course with this event still
being a few days out it`s too early to assess all the mesoscale
details that will determine the magnitude of the event. With any
severe event it`s always a good idea to look for potential failure
modes, not to downplay the threat but in order to assess all the
factors. Two potential failure modes would be if any activity
developing upstream or with the warm front feature Wednesday night
causes contamination of the instability in the warm sector, or if
the trough orientation changes in a way that the forcing/height
falls become too weak. The former does not appear likely at this
time but will continue to monitor, with guidance moving activity
north of the area Wednesday night/Thursday morning probably aided
by the EML. The latter would be dependent on if any changes occur
with phasing of the northern and southern stream which models can
sometimes struggle with. There can be a fine line with just enough
weak forcing/height falls to keep storms more cellular/discrete
vs. too much forcing or not enough forcing. Regardless, everyone
in Central Alabama needs to remain weather aware and have their
severe weather plan ready on Thursday. Another brief period of
cooler and drier air moves in for Friday into next weekend.

32/Davis

 

[JPWX]

I thought this was an insightful AFD from KBMX this morning and to some of the finer details and analysis as to the upcoming threat on Thursday.
Of coarse I've edited parts of it for emphasis.

AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
328 AM CST Sun Feb 12 2023

LONG TERM...
(Monday through Saturday)
Issued at 327 AM CST SUN FEB 12 2023

A southern stream shortwave trough will eject out over the Southern
High Plains Monday night, and then lift northeastward with a
negative tilt from the Southern Plains to the Mid Mississippi Valley
on Tuesday. Meanwhile a double barrel deep surface low will move
eastward from the Central Plains to the Mid Missouri Valley.
Strong southerly flow ahead of this system will result in another
spring-like day with temperatures out-performing guidance. With
925mb winds at or above 40 kts, mixing may allow wind gusts to
once again be near wind advisory criteria in our northwest
counties and will add this potential to the HWO. The forcing/height
falls will be out-running the low-level moisture return by late
Tuesday afternoon, and the front will stall near the Mississippi
River. Therefore only light to moderate showers are expected
Tuesday night as a pre-frontal axis of 1.3 to 1.4 inch PWATs moves
into the forecast area. Continued southerly winds will result in
mild overnight lows Tuesday night especially west of I-65. Height
rises are expected by Wednesday as the next shortwave/upper low
consolidates near and east of the Four Corners and a subtropical
ridge strengthens between Cuba and the Bahamas. The remnant
moisture axis from the Tuesday system will remain over the area,
with PWATs increasing to 1.5 inches. This axis will act as an
effective warm front and move northward Wednesday afternoon and
Wednesday night ahead of the next system, serving as a continued
focus for shower and thunderstorm activity. Steep mid-level lapse
rates will be present associated with an elevated mixed layer
(EML), and combined with strengthening bulk shear this could allow
for some strong storms with hail Wednesday afternoon/Wednesday
night. However, the lack of forcing and only modest MUCAPE values
suggest the probability of an isolated severe storm is too low to
mention in the HWO at this time.

The Four Corners upper low will lift northeastward to the Mid-
Missouri Valley Wednesday night and shear out as the associated
trough starts to phase with a northern stream trough. The net result
will be a fairly amplified positively tilted trough with an
elongated strong shear vorticity axis on its eastern side moving
into the Mid-South region. The southern end of height falls will
move into Alabama during the afternoon and evening hours, along with
of broad area of upper-level divergence. At the surface, low
pressure will deepen as it moves northeastward from Missouri to
Michigan Wednesday night and Thursday, while the associated cold
front moves into West Alabama Thursday afternoon. Mid 60s dew
points and decent mid-level lapse rates associated with the
remnant EML will contribute to CAPE values of at least 500 to 1000
J/kg, potentially higher as temperatures will probably be a bit
warmer than raw model output, and if dew points trend any higher.
0-6km bulk shear vectors around 65 kts with a large component
normal to the front will favor supercells with 0-1km SRH generally
around 250-350 m2/s2. These parameters certainly check a lot of
boxes when it comes to assessing tornado potential in Alabama. Of
some concern would be the broad warm sector and positively tilted
trough orientation allowing for supercells to remain sustained
for a while ahead of the front. Of course with this event still
being a few days out it`s too early to assess all the mesoscale
details that will determine the magnitude of the event. With any
severe event it`s always a good idea to look for potential failure
modes, not to downplay the threat but in order to assess all the
factors. Two potential failure modes would be if any activity
developing upstream or with the warm front feature Wednesday night
causes contamination of the instability in the warm sector, or if
the trough orientation changes in a way that the forcing/height
falls become too weak. The former does not appear likely at this
time but will continue to monitor, with guidance moving activity
north of the area Wednesday night/Thursday morning probably aided
by the EML. The latter would be dependent on if any changes occur
with phasing of the northern and southern stream which models can
sometimes struggle with. There can be a fine line with just enough
weak forcing/height falls to keep storms more cellular/discrete
vs. too much forcing or not enough forcing. Regardless, everyone
in Central Alabama needs to remain weather aware and have their
severe weather plan ready on Thursday. Another brief period of
cooler and drier air moves in for Friday into next weekend.

32/Davis

It wasn't until @Fred Gossage posted on here about the positive tilted troughs being significant severe weather producers as well. Before that, I had always assumed that you just looked for the negative titled ones for severe weather.

 

[UncleJuJu98]

This is the kinda stuff that make me aggravated. Putting out a higher end severe risk area that doesn't collaborate with the actual SPC

 

[KevinH]

It wasn't until @Fred Gossage posted on here about the positive tilted troughs being significant severe weather producers as well. Before that, I had always assumed that you just looked for the negative titled ones for severe weather.

Same

 

[UncleJuJu98]

Globals still riding with the idea of a MCS tracking through Mississippi/ Alabama through the late night wensday and early Thursday and clearing out for bad weather later that afternoon.

 

[UncleJuJu98]

If anything I think a substantial severe threat will shape up in the deep south; Mississippi/Alabama. Past analogs support this almost to a tee and just looking at the data; if your worried about mositure transportation those areas don't have as far as the rest of the risk area. A cold pool aloft from a morning MCS will only further instability in those areas and potentially lay down boundaries to support heightened severe risks later that day.

 

[Clancy]

For the past few days FFC wasn't making much mention of this next week's system, but there is some on the disco today.

At the same time on Wednesday, another shortwave rounding the
moderately deep trough across the Western CONUS will help to further
amplify this pattern, continuing moisture and warm air advection.
This second system then makes its way northeast out of Colorado and
quickly develops a surface low feature. While this surface feature
does not bottom out quite as low as the first, it is able to make
its way further East/Southeast than the first system. This means
that supportive dynamics for storm development will be more readily
available than the first system and should be able to tap into the
warm moist air already in place across the Southeast. Some
uncertainty in the northward extent of the surface low track means
slightly reduced confidence in the exact strength and arrival time
of the associated surface cold front. As such, will continue to
advertise thunderstorms across central and north GA, however a few
storms may be strong to severe if the system is able to hold
together further eastward. Current model trends have the front
moving through in the overnight hours Thursday night, on the tail
end of peak heat. Models do agree that storms along the cold front
could be efficient rain makers as PWATs climb higher than 1.5"
across most of Central and North GA.

 

[UncleJuJu98]

I thought this was an insightful AFD from KBMX this morning and to some of the finer details and analysis as to the upcoming threat on Thursday.
Of coarse I've edited parts of it for emphasis.

AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
328 AM CST Sun Feb 12 2023

LONG TERM...
(Monday through Saturday)
Issued at 327 AM CST SUN FEB 12 2023

A southern stream shortwave trough will eject out over the Southern
High Plains Monday night, and then lift northeastward with a
negative tilt from the Southern Plains to the Mid Mississippi Valley
on Tuesday. Meanwhile a double barrel deep surface low will move
eastward from the Central Plains to the Mid Missouri Valley.
Strong southerly flow ahead of this system will result in another
spring-like day with temperatures out-performing guidance. With
925mb winds at or above 40 kts, mixing may allow wind gusts to
once again be near wind advisory criteria in our northwest
counties and will add this potential to the HWO. The forcing/height
falls will be out-running the low-level moisture return by late
Tuesday afternoon, and the front will stall near the Mississippi
River. Therefore only light to moderate showers are expected
Tuesday night as a pre-frontal axis of 1.3 to 1.4 inch PWATs moves
into the forecast area. Continued southerly winds will result in
mild overnight lows Tuesday night especially west of I-65. Height
rises are expected by Wednesday as the next shortwave/upper low
consolidates near and east of the Four Corners and a subtropical
ridge strengthens between Cuba and the Bahamas. The remnant
moisture axis from the Tuesday system will remain over the area,
with PWATs increasing to 1.5 inches. This axis will act as an
effective warm front and move northward Wednesday afternoon and
Wednesday night ahead of the next system, serving as a continued
focus for shower and thunderstorm activity. Steep mid-level lapse
rates will be present associated with an elevated mixed layer
(EML), and combined with strengthening bulk shear this could allow
for some strong storms with hail Wednesday afternoon/Wednesday
night. However, the lack of forcing and only modest MUCAPE values
suggest the probability of an isolated severe storm is too low to
mention in the HWO at this time.

The Four Corners upper low will lift northeastward to the Mid-
Missouri Valley Wednesday night and shear out as the associated
trough starts to phase with a northern stream trough. The net result
will be a fairly amplified positively tilted trough with an
elongated strong shear vorticity axis on its eastern side moving
into the Mid-South region. The southern end of height falls will
move into Alabama during the afternoon and evening hours, along with
of broad area of upper-level divergence. At the surface, low
pressure will deepen as it moves northeastward from Missouri to
Michigan Wednesday night and Thursday, while the associated cold
front moves into West Alabama Thursday afternoon. Mid 60s dew
points and decent mid-level lapse rates associated with the
remnant EML will contribute to CAPE values of at least 500 to 1000
J/kg, potentially higher as temperatures will probably be a bit
warmer than raw model output, and if dew points trend any higher.
0-6km bulk shear vectors around 65 kts with a large component
normal to the front will favor supercells with 0-1km SRH generally
around 250-350 m2/s2. These parameters certainly check a lot of
boxes when it comes to assessing tornado potential in Alabama. Of
some concern would be the broad warm sector and positively tilted
trough orientation allowing for supercells to remain sustained
for a while ahead of the front. Of course with this event still
being a few days out it`s too early to assess all the mesoscale
details that will determine the magnitude of the event. With any
severe event it`s always a good idea to look for potential failure
modes, not to downplay the threat but in order to assess all the
factors. Two potential failure modes would be if any activity
developing upstream or with the warm front feature Wednesday night
causes contamination of the instability in the warm sector, or if
the trough orientation changes in a way that the forcing/height
falls become too weak. The former does not appear likely at this
time but will continue to monitor, with guidance moving activity
north of the area Wednesday night/Thursday morning probably aided
by the EML. The latter would be dependent on if any changes occur
with phasing of the northern and southern stream which models can
sometimes struggle with. There can be a fine line with just enough
weak forcing/height falls to keep storms more cellular/discrete
vs. too much forcing or not enough forcing. Regardless, everyone
in Central Alabama needs to remain weather aware and have their
severe weather plan ready on Thursday. Another brief period of
cooler and drier air moves in for Friday into next weekend.

32/Davis

Lol didn't notice but bmx notes this event checks a lot of boxes for a Alabama tornado event. And only one major fail mode seems possible with the other seeming unlikely

 

[UncleJuJu98]

At the end of the 18z nam it's really trying to start pushing convection ahead of the cold front a good bit out (potential supercells)

I have a feeling this will be nasty event for your usual suspects Alabama and Mississippi..

I'f I had to guess the best mesh point will be here.

 

[UncleJuJu98]

Confluence? Outflow? These would be ideal target places for supercells to pop. A lot of little things leading into this event that could make it major.

 

[MichelleH]

At the end of the 18z nam it's really trying to start pushing convection ahead of the cold front a good bit out (potential supercells)

I have a feeling this will be nasty event for your usual suspects Alabama and Mississippi..

I'f I had to guess the best mesh point will be here. View attachment 17758

Peachy. I live in that circle.

 

[UncleJuJu98]

Peachy. I live in that circle.

Lol me too, no guarantee. But from my amateur knowledge and some wisdom from many weather events that's where I'd take the best activity.