Severe Weather Threat - Jan 11-12th, 2024

[KevinH]

SPC has highlighted a 15% risk area for Thursday, January 11th and Friday, January 12th.





Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CST Mon Jan 08 2024

Valid 111200Z - 161200Z

...DISCUSSION...
The latest medium-range guidance (including the ECENS/GEFS and ECMWF/GFS) appear similar with the depiction of the evolving pattern
late this week. Of particular note, one vigorous short wave impulse (emanating from the northern mid-latitude Pacific, before digging inland across the Pacific coast into the Great Basin by early Thursday) is forecast to continue digging across the southern Rockies and Southwestern international border vicinity during the day Thursday, before rapidly pivoting across the southern Great Plains/lower Mississippi Valley through the upper Ohio Valley/lower Great Lakes by 12Z Saturday. As it does, there appears increasing consensus that it will support strong surface cyclogenesis across the Mid South through lower Great Lakes vicinity late Thursday night through Friday evening.

Latest guidance indicates that this will be accompanied by sufficient low-level moisture return off the Gulf of Mexico to support a destabilizing warm sector across parts of eastern Texas into the lower Mississippi Valley late Thursday through Thursday night, aided by strengthening mid/upper forcing for ascent. Coupled with intensifying wind fields and shear, this is expected to support the initiation of severe thunderstorm development, which seems likely to organize and be maintained within the swath of mid/upper support overspreading much of the Gulf through southern Atlantic Coast states by Friday night. This may be accompanied by a swath of strong, damaging winds and the risk for tornadoes.

 

[Clancy]

Watch the wind fields closely. I'm not sure the models are handling their presentation correctly (though they are still more than plenty for a tornado threat).

 

[Clancy]

Strong signals from CIPS and CSU probs.

 

[ashtonlemleywx]

Louisville MS at 18z Friday from 06z GFS. The kinematics of both systems this week are nuts.

 

[Clancy]

BMX also skeptical of the somewhat veered wind profiles over parts of AL, per their LR-AFD.

Broad troughing remains across much of the CONUS through the end
of the week. Within this trough a fast-moving low-amplitude
shortwave trough will round the base of the larger scale trough
Thursday night, taking on a negative tilt as it lifts
northeastward from the Lower Mississippi Valley to the Ohio Valley
on Friday. A surface low will take advantage of the strong thermal
gradient between warm moist air over the Gulf and an Arctic air
mass moving down the Plains to rapidly deepen as it lifts
northeastward on Friday on an overall similar path as today`s
system. Showers and storms will increase across the area after
midnight Thursday night with warm air advection north of a lifting
warm front. There could be at least some small hail with this
activity with cold temperatures aloft. A narrow but robust warm
sector with low to mid 60s dew points and a few hundred J/kg of
CAPE across should lift northward Friday morning into at least
some of our southern counties with very strong 0-6km bulk shear
values of 80 to 90 kts. At minimum this should be favorable for at
least damaging winds, with hail also possible given decent mid-
level lapse rates with cool temperatures aloft as well as a
westerly component to the flow aloft. There also appears to be a
threat for tornadoes assuming activity is able to develop in the
warm sector and remain surface-based before crossing the warm
front. Some models indicate veered winds at the surface though
this seems suspect to me given the rapidly deepening low. Plenty
of uncertainty regarding details this far out, but there does
appear to be enough model/ensemble agreement to mention a threat
of severe storms in the HWO. Will also mention a threat of
gradient wind gusts once again reaching wind advisory criteria.
Will have to keep an eye on rainfall amounts for any flooding
especially in areas that get a lot of rain tonight. Cooler and dry
conditions are expected over the weekend as a modified version of
the Arctic air mass moves in.

 

[Scott81]

Looks like another south alabama event.

 

[KevinH]

Looks like another south alabama event.

I wouldn’t say that JUST yet. The SPC highlighted just about *ALL* of MS, AL, GA, SC, and NC in the D4-8 outlook this morning.

I am sure the risk levels and locations will be updated in coming days, as usual. lol

 

[KevinH]

Updated AFD from FFC for Friday:

Text Products for AFD Issued by FFC

Area Forecast Discussion
National Weather Service Peachtree City GA
322 PM EST Mon Jan 8 2024

...Afternoon Area Forecast Discussion...

.SHORT TERM...
(This evening through Tuesday)
Issued at 321 PM EST Mon Jan 8 2024

Key Messages:

- Numerous hazards across the forecast period, including high
winds, flooding rain, and severe weather.
- Best timing for severe will begin near the Columbus area during
morning hours and spread east and north through the afternoon.
- Heavy rainfall overnight will lead to a flash flood threat,
especially as the main line pushes through. Flash Flood Watch is
in effect for locations north of the fall line through evening.
- Strong winds will precede the front tonight and tomorrow
morning. Winds of 15-30 mph sustained with gusts up to 40 mph
will occur across the area. The mountains could see gusts up
to 50 mph, where a High Wind Warning is in effect.

Forecast Overview:
Extremely dynamic system will impact the CWA tonight into tomorrow.
Deep 500 mb trough over the Southern Plains will take on
increasingly negative tilt as shortwave rotates through it over the
southeast. 500 mb winds of 125+ kt will overspread the area on
Tuesday, aiding in deep ascent through the tropospheric column. On
top of this, cool post frontal airmass is in place across the
southeast being reinforced by surface high off the NE coast. Strong
WAA driven by deep surface low and powerful 80+ kt LLJ will
overspread the CWA tonight bringing copious moisture into the area
that will experience isentropic upglide. Rain, heavy at times, will
occur across much of the CWA tonight, before the main show arrives
ahead of the cold front tomorrow. The warm sector should expand
northward overnight through much of the CWA, allowing for surface
based storms in central Georgia and some points northward. These
will push through during the morning and afternoon with damaging
winds and the potential for some tornadoes.

Severe Threat:
Very impressive parameter space looks to set up over the CWA during
the early morning hours and into the afternoon on Tuesday. Strong
WAA overnight will allow for two not so great things - the first, it
will keep the boundary layer well mixed, likely preventing any
nocturnal inversion from setting up, and second, will likely help
break down our CAD/wedge in place. Normally I would say the wedge
will win out, but with a 80+ kt jet at 850mb overspreading the
region, that will aid greatly in mixing it out. That being said, the
best winds in that won`t arrive until the morning hours as the line
begins pushing through, so it may take a bit of time for the warm
sector to lift through the CWA. The current SPC outlook reflects
this nicely, showing biggest risks from Columbus to Macon and then
pushing north.

The wind threat will likely be the biggest risk right out. With the
very strong kinematics, mixing down big winds in the strongest
storms won`t take much in the way of instability. QLCS tornadoes
will likely be in play, especially given fish hook look to the
hodographs which give tremendous SRH values of 200-400 m2/s2. The
big question mark is the instability. This has potential to be a
classic HSLC event, but the ability to be fully surface based will
likely be dependent on how quickly and how strong the WAA occurs.
This creates uncertainty in the northern extent, and certainly won`t
rule out seeing some severe weather as far north as the metro if
WAA really gets moving.

 

[JBishopwx]

NAM:

 

[ctopher5]

New day 4 from the SPC maintains a 15% risk, but mentions a possible need for an increase in later outlooks. Also mentions an environment potentially supportive of strong tornadoes.

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0358 AM CST Tue Jan 09 2024

Valid 121200Z - 171200Z

...DISCUSSION...
Medium-range model output (including the ECENS/GEFS and ECMWF/GFS)
continues to indicate that rapid, strong cyclogenesis will proceed
Friday across the Mississippi Valley through Atlantic Seaboard, as a
vigorous short wave impulse pivots northeast of the southern Great
Plains. As the center of the growing cyclone tracks from Arkansas
into and through the lower Ohio Valley during the day Friday, lowest
surface pressures may fall as much as 15-20 mb in 12 hours.

Latest guidance is more suggestive that the stronger mid/level
cooling might tend to shift north of the moistening warm sector
overspreading the central into eastern Gulf Coast states by midday.
While warm mid/upper layers could potentially be mitigating to
destabilization and severe weather potential during the afternoon
through evening across Alabama and Georgia into the Carolinas, this
may be compensated for by a continued increase in low-level
moisture.

Increased inhibition and weaker mid/upper support might actually be
more conducive to discrete supercell development in the presence of
intense wind fields (including 50-80+ kts in the 850-700 mb layer)
and low-level shear. And models suggest that a dryline structure
might develop ahead of the cold front trailing the cyclone as it
progresses eastward. Due to lingering uncertainties severe weather
probabilities are being maintained at 15 percent across the eastern
Gulf into southern Atlantic Coast states vicinity. However, it is
still possible that severe weather probabilities will need to be
increased in later outlooks for this period. Conditionally the
environment appears potentially conducive to strong tornadoes and
high convective wind gusts.

Following diminishing convective potential over the coming weekend,
model output remains quite varied concerning the possibility for
another developing surface cyclone across the Gulf of Mexico through
Atlantic Seaboard vicinity early next week.

..Kerr.. 01/09/2024


Sent from my iPhone using Tapatalk

 

[Clancy]

New day 4 from the SPC maintains a 15% risk, but mentions a possible need for an increase in later outlooks. Also mentions an environment potentially supportive of strong tornadoes.

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0358 AM CST Tue Jan 09 2024

Valid 121200Z - 171200Z

...DISCUSSION...
Medium-range model output (including the ECENS/GEFS and ECMWF/GFS)
continues to indicate that rapid, strong cyclogenesis will proceed
Friday across the Mississippi Valley through Atlantic Seaboard, as a
vigorous short wave impulse pivots northeast of the southern Great
Plains. As the center of the growing cyclone tracks from Arkansas
into and through the lower Ohio Valley during the day Friday, lowest
surface pressures may fall as much as 15-20 mb in 12 hours.

Latest guidance is more suggestive that the stronger mid/level
cooling might tend to shift north of the moistening warm sector
overspreading the central into eastern Gulf Coast states by midday.
While warm mid/upper layers could potentially be mitigating to
destabilization and severe weather potential during the afternoon
through evening across Alabama and Georgia into the Carolinas, this
may be compensated for by a continued increase in low-level
moisture.

Increased inhibition and weaker mid/upper support might actually be
more conducive to discrete supercell development in the presence of
intense wind fields (including 50-80+ kts in the 850-700 mb layer)
and low-level shear. And models suggest that a dryline structure
might develop ahead of the cold front trailing the cyclone as it
progresses eastward. Due to lingering uncertainties severe weather
probabilities are being maintained at 15 percent across the eastern
Gulf into southern Atlantic Coast states vicinity. However, it is
still possible that severe weather probabilities will need to be
increased in later outlooks for this period. Conditionally the
environment appears potentially conducive to strong tornadoes and
high convective wind gusts.

Following diminishing convective potential over the coming weekend,
model output remains quite varied concerning the possibility for
another developing surface cyclone across the Gulf of Mexico through
Atlantic Seaboard vicinity early next week.

..Kerr.. 01/09/2024


Sent from my iPhone using Tapatalk

 

[Clancy]

Not a fan of some of the SPC's wording, underlined below.

...DISCUSSION...
Medium-range model output (including the ECENS/GEFS and ECMWF/GFS)
continues to indicate that rapid, strong cyclogenesis will proceed
Friday across the Mississippi Valley through Atlantic Seaboard, as a
vigorous short wave impulse pivots northeast of the southern Great
Plains. As the center of the growing cyclone tracks from Arkansas
into and through the lower Ohio Valley during the day Friday, lowest
surface pressures may fall as much as 15-20 mb in 12 hours.

Latest guidance is more suggestive that the stronger mid/level
cooling might tend to shift north of the moistening warm sector
overspreading the central into eastern Gulf Coast states by midday.
While warm mid/upper layers could potentially be mitigating to
destabilization and severe weather potential during the afternoon
through evening across Alabama and Georgia into the Carolinas, this
may be compensated for by a continued increase in low-level
moisture.

Increased inhibition and weaker mid/upper support might actually be
more conducive to discrete supercell development in the presence of
intense wind fields (including 50-80+ kts in the 850-700 mb layer)
and low-level shear. And models suggest that a dryline structure
might develop ahead of the cold front trailing the cyclone as it
progresses eastward. Due to lingering uncertainties severe weather
probabilities are being maintained at 15 percent across the eastern
Gulf into southern Atlantic Coast states vicinity. However, it is
still possible that severe weather probabilities will need to be
increased in later outlooks for this period. Conditionally the
environment appears potentially conducive to strong tornadoes and
high convective wind gusts.

FFC is concerned and watching it closely. Could be a daytime event for us, which is quite rare.

Another storm system will approach the area Thursday night, bringing
a chance of showers and thunderstorms. This system will lift NE on
Friday as a negatively tilted trough, reaching the Great Lakes by
Friday night. A 996 mb surface low is progged to be near Little Rock
by Friday morning. A large area of isentropic lift is forecast to
precede the low, with increasing MUCAPE and wind shear across most
of the forecast area. There will be another threat of severe weather
with this system during the day Friday, and the threat area looks to
be farther to the N than with today`s system. GFS MUCAPE values are
forecast to reach near 1000 J/kg as effective shear increases to
over 40 knots in the Atlanta metro area. This will coincide maximum
daytime heating in the early afternoon, with surface temperatures
reaching over 60 degrees and dew points reaching the lower to mid
50s. The wedge/CAD is forecast to hang into NE GA during this time
period, but present indications are that it will be NE of the
Atlanta metro area. Storm total rainfall amounts with this system are
forecast to range from around a quarter inch S of Columbus to close
to an inch across N GA. Residents should continue to monitor the
latest forecast regarding this storm system.

 

[UncleJuJu98]

Shifting gears to this one now.

 

[UK_EF4]

That trough shape is very, very impressive - not only is it very strong but the orientation is much more favourable for discrete/semi-discrete storms. Very good thing this is not happening in April, or even March. Nevertheless, I'm concerned that if we see uptrends in the warm sector depth and extent, we could be looking at a fairly robust tornado event - even without that, we could see a similar threat to today with significant tornado potential along the Gulf Coast.

 

[Clancy]

That trough shape is very, very impressive - not only is it very strong but the orientation is much more favourable for discrete/semi-discrete storms. Very good thing this is not happening in April, or even March. Nevertheless, I'm concerned that if we see uptrends in the warm sector depth and extent, we could be looking at a fairly robust tornado event - even without that, we could see a similar threat to today with significant tornado potential along the Gulf Coast.

SPC seems pretty bullish about destabilization and WS propagation on this one. Either way, seems like someone will have a bad time with this system.

 

[Clancy]

Strong signals from CSU guidance.

 

[UncleJuJu98]

SPC seems pretty bullish about destabilization and WS propagation on this one. Either way, seems like someone will have a bad time with this system.

I like to use surface theta e for looking at potential surface based instability. I would agree with SPC. Potential is there rather long warm sector, not super broad but a lot bigger than todays sector, that cuts off about the Tennessee state line.

Reminds me of similar scope to Easter 2020 outbreak won't be as large though.
. Long wave trough that gives pure westerlies and cut off very sharp on northward extent..

Won't be identical in magnitude hopefully but I kinda thought there was a few similarities

 

[Clancy]

I like to use surface theta e for looking at potential surface based instability. I would agree with SPC. Potential is there rather long warm sector, not super broad but a lot bigger than todays sector, that cuts off about the Tennessee state line.

Reminds me of similar scope to Easter 2020 outbreak won't be as large though.
. Long wave trough that gives pure westerlies and cut off very sharp on northward extent..

Won't be identical in magnitude hopefully but I kinda thought there was a few similarities

Huh, thanks for the tip; still always learning new model things! FFC seems confident the CAD wedge will be moving, even ahead of model forecasts, so that sort of raises some red flags for me.

 

[KevinH]

Strong signals from CSU guidance.
View attachment 23163

So basically most of the same areas as today SMH

 

[UncleJuJu98]

Huh, thanks for the tip; still always learning new model things! FFC seems confident the CAD wedge will be moving, even ahead of model forecasts, so that sort of raises some red flags for me.

No problem. I thought a lot of people knew that lol. We are all noobs learning new stuff lol