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Severe WX Severe Weather Threat Jan 12th, 2023

Nws of bham notes how fast the frontal boundary will be moving saying it could intensify storms a little more.. I'm guessing the directional winds will be better with better placement of convection if it's quicker..?low level winds are still veered although there closer to being from the south instead of southwesterly in portions of central Alabama.

May have a few spin ups with this damaging wind QCLS. Especially if low level winds are going to be more southerly than southwesterly with the quicker arrival of a frontal boundary.
 
The HRRR keeps indicating the line being more cellular or broken with updraft streaks. Keep the winds at surface southerly and a east moving storm motion I'll take a increased tornado threat, pretty good streamwise vorticity
 
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My hot take is a increased tornado threat maybe 5 -10% smaller area southeast of the i20 corridor into Georgia. Banking this on a faster and more due east storm track, meshes better with a possibly southerly low level winds. Quite a few event have taken advantage of this before. Actually if I'm not mistaken correct me if I'm wrong a Carolina tornado event was enchaned by a easterly storm motion with winds from the south a couple years ago.
 
Short range HRRR is starting to get in range the instability was underdone a decent bit I'n some areas compared to the long range HRRR. With a whopping 63-64 dewpoint in south central Alabama by 3 am with close to 1000 j of instability in areas of Alabama. Wow!
 
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xJownage said:
I'm not enamored by this setup at all. The cape profiles are very skinny which will make it difficult to get robust supercells going. Lacking MLLRs don't help with that.
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It's enough for your winter low topped supercell events, it's your typical spin up broken QCLS event in the winter in Alabama lol

Usually Alabama's winter events include a skinnier QCLS that's semi broken with low thermodynamics but pretty good shear. Always includes a lot of spins up that are hard to warn.
 
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UncleJuJu98 said:
It's enough for your winter low topped supercell events, it's your typical spin up broken QCLS event in the winter in Alabama lol

Usually Alabama's winter events include a skinnier QCLS that's semi broken with low thermodynamics but pretty good shear. Always includes a lot of spins up that are hard to warn.
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The issue is you usually look for fatter instability in the low levels, and furthermore better lapse rates to supplement updrafts. You also look for better kinematics in the form of SFC backing creating long, curved hodos. I'm not seeing those. I know you were discussing earlier that we might see better SFC backing than modeled due to faster progression of the front, and as a consequence there will be at least some QLCS risk, but I'm not seeing the ability for storms to generate robust discrete updrafts in the warm sector.
 
xJownage said:
The issue is you usually look for fatter instability in the low levels, and furthermore better lapse rates to supplement updrafts. You also look for better kinematics in the form of SFC backing creating long, curved hodos. I'm not seeing those. I know you were discussing earlier that we might see better SFC backing than modeled due to faster progression of the front, and as a consequence there will be at least some QLCS risk, but I'm not seeing the ability for storms to generate robust discrete updrafts in the warm sector.
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I know, it's a QCLS event first and foremost with potential for a better tornado threat inside of the QCLS just depends on some of the minute details. The skinny instability and meager lapse rates are apart of the typical winter events.

I may be wrong on this but the low topped supercells can thrive on lesser than ideal environments sometimes. There not going to be your ef3 or above type tornadoes but they'll still do some damage and be as quickly gone as they came. They usually don't need a long enlarged hodo either, too much wind shear and it tears everything up sometimes
 
Today's AFD from Peachtree City. Low-end tornado threat and elevated wind damage threat along the line. Elevated DCAPE will contribute to increased risk for downbursts, and weak tornadoes may form without warning. Could be a potent wind event for E AL and W GA.
Within the fairly active upper-level pattern, a stout shortwave
trough will be kicking through the broader subtropical jet stream
tomorrow. This shortwave trough will have an accompanied surface low-
pressure system that will be lifting across the Midwest, into the
eastern Great Lakes region by Thursday afternoon. A cold front
associated with the low-pressure system will also push through the
forecast area during the same time, bringing with it a line of
showers and thunderstorms with some severe potential. Let`s touch on
that a bit further...

At the 850 hPa level, a 45-50 mph jet streak will be lifting through
the forecast area Thursday afternoon. A portion of these winds could
mix down to the ground ahead of a line of storms, with wind gusts
upwards to 30-40 mph in the late-morning and afternoon. This mid/low-
level jet combined with the stout aforementioned cold front will
force a line of convection along the frontal zone that will push into
NW Georgia by late morning and very quickly push through the
forecast area, likely exiting the CWA before midnight with a high-
shear, low-CAPE setup. Dewpoints will surge to near 60 degrees ahead
of the line of storms due to the strong pull from the mature
Midwestern low-pressure system which, for once, doesn`t look to be
occluded and weakening by the time the cold front pushes into
Georgia. With the extra moisture combined with optimal daytime
heating, SBCAPE values will rise to 500-1000 J/kg, not a lot, but
enough for a strong thunderstorms to form under favorable upper-level
atmospheric dynamics. The low-level jet will also support strong SFC-
500 hPa bulk shear over 50kts, with continual speed shear with
height through the lowest 6 km of the troposphere. 0-1 km SRH values
will also be over 200 m2/s2 with hodographs ahead of the convective
line showing good curvature, with potential for streamwise vorticity
flow into rightward-moving updrafts. Additionally, models are
showing signs of drier air in the 700-500 hPa height range, which
means DCAPE values will be elevated to near 500 J/kg.

This combination of parameters should combine to produce a quasi-
linear convective system with embedded circulations which could
spawn a few weak, brief tornadoes within the convective line. Low-
level winds are expected to be mostly parallel to the front, which
will enhanced surface vorticity along the baroclinic zone that could
easily be stretched by thunderstorm updrafts and produce rapid
tornadogenesis along the line. The larger threat, however, will be
severe wind gusts. With elevated DCAPE values, uncharacteristic of
January severe setups, downburst potential will also be elevated.
Furthermore, stronger downdrafts will be more efficient to bring
severe 50+ kt wind speeds from aloft down to the ground,
potentually producing bowing segments along the line of storms and
causing locally scattered to widespread damage to trees and
powerlines.

While this does look like a decent January setup for severe weather
which has prompted SPC to issue a Slight Risk for Severe
Thunderstorms for the forecast area, there are some limiting factors
working in our favor. First being low PWATS around 1 inch, which
could leave storms moisture-starved and struggling to produce
strong, water-evaporative fueled downdrafts which may limit the
severe wind potential. There are some CAMs that are struggling to
produce robust storms at all given the lower than usual PWATs.
Second in the near-parallel flow ahead of the line which should
prevent any strong or long-track tornadoes from forming. So while
several parameters look favorable for sever weather, several
questions still remain with clarity expected as the storms approach
the forecast area over the next 24-36 hours.
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HREF ensemble STP (valid 18Z tomorrow) and 24-hour UH. 12Z NAM 3KM is quite aggressive with instability for tomorrow, and accordingly has some pretty hefty STP values over West-Central Georgia during the afternoon, but thankfully so far seems like an outlier.
1673457797978.png1673457806181.png
1673457904628.png1673458024980.png
 
Kinda surprised to see SPC's reluctance to introduce a 5% tor risk. Pretty good signal for QLCS tors and SPC disco mentions a couple of tornadoes possible. Not a huge deal or anything just a detail I found a bit strange.
spccoday2.tornado.latest.png
 
MattPetrulli said:
Kinda surprised to see SPC's reluctance to introduce a 5% tor risk. Pretty good signal for QLCS tors and SPC disco mentions a couple of tornadoes possible. Not a huge deal or anything just a detail I found a bit strange.
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Wouldn't be particularly surprised to see a 5% tomorrow morning.
 
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