Not a fan of seeing the word supercell :/One thing I noticed on the latest GFDL and every latest model output there's not really a big complex out ahead of the main squall line that comes in late Monday night/early Tuesday morning. The exception being the 3km NAM but even that doesn't show widespread storm activity. That would if verified potentially destabilized the atmosphere more assuming that there are breaks in cloud cover during the day Monday. It would also given room for more cellular/supercell storms out ahead of the main line as well.
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EAST TEXAS
INTO PARTS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST...
Severe thunderstorms will be possible Monday afternoon into Monday
night from east Texas into parts of the lower Mississippi Valley and
Southeast. Damaging wind and a few tornadoes are expected to be the
primary hazards, though some hail will also be possible.
A complex mid/upper-level trough will gradually shift eastward
across the central CONUS on Monday, as a vigorous vorticity maximum
and related mid/upper-level jet move through the base of the trough
from the southern Plains into the lower/mid MS Valley. A surface
cyclone initially over OK is forecast to move eastward toward the
lower MS Valley during the day, then northeastward toward the lower
OH Valley Monday night. Relatively rich low-level moisture will
stream northward in advance of the cyclone and trailing cold front,
with mid/upper 60s F dewpoints becoming established across east TX
into LA during the day, and into parts of MS and western AL by
Monday evening into the overnight.
...East TX/ArkLaTex into the lower MS Valley and Southeast...
Thunderstorms capable of all severe hazards will be possible from
east TX into the lower MS Valley Monday afternoon and evening, but
uncertainties remain regarding favored corridors of greater threat
and the longevity of the threat Monday night within a lower CAPE
(but high shear) environment.
Modest heating of an increasingly moist environment will support
prefrontal MLCAPE approaching 1000 J/kg Monday afternoon from near
the ArkLaTex region southward across east TX. Scattered thunderstorm
development will be possible near the surface low and cold front,
and also potentially within an increasingly moist prefrontal warm
sector. Wind profiles may initially be rather unidirectional, but
strong mid/upper-level flow will support effective shear of 50-60
kt, more than sufficient for supercells. Large hail and locally
damaging gusts will be the primary initial threats. Some tornado
threat will potentially evolve with any persistent supercells as
low-level shear/SRH generally increases with time.
A transition to more of a cluster or linear mode is expected as
storms move east-northeastward and increase in coverage across the
ArkLaMiss region, with some increase in damaging-wind potential.
Some tornado threat may continue into Monday night as well, in
association with any persistent supercells and/or stronger
line-embedded mesovortices. The severe threat may persist as far
east as western AL, though a gradual decreasing trend is expected
with time and eastward extent, as the surface cyclone and stronger
large-scale ascent move northeastward away from the warm sector
early Tuesday morning.
A broad Slight Risk has been maintained with this outlook, though a
corridor of somewhat greater tornado/wind threat may eventually
evolve within this area, including the potential for a strong
tornado. Due to lingering uncertainties regarding the strength of
low-level mass response and the extent of sufficient instability,
confidence remains too low for greater unconditional probabilities
at this time.
That's a huge 5% tornado risk area lol.
Aside from severe, northern AL and GA might get some gusty winds ahead of the front....Synopsis...
A deep mid/upper-level trough is expected to move across parts of
the MS/OH Valleys and Southeast on Tuesday, though considerable
spread remains regarding the synoptic-scale details. The primary
surface cyclone is forecast to move toward the lower Great Lakes,
with secondary cyclogenesis possible across parts of the
Carolinas/Mid Atlantic late in the period. A cold front will
continue to move through portions of the Southeast.
...Parts of AL and the FL Panhandle into southwest GA...
At the start of the period Tuesday morning, rather strong low-level
and deep-layer shear will likely overlap a moist and weakly unstable
environment across parts of south AL and the FL Panhandle, in
advance of the cold front. Storms may persist along/ahead of the
front through the morning, as a continuation of widespread
convection from late in the D2/Monday period. Storm intensity and
coverage may tend to wane with time, as stronger large-scale ascent
becomes increasingly displaced from the warm sector, and instability
weakens with eastward extent. However, some threat for isolated
damaging wind and a brief tornado or two may persist during the day
across southeast MS, south AL, the FL Panhandle, and possibly into
parts of southwest GA.
...Carolinas and southern Mid Atlantic...
Substantial spread persists among model guidance with regard to the
synoptic pattern late on D3/Tuesday across parts of the Carolinas
and Mid Atlantic. The deterministic GFS and some GEFS members
develop a mid/upper-level cyclone near the lower MS Valley, while
most other guidance is notably less amplified, with a broad,
positively tilted trough approaching the region.
With rather strong low-level and deep-layer shear generally forecast
to overspread an increasingly moist but only weakly unstable
environment, the strength of large-scale forcing will be crucial for
determining the potential for organized deep convection. Given the
unusually large uncertainty at this forecast range, and the
likelihood for instability to remain quite weak even in the stronger
scenarios, no probabilities have been included with this outlook.
However, if guidance trends towards a more strongly forced scenario
across this region, then severe probabilities may eventually be
needed for Tuesday night into Wednesday morning.