ACUS01 KWNS 051254
SWODY1
SPC AC 051253

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0653 AM CST Tue Mar 05 2024

Valid 051300Z - 061200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
ARKLATEX TO THE LOWER MISSISSIPPI VALLEY...AND PARTS OF PENINSULAR
FLORIDA...

...SUMMARY...
Strong to marginally severe thunderstorms are possible today over
the region from the Arklatex to the lower Mississippi Valley, then
mainly tonight over parts of peninsular Florida.

...Synopsis...
In mid/upper levels, a low-amplitude, zonal to gently cyclonic flow
pattern is present over most of the CONUS, ahead of a synoptic
trough over the northeastern Pacific between 130W-140W. That trough
will approach coastal northern/central CA near the end of the period
with an embedded 500-mb low west of MRY, then move inland on day 2.
Downstream, a southern-stream shortwave trough -- with several associated/small-scale vorticity maxima -- was apparent in
moisture-channel imagery over eastern parts of OK/TX to the
mid/upper TX Coast. This feature is expected to shift eastward
across the Gulf Coast States and northern Gulf through the period,
reaching parts of MS/AL and the FL Panhandle by 00Z, then moving
across GA/FL in piecemeal fashion around the end of the period and
early day 2. A weaker perturbation -- initially evident over parts
of the Mid-Atlantic region and adjoining ocean waters -- should
deamplify as it moves northeastward across New England through
tonight.

At the surface, a cold front was analyzed at 11Z from western QC
across Lake Huron to southern MO, southeastern OK, north-central TX,
and the TX South Plains region. A weak, attached low initially east
of DAL should drift southward with the boundary and weaken further
today, while another frontal-wave low forms ahead of the front over
northern AL overnight. The front itself should move slowly
southward across central/east TX, AR, and the lower Ohio Valley
through the period.

...Arklatex to lower Mississippi Valley/Delta regions...
The threat for marginally severe hail is ongoing with widely
scattered elevated thunderstorms ongoing over portions of AR into
the Arklatex region and nearby LA/east TX. Though predominantly
multicellular in character, due to lack of more intense vertical
shear, MUCAPE in the 1000-2000 J/kg range, supported by patches of
favorable low-level moisture away from convectively modified air
masses, should continue to support episodic development generally
shifting eastward to east-southeastward across the outlook area into
this afternoon.

Sporadic large hail on a pulse basis will remain a threat, though
isolated damaging to severe gusts cannot be ruled out as well.
Several clusters or small complexes of thunderstorms may develop as
the morning activity moves toward the lower Mississippi Valley, with
the messier mode lessening hail potential locally but maintaining
some pulse-wind threat. Strongest mid/upper winds also will be
displaced over the Great Lakes and northern Gulf in distinct
northern and subtropical streams -- north and south of the greatest concentrations of convection. This should maintain modest deep
shear and a mostly multicell mode for inland activity.

Though the prefrontal boundary layer should destabilize diurnally,
especially over western parts of the outlook area ahead of the cold
front -- mid/upper forcing for ascent will be displaced farther east
into the Delta region with time -- and ultimately over parts of the
Southeast containing less-suitable low-level moisture and
instability. Though isolated strong-severe afternoon thunderstorms
may form closer to the front in east TX, AR and LA, large-scale
subsidence behind the trough will foster stable layers that may
inhibit sustained convection over the greatest low-level instability
today. With associated coverage uncertainties, overall
unconditional severe probabilities are kept at marginal levels for
the time being.

...FL...
As the large-scale ascent/destabilization passes over the north- central/northeastern Gulf waters -- including the Loop Current -- low/middle-level lapse rates should steepen with weakening MLCINH.
This may support upscale organization of convection now near and off
the northern coastline into a quasi-linear MCS that would move east-southeastward across the Gulf, reaching the West Coast of FL
late this evening or overnight, before shifting eastward over at
least parts of the peninsula. Additional convection may form late
during the diurnal heating cycle this afternoon, and/or in a zone of
increasing warm advection and low-level convergence/lift ahead of
the MCS this evening.

While both synoptic and convection-allowing guidance is inconsistent
on mesoscale timing of the complex, or greatest coverage areas of
pre-MCS activity, the general notion of increasing convective
potential from late afternoon onward over FL is supported by the
pattern and by ongoing offshore convective trends. As such, while
the severe threat still looks conditional (especially given some
nocturnal stabilization likely to occur inland over FL), at least a
marginal unconditional risk now is apparent, given increasing deep
shear progged across most of the area, and at least marginal
low-level instability with around 500-1500 J/kg MLCAPE away from
convective outflows. Progged hodographs generally are not
particularly large, though storm-scale and boundary interactions can
modify them locally to become more favorable, amidst 35-45-kt
effective-shear magnitudes.

..Edwards/Jewell.. 03/05/2024

$$
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ACUS01 KWNS 061253
SWODY1
SPC AC 061252

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0652 AM CST Wed Mar 06 2024

Valid 061300Z - 071200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
PENINSULAR FLORIDA...SOUTH CAROLINA AND PARTS OF WEST-CENTRAL TO
NORTH TEXAS...

...SUMMARY...
Isolated severe thunderstorms are possible today over parts of
peninsular Florida and South Carolina, and late afternoon into
tonight over parts of west-central to north Texas.

...Synopsis...
In mid/upper levels, a progressive and amplifying pattern is
forecast over the CONUS through the period, mainly related to a
well-developed trough now approaching the CA coastline. The
accompanying 500-mb low should move over the Point Conception area
around 18Z, then weaken inland across southern CA overnight.
However, the trough will remain strong as an open-wave feature, as
it approaches the lower Colorado River Valley around 12Z.
Downstream, a series of minor perturbations embedded in the subtropical/southern stream will traverse northern MX and much of
TX. Farther east, a shortwave trough was quite evident in
moisture-channel imagery over parts of TN, AL and GA, extending
southward to the northeastern Gulf. This initially rather broad
perturbation will consolidate somewhat and cross parts of GA and the western/upstate Carolinas by 00Z, then move northeastward into the
Mid-Atlantic by the end of the period.

At the surface, 11Z analysis showed a series of weak lows and
troughs scattered across the Southeast amid weak surface flow, with
a warm front along the SC and southern NC coast, then bending
southeastward offshore from HSE. Northward movement of this
boundary will be delayed by precip/clouds this morning, but should
occur this afternoon across the inland Carolinas. Meanwhile,
another frontal zone -- initially drawn over deep south TX -- should
migrate northward as a warm front today and tonight across much of central/north TX and into OK tonight, connecting to overnight
surface cyclogenesis progged for the northwestern TX Panhandle.

...FL...
Widely scattered to scattered thunderstorms are expected to develop
this afternoon along sea-breeze boundaries and smaller-scale zones
of lift, amidst diabatically weakened MLCINH and favorable low-level
moisture. The best-organized convection may produce damaging to
isolated severe downdrafts and isolated severe hail.

The southern fringes of cooling aloft related to the southeastern
CONUS perturbation, atop upper 60s to low 70s F surface dewpoints,
in a deep troposphere, will lead to peak/preconvective MLCAPE in the
1500-2500 J/kg range. Activity should be predominantly
multicellular, with modest low/middle level flow limiting most
measures of bulk shear. However, relatively strong upper/anvil-
level winds will ventilate convection to some extent and contribute
to around 50-70 kt of shear from LCL to EL. Near the East Coast sea
breeze, some backed low-level flow is possible that may augment
low-level and deep shear enough for at least transient storm-scale
rotation and a marginal/brief tornado potential as well.

...SC and vicinity...
An extensive plume of precip -- with isolated to widely scattered,
sporadic, embedded thunderstorms -- is shifting roughly
northeastward across parts of GA, the Carolinas and eastern TN.
This activity is supported regionally by a combination of warm
advection and moisture transport, with related modest, elevated destabilization. Severe conditions are not expected with this
activity due to insufficiency of both buoyancy and shear.

However, especially over the Low Country/coastal plain and perhaps
central SC, a second round of convective development is expected
late this afternoon into evening, offering marginally severe hail or strong/damaging gusts. This activity should follow several hours of
airmass recovery through a combination of diabatic heating,
continued low-level warm advection, and DCVA/cooling aloft nearer to
the "cold-core" region of mid/upper-level perturbation. These
processes should steepen low-level lapse rates and weaken MLCINH,
while slightly increasing previously poor midlevel lapse rates by
late afternoon. In combination with favorable near-surface moisture
(dewpoints generally low/mid 60s F), this should support around
800-1200 J/kg MLCAPE. Though low-level hodographs/SRH/bulk shear
shouldn't be large, around 30-40 kt effective-shear magnitudes are
expected, with some organized multicell or transient supercell
structures possible. Convection should weaken and exit the area by
late evening.

...West-central/northwest/north-central TX...
Isolated to widely scattered thunderstorms are possible from late
afternoon into the overnight period -- initially over parts of the
Big Country/Concho Valley regions of west-central TX, then
spreading/shifting northward and northeastward with time tonight.
Isolated severe hail is the main concern, though strong/locally
severe gusts cannot be ruled out either. The northward-returning
frontal zone appears to be the most probable source of low-level
lift, through some chance exists for surface parcels to reach
convective temperature on southwestern parts of the outlook area.
Low-level warm advection and moisture transport/recovery will
strengthen considerably from late afternoon through overnight across
the region, as the Pacific mid/upper trough approaches, the subtle southern-stream perturbations move overhead, and southwest flow
increases aloft. This should lead to increasing convective
coverage, though uncertainty lingers on spatial extent and density,
given the subtlety of overall lift.

Environmentally, upstream high-cloud cover prevalent in satellite
imagery should thicken through the day, lending further uncertainty
to specific initiation timing/location, but still allowing enough
heating to weaken MLCINH by late afternoon. CINH will weaken
further this evening into tonight because of warm advection/
isentropic ascent to LFC -- particularly as the southerly LLJ
strengthens overnight to around 40-50 kt. The moisture increase
(especially above the surface) and warm advection will contribute to
MUCAPE around 1000 J/kg, most of it in low/middle levels below a
more-stable mid/upper regime related to the cloud deck. Some
convective organization is possible, amidst 30-40 kt effective-shear magnitudes.

..Edwards/Jewell.. 03/06/2024

$$
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