SPC 1300Z Day 1 Outlook
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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