SPC AC 081300
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0700 AM CST Wed Feb 08 2023
Valid 081300Z - 091200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF EASTERN LOUISIANA AND WESTERN/CENTRAL MISSISSIPPI...
Severe thunderstorms are most probable today and tonight from east
Texas across the lower Mississippi Valley to parts of the Mid-South
and Delta regions. This includes the potential for tornadoes,
damaging winds and isolated large hail.
In mid/upper levels, a synoptic-scale split-flow pattern is apparent
over the central CONUS, between an amplifying northern stream and a
cyclone over the southern High Plains strongly distorted along a
south-southwest/north-northeast axis. A northern-stream trough will
dig south-southeastward over the northern/central Rockies. As that
occurs, the southern perturbation will become more compact, pivoting
eastward over northwest TX today, then ejecting northeastward the
Ozarks and mid Mississippi Valley by 12Z tomorrow.
At the surface, 11Z analysis showed a primary frontal-wave low over
northeast TX, between PRX-TYR, with a wavy/slow-moving cold front
southwestward over east-central and south-central TX. The low
should move northeastward to near the FSM/FYV corridor by 00Z,
deepening considerably overnight as the mid/upper trough ejects,
then reaching west-central/central IL by 12Z. The cold front should
reach western parts of AR, the lower Sabine Valley and the
northwestern Gulf by 00Z. By 12Z, the front should reach western
KY, western/middle TN, and southeastern portions of MS/LA.
...East TX to Mid-South, Delta region and Tennessee Valley...
Scattered thunderstorms are expected to develop along and ahead of
the cold front into tonight, with tornadoes, damaging to severe
gusts, and isolated severe hail possible. In aggregate, potential
coverage of supercells in a favorable environment appears greatest
over the 10% tornado threat area.
This afternoon, amidst the mass response to the approaching mid/
upper trough, a prefrontal zone of low-level confluence/convergence
should intensify over the Gulf off the upper Texas Coast, extending
northeastward into parts of western/central LA. This corridor of
maximized warm-sector lift then should expand/extend to western MS
into early evening. Meanwhile, theta-e advection will destabilize
the warm sector, along with a period of muted diurnal heating,
leading to minimal MLCINH. Convection should develop gradually
throughout this prefrontal lift zone and move northeastward, some of
it evolving into supercells and small bowing/LEWP-producing
formations, given the ambient wind profiles. Meanwhile, a band of
thunderstorms developing along the front should impinge on favorable
moisture, buoyancy and shear west of the convergence zone, initially
over parts of east TX, the Arklatex and AR. As this activity moves
east, it also will offer sporadic severe potential in all phases.
These two regimes may merge slowly this evening and overnight across
parts of MS, before convection outruns optimal warm-sector
destabilization and severe potential marginalizes farther east late
Surface dewpoints in the mid 60s to near 70 F should spread inland
through the warm sector in much of LA, MS and southern AR,
contributing to development of peak afternoon MLCAPE in the 1000-
1500 J/kg range (locally/briefly higher values possible). This will
coincide with strengthening low/midlevel winds from midafternoon
into evening, and enlarging low-level shear vectors/hodographs, with
forecast soundings reasonably depicting 40-50 kt effective-shear
magnitudes and 200-400 J/kg effective SRH -- a substantial fraction
of which may be in the lowest 1/2 km. Buoyancy will diminish with
northward extent across the Mid-South region toward the MO Bootheel
and into the northern area of more conditional/isolated severe
potential discussed next.
...Mid Mississippi/Lower Ohio Valley regions...
The northern part of the aforementioned frontal thunderstorm band
may build northward tonight from the Mid-South into southeastern MO
and parts of IL, with potential for isolated damaging to severe
gusts and perhaps a line-embedded tornado or two. As the deep-layer
cyclone/trough eject toward this region tonight, intensifying deep-
layer lift will lead to a band of strongly forced, low-buoyancy
convection near the front. DCVA/ascent in midlevels will overlie
enough warm advection and moistening near the top of the boundary
layer to foster 300-800 J/kg MUCAPE. The main limiting factor will
be lack of more time for boundary-layer warm advection to overcome
antecedent low-level stability reinforced by prefrontal precip.
However, momentum transfer in the strongest downdrafts may allow
isolated severe gusts to reach the surface, and low-level hodographs
will be large and favorably shaped for tornado potential wherever
surface-based effective-inflow parcels can be encountered by the
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