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...

   ...SUMMARY...
   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.

   ...Synopsis...
   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
   tonight.

   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
   convection.

   ..Edwards/Leitman.. 02/08/2023

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