SPC AC 261250

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0650 AM CST Sat Nov 26 2022

   Valid 261300Z - 271200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER THE
   NORTH-CENTRAL GULF COAST AND VICINITY...

   ...SUMMARY...
   A marginal damaging-wind and tornado threat exists today and tonight
   over the north-central Gulf Coast and vicinity.

   ...Synopsis...
   In mid/upper levels, a positively tilted shortwave trough located
   over the northwestern CONUS is expected to move southeastward across
   the Great Basin to the southern Rockies through the period.  As this
   occurs, a strong cyclone -- centered initially near MAF and covering
   much of the southern Plains and northern MX -- is expected to eject
   northeastward.  By 00Z, the 500-mb low should be near DFW, with
   trough southward to south-southeastward over parts of east-central/
   southeast TX.  By 12Z, that low should accelerate northeastward to
   near MVN, with trough to near the MS/AL border.

   At the surface, 11Z analysis showed an elongated area of low
   pressure from the TX Coast between GLS-PSX, north-northwestward to
   near UTS, and an inverted trough farther inland past the DFW
   Metroplex.  A cold front was drawn from the coastal part of the low
   southward then south-southwestward across the northwestern Gulf.  A
   marine/warm front -- demarcating low 60s F temperatures and
   dewpoints inland from mid-70s F temperatures and low/mid-70s
   dewpoints over the open Gulf -- was drawn from just SE of GLS
   eastward across southeast TX/southern LA shelf waters.  A modified
   version of this boundary should extend inland over parts of the
   AL/western FL Panhandle coasts tonight as the surface low wraps
   through cool inland air toward the mid/upper cyclone center.  The
   more purely unmodified Gulf air south of the boundary may brush
   across the mouth of the Mississippi River between about 21Z-00Z.

   ...North-central Gulf Coast and vicinity...
   A band of scattered thunderstorms now over the northwestern Gulf is
   expected to move east-northeastward through the day, its northern
   parts extending progressively further inland while rooted in an
   elevated unstable layer.  Where the line breaks into discrete
   lightning-producing elements farther south over the open Gulf, well
   east of BRO and south of BPT, satellite signatures indicate possible
   supercell(s).  Ahead of the line, up until earlier this hour, a
   persistent, cyclic, right-moving, and possibly tornadic supercell
   was noted for a few hours in radar imagery offshore from the mid/
   upper TX Coast.  This storm moved through northwestern parts of the
   highest-theta-e maritime/tropical air mass, before penetrating the
   marine frontal zone and weakening.  Still, its longevity and
   organization affirmed a favorable environment along and south of the
   boundary, and for a short distance to its north.

   Vertical shear will remain favorable area-wide, amid strengthening
   mass response to the progressive cyclone.  This will contribute to
   50-60-kt effective-shear magnitudes and 200-400 J/kg effective SRH.
   Thermodynamic support appears more tenuous.  Considerable
   uncertainty remains as to how much of the relatively unmodified
   maritime/tropical air mass can get inland to support more than
   marginal/conditional severe potential, given that substantial
   precip/cloud cover is likely to its north.  Modified RAOBs and model
   soundings consistently suggest a deep, nearly saturated overland
   boundary layer with very low LCL, but also, greatest static
   stability near the surface.  Even where nominally surface-based
   effective-inflow parcels are present in forecast soundings, at least
   a shallow layer of stable lapse rates near surface may impede
   tornado/wind potential.

   200-800 J/kg MLCAPE may extend farther inland with eastward extent
   tonight across southern AL and the western FL Panhandle, as the
   cyclone and its associated large-scale lift fields shift further
   inland/poleward of the Gulf Coast.  This will occur amidst a strong
   low-level warm-advection/moisture-transport regime, but also, large
   areas of precip and messy convective modes that cast doubt on
   potential for sustained supercells, in an otherwise favorable
   vertical-shear environment.  If just a little more destabilization
   and/or less-messy potential convective mode becomes evident inland
   tonight over parts of southern AL and the western FL Panhandle,
   greater unconditional probabilities may be needed.  However,
   uncertainty remains too great to upgrade that portion of this
   outlook presently.

   ..Edwards/Broyles.. 11/26/2022

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