SPC AC 151247

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0647 AM CST Sat Jan 15 2022

   Valid 151300Z - 161200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   COASTAL FLORIDA PANHANDLE...

   ...SUMMARY...
   Scattered strong-severe thunderstorms are expected to move eastward
   across the northern and eastern Gulf this afternoon into tomorrow
   morning.  This activity will pose a marginal to slight tornado and
   severe-gust threat, around that part of the coast from near the
   mouth of the Mississippi River to west-central/northwest Florida.

   ...Synopsis...
   In mid/upper levels, the persistent mean troughing over the eastern
   CONUS will be reinforced this period into tomorrow by a strong
   shortwave trough and accompanying closed cyclone -- the center of
   which is apparent in moisture-channel imagery over the KS/OK line
   between END-ICT.  The 500-mb low should pivot southeastward over the
   Arklatex region by 00Z, then eastward to near the MS/AL line by the
   12Z tomorrow.

   At 11Z, the associated surface low was analyzed in the Arklatex
   area, along a cold front extending across easternmost TX, middle TX
   coastal waters and deep south TX.  The surface cyclone should be
   elongated along the front and reach east-central/southeastern MS by
   00Z, with the trailing cold front southward over the MS coastline
   and arching across the north-central/southwestern Gulf.  By 12Z, the
   low should reach west-central/southwestern GA, with the front across
   the Apalachee Bay region to the south-central Gulf.

   ...Gulf Coast:  Southeastern LA to western FL...
   At least isolated damaging gusts and a tornado or two may occur from
   west to east around the Gulf Coast, from this afternoon onward,
   roughly between BVE and PIE.  Unconditional severe probabilities
   appear greatest tonight over near-coastal areas of the central/
   eastern FL Panhandle, and a small area of "slight" probabilities has
   been introduced there.  

   Weak low-level instability will greatly limit the inland extent of
   the severe threat.  Elevated thunderstorms are possible well inland,
   near and north of the surface low, and atop a relatively stable
   boundary layer still very incompletely modified behind the last
   cold-frontal passage.  However, the main severe-weather concern will
   be where at least marginal surface-based buoyancy is expected to
   develop overland, from southeastern LA to the western FL Panhandle
   this afternoon and evening, shifting eastward across the Panhandle
   tonight, then down the West Coast of the peninsula tomorrow morning.
    
   The most intense, surface-based convection is expected to form
   tonight over open Gulf waters, especially over and near the Loop
   Current.  In that part of the Gulf, ocean heat content is greatest
   and boundary-layer thermodynamic fluxes will support the most
   favorable boundary-layer airmass modification for the longest time. 
   Some of the better-organized surface-based convection (both as the
   northern rim of a strengthening squall line and isolated preceding
   supercells) may penetrate inland across parts of the central/eastern
   FL Panhandle before weakening, with accompanying low-CAPE/strong-
   shear tornado and gust threat.  Potential for both supercells and
   line-embedded mesocirculations will be supported by a 50-60-kt LLJ
   enlarging hodographs, and gradient flow aloft that strengthens ahead
   of the mid/upper cyclone.  Forecast soundings suggest 150-250 J/kg
   effective SRH and 40-50-kt effective-shear magnitudes, where enough
   moisture for preconvective surface dew points in the 60s can
   penetrate inland tonight.  The latter should offset modest
   low/middle-level lapse rates enough for 200-500 J/kg MLCAPE along
   those parts of the coastline, decreasing quickly inland. 

   Considerable uncertainty remains on the timing of the squall line's
   west-central/northwest FL landfall between CTY-SRQ, relative to the
   12Z cutoff that marks the end of the forecast period and the start
   of day 2.  No changes were made to that part of the categorical
   outlook in deference to the timing questions.

   ..Edwards.. 01/15/2022

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