SPC AC 231249

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0749 AM CDT Sat Mar 23 2024

   Valid 231300Z - 241200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   SOUTH FLORIDA AND THE KEYS...

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur today across parts
   of south Florida and the Keys.

   ...Synopsis...
   In mid/upper levels, a series of shortwaves -- including the open-
   wave remnants of a cyclone now moving toward the Pacific Northwest
   Coast -- will contribute to development of a large synoptic trough
   over the West by 12Z tomorrow.  Meanwhile, a downstream/southern-
   stream perturbation -- evident in moisture-channel imagery over the
   southern Appalachians to the FL Panhandle and central Gulf -- will
   shift eastward.  By 00Z, the trough should extend from the Carolinas
   and coastal GA south-southwestward across northern FL and the
   extreme eastern Gulf.  By 12Z, the trough should be offshore from
   the southern Atlantic Coast, including FL.

   At the surface, 11Z analysis showed a frontal-wave low over
   northeastern NC in the RDU/RWI area, with cold front across central
   portions of SC/GA to the west-central FL Panhandle and central Gulf.
   A prefrontal trough with northwesterly wind shift was drawn across
   southern GA, the FL coastal bend, and the east-central Gulf.  A warm
   front -- poorly defined due to the presence of convection and dense
   precip on both sides -- was apparent from the low southeastward over
   parts of the Outer Banks.  The low should move swiftly northeastward
   today, reaching near Montauk Point around 00Z, with the trailing
   cold front effectively catching the trough and moving offshore from
   the remainder of the Atlantic Coast (including FL). 

   ...South FL/Keys...
   Widely scattered to scattered thunderstorms are possible through
   midafternoon in the destabilizing, prefrontal warm sector over south
   FL.  The most vigorous cells may produce marginally severe gusts.

   The prefrontal air mass over the region will remain characterized by
   surface dewpoints around 68-72 F over most of south FL.  Modified
   RAOBs and forecast soundings suggest this will support around 1000-
   1500 J/kg MLCAPE with minimal CINH, and that convection now over
   parts of south FL already may be surface-based in the recovery zone
   of warm advection behind the prior night's activity.  However, light
   and variable winds near the surface will become southwesterly to
   westerly through midday, while flow from just above the surface
   through 850 mb veers more.  Though this will reduce hodograph size
   markedly, sufficient speed shear will remain to yield effective-
   shear magnitudes around 45-60 kt.  Weak/intermittent supercell
   characteristics may be noted, while fast cell motions contribute to
   locally damaging downdrafts. 

   ...Eastern NC...
   Somewhat organized thunderstorms extend from near HSE south-
   southwestward over Atlantic waters, moving northeastward.  The most-
   intense activity should remain offshore where low-level instability
   and deep bulk shear each should be most favorable.  Persistent
   overland precip has minimized buoyancy, and deep shear should
   continue to diminish as flow aloft weakens with time nearest the
   trough aloft.  Behind the early precip area, some destabilization,
   related to both warm advection and patchy insolation, is expected
   diurnally.  This may support isolated to widely scattered convection
   along/ahead of the cold front.  However, with the low and associated
   isallobaric forcing moving quickly away from the region and up the
   Mid-Atlantic Coast through 18Z, warm-sector flow will veer, further
   reducing both vertical shear and low-level convergence.  As such,
   unconditional potential appears too low to maintain a severe
   outlook.

   ..Edwards/Grams.. 03/23/2024

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