SPC AC 150656

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1256 AM CST Sat Jan 15 2022

   Valid 161200Z - 171200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE FLORIDA PENINSULA/KEYS AND COASTAL NORTH CAROLINA...

   ...SUMMARY...
   Isolated strong to marginally severe storms may impact parts of the
   Florida Peninsula/Keys and coastal North Carolina on Sunday.
   Occasional damaging winds and a tornado or two should be the main
   threats.

   ...Synopsis...
   A closed upper low centered over the Deep South Sunday morning will
   advance northeastward across the southern Appalachians through the
   day, eventually reaching the Mid-Atlantic by late Sunday night. The
   primary surface low should develop over coastal SC into
   central/eastern NC by Sunday evening while gradually deepening, with
   a trailing cold front sweeping east-southeastward across much of the
   FL Peninsula through the day.

   ...Florida Peninsula and the Keys...
   Latest guidance is in reasonably good agreement that a pre-frontal
   squall line will likely be ongoing at the start of the period
   along/near the coast of the west-central FL Peninsula. A narrow
   plume of low 60s surface dewpoints will probably be present along
   and just ahead of the convective line. This low-level moisture may
   be barely sufficient to support enough weak MLCAPE for surface-based
   storms. As the line moves inland over the central FL Peninsula
   Sunday morning, strong low-level and deep-layer should support storm
   organization even with minimal instability. Isolated strong/damaging
   winds and a brief tornado or two appear possible.

   There will be some potential for this line to maintain intensity as
   it moves eastward over the central/southern FL Peninsula and the
   Keys through Sunday afternoon. Modest low-level moisture return
   ahead of the front and poor lapse rates should limit the degree of
   instability that develops across this region. Still, enhanced
   low/mid-level winds associated with the upper low will be slow to
   decrease through the day, even as better large-scale ascent shifts
   northward into GA and the Carolinas. Various forecast soundings from
   the 00Z NAM and 03Z RAP show weak instability (generally 250-500
   J/kg of MLCAPE) and at least 30-40 kt of deep-layer shear ahead of
   the line.

   Some convection-allowing models suggest the line will either
   maintain its intensity or restrengthen Sunday afternoon across the
   eastern FL Peninsula and the Keys as it encounters slightly greater
   low-level moisture. If this occurs, then the threat for isolated
   damaging winds and a brief tornado or two could continue over these
   areas. Therefore, have expanded the Marginal Risk to include all of
   the central/southern FL Peninsula and the Keys to account for this
   potential. The lack of stronger forecast instability still suggests
   the overall severe threat will probably remain isolated/marginal.

   ...Coastal North Carolina...
   Rather strong low/mid-level winds are expected to overspread NC
   through the day as the upper cyclone progresses northeastward.
   Pronounced low-level mass response across eastern NC may encourage
   low 60s surface dewpoints to advance very slightly inland over
   portions of coastal NC by Sunday afternoon. Even with widespread
   cloud cover and precipitation, this increasing low-level moisture
   may support very weak instability (around 250 J/kg of MLCAPE) and
   the potential for surface-based storms to scrape the coast. While
   greater severe potential will clearly remain over the Gulf Stream
   and offshore, it appears possible that this barely sufficient
   boundary-layer instability coupled with the very strong low-level
   and deep-layer shear may support an isolated severe threat along the
   immediate coastal areas of NC Sunday afternoon/evening. Occasional
   damaging winds and a brief tornado should be the main threats.

   ..Gleason.. 01/15/2022

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