SPC Dec 16, 2023 1300 UTC Day 1 Convective Outlook

[NorthGeorgiaWX]

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0638 AM CST Sat Dec 16 2023

Valid 161300Z - 171200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE FL
PENINSULA AND KEYS...

...SUMMARY...
The threat for a few damaging gusts and tornadoes will increase by
tonight into Sunday morning across the Florida peninsula and Keys.

...FL through Sunday morning...
No changes to previous outlook area.  Cyclogenesis is underway
across the central Gulf of Mexico in association with a southern
stream shortwave trough.  The cyclone is expected to
consolidate/deepen and move toward central/north FL by the end of
the period, as a result of phasing with an upstream trough now near
the TX coast, and due to convective feedback.  These processes will
result in strengthening wind fields and northward moisture transport
across the FL peninsula, especially tonight into Sunday morning.  As
boundary-layer dewpoints of 68-72 F spread northward,
destabilization should be sufficient for surface-based storms later
today through Sunday morning.

Isolated, weakly rotating storms will be possible today in the warm
advection zone, starting late this morning across the Keys and
spreading northward along the Atlantic coast this afternoon. The
primary ascent band/convection and associated wind shift are
expected to approach the FL Gulf coast near or after 03z and
continue eastward across the peninsula through 09-12z Sunday.  A
somewhat broken band of storms is expected just ahead of the wind
shift in an environment of 500-1000 J/kg MLCAPE, modest lapse rates
aloft and strengthening vertical shear.  Forecast profiles show
large, curved hodographs in the low levels and sufficient hodograph
length/deep-layer vertical shear for supercells.  Assuming moisture
advection and overnight mechanical mixing are strong enough inland,
the potential for damaging gusts and a few tornadoes will spread
inland from the Gulf coast.  Other supercells with the potential for
damaging gusts and tornadoes could also form in the convergence zone
and somewhat richer low-level moisture along the east-central and
southeast FL coasts overnight.

The main uncertainties in this forecast will be the magnitude of the
mass response/vertical shear, and the degree of low-level
warming/moistening inland overnight.  Both will be a function of how
quickly the Gulf cyclone consolidates and deepens in a data sparse
area.  Given the modest lapse rates aloft, maintenance of
surface-based convection will be sensitive to a few degrees of
temperature/dewpoint up to the cyclone track.

..Thompson/Broyles.. 12/16/2023

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