SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0652 AM CST Sat Jan 02 2021

Valid 021300Z - 031200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN
FLORIDA PANHANDLE INTO SOUTHEASTERN GEORGIA...

...SUMMARY...
Isolated strong to briefly severe thunderstorms may develop this
afternoon and evening, from the eastern Florida Panhandle into
southeastern Georgia.

...Synopsis...
A strongly amplified, progressive, split-flow pattern dominates the
CONUS this morning, the most prominent feature being a synoptic-
scale trough from the western Ozarks region southwestward across OK
and west-central TX, to north-central MX.  This feature is expected
to evolve a broadly closed 500-mb cyclone today over OK. The
circulation center should reach the Ozarks of southern MO by 00Z,
while a basal vorticity max now over north TX ejects over parts of
AR and the Mid-South region.  As the parent trough deamplifies
considerably, and a strong, compact shortwave trough digs
southeastward from the northern Rockies to the central High Plains,
the mid/upper low should reach the OH/IN border region by 12Z
tomorrow.

At the surface, 11Z analysis showed an occluded low over NY near
SYR, with a triple-point low near BID and cold front southwestward
to eastern NC, becoming quasistationary to a weak frontal-wave low
near AAF.  The slow-moving cold front extended from there
southwestward across the central Gulf.  Another weak low should form
along the front over the northern Gulf today and ripple
northeastward along the boundary over the FL Panhandle and portions
of GA today, delaying eastward shift of the frontal zone to its
northeast until the low passes.  The low should reach eastern NC by
the end of the period.  The front to its south will shift slowly
eastward/southeastward, reaching eastern SC and the northwestern FL
Peninsula by 12Z.

...FL Panhandle/Southeastern GA...
Isolated strong-severe gusts are possible today into this evening in
a corridor of thunderstorms along/ahead of the front, from the
northeastern Gulf to parts of southeastern Georgia. 

As the mid/upper low ejects northeastward, largely abeam of this
region, peripheral height gradients should tighten enough to
strengthen both winds aloft and deep shear.  Simultaneously, mass
response to the distant passing wave will strengthen low-level mass
convergence and theta-e advection within a pre-existing belt from
the northeastern Gulf across the central/eastern FL Panhandle and
parts of southern GA.  Forecast soundings indicate boundary-layer
theta-e will be just enough to yield marginal but uninhibited MLCAPE
in the 300-800 J/kg range, amidst 40-50 kt effective-shear
magnitudes favorable for at least transient supercellular
characteristics.  Forecast hodographs show about 150-250 J/kg 0-1-km
SRH, with somewhat smaller effective SRH.  

The main limiting factors will include weak lapse rates (including
within the boundary layer), leading to modest buoyancy, and the
band-parallel nature of cell motion, contributing to messy
convective modes.  A strong preponderance of convective guidance
indicates more-westward axis of the convective corridor, especially
during the diurnal to early evening period when inflow-layer
buoyancy will be relatively maximized.  As such, the outlook area is
shifted slightly back toward the front.

..Edwards/Leitman.. 01/02/2021

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