SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0652 AM CST Thu Jan 07 2021

Valid 071300Z - 081200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms are possible over parts of the Southeast. 
The severe-weather potential inland appears very minimal.

...Synopsis...
In mid/upper levels, a fairly high-amplitude, complex and
progressive pattern will continue over the CONUS, with these as the
principal convectively pertinent features:
1.  A cyclone with 500-mb low now located over northern LA, and
forecast to move eastward to the southern Appalachians by the end of
the period.
2.  A strong, somewhat positively tilted shortwave trough -- now
evident in moisture-channel imagery near 140W, west of the Pacific
Coast.  This perturbation, which has been producing considerable
lightning over the north-central Pacific, should assume negative
tilt before reaching the coast around 12Z tomorrow morning, and will
be preceded by the risk for isolated thunderstorms in its plume of
DCVA/cooling aloft. 

The surface manifestation of the cyclone at 11Z was centered just
north of MLU, nearly vertically stacked with the mid/upper
circulation center.  An occluded front extended southeastward to
between the mouth of the Mississippi River and GPT, with warm front
southeastward over the east-central Gulf and cold front
southwestward across the west-central Gulf.  The surface low will
move eastward in cool air and weaken through the period, while a
"handoff" redevelopment process occurs with a second low forming off
the SC/GA coastline by around 06Z.  That will become the primary low
and move northeastward just off the SC/NC coastline through the rest
of the period.  The cold front will move eastward across the rest of
the northern/eastern Gulf, preceded by a convective band.  The cold
front should reach southeastern FL around 12Z. 

...FL...
The prefrontal band of convection, with isolated to scattered
embedded thunderstorms, should continue to move eastward across the
Gulf.  Analyses, modified RAOBs, forecast soundings and planar progs
all indicate that airmass recovery across coastal and inland areas
of the FL Panhandle will be insufficient north of the warm front to
support enough theta-e for surface-based effective inflow parcels. 
That, in turn, minimizes the potential for severe, given the
unsupportive thermodynamic profile for hail.  As such, any organized
severe wind or tornado threat should remain offshore, though strong
gusts may penetrate the stable boundary layer in the immediate
coastal Cape San Blas/AAF areas as the northern end of the MCS
passes overhead in a few hours.

Farther east, the band of convection should approach western FL late
this afternoon, likely reaching the coast in the PIE/SRQ area this
evening, then further south with time tonight.  While considerable
airmass modification is possible in the boundary layer over the
Gulf, stable layers and poor lapse rates aloft, combined with the
persistence of trajectories from a lower-theta-e air mass over the
peninsula, should keep all but very weak, perhaps mostly elevated
buoyancy from extending inland.  While favorable low-level
hodographs and 0-6-km shear are forecast as the line approaches, a
preponderance of guidance reasonably indicates that it should weaken
rapidly soon before reaching the coast (losing organized severe
threat) while penetrating the unfavorable thermodynamic profiles.

..Edwards/Leitman.. 01/07/2021

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