SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0641 AM CST Thu Dec 03 2020

Valid 031300Z - 041200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk for severe thunderstorms appears negligible across the U.S.
today through tonight.

...Synopsis/Discussion...
As a substantial mid/upper-level synoptic cyclone moves northward
across northern QC to Baffin Island, strong cyclonic flow will be
maintained across the Great Lakes by a series of shortwave troughs
digging southeastward from western Hudson Bay across the upper Great
Lakes and northern ON.  Meanwhile, a closed cyclone initially
centered over OK will move slowly east-northeastward across the
Ozarks, gradually detaching from the AZ/NM portion of a trailing
trough.  By 12Z tomorrow, the AZ/NM vorticity lobe at 500 mb should
evolve into a distinct cyclone centered over eastern Sonora or
northwestern Chihuahua.

At the surface, 11Z analysis showed weak lows over southeastern OK
and the northwestern Gulf south of LCH, connected by a trough.  A
cold front was drawn from the Gulf low southwestward to east-central
MX.  A diffuse warm front arched eastward and southeastward from the
low over the Gulf.  The Gulf low should move north-northeastward and
inland through the period, reaching western or northern AL by 12Z,
with the trailing trough/cold front south-southwestward to near the
Mississippi River mouth and central/southwestern Gulf.  

A plume of convection, with isolated to widely scattered embedded
thunderstorms, will occupy part of a warm-advection conveyor near
the surface trough/front and shift eastward across the outlook area.
This activity largely will be elevated above a relatively stable
near-surface layer.  Weak surface-based buoyancy may reach immediate
coastal areas of southeastern LA, though an extensive area of precip
over the Gulf should preclude substantial destabilization inland. 
The best-organized convection will remain over the open Gulf, with
access to more-complete inflow-layer airmass modification and richer
theta-e.  Some marginally favorable boundary-layer parcels may reach
shore near the MOB-PNS corridor late in the period (after about
09Z), if additional Gulf convection does not stabilize upstream
trajectories.  However, at this time, overland severe potential
appears too meager to introduce any unconditional probabilities.

..Edwards.. 12/03/2020

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