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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