SPC AC 071241

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0641 AM CST Tue Dec 07 2021

   Valid 071300Z - 081200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Severe thunderstorms are not forecast across the contiguous United
   States today and tonight.

   ...Synopsis/Discussion...
   In mid/upper levels, a split-flow pattern will exist near the West
   Coast, related to a shortwave trough and compact cyclone digging
   south-southeastward, just offshore from CA.  Ridging to its north
   will move quickly eastward from the Pacific Northwest to the central
   Rockies and northern High Plains.  Farther east, broadly cyclonic
   flow covers most of the country east of the Rockies.  A series of
   shortwave perturbations at varying latitudes will help to maintain
   that cyclonic-flow field from the Mississippi Valley eastward
   through tonight, south of a 500-mb low moving eastward along the
   southern shore of Hudson Bay.  A southern-stream perturbation --
   apparent in moisture-channel imagery over Coahuila -- will maintain
   positive tilt as it moves eastward to coastal LA and the
   northwestern Gulf by 00Z.  By 12Z, this feature should weaken and
   reach northern FL.

   At the surface, a cold front was drawn at 11Z from offshore of the
   Carolinas southwestward to near the southeastern corner of GA, to
   near AAF, west-southwestward to a weak low south of GLS and east of
   CRP, then south-southwestward over northeastern MX.  This front
   should stall today over the northern FL/southern GA area and near
   the central/eastern coastline of LA, and offshore from the
   lower/middle TX coast, with some mesoscale oscillations tonight. 
   The existing weak frontal-wave low, or a new one ahead of the
   southern-stream perturbation, may ripple northeastward from near the
   mouth of the Mississippi to southern GA overnight.  This feature
   will encounter a progressively cooler and more-stable near-surface
   layer inland, over which the bulk of convection should develop
   tonight.

   Overland thunderstorm coverage in the associated regime of elevated
   warm advection, moisture transport and low-level convergence should
   be isolated today and increase after about 06Z.  Forecast soundings
   suggest weak deep-layer lapse rates will limit magnitude and depth
   of buoyancy, keeping MUCAPE in the 500-800 J/kg range near the coast
   and under 500 J/kg over most areas inland.  Forecast soundings
   indicate that, despite strong upper-level winds, shallowness of
   buoyancy (EL below most of the greatest upper flow) should keep
   effective-shear magnitudes under 35 kt.

   ..Edwards.. 12/07/2021

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z