SPC AC 091244

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0644 AM CST Thu Dec 09 2021

   Valid 091300Z - 101200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Severe thunderstorms are not expected today.

   ...Synopsis/Discussion...
   In mid/upper levels, a pattern transition is underway toward one
   characterized by western CONUS mean troughing, as a series of
   northern- and southern-stream shortwaves move inland and become more
   phased.  The three primary perturbations involved in this process
   are evident in moisture-channel imagery west of Baja, just offshore
   from northern CA/southwestern OR, and west of WA.  By 00Z, they
   should be located respectively from northern Baja southwestward,
   from the southern Sierra across the SBA area, and over the inland
   Pacific Northwest.  Until then, superposition of cooling midlevels
   and the moist marine layer near the coast should yield modestly
   buoyant profiles extending into icing layers suitable for isolated
   lightning generation.

   By 12Z tomorrow, the southern two features should accelerate
   eastward to northeastward and weaken, amidst height falls and
   intensifying cyclonic flow related to the strengthening northern
   perturbation, as the latter reaches the northern Great Basin.  The
   broader synoptic trough then will be centered from SK across UT and
   AZ to northern Baja.  Convection in relatively shallow buoyancy
   (below 500 mb and in layers generally warmer than -20 C) may develop
   over parts of AZ ahead of these perturbations.  However, thunder
   potential appears too isolated and conditional for a 10% areal
   outlook. 

   At the surface, 11Z analysis showed a cold front over Atlantic
   waters east of central FL, becoming quasistationary over central FL
   and the northeastern Gulf, when a warm front over shelf waters south
   of BVE, to southeast/south-central TX.  This front should weaken and
   return northward as a diffuse warm front into parts of the Southeast
   and southern Plains through the period.  A broad zone of elevated,
   low-level warm advection north of the front, along with sufficient
   moisture advection/transport to enable deep buoyancy, will lead to
   the inland spread of potential for isolated thunderstorms across
   parts of the South from midday today into tonight.  Meanwhile,
   cyclogenesis will occur over CO.  By 12Z tomorrow, a deepening
   surface low should be located over western KS, with warm front
   eastward over central MO to near the IL/KY border.  However,
   associated deep-convective potential with this system should wait
   until a much more robust moisture return through the warm sector on
   day 2.

   ..Edwards.. 12/09/2021

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