SPC AC 041950

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0150 PM CST Sun Dec 04 2022

   Valid 042000Z - 051200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk for thunderstorms appears negligible across much of the
   U.S. this afternoon through tonight.

   ...20Z Update...

   ...Northern California...
   Orographic forcing along the western slopes of the northern Sierra
   Nevada might still contribute to isolated convective development
   vigorous enough to pose some risk for producing lightning.  However,
   in the wake of one perturbation pivoting around the periphery of the
   offshore low, mid-levels are in the process of gradually warming
   from southwest to northeast.  Even with insolation this afternoon,
   this will tend to limit further boundary-layer destabilization,
   which remains negligible at this time.  

   Otherwise, widely scattered convection capable of producing
   lightning remains possible near immediate coastal areas, mainly late
   this evening into the overnight hours with the approach of the
   remnant upstream cyclonic mid-level circulation.

   ...Southwest...
   A continued increase in low-level moisture may now be contributing
   to weak conditional boundary-layer instability across southeastern
   Arizona into adjacent portions of southwestern New Mexico.  However,
   VWP from Tucson indicates that low/mid-level wind fields have been
   gradually veering through the day, in the wake of one weak
   low-amplitude mid-level perturbation.  And model output generally
   suggests that forcing associated with any upstream perturbations
   will be weaker and largely confined to areas near or south of the
   international border late this afternoon into tonight.

   ..Kerr.. 12/04/2022

   .PREV DISCUSSION... /ISSUED 1010 AM CST Sun Dec 04 2022/

   ...Discussion...
   A mid/upper-level low west of the OR/CA border area will drift
   towards the coast through early Monday. Bands of ascent associated
   with embedded perturbations along with moderately steep lower-level
   lapse rates and weak buoyancy will support potential for isolated
   thunderstorms from the northern CA coast into the Sacramento Valley
   through tonight. Small hail is possible in low-topped convection
   along the immediate coast where buoyancy should be relatively
   greater, but the bulk of strong mid/upper speed shear will exist
   above the buoyancy profile owing to a pronounced inversion between
   500-350 mb.

   Weak elevated convection will remain possible across southeast AZ
   and far southwest NM, within a persistent subtropical moisture
   plume. Scant buoyancy might support sporadic lightning flashes.

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