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   PID: Synchronet 3.21a-Linux master/123f2d28a Jul 12 2025 GCC 12.2.0   
   TID: SBBSecho 3.28-Linux master/123f2d28a Jul 12 2025 GCC 12.2.0   
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   ACUS01 KWNS 231621   
   SWODY1   
   SPC AC 231620   
      
   Day 1 Convective Outlook   
   NWS Storm Prediction Center Norman OK   
   1020 AM CST Tue Dec 23 2025   
      
   Valid 231630Z - 241200Z   
      
   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF   
   COASTAL CALIFORNIA...   
      
   ...SUMMARY...   
   An isolated threat for severe/damaging gusts and perhaps a brief   
   tornado may develop late tonight/early Wednesday morning across   
   parts of coastal California.   
      
   ...California...   
   Within large-scale upper troughing over the eastern Pacific, an   
   embedded mid-level shortwave trough will move quickly eastward and   
   approach the CA Coast late tonight/early Wednesday morning. A   
   corresponding strengthening and increase in the flow through much of   
   the troposphere is anticipated late in the period, with a surface   
   low also forecast to deepen along/near the coast of northern CA. A   
   cold front attendant to this surface low will sweep quickly   
   eastward, and should be approaching/onshore across parts of coastal   
   northern/central CA by 12Z early Wednesday morning. Current   
   expectations are for the thermodynamic profile to remain mostly   
   saturated, with poor lapse rates generally limiting instability.   
   Even so, it appears that a gradual increase in low-level moisture   
   ahead of the cold front and slightly cooling mid-level temperatures   
   with the approach of the shortwave trough may support weak but   
   sufficient MUCAPE for an organized band of low-topped thunderstorms   
   late tonight.   
      
   Most guidance suggests this convection will not impact parts of   
   coastal CA until after 24/06Z, and there is still significant   
   uncertainty whether enough boundary-layer instability will be   
   present to support surface-based convection. There is also a signal   
   for pre-frontal convection in the low-level warm advection regime   
   across parts of central into coastal southern CA. Given the strength   
   of the low/mid-level flow forecast, and related strong   
   low-level/deep-layer shear, it appears that convectively enhanced   
   winds may be capable of reaching severe levels and producing damage   
   on an isolated basis even if instability remains minimal. A brief   
   tornado may also occur if convection can become truly surface based,   
   as effective SRH will be enhanced by a 50-70 kt southerly low-level   
   jet. Based on latest guidance trends, the Marginal Risk has been   
   expanded southward along the coast to include more of   
   central/southern CA. This isolated severe threat is expected to   
   continue beyond 12Z Wednesday into the Day 2 period.   
      
   ..Gleason/Thornton.. 12/23/2025   
      
   $$   
      
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