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   ACUS01 KWNS 241952   
   SWODY1   
   SPC AC 241950   
      
   Day 1 Convective Outlook   
   NWS Storm Prediction Center Norman OK   
   0150 PM CST Wed Dec 24 2025   
      
   Valid 242000Z - 251200Z   
      
   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF   
   COASTAL CALIFORNIA AND PORTIONS OF THE CENTRAL VALLEY...   
      
   ...SUMMARY...   
   An isolated risk for severe/damaging gusts and perhaps a brief   
   tornado will exist today into tonight along much of the California   
   Coast and portions of the Central Valley.   
      
   ...20Z Update...   
      
   ...Central/Northern California...   
   Water vapor imagery shows the shortwave trough already moving   
   inland. In the wake of this activity, visible satellite shows   
   potential for cloud cover to reduce within the Central Valley from   
   west to east. Some forecast soundings show destabilization is   
   possible by late afternoon. Given the southeast flow within the   
   Valley and strong flow aloft, a conditional threat for a marginal   
   supercell/brief tornado could develop.   
      
   Greater confidence exists with activity later in the evening into   
   Thursday morning associated with a secondary, stronger shortwave   
   trough. Another narrow band of convection is expected ahead of this   
   shortwave and will impact parts of the central/northern California   
   Coast and eventually parts of the Central Valley as well. Isolated   
   damaging winds and a brief tornado would be possible with this   
   activity.   
      
   ...Southern California...   
   A spatially limited threat for wind damage and a brief tornado will   
   exist for another few hours this afternoon. A low-topped band of   
   convection recently moved through much of the LA Basin and will   
   generally continue eastward. There may be a narrow sliver of   
   dewpoints near 60 F just east of this activity. Dewpoints closer to   
   San Diego are only in the upper 50s F, however. Strong wind shear at   
   low levels will maintain this marginal risk, though decreasing   
   buoyancy southward and inland should lead to a downward trend in   
   intensity.   
      
   ..Wendt.. 12/24/2025   
      
   .PREV DISCUSSION... /ISSUED 1025 AM CST Wed Dec 24 2025/   
      
   ...California...   
   A shallow band of pre-frontal convection may continue to pose a   
   threat for locally severe/damaging winds (especially across higher   
   terrain/ridgetops) and perhaps a brief tornado this morning across   
   parts of coastal southern CA. This activity is being supported by   
   strong low-level warm advection and large-scale ascent associated   
   with an enhanced mid/upper-level jet. Current expectations are for   
   this activity to continue moving eastward through the afternoon   
   across the remainder of coastal southern CA in a strongly sheared   
   environment. However, various NAM/RAP forecast soundings across this   
   area suggest that even with low 60s surface dewpoints and   
   modest/filtered daytime heating, the overall severe threat will   
   likely remain isolated due to poor lapse rates aloft and limited   
   boundary-layer instability. Reference Mesoscale Discussion 2269 for   
   more details on the near-term severe threat across southern CA.   
      
   Additional rounds of convection are expected later this evening and   
   overnight into early Thursday morning over portions of   
   northern/central CA, as multiple mid-level shortwave troughs   
   embedded within persistent large-scale upper troughing over the   
   eastern Pacific overspread these areas. One such shortwave trough is   
   forecast to advance over coastal central CA and vicinity around   
   25/00-06Z this evening, with cool temperatures aloft (less than -20C   
   at 500 mb) supporting weak MUCAPE. Both low-level and deep-layer   
   shear are expected to gradually increase this evening as the   
   shortwave trough approaches, with some updraft organization   
   possible. Strong to locally severe winds and a brief tornado or two   
   appear possible with this activity, but uncertainty is still   
   substantial whether sufficient instability will be present to   
   support surface-based thunderstorms.   
      
   A stronger mid-level shortwave trough will move east-northeastward   
   from the eastern Pacific and approach the northern CA Coast by 12Z   
   Thursday morning, along with a deepening surface low and attendant   
   cold front. A 70-80+ kt mid-level jet will accompany this shortwave   
   trough, along with a 50-60 kt south-southwesterly low-level jet. A   
   broken band of low-topped thunderstorms will likely develop in   
   association with this shortwave trough along/ahead of the front, and   
   overspread coastal portions of northern/central CA late tonight   
   through early Thursday morning (25/06-12Z). A strongly sheared   
   environment and weak but sufficient MLCAPE may exist to support at   
   least an isolated threat for severe/damaging winds and a tornado or   
   two as this activity spreads inland through the end of the period.   
   Still, the overall severe threat should be tempered by the lack of   
   stronger instability.   
      
   Finally, some chance for low-topped/mini supercells may exist late   
   this afternoon/evening across parts of the Central Valley of CA. If   
   these thunderstorms can develop and be sustained, they could pose a   
   threat for both damaging winds and a brief tornado. But, confidence   
   in this scenario occurring remains rather low.   
      
   $$   
      
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   --- SBBSecho 3.28-Linux   
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