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   CAZ000-241614-   
      
   Mesoscale Precipitation Discussion 1271   
   NWS Weather Prediction Center College Park MD   
   515 AM EST Wed Dec 24 2025   
      
   Areas affected...portions of northern and central California   
      
   Concerning...Heavy rainfall...Flash flooding possible   
      
   Valid 241014Z - 241614Z   
      
   Summary...Areas of moderate to heavy rainfall will continue across   
   the discussion area through around 16Z/8a Pacific Time.   
   Flood/flash flood concerns could exist near sensitive ground   
   conditions (urban areas, burn scars, and near flooded water sheds).   
      
   Discussion...A strong area of low pressure was moving slowly   
   northeastward toward northwestern California near Eureka this   
   morning.  Ahead of this low, strong low-level flow (50-70 knots at   
   850mb) has developed across the discussion area that was advecting   
   a very moist airmass (1-1.2 inch PW values) through much of the   
   region.  Additionally, weak surface-based buoyancy near coastal   
   areas was noted per mesoanalyses.  The result of this pattern has   
   been several areas of moderate to heavy rainfall that has   
   exhibited an uptick in intensity over the past 1-2 hours.=20   
   Low-level flow against upslope areas has promoted localized   
   0.2-0.4 inch/hr rain rates, and these rates are expected to   
   continue (or perhaps increase into the 0.5 inch/hr range) through   
   the overnight and early morning hours. Additionally, heavier   
   convective development was noted just offshore of central coastal   
   areas.   
      
   These conditions are expected to continue through around 16Z or so   
   as a front sweeps eastward across the discussion area.  Ahead of   
   this front, areas of 0.25-0.5 inch/hr rain rates should continue   
   especially in terrain-favored areas.  Additionally, deeper   
   convective development approaching the central coastal ranges   
   should eventually impact urban areas in/near San Francisco over   
   the next 1-3 hours (through 13Z/5a Pacific) that could result in   
   urban flash flooding.  The ongoing threat of flooding and flash   
   flooding should gradually end from west to east, but should also   
   be most pronounced near 1) burn scars, 2) urban areas, and 3)   
   watersheds that have already experienced heavier rainfall over the   
   past week (upslope Sierra areas) that have wet soils and   
   anomalously strong streamflows.  Flash flooding is possible in   
   this scenario.   
      
   Cook   
      
   ...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=   
   DZ3fjg!90s1Les1NlfJHKgB8Pm6TKIGfAJycEhNlKEi1VyWTlT_l0v2PlSAcKXbKz2Mfl29lBSY=   
   abJ58tD_UjcTZnBlv5-zHDE$  for graphic product...   
      
   ATTN...WFO...EKA...HNX...LOX...MFR...MTR...REV...STO...   
      
   ATTN...RFC...RSA...NWC...   
      
   LAT...LON   41562233 41042137 40172081 38281986 37841933=20   
               37111911 37472000 37942098 37052106 35942083=20   
               35332100 36042177 37872288 40112426 40732426=20   
               41032393=20   
      
   =3D =3D =3D   
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