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   TID: SBBSecho 3.28-Linux master/123f2d28a Jul 12 2025 GCC 12.2.0   
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   FOUS30 KWBC 200001   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   701 PM EST Fri Dec 19 2025   
      
   Day 1   
   Valid 01Z Sat Dec 20 2025 - 12Z Sat Dec 20 2025   
      
   The probability of rainfall exceeding flash flood guidance is less=20   
   than 5 percent.=20   
      
   Kleebauer   
      
      
   Day 2   
   Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF   
   NORTHERN CALIFORNIA|...   
      
   20Z Update: Continuity from the previous forecast was maintained as   
   12z model suite continued to project similar results from earlier   
   runs leading to little/no variability in the forecast. Expecting   
   areas within the northern Sierra Nevada to receive the most   
   appreciable precipitation given the trajectory of the IVT pulse and   
   persistent 850-600mb moisture feed with added upslope components   
   near the terrain. Greatest flood concerns likely in the adjacent   
   foothills on the windward side of the Sierra's. Highest probs for   
   >5" are across the I-80 corridor at the CA/NV border with the   
   highest terrain still likely to be snow, limiting the threat for   
   flash flooding for the period to more of a MRGL stance. Thus, kept   
   the previous forecast with no change.   
      
   Kleebauer   
      
   ..Previous Discussion..   
      
   A relative lull in moisture surges expected during the majority of   
   this period before the next stronger atmospheric river from the   
   Pacific reaches northern California towards the end of Day 2.   
   Although there may be some overlap in heavy rainfall, the axis of   
   the strongest on-shore winds and the greatest on-shore moisture   
   transport looks to be south of the axis of the previous event.   
      
   Precipitable water values increase to between 1.2 and 1.4 inches   
   along the northern California coast north of San Francisco south of   
   the Oregon/California border by early Saturday evening. Given such   
   high snow levels...there is not a lot of concern about   
   precipitation type until the moisture laden flow reaches the   
   northern end of the Sierra Nevada range (save for a few mountain   
   tops along the trajectory inland from the coast). The urban centers   
   between Sacramento to San Francisco will be more at play this   
   period lead   
      
   Campbell/Bann   
      
      
   Day 3   
   Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025   
      
   ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR   
   NORTHERN CALIFORNIA...   
      
   20Z Update: A more substantial IVT pulse will impact the northern   
   half of California come Sunday leading to overlap of impacted   
   areas from D2. Multi-day accumulations coupled with higher rates   
   will induce greater flash flood potential over a large area with   
   the greatest risk over the northern Sierra Nevada foothills.   
   Multi-day totals of 5-10" are still forecast in that region of the   
   state, enough to warrant a continuation of a SLGT risk with   
   probabilities approaching the higher end of the risk threshold as   
   of this time. There is an opportunity for an upgrade in the   
   following updates, so please stay tuned for the latest in this   
   evolving threat.   
      
   Kleebauer   
      
   ..Previous Discussion..   
      
   The Atmospheric River will strengthen over the northern half of   
   California resulting in scattered to widespread areas of enhanced   
   rainfall overlapping much of the same footprint from the Day 2   
   period. The latest guidance is suggesting daily accumulations of 3   
   to 7 inches, with 48 hour totals nearing 5 to 9 inches. A Slight   
   Risk is in effect from the West Coast to much of the Sierra Nevada   
   Range. There may be a need for an upgrade for portions of the   
   Sierra Nevada should guidance continue to increase over this area.   
      
   Campbell   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!8P93n7_w_uvpLcaK-QK66PLA-iZ52Yy0jgv5QnGHhksC=   
   RcvW6lm2B0cbskuOsinmMtWL9lkiSjL60Nczv3yUNmgFn5E$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!8P93n7_w_uvpLcaK-QK66PLA-iZ52Yy0jgv5QnGHhksC=   
   RcvW6lm2B0cbskuOsinmMtWL9lkiSjL60Nczv3yUKlzJxXk$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!8P93n7_w_uvpLcaK-QK66PLA-iZ52Yy0jgv5QnGHhksC=   
   RcvW6lm2B0cbskuOsinmMtWL9lkiSjL60Nczv3yUJqQZrok$=20   
      
   =3D =3D =3D   
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