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   FOUS30 KWBC 170823   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   323 AM EST Wed Dec 17 2025   
      
   Day 1   
   Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.=20   
      
   Bann   
      
   Day 2   
   Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER WESTERN   
   OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND   
   CALIFORNIA...   
      
   The next in a series of atmospheric rivers will arrive along the   
   west coast of North America early on Thursday. The threat for=20   
   significant rainfall remains elevated across the western half of=20   
   Oregon with a focal point for maximum precipitation centered over=20   
   the southern Cascades and the adjacent valleys on either   
   side...although a subtle northward shift was noted in the 17/00Z   
   guidance. The key in this threat is the projected "spillover" of=20   
   heavier precip to the leeward side of the Cascades due to a=20   
   pronounced 700mb jet from the Pacific leading to significant=20   
   Pacific moisture being drawn inland. This is the area where ARI=20   
   forecasts are hovering between the 25-100 year exceedance=20   
   intervals, matching the output from the past several model runs and   
   deterministic QPF from WPC. As a result, Day 2 excessive rainfall   
   outlook was expanded the Slight Risk northward across portions of   
   the Washington Cascades in response to the subtle northward shift   
   noted earlier...with little reason to expand any farther eastward.   
      
   Bann   
      
   Day 3   
   Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER=20   
   PORTIONS OF NORTHWEST CALIFORNIA...   
      
   The atmospheric river that came on-shore on Thursday will be on-   
   going across much of Oregon as the Day 3 period begins at 12Z on   
   Friday. A well-defined plume of deep layer moisture will continue   
   to be drawn from the eastern North Pacific Ocean eastward into   
   parts of the northern Great Basin by fast westerly flow aloft. IVT   
   values at or above 600 units is forecast to cover much of Oregon=20   
   initially...then weaken as the axis of the moisture plume and   
   associated precipitation settles into northern California. The   
   system looks to have trended a bit more progressive on Friday than   
   suggested by earlier runs...so some of the QPF values over Oregon   
   and northwest California have come down a bit. Even so...opted to   
   maintain a large amount of continuity with Slight Risk area over   
   northwest California and a portion of adjacent southwest Oregon   
   given the possibility of further wobbles in the placement of the   
   axis or variations in model QPF. As it stands...the area average=20   
   precipitation amounts are currently in the range of 1-2 inches=20   
   with localized higher amounts maxima in the terrain.   
      
   Bann   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!99E-iz9V5MYM72IYJu3Tk0zY0uw23YmCltPqA4VKBowd=   
   lWeNGN2Lvnew3yKA47WyYjJiFoG508eayEKfTNLFF-FZhhg$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!99E-iz9V5MYM72IYJu3Tk0zY0uw23YmCltPqA4VKBowd=   
   lWeNGN2Lvnew3yKA47WyYjJiFoG508eayEKfTNLFKfFfDlU$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!99E-iz9V5MYM72IYJu3Tk0zY0uw23YmCltPqA4VKBowd=   
   lWeNGN2Lvnew3yKA47WyYjJiFoG508eayEKfTNLF4TeqL_8$=20   
      
   =3D =3D =3D   
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