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   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   241 PM EST Sun Dec 14 2025   
      
   Day 1   
   Valid 16Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF   
   WESTERN WASHINGTON...   
      
   Maintained the Marginal Risk area over parts of the Olympic and   
   northern Cascade Ranges in Washington as the next real push of   
   moisture approaches later tonight into the early morning hours of   
   Monday. Any rainfall in Washington before then should be light and   
   on the periphery of a rain area directed on-shore north of the   
   international border. By 15/00Z...precipitable water values should   
   be approaching 1 inch along the coast as 850 mb winds approach the   
   Washington/Oregon coast. Initially the 850 mb winds should have   
   more of a southerly than a westerly component...but eventually they   
   do take on a more orthogonal component to the Washington coast   
   ranges and Olympics. That is when the best chance for any excessive   
   rainfall is expected. Model guidance remains in the 0.5 to 0.75   
   inch range with locally 1.5 inches of precipitation focused in the   
   terrain. While these amounts are pretty modest for this part of the   
   country...the area remains hydrologically sensitive given the   
   recent heavy to excessive rainfall event from earlier in the week   
   and even this amount of rainfall could result in renewed hydrologic   
   concerns.   
      
   Cook/Bann   
      
   Day 2   
   Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER WESTERN   
   WASHINGTON AND NORTHWEST OREGON...   
      
   ...2000 UTC Update...   
   Trimmed a little bit of the Slight Risk area on the western slopes   
   of the Cascades (above 3500 ft) due to the lowering snow levels=20   
   with time during the period. Otherwise, also made minor adjustments   
   to the Marginal Risk area over northeast WA-northern ID-northwest   
   MT, based on the new (12Z) guidance QPFs and HREF exceedance   
   probabilities.   
      
   Hurley   
      
   ...Previous discussion...   
   Areal coverage of rainfall expands and rain rates increase on=20   
   Monday as a well defined atmospheric river continues to direct=20   
   abundant moisture into the Washington coastal ranges and Cascades.=20   
   IVT values approaching 800 is currently forecast along or near the=20   
   Washington coast as the Day 2 period begins...then weakens somewhat   
   as the axis progresses southward into Oregon. Given antecedent=20   
   conditions from the excessive rainfall event from earlier in the=20   
   week plus whatever falls on in the Day 1 period...the concern is=20   
   for renewed flooding potential in addition to worsening any on-=20   
   going flooding. Given how water-logged the soils have been...the=20   
   potential is there for additional landslides or mudslides. Saw=20   
   little reason to modify the Slight risk area too much...but=20   
   continued the idea from yesterday in shrinking the Slight risk area   
   to minimize the overlap with heavy snow areas (especially in the=20   
   northern part of the Cascades as depicted by the WPC Winter Weather   
   desk). That being said...the overall forecast reasoning changed=20   
   little given the consistent magnitude of the IVT/precipitable water   
   values and QPF forecast by the global models. The focus of the=20   
   heavy rainfall should gradually shift southward into an area that=20   
   did not receive as much rainfall from the previous atmospheric=20   
   river.   
      
   Introduced a Marginal Risk area mainly focused over the Idaho   
   panhandle and a small portion of neighboring eastern Washington   
   mainly for later in the period. The Atmospheric River moisture   
   plume will be spreading increasing amounts of moisture into the   
   eastern part of Washington and northern Idaho. Deterministic QPF   
   approaching an inch is forecast for areas that had hydrologic   
   problems recently and concern is for additional problems.   
      
   Bann   
      
   Day 3   
   Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL LINGERING OVER   
   PARTS OF THE PACIFIC NORTHWEST INTO FAR NORTHWEST CALIFORNIA...   
      
   ...2000 UTC Update...   
   Based on the latest (12Z) model QPFs and trends (lower ensemble=20   
   means), along with the lowering snow levels, have removed the=20   
   Marginal Risk area that was in play across northern ID into   
   northwest MT). QPFs across the Sierra meanwhile average between   
   0.5-1.0" during the 24 hr period; given this along with the absence   
   of any elevated instability, have removed the Marginal area that   
   was in effect over the northern Sierra.=20   
      
   Hurley   
      
   ...Previous Discussion...   
   Precipitation lingers from Washington southward along the Cascades   
   and the coastal ranges into northwest California on Tuesday and=20   
   into the early morning hours on Wednesday. With much of that=20   
   falling post-frontal and the heavier precipitation amounts falling=20   
   in the form of snow in the northern Cascades...will maintain the=20   
   Marginal Risk area for the time. Once again the main adjustments to   
   the outlook areas were to limit the overlap of excessive rainfall=20   
   with heavy areas mainly in Washington.=20   
      
   Bann   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!5yNkxCb8_S9oSxzEgKFF_kaPOuaQpTkqelgWNjRux00H=   
   I4trA3hRUQejMzBLt2TLBMb0F_UoK6zKNyueAVb5PaMqkXU$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!5yNkxCb8_S9oSxzEgKFF_kaPOuaQpTkqelgWNjRux00H=   
   I4trA3hRUQejMzBLt2TLBMb0F_UoK6zKNyueAVb5KaM9wlw$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!5yNkxCb8_S9oSxzEgKFF_kaPOuaQpTkqelgWNjRux00H=   
   I4trA3hRUQejMzBLt2TLBMb0F_UoK6zKNyueAVb5U5Ko5jA$=20   
      
   =3D =3D =3D   
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