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   FOUS30 KWBC 160031   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   731 PM EST Mon Dec 15 2025   
      
   Day 1   
   Valid 01Z Tue Dec 16 2025 - 12Z Tue Dec 16 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF   
   WASHINGTON AND OREGON TODAY AND TONIGHT...   
      
   While IVT values continue to drop off across western=20   
   Washington/Oregon as the moisture axis pushes east and south, a   
   renewed surge of heavy rainfall is possible around the coast of WA   
   at the end of the period early Tuesday morning. Snow levels will=20   
   lower to near 3000 ft for the northern Cascades by 12Z Tuesday.   
      
   The Slight Risk was maintained given the wet antecedent conditions   
   and ongoing rainfall. The potential will exist for an additional 1   
   to 2 inches of rain through 12Z (maximum values), with hourly rain   
   amounts maximizing in the 0.25-0.50" range where weak instability=20   
   combines with strong left- exit jet stream forcing and continued=20   
   onshore flow. The main adjustment to the ERO areas was to remove   
   portions of their southern areas in OR where the 18z HREF no=20   
   longer supports heavy rains.   
      
   A surge of heavier rainfall impacting portions of the northern=20   
   Rockies early on with hourly rain amounts of 0.5"+ should weaken   
   overnight.=20   
      
   Roth   
      
      
   Day 2   
   Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF   
   THE PACIFIC NORTHWEST...   
      
   Maintained the previously issued Marginal Risk area from   
   Washington southward along the Cascades and the coastal ranges into   
   northwest California on Tuesday and early Wednesday. Latest   
   deterministic and ensemble guidance showed the highest QPF in the   
   complex terrain...rivaling the QPF on Day 1 in some places in   
   Washington. The main reason for holding with a Marginal Risk area   
   was due to the lowering snow-levels given post-frontal lowering of   
   heights/thickness values that result in snow. Even so...did expand   
   the eastern boundary of the Marginal Risk area a bit to the east in   
   Washington and a portion of nearby Oregon. While this resulted in   
   some additional overlap with snow areas...the idea was to capture   
   some of the higher QPF amounts from regions where (presumably) the   
   precipitation started as rain and then transitioned to snow. Tried   
   to avoid overlap with the Winter Weather Desk snow amounts of 6   
   inches or greater.   
      
   The overall synoptic pattern continued to show the deepest moisture   
   and broadest coverage of rainfall arriving in association with the   
   surface cold front around 17/00Z and the diminishing QPF as the   
   area gets whisked eastward.   
      
   Cook/Bann   
      
   Day 3   
   Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025   
      
   ...THE MARGINAL RISK OF EXCESSIVE RAINFALL AREA LINGERS OVER PARTS   
   OF THE PACIFIC NORTHWEST. ON WEDNESDAY...   
      
   There should be a relative lull in activity across parts of   
   Washington...Oregon and northern California in the wake of a system   
   on Tuesday into early Wednesday. Even though there may still be   
   some rainfall that lingers into Day 3...the Marginal Risk area was   
   maintained in deference to the approach of the next and seemingly   
   stronger AR on Day 4 and to account for the possibility that the   
   guidance could be too slow with the onset of rainfall with this   
   system. Refer to guidance from the WPC Medium Range Desk for   
   additional info. Even if the rainfall associated with the next   
   system does not arrive prior to 12Z Thursday as shown by the   
   models...any lingering rainfall still has the potential for be   
   impactful in the most hydrologically sensitive areas.   
      
   Cook/Bann   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!-otCM6UTTMIpZelTUFFMs4gE4dTzxJyZzFgGZ6glWCWF=   
   BO9yAHV9ZZW-Y-oLbsaSKq8Vk9dxdoZsjDZAgqIBZ2oktpU$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!-otCM6UTTMIpZelTUFFMs4gE4dTzxJyZzFgGZ6glWCWF=   
   BO9yAHV9ZZW-Y-oLbsaSKq8Vk9dxdoZsjDZAgqIBeSvYnis$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!-otCM6UTTMIpZelTUFFMs4gE4dTzxJyZzFgGZ6glWCWF=   
   BO9yAHV9ZZW-Y-oLbsaSKq8Vk9dxdoZsjDZAgqIBstkXtjM$=20   
      
   =3D =3D =3D   
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