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   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   717 PM EST Sat Dec 6 2025   
      
   Day 1   
   Valid 01Z Sun Dec 07 2025 - 12Z Sun Dec 07 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   Bann   
      
      
   Day 2   
   Valid 12Z Sun Dec 07 2025 - 12Z Mon Dec 08 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   Orrison   
      
      
   Day 3   
   Valid 12Z Mon Dec 08 2025 - 12Z Tue Dec 09 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE   
   PACIFIC NORTHWEST...   
      
   The 06Z/12Z model guidance suggests a slightly more suppressed   
   axis of greater IVT magnitudes impacting the Pacific Northwest on   
   the front end of the upcoming atmospheric event for the region. The   
   NAM/GFS/ECMWF solutions though still support very strong warm air   
   advection with enhanced IVT magnitudes reaching 800 to 1000+ kg/m/s   
   across the western WA and northwest OR coastal ranges with the   
   first wave that arrives in the 12Z/08 to 00Z/09 time frame. As   
   strong surface low pressure and associated shortwave/jet energy   
   crashes into British Columbia, the southern flank of the attendant   
   cold front will slow as it is crosses WA state and this should   
   allow for a relatively longer persistence of greater IVT values   
   across southern WA and northern OR going into the 00Z to 12Z/09   
   time period.   
      
   The deeper layer moisture fetch will have a trans-Pacific origin   
   that extends down to just west of Hawaii, and satellite data would   
   suggest a likelihood for tropical and subtropical moisture feeds   
   into this atmospheric river event which will drive very efficient   
   and high rainfall rates that may reach well into the 0.50" to   
   1"/hour range near the periods of max IVT and deeper layer ascent. The   
   coastal ranges in particular across southwest WA and northwest OR   
   along with the west-facing slopes of the Cascades farther inland   
   should see enhanced rainfall totals that reach as high as 4 to 6+   
   inches which will heavily aided by deep layer orthogonal flow   
   relative to the terrain.   
      
   Given the subtle southward shift in the axis of greater IVT   
   magnitudes and overall higher rainfall rates/totals for the   
   northern parts of the Olympic Peninsula and the northern WA   
   Cascades, the Slight Risk for this area was trimmed just a tad,   
   with very little to no change elsewhere. This is consistent with   
   the overall 06Z/12Z guidance QPF footprint. Regardless, the wet   
   antecedent conditions and heavy rainfall totals are expected to   
   drive concerns for locally enhanced areal and riverine flooding,   
   with urban flooding also likely to become a concern. A threat for   
   landslides will exist, especially toward the end of the period and   
   thereafter as additional upstream atmospheric river   
   activity/moisture transport arrives with more heavy rainfall.   
      
   Orrison   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!8DIcwer1Y2soXXxJddbbu_flcMRaSTkMzv8JHoK5W_bW=   
   h5EXiOh6Zc8qgrNNR9yForPr-w8BOcahCqFrvfrvDBOlAmc$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!8DIcwer1Y2soXXxJddbbu_flcMRaSTkMzv8JHoK5W_bW=   
   h5EXiOh6Zc8qgrNNR9yForPr-w8BOcahCqFrvfrvBDO0QMc$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!8DIcwer1Y2soXXxJddbbu_flcMRaSTkMzv8JHoK5W_bW=   
   h5EXiOh6Zc8qgrNNR9yForPr-w8BOcahCqFrvfrvujmBBU4$=20   
      
   =3D =3D =3D   
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