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   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   1059 AM EST Sun Dec 21 2025   
      
   Day 1   
   Valid 16Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025   
      
   ...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR   
   PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...   
      
   ...16Z update...   
      
   Moderate to heavy rain was ongoing across northern California this   
   morning with the atmospheric river oriented southwest to northeast   
   into and across the coastline. Through 15Z, 24 hour localized=20   
   totals of 3 to 5 inches have been reported across the King Range of   
   southern Humboldt County and 3 to 6+ inches across the northern=20   
   Sierra Nevada. IVT values peaking near 800 kg/m/s were estimated=20   
   this morning at 15Z in/around Mendocino County with slow but steady   
   southward translation and weakening forecast over the next 12-24=20   
   hours. Additional 24 hour totals of 4 to 8 inches (perhaps local=20   
   maxima near 10 inches) are anticipated for the northern Sierra=20   
   Nevada with 2 to 4 inches (local 5+) for the Coastal Ranges from=20   
   Cape Mendocino to Monterey Bay. Valley locations will receive much   
   less, but higher than the 0 to 0.1 inch forecast values depicted by   
   the hires guidance.   
      
   A few landslides/debris flows have already been reported and   
   additional flood related impacts will be likely within regions=20   
   that receive additional high rainfall totals with peak hourly rates   
   over 0.5 inches at times, locally up to 1 inch in an hour.   
      
   Otto   
      
   ...previous discussion follows...   
      
      
   A significant surge in Pacific moisture will overspread much of   
   northern California during this period within the reinforced   
   atmospheric river and will lead to widespread heavy rainfall.   
   Within the Moderate Risk area over the portions of the Sierra   
   Nevada range there are several hours of >50% HREF probabilities of   
   at least 0.50"/hr rates between 12Z Sun and 03Z Mon, while HREF   
   probabilities of >8" within the 24 hour Day 2 period are >60% for   
   much of the area. There will likely be many areas where flash   
   flooding may arise, along with sloughing and debris flows. For   
   additional details please refer to WPC MPD #1267.   
      
   Campbell/Hurley   
      
      
   Day 2   
   Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025   
      
   ...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR   
   PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...   
      
   The atmospheric river will move southward during this period as   
   will the heavy rainfall footprint spread further down the Sierra   
   Nevada Range and along the coastline. Much of the same area of the   
   Sierra Nevada is projected to receive additional 2-3 inches over   
   the water logged area from Day 1. A Moderate Risk was maintained   
   along with expanding a touch to the south. Multi-day accumulations   
   will likely be well into the double digits by this time and leading   
   to several instances of rapid runoff, sloughing and debris flows   
   along the foothills/adjacent locations.   
      
   Campbell   
      
      
   Day 3   
   Valid 12Z Tue Dec 23 2025 - 12Z Wed Dec 24 2025   
      
   ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR   
   PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA, ALONG THE   
   COASTLINE OF CENTRAL CALIFORNIA AND FOR SOUTHERN CALIFORNIA....   
      
   Another reinforcing surge of Pacific moisture will be moving   
   onshore northern California while the southward moving impulse will   
   lead to a rapid uptick in rainfall in southern California. The   
   latest guidance is depicting another 1 to 4 inches for northern and   
   central California and 2 to 4+ for the higher terrain of southern   
   California. A Slight Risk covers much of the coastline from central   
   to northern California and into the northern part of the Sierra   
   Nevada. Additionally, another Slight Risk is in place for the   
   favored terrain of southern California.   
      
   Campbell   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!4wDDyzwZg3qev0xieMt207QFE3qrSTJtWCW-B2ZHMtUV=   
   Q3I6N5E81ay7Y3rElHnw3glBMElyCLn5NRoeJ-eX1OgDb0U$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!4wDDyzwZg3qev0xieMt207QFE3qrSTJtWCW-B2ZHMtUV=   
   Q3I6N5E81ay7Y3rElHnw3glBMElyCLn5NRoeJ-eXmZ6ZgUA$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!4wDDyzwZg3qev0xieMt207QFE3qrSTJtWCW-B2ZHMtUV=   
   Q3I6N5E81ay7Y3rElHnw3glBMElyCLn5NRoeJ-eXD2cT0mA$=20   
      
   =3D =3D =3D   
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