FOUS30 KWBC 140821 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 321 AM EST Sun Dec 14 2025 Day 1 Valid 12Z 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. 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... Areal coverage of rainfall expands and rain rates increase on Monday as a well defined atmospheric river continues to direct abundant moisture into the Washington coastal ranges and Cascades. IVT values approaching 800 is currently forecast along or near the Washington coast as the Day 2 period begins...then weakens somewhat as the axis progresses southward into Oregon. Given antecedent conditions from the excessive rainfall event from earlier in the week plus whatever falls on in the Day 1 period...the concern is for renewed flooding potential in addition to worsening any on- going flooding. Given how water-logged the soils have been...the potential is there for additional landslides or mudslides. Saw little reason to modify the Slight risk area too much...but continued the idea from yesterday in shrinking the Slight risk area to minimize the overlap with heavy snow areas (especially in the northern part of the Cascades as depicted by the WPC Winter Weather desk). That being said...the overall forecast reasoning changed little given the consistent magnitude of the IVT/precipitable water values and QPF forecast by the global models. The focus of the heavy rainfall should gradually shift southward into an area that did not receive as much rainfall from the previous atmospheric 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... Precipitation lingers from Washington southward along the Cascades and the coastal ranges into northwest California on Tuesday and into the early morning hours on Wednesday. With much of that falling post-frontal and the heavier precipitation amounts falling in the form of snow in the northern Cascades...will maintain the Marginal Risk area for the time. Once again the main adjustments to the outlook areas were to limit the overlap of excessive rainfall with heavy areas mainly in Washington. The complex terrain of northern Idaho and northwest MT made it difficult to avoid overlapping but the idea is for any excessive rainfall to occur at lower elevation locations in light of lowering thickness vales/snow levels. Bann Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt