FOUS30 KWBC 110734 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 234 AM EST Thu Dec 11 2025 Day 1 Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN MONTANA... ...Western Washington... The multi-day atmospheric river (A.R.) event of much of the past week will finally conclude across western Washington today. Northward-building ridging both at the surface and at the jet stream level will push the remaining moisture plume from the already weakening A.R. north into Canada, leaving much of western Washington with residual moisture from the weakening and drying westerly flow. Heavy rain is ongoing across much of western Washington, roughly from Tacoma's latitude north. CAMS guidance shows the rain should progress a bit further south over the next few hours as a cold front offshore pushes inland. After that it will stall out, and the rain rates will diminish in place. Thus, the heaviest rain over the area for this period will be over the next few hours this morning, followed by tapering through the afternoon and into tonight. Record and in some areas historic flooding is ongoing from the multiple consecutive days of heavy rain with the A.R. Comparatively speaking, today's rainfall totals won't be anything near previous days' totals. Nevertheless, the ongoing moderate to heavy rain across northern Washington will continue to keep river levels up, or even rising through the morning until rain rates can diminish a bit. The Marginal Risk therefore is a compromise between the ongoing highly impactful flooding and steady rain expected to continue into the morning, and the fact that the second half to two-thirds of the period should feature only light rain with the conclusion of the A.R. event. That is to say that for all of the Marginal Risk area, ongoing major flooding will continue through today despite the diminishing rain, and precautions and avoidance of flooded areas should be taken. The Marginal Risk may be able to be dropped with the evening update. ...Northern Idaho and Far Western Montana... Continuous steady rain is expected to continue through the entire period across the Marginal Risk area in northern Idaho and far western Montana today. While the A.R. is ending out west, it will take longer to do so for Idaho and Montana as the forcings supporting the steady rain will persist throughout the period. Despite the heavy rain on the order of 1-2 inches over the past 24 hours, in addition to the multiple inches that fell in this same area in days prior, impacts from flooding have been minimal across this region. Now, with today being the tail end of the A.R., it's probable that if flooding impacts were to occur, they would happen today. Thus, balancing these two offsetting factors, and in coordination with OTX/Spokane, WA forecast office, the inherited Slight Risk for this region was downgraded. Isolated instances of flash flooding are still possible given the expectation of another 24 hours or so of steady rain into the west facing slopes of the Bitterroots. However, given the lack of impacts thus far, it seems probable that the same trends will continue through tonight. Steady precipitation should taper off soon after the 12Z Friday end time for the period, as an Arctic air mass further east also works to transition any remaining rain over to snow. Wegman Day 2 Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman 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