


Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
627 FOUS11 KWBC 120744 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 344 AM EDT Sun Oct 12 2025 Valid 12Z Sun Oct 12 2025 - 12Z Wed Oct 15 2025 ...Northern Rockies & Pacific Northwest... Days 1-2... By the start of the forecast period (12Z Sunday), a potent shortwave upper-level trough will be quickly exiting the northern Rockies along with an associated strong surface low pushing northeastward into southern Saskatchewan. Gradually increasing heights are then expected across the northern Rockies through the remainder of the day 1 forecast period, while a rapidly deepening upper low drops southward along the coast of the Pacific Northwest. At the surface, cold Canadian high pressure nosing southward into northwest MT will allow for favorable upslope ascent in this region, with general low-to-mid level convergence extending across northern WA and ID along a sinking frontal boundary. This will favor light to moderate snow across areas above 5,000ft, but with snow levels dropping enough for flakes to reach into parts of the MT Front Range and adjacent High Plains at times on Sunday night. For the Cascades of WA and OR, snowfall will be tied to the dropping upper low as snow levels start around 4,000-5,000ft (lowest in the northern WA Cascades) before eventually lowering to around 3,000ft in WA and 4,500ft in OR on day 2. WPC probabilities show moderate-to-high probabilities (50-80%) for storm-total snowfall amounts >8" from the Cascades on eastward into the northern Idaho Panhandle to the Lewis Range of Montana. Mountains within and around Glacier Nat`l Park even have moderate chances (40-60%) for over 12" of snow, particularly above 7,000ft. The WSSI shows mostly Minor Impacts due to potentially slick travel conditions, while some passes in Montana and Glacier Nat`l Park may contend with Moderate Impacts that could result in road closures. ...California... Days 2-3... ...First heavy snowfall event of the season set to impact the Sierra Nevada beginning Monday night... By day 2, the upper low dropping southward along the West Coast is forecast to deepen into a robust 500mb low off the northern California coast. This sudden amplification of the 500mb trough (18Z ECMWF shows 500mb heights below the 0.5 climatological percentile and nearing October records off the California coast Monday afternoon) is due to an impressive anti- cyclonic weak break over British Columbia. The dramatic height falls and modest 500-700mb CAA aloft will support lowering snow levels down to around 6000-6500ft through the Siskiyou and the Sierra Nevada starting Monday and continuing into the first half of next week. All guidance also shows a healthy IVT topping 400 kg/m/s helping to direct plenty of Pacific moisture at the mountain ranges. Snow arrives over the northern California mountains on Monday with the heaviest snowfall occurring Monday night into Tuesday over the Sierra Nevada. Guidance has come in snowier over the past 12-24 hours, and given the lack of deep, cold air aloft, snow is likely to be a heavy/wet snowfall along the Sierra Nevada. This could raise concerns for potential impacts to trees and infrastructure given this is the first significant mountain snowfall in the Sierra Nevada this season. WPC probabilities show moderate-to-high chances (50-80%) for at least 24" of snowfall throughout the central Sierra Nevada (above 8,000 feet) by Wednesday morning, with maximum amounts up to 36" possible. Latest WSSI-P shows high chances (70-99%) for Moderate Impacts along the central Sierra Nevada with the Snow Amount, Snow Load, and Snow Rate impacts being the main concerns for the first significant snow of the season. Current WSSI also highlights Major to Extreme Impacts, which would imply difficult to impossible travel at times between Monday night and much of the day on Tuesday, including for many major passes. The probability of significant freezing rain across CONUS is less than 10 percent. Snell/Mullinax $$