Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 426 PM EDT Sun Oct 06 2019 Valid 00Z Mon Oct 07 2019 - 00Z Thu Oct 10 2019 Day 1... The probability of receiving at least 4-inches of snow and/or 0.25-inch of ice below 7500 feet is less than 10 percent. Day 2-3... ...Pacific Northwest/Northern Rockies and High Plains... An amplifying upper trough and associated cold front are expected to sweep south across the northwestern U.S. Tuesday and Wednesday, bringing sharply colder air and another strong early-season winter storm to portions of the northern Rockies. As the trough digs into the Pacific Northwest on Tuesday, snow levels are forecast to drop to around 3000 ft, with some significant accumulations possible for areas above 8000 ft in the northern Cascades. By late Tuesday, snows will begin to develop and spread south along the northern Rockies. Strong low to mid-level frontogenesis/upslope flow will support heavy snows developing across the northwestern Montana ranges, with locally heavy accumulations expected within Glacier National Park by Tuesday evening. As the upper trough continues to amplify and its associated frontal band pushes farther southeast, snows will continue to develop and spread south and east across Montana through Tuesday night into Wednesday. With snow levels continuing to drop through the day, a surface wave developing along the front over southeastern Montana is expected to enhance the low level inflow and increase the potential for locally heavy amounts across the central to southwestern Montana ranges. WPC Day 3 probabilities (ending 00Z Thu) show a High Risk for accumulations of 8-inches or more across the higher elevations of the Big Snowy and Little Belt Mountains south into the Absaroka and Madison ranges. Lighter amounts are expected to spread northeast along an axis of strong low to mid-level frontogenesis extending from central into northeastern Montana and northwestern North Dakota, where WPC Day 3 probabilities indicate at least a Slight Risk for accumulations of 4-inches or more. Pereira