Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 415 PM EDT Fri Nov 02 2018 Valid 00Z Sat Nov 03 2018 - 00Z Tue Nov 06 2018 ...Northern and Central Rockies... Days 1-3... A busy period of winter weather is expected across the higher terrain of the central and northern Rockies over the next 3 days. One shortwave trough crosses the Rockies today, with Mid-level vorticity advection and upper level divergence maxima combining with upslope enhancement helping produce snowfall...with the highest amounts expected across the CO Rockies. Should end up with pretty good coverage of 4"+ above ~9000 feet today into the day Saturday...with some 8"+ totals likely along the highest terrain. The arrival of the next upper level wave and jet max Saturday night into Sunday brings another surge of moisture and lift, so snow is expected to redevelop in the ranges of northwest WA across western MT and ID, with the snow eventually reaching northwest WY by Sun morning and the CO Rockies by Sunday afternoon. Three day snowfall totals of 1-2 feet, locally higher, are likely across the higher terrain of northern ID, western MT, western WY into eastern ID, and the CO Rockies into southern WY. Models are in relatively good agreement, with WPC favoring a multi model blend along with the NBM for snowfall across this area. ...Northern Plains and Upper MS Valley... Days 1-3... An Alberta Clipper will move steadily southeast into the northern Plains tonight into Saturday, with an area of low pressure then redeveloping over the central Plains and pushing northeast into the Upper MS Valley through Sunday. Areas of accumulating snowfall will be possible to the north of the low track. Thermal profiles will be borderline for snow from northeast MT into western ND...although the overnight timing and stronger frontogenetic band favors enough thermal cooling for some accumulating snowfall tonight, and colder air filtering in behind the clipper supports some lingering light snowfall into the daylight hours Saturday. The general consensus is for a swath of 1-3", however a narrower swath of 4-6" is possible. The greatest threat of these higher totals is across southwest ND, where our winter weather super ensemble shows a 50-80% chance of exceeding 4", and a 20-40% chance of localized 6" totals. Some light snow accumulations are also possible across northern WI into northern MI and far northeast MN Saturday night into early Sunday. Again thermal profiles are marginal, but our ensemble shows ~30-50% chance of a corridor of 2"+ totals, and most recent deterministic runs also show some light accumulating snowfall. With sunrise Sunday, diurnal heating combined with a northward lifting low will result in warming profiles and a changeover to rain from south to north...thus the window for accumulating snow is pretty small. Chenard