Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 407 AM EDT Sat Nov 03 2018 Valid 12Z Sat Nov 03 2018 - 12Z Tue Nov 06 2018 ...Northern and Central Rockies... Days 1-3... One jet streak extending across western MT today triggers upper level divergence maxima. This maxima combines with upslope enhancement to produce snowfall today...with the amounts expected to be 4"-8" today 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. Two day snowfall totals of 1-2 feet are likely across the higher terrain of central ID, western MT, western WY into adjacent eastern ID, and the Rockies near the northern CO/ southern WY border. Models are in good agreement, with WPC favoring a multi model blend and continuity for snowfall across this area. On day 3, the continued upper jet maxima across the Pacific northwest to northern Great Basin provides favorable upper divergence maxima in the northern Rockies with 700 mb vertical velocity maxima and high relative humidity leading to the likelihood of several inches of snow in the ranges of northern ID to western MT. Snow extends into the Bighorn range of northern WY and the Snowy range/Medicine Bow National Forest near the WY/CO border. ...Northern Plains and Upper MS Valley/Upper Great Lakes... Days 1-3... An area of low pressure redevelops over the central Plains and moves 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 near the ND/SD border with colder air filtering in supporting light snowfall today. Low pressure is forecast to moves from eastern IA norther across WI to Lake Superior. Snow accumulations are possible along the cyclone's path across northern WI into the UP of MI and the northeast MN arrowhead early Sunday. Thermal profiles are marginal, with a split in model runs, as the typically colder NAM has potential for higher amounts, vs lower amounts in the warmer GFS. The 00z ECMWF trended a bit cooler with potential for 4-6 inches in northern WI to the MI border. On Sunday, diurnal heating combined with a northward lifting low will result in warming profiles and a changeover to rain from south to north. The probability of significant icing is less than 10 percent days 1-3. Petersen