Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 331 AM EST Wed Jan 01 2020 Valid 12Z Wed Jan 01 2020 - 12Z Sat Jan 04 2020 ...Pacific Northwest through the Northern and Central Rockies... Days 1-3... Pacific moisture streaming across the Pacific inland continues inland on northwest flow today, with 700 mb moisture and overlapping lift producing snow in the ranges from the WA Cascades downstream across the ID Bitterroots, WY Tetons, and then the northern UT Wasatch/Uintas and ranges of northwest CO. Day 1 WPC probabilities for one foot or more are low to moderate across favored terrain in these ranges. Snow amounts and coverage in the central Rockies decline Wednesday night/Thursday as the upper trough departs the Rockies and moves across the Great Plains. The next trough approaches the Pac NW Friday with leading warm frontal precip reaching northern WA Thursday evening with preliminary snow levels of 4000 to 5000ft in the WA Cascades. A break develops as this wave moves inland. Another wave develops in the northeast Pacific and moves ashore Fri night, with the surge of moisture and ascent leading to potential for several more inches of snow. The greatest moisture and snowfall totals are in BC rather than the Pac NW, although the repeated episodes lead to a high likelihood of a few feet of snow in the northern WA Cascades over the 3 day period. ...Lower Great Lakes... Day 1... Cross lake trajectories and lee shore convergence have supported lake enhanced snow showers downstream from Lake Erie and Lake Ontario tonight. The activity continues into the morning while the layer relative humidity is high, but drier air is forecast to advect into the lower lakes from the Ohio Valley as a low level ridge moves east. The drier air arrives over Lake Erie and arriving in southwest NY early this afternoon, bringing a sharp reduction in snow shower coverage/intensity. The drier air crosses Lake Ontario and adjacent Tug Hill/western Adirondacks, bringing the event to a close. Several additional inches are possible today across the Tug Hill. The probability of 0.25 inches of icing is less than 10 percent Days 1-3. Petersen