Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 357 PM EST Mon Feb 01 2021 Valid 00Z Tue Feb 02 2021 - 00Z Fri Feb 05 2021 ...Mid-Atlantic through the Northeast... Days 1-2... ...Major nor'easter will continue to spread heavy snow from eastern Pennsylvania through Maine through Tuesday... Upper level low pressure will reclose over the central Mid-Atlantic coast this evening and merely drift north through Maine through Wednesday. In the low levels, strong frontogenesis has allowed a TROWAL to develop as the WCB wraps northward around the low, and a potent CCB drives westward now north of New York City. The heavy snow associated with this TROWAL will continue to pivot northeast across increasingly interior New England and stretch southeast back to the central Mid-Atlantic tonight before the new low forms/shifts into the Gulf of Alaska Tuesday morning, refocusing heavy snow in Maine (and pivots into interior northern Maine Tuesday evening). Within this potent band, snowfall rates in excess of 2"/hr are likely, with moderate to at times heavy snow spreading as far northward as the Canadian Border. Additionally, as the low pivots northeast slowly, the deformation/comma snows will try to pivot southward as far as the Mason-Dixon line with uncertainty exactly how far south this band will stretch. Day 1 snow probabilities (starting at 00Z) favor terrain and particularly northeast facing terrain which is windward in this Nor'easter with moderate to high probabilities for an additional 8 or more inches in the Poconos, Catskills, Worcester Hills, Green Mtns, and White Mtns with a continuous swath of low probabilities from interior southeast PA up to northern Maine. Day 1.5 snow probabilities are moderate to high for 8 or more inches farther inland and include the Adirondacks and northwestern and far northern Maine. Low pressure finally lifts away from Maine Wednesday night. Light freezing rain and sleet is likely across eastern ME as the surface low gets pulled inland allowing warm air to wrap northward atop the continued cold surface temperatures within Canadian high pressure. Day 1.5 WPC probabilities for 0.1" of ice accumulation are 20 to 30 percent in eastern Maine. ...Southern Appalachians... Day 1... Low level northerly flow around the deep low along the Mid-Atlantic coast with streamlines in this flow back to Lakes Erie and Huron. Aloft, a series of reinforcing shortwave troughs will enhance lift in this somewhat moistened continental air tonight, promoting periodically heavy upslope snow for the Great Smokies and highest southern Appalachians. Day 1 WPC probabilities are high for 6 inches in a narrow corridor of the Smokies primarily on the west /upwind/ side, with local storm total maxima of more than 12 inches likely. ...Western U.S and Northern Plains.... Days 1-3... A potent and positively tilted mid-level trough will persist off the Pac NW coast through Tuesday before a reinforcing trough arrives Tuesday night and ejects the long wave trough southeast across the Intermountain West, crossing the central and northern Rockies Wednesday night. Ahead of the trough through Tuesday, persistent backed but confluent mid-level flow overlapped with a Pacific jet streak will continue to drive a modest atmospheric river (AR) into northern CA and the Pacific Northwest, with residual moisture spilling over into the Northern Rockies. This moist airmass will be warm, driving snow levels above 5000 ft. WPC probabilities on Days 1 and 2 are moderate for 12 or more in the Olympics, higher Cascades, the northern/central Sierra Nevada, and the Tetons. As the trough axis spills onto the northern Plains Wednesday night and Thursday, the associated sweeping cold front brings a risk of snow. Day 3 snow probabilities are high for 6 or more inches in the CO Rockies and low over northern MN. Southerly flow over cold antecedent conditions brings risk of mainly light freezing rain to the Upper Midwest (MN/WI) on Day 3. Jackson