Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 335 AM EST Sun Jan 09 2022 Valid 12Z Sun Jan 09 2022 - 12Z Wed Jan 12 2022 ...Great Lakes... Days 1-3... An Arctic low pressure system up over Hudson Bay has an attendant cold front pushing across Lake Superior early this morning and will cross all the lakes by late this afternoon. Strong CAA on WNWly flow follows this front with 850mb temps dropping to -20 to -25C over Superior and northern Lake Michigan and the more dendritic favorable -15 to -20C over the lower/eastern Lakes into Monday night. This particularly cold air is atop the still relatively warm and open Great Lakes and will produce an extended period of heavy LES in the favored WNW/NW snow belts. The best forcing/lift is farther north with the eastern UP, Huron/Georgian Bay, and Lake Ontario favored for heavy LES. Inversion heights climb to 10,000 ft due to as high as 1000 J/kg of instability, snowfall rates will become intense, especially downstream of Lake Ontario streamlines make the effective fetch/additional moisture from Lakes Superior and Huron overlap with long fetch over Lake Ontario directly into orographic lift of the southern Tug Hill late tonight into Monday night. Snowfall of 1.5 to 2"/hr are the mean from the 00Z HREF over this area for at least 20 hours. While the actual single-band will waiver slightly through this time, 24"+ are likely. Flow veers to NWly/Nly late Monday night with bands shifting south through Tuesday with continued snow for the eastern UP and some 4" Day 2 probabilities off Lake Erie. ...Mid-Atlantic through central New England... Days 1-2... Cold conditions with mainly mid 20s are across central/eastern PA, northern NJ, southern NY into central New England. Warm air advection ahead of a cold front that crosses the OH valley this morning will spread precipitation atop the cold surface temperatures. As 850mb temps climb above 0C, and the DGZ, at least initially, lacks saturation, a period of light to moderate freezing rain is likely from WV northeastward into southern New England and upstate New York. Surface wet bulb temperatures in the upper 20s will lead to high accretion efficiency, at least for several hours after some mixing of sleet, but the lack of any dry/NE flow to maintain low wet-bulb temperatures and diurnal trends should gradually cause a reduction in efficiency and cause many areas to transition to rain, especially in the Mid-Atlantic, with enough CAA behind the front leading to light snow across New England. Day 1 ice probabilities are moderately high for 0.1" from central through northeastern PA, southern NY including the Catskills, Mohawk and Hudson Valleys, Litchfield Hills, Berkshires, southern Green Mountains, and toward Monadnock in NH. Ice accretion of greater than 0.01" is likely west of the the I-95 corridor from Washington, D.C. through Portland, ME. Behind the front, the environment is favorable for some scattered intense snow squalls Sunday evening and Monday across Upstate New York and northern New England. 0-2 km CAPE rises to 200 J/kg coincident with intense low-level fgen and climbing values of the snow squall parameter. There is some concern that RH will be drying out rapidly behind the front which could limit the snow squall potential, but the potential exists for briefly heavy snow rates to cause travel disruptions. Jackson