Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 219 AM EST Mon Jan 13 2025 Valid 12Z Mon Jan 13 2025 - 12Z Thu Jan 16 2025 ...Northern Rockies/Western High Plains... Day 1... Weak shortwave diving through central/eastern MT this morning will sink southward through WY atop a surface boundary over eastern MT into the Black Hills, supporting generally light snow with some terrain enhancement. Areas in the Black Hills have a high chance (>70%) of at least 4 inches of snow today. ...Great Lakes... Days 1-3... Occluded area of low pressure over Lake Superior this morning will only slowly move to the east, leaving a surface trough across the region and NW flow into the U.P. of Michigan. Additional height falls via a cold closed low moving out of Canada into northern MN will maintain/invigorate cyclonic flow across all the Great Lakes behind the cold front moving into New England. Lake effect snow will pick up in earnest over the eastern Great Lakes and maintain itself over Lake Superior into the U.P. and northwest Lower MI for the next 2-3 days. Snow will gradually wind down from NW to SE late D2 into D3 ahead of a Canadian system. For the period, WPC probabilities of at least 8 inches of snow are >50% over the Keweenaw Peninsula and over the eastern U.P. on NW flow, as well as into northwestern Lower MI. East of Lake Erie, WPC probabilities for at least 8 inches of snow are >50% from Erie, PA through the Chautauqua Ridge to near the Buffalo southtowns with some totals likely over a foot. East of Lake Ontario, snowfall will maximize into the Tug Hill Plateau where WPC probabilities for at least 12 inches of snow are high (>70%) and even have a small area of >50% probs for at least two feet around Redfield. ...PA/NY... Days 1-2... Approaching cold front today may instigate some snow squalls across the region given relatively steep low-level lapse rates. On Tuesday, approaching vort max may again provide an atmosphere conducive for some snow squalls, with the models generally showing an area of >1 in the snow squall parameter. Amounts will generally be light but these can be hazardous to drivers. For the Day 1-3 period, the probability of significant icing of at least 0.10" is less than 10 percent across the CONUS. Fracasso