Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 303 AM EST Thu Feb 27 2025 Valid 12Z Thu Feb 27 2025 - 12Z Sun Mar 02 2025 ...Northeast... Day 1... The first in a pair of winter storms tracks through the Northeast today. NAEFS shows a sub 1004mb low tracking through the eastern Great Lakes that is below the 10th percentile. This low is also directing a narrow >500 kg/m/s IVT towards New England that is above the 90th climatological percentile. As anomalous moisture is directed towards the northern Appalachians, a sufficiently cold air-mass located over New England will support periods of snow, particularly in the northern Appalachian ranges. With low-level WAA and 290k isentropic glide aloft, periods of snow will be ongoing from the Adirondack on east through the Green and White Mountains this morning. As low pressure tracks into the Champlain Valley around midday, snow will track into the northern two-thirds of Maine with a wintry mix just north of the Maine coastline. The storm will race northeast into the St. Lawrence Valley of southern Quebec by Thursday evening with a dry slot moving in aloft that effectively shuts off most accumulating snowfall beyond 00Z Friday. WPC probabilities show low-to-moderate chances (30-50%) for snowfall >6" in the peaks of the Green and White Mountains. Most snowfall totals >500ft in elevation that are not in the Green and White Mountains are most likely to see anywhere from 1-4" of snowfall through Thursday afternoon. The WSSI does show a swath of Minor Impacts from southern VT and central NH on east through the southern half of Maine. Residents in these areas could contend with hazardous driving conditions, particularly in areas with complex terrain. ...Upper Great Lakes through the Northeast... Days 2-3... An unusually strong clipper system diving southeast from southern Canada will head for the Upper Great Lakes on Friday. The storm will reside beneath the diffluent left-exit region of a 90-100 knot 500mb jet streak, while also sporting an unusually strong NWrly IVT that surpasses 300 kg/m/s on the western flank of the Clipper. The low-level circulation at 850mb is also rather potent with heights that are below the 0.5 climatological percentile by 18Z Friday according to NAEFS. This equates to what would be a "front-end thump" of heavy snow late Thursday night across the Minnesota Arrowhead, then across the Michigan U.P. and far northern Michigan Friday morning where the best 850mb FGEN ensues. Just north of the 850mb FGEN is where snowfall rates of 1-2"/hr are possible for several hours. A dry slot and warming boundary layer should limit snowfall over the Michigan U.P. and northern Michigan Friday afternoon. As the storm heads east though, additional snow is likely on the back side of the storm as low-level CAA over Lake Superior increases Friday evening. Snow should taper off by Saturday morning in the Upper Great Lakes. WPC probabilities show moderate-to-high chances (50-70%) for snowfall totals >6" in the MN Arrowhead with similar chances for >8" in the Keweenaw Peninsula, the, Huron Mountains, and eastern Michigan U.P.. Localized amounts approaching a foot are possible closer to Sault Ste. Marie, MI. The storm continues its march east into southern Ontario Friday evening with the same method of producing periods of heavy snow as far east as the Tug Hill and Adirondacks of northern New York. Unlike the Upper Great Lakes, however, the storm track is farther north through the St. Lawrence Valley. WPC's Snowband Probability Tracker, utilizing the 00Z HREF guidance, shows the potential for 1"/hr rates from the Tug Hill to as far east as the Green and White Mountains Friday night. The dryslot and warming low level- temperatures arrive Saturday morning with only northern Maine likely to still see periods of moderate-to-heavy snow through rest of the day Saturday. Snow should taper off throughout the Interior Northeast by Saturday night. WPC probabilities show moderate-to- high chances (50-70%) for snowfall >6" in the Tug Hill and Adirondacks neighboring the Tug Hill through Saturday morning. Mullinax