Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 129 AM EST Thu Dec 5 2024 Valid 12Z Thu Dec 05 2024 - 12Z Sun Dec 08 2024 ...Eastern Great Lakes and Northeast... Days 1-3... Strong low pressure moving through Quebec this morning will continue eastward, with WAA-driven snow over northern New England. 500mb heights/wind are near the CFSR reanalysis min/max (respectively) with this potent system. The associated cold front, responsible for numerous snow squalls yesterday afternoon and overnight, will help feed moisture into northern/interior Maine where sub-freezing temperatures will support all snow this morning. Low pressure will quickly translate into Atlantic Canada early this afternoon, with the FROPA turning winds around to the northwest and helping to enhance orographic lift across much of the Northeast into the central Appalachians. Strong pressure gradient will also maintain windy conditions with blowing/drifting snow over the interior and near-blizzard/blizzard conditions in the higher elevations (esp WV). Lake-effect snow, already in progress over MI, will redevelop/strengthen over the eastern Great Lakes by this afternoon on NW flow with some double (Lake) dip increase in moisture. CAM guidance continues to depict some rather robust single bands off some of the lakes with a far reach inland of at least lighter snow. Winds will eventually back and lighten by tomorrow with less coverage/intensity overall but still some more potent bands possible. A trailing shortwave out of Canada will swing through the Lakes late Friday, again enhancing some lake- effect snows across MI into NY and NW PA. WPC probabilities for at least 12 inches of additional snow after 12Z Thu are highest (>50%) east of Lake Erie (NW PA into SW NY) and southeast of Lake Ontario (between ART and SYR). Moderate snow (>8") is likely over the higher terrain of the Adirondacks into the Green and White Mountains due to upslope flow. In addition, the eastern U.P. of Michigan and the western side of Lower Michigan show moderate (40-70%) and low (10-40%) probabilities, respectively, of at least another 8 inches of snow through Saturday. Lastly, with the progression of the cold front this morning, the threat of snow squalls remains for parts of the northern Mid- Atlantic into New England. This may produce a quick drop in visibility coincident with gusty winds and slippery travel. ...Pacific Northwest/Northern Rockies... Day 3... Upper low in the northeastern Pacific will stream eastward along 50N into British Columbia, bringing in a surge of moisture to the Cascades then into the northern Rockies on Saturday. Snow levels will be on the higher side, about 8000ft at precip onset, but will lower to around 5000-6000ft Saturday afternoon as the front moves in, and falling farther to around 3500ft as the precipitation lightens into Sunday morning. Snow will likely affect the higher passes, where the probability of at least 6 inches is >50% above 4000ft or so. East of the Cascades, some icing and/or a wintry mix of sleet/freezing rain will be possible as colder surface temperatures are overrun by mild air aloft. Into the northern Rockies, moisture will get wrung out over the higher terrain with several inches likely (>50% chance of 6 inches) on the higher mountain ridges. The probability of significant ice >0.25" across the CONUS is less than 10 percent. Fracasso ...Winter Storm Key Messages are in effect. Please see current Key Messages below... https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png