Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 337 AM EST Fri Dec 16 2022 Valid 12Z Fri Dec 16 2022 - 12Z Mon Dec 19 2022 ...Significant winter storm set to deliver significant impacts to the Northeast today through Saturday... ...Northeast... Days 1-2... The interior Northeast is in for a very snowy Friday as a strengthening storm system slowly tracks north along the coast. This storm system has plenty of synoptic-scale support, placed beneath the divergent left-exit region of a 160 knot 250mb jet streak and WAA within the 850-700mb layer just north of the negatively tilted 500mb trough axis. The 850mb low will direct strong and moist easterly flow towards the Northeast. This 850mb easterly fetch is highly anomalous according to NAEFS, registering below the lowest 1% in climatological percentiles over the Northeast Friday morning. As this warm conveyor belt of Atlantic moisture feeds into the Northeast, strong vertical ascent via synoptic scale forcing and upsloping flow into the Northeast mountain ranges will result in periods of heavy snowfall. The 18Z HREF did contain >60% probabilities for >1"/hr snowfall rates for the Catskills, Adirondacks, Berkshires, Green, and White Mountains. WPC PWPF showed a large swath of high probabilities >80% for snowfall totals >6" for many of these ranges. The ranges with the highest probabilities of seeing >12" of snowfall on Friday are in the Adirondacks, the Green, and the White Mountains. Closer to the center of the storm, the aforementioned anomalous 850mb easterly winds will maintain an upsloping component as far south as Orange County in southern NY, as well as far northern NJ. Boundary layer temperatures here will be marginal, relying on strong vertical velocities to support a changeover to a heavy, wet snow. This is an area that is most "boom or bust", with totals potentially reaching another 4-6", or only an inch or so if the boundary layer is too mild from too much oceanic influence. In terms of impacts, the WSSI is depicting a large area of "Major" impacts from Catskills and Adirondacks to much of interior New England. There are also some embedded "Extreme" areas in several of the mountain ranges mentioned earlier (Catskills, Adirondacks, Berkshires, Green). It is here where not just snowfall totals, but also snow load (heavy, wet consistency) will be the primary drivers in causing widespread travel disruptions, downed tree limbs, and scattered power outages. Look for snow to taper off in the interior Northeast by Saturday morning, but heavy snow will linger across northern New England through Saturday afternoon. ...Northern Plains... Day 1... While snowfall rates and accumulations will be tapering off throughout the day, it is worth noting the tight pressure gradient over the region will still generate strong wind gusts that could top as high as 45-60 mph. Latest WSSI still depicts "Minor" to "Moderate" impacts to travel and infrastructure in central ND and some portions of SD due to blowing snow. Motorists should use caution while driving as strong wind gusts causing blowing/drifting snow may result in near zero visibility at times. ...Great Lakes... Days 1-3... As the storm system responsible for the blizzard in the Northern Plains and Upper Midwest moves east, cyclonic flow around the storm will kick-start lake enhanced snow bands in the MN Arrowhead and western MI. Most lake effect bands will be multi-banded in these areas, but this will not be the case downwind of Lakes Erie and Ontario on Saturday. As cyclonic, SW flow races over Lake Erie, converging winds off southern Ontario and northern OH will foster an intense single band of lake effect snow that will be aimed at the Buffalo metro area Saturday morning. The band will meander south on Saturday, but heavy snowfall rates up to 2"/hr are likely within the band. Lake effect snow here will gradually shift south Saturday night into Sunday as mean winds in the surface-850mb layer become westerly to eventually out of the WNW. Farther north though, the wind shift to the west turns on the lake effect snow machine downwind of Lake Ontario. Areas from near Pulaski on east to the Tug Hill Plateau can expect similar snowfall rates, that could even eclipse 3"/hr at times late Saturday through Sunday. Latest WPC 48hr PWPF for the upcoming weekend shows high probabilities (70-90%) for snowfall totals >12" near and just south of the Buffalo metro area, and near the Tug Hill Plateau, where there is an 80% chance for snowfall amounts >18" by the time the weekend has concluded. Travel will be dangerous in these areas with the latest WSSI depicting "Extreme" impacts in the Tug Hill and "Major" impacts north of Oswego along I-81. "Major" impacts around Buffalo and its southern suburbs which suggest the potential for widespread closures and dangerous, to even impossible, driving conditions. Key Messages for December 9-17 Winter Storm: - Blizzard conditions will linger today across parts of the Northern Plains and Upper Midwest as additional rounds of heavy snow and strong winds gusting to 45-60 mph persist. - Near zero visibility and snow-covered roads will make travel difficult to impossible, along with scattered power outages, and harsh livestock conditions. - Deteriorating conditions are expected today across the interior of New York and New England as a coastal storm moves nearby the Northeast. - Heavy snowfall rates of 1-2 inches/hour are likely across interior New York and central New England with storm totals reaching 1 to 2 feet by Saturday across portions of the Adirondacks, Mohawk Valley, and the Green and White Mountains. Dangerous travel conditions and scattered power outages are expected. - Lake-effect snow will develop downwind of the Great Lakes in the wake of the storm across parts of western New York south of Buffalo, and near the Tug Hill Plateau. Major impacts due to heavy snow will begin Saturday and continue into Sunday across these areas. Mullinax