Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 404 PM EST Fri Dec 16 2022 Valid 00Z Sat Dec 17 2022 - 00Z Tue Dec 20 2022 ..Significant winter storm for the Northeast through Saturday... ...Northeast... Days 1-2... To the southeast of the Great Lakes upper low, a mid-level shortwave beneath a 160kt jet streak has continued to spur deepening of a coastal low now moving through the NY Bight. Strong upper ridging near the Davis Strait will block the coastal system from gaining too much latitude as it moves through the Gulf of Maine early Saturday and eventually near the coast of Nova Scotia Sunday. Strong easterly flow (impressive U wind anomalies <1st percentile) into Maine will support upslope into the northern Appalachians with heavy snow rates > 1"/hr overnight into Saturday per the WPC Snowband Tool. Due to the stronger low-level flow, terrain enhancements and shadowing will be quite prevalent, and coupled with marginal temperatures (near to just above freezing in many valleys but sub-freezing in the mountains), the snowfall will be quite exaggerated this evening between the Hudson/Champlain/CT River Valleys vs the Green/White Mountains, Berkshires, Adirondacks, etc. However, as the system starts to draw in colder air overnight, rain or a mix will change to snow from northwest to southeast and into lower elevations. WPC probabilities of at least 8 inches of snow over the next 2 days will be high (>70%) over interior Maine, and moderate (>40%) over the Green and White Mountains as well as most of Maine away from the coastal plain. ...Great Lakes... Days 1-3... Upper low over the Great Lakes will continue to promote a large area of light snow but gusty winds associated with the old parent low of the Northern Plains blizzard. In addition, as it slowly moves eastward across Michigan and into Ontario, westerly flow will invigorate multi-band lake effect snow over western Lower Michigan tonight/Saturday. West-southwest flow over the eastern lakes will favor a single band over and just south of Buffalo where 2"/hr snowfall rates are likely. On Sunday, the band will shift a bit southward as the upper low passes by 80W in Canada. Off Lake Ontario, single band into the Tug Hill will start farther north (just south of Watertown) Sunday on W to WSW flow before sinking southward by Monday as the flow becomes more W to WNW. WPC probabilities for at least 12 inches of snow are high (>70%) within these bands where three-day totals may exceed two to three feet. ...Northwest... Days 2-3... Upper low and trailing vort max on its western/southwester side will settle into southwestern Canada and across the border into WA/ID/northwestern MT. This will drive an arctic front southward with much colder air into western Washington as an increasing upper jet provides broad scale lift over the region, promoting generally light to modest precipitation to the region. Westerly flow will maximize upslope into the Cascades with additional lift across the Idaho panhandle and into northwestern Montana where more than six inches of snow is likely. Snow levels will drop to the valley floor over much of western Washington with some light accumulation possible in the lowlands. 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. Fracasso