Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 231 PM EST Sun Jan 09 2022 Valid 00Z Mon Jan 10 2022 - 00Z Thu Jan 13 2022 ...Great Lakes... Days 1-3... A cold front moving across the Great Lakes and into New England tonight will leave strong CAA on WNW flow in its wake. Within this intense CAA, 850mb temps will crash to -20C to -25C, while lake temperatures are still relatively warm and ice-free. This will allow for an extended period of favorable LES in the typical W/NW snow belts downwind of Lake Superior, Erie, and Ontario D1 into D2. The most intense snowfall is likely D1 east of Lake Ontario where favorable ascent into the DGZ combined with impressive instability nearing 1000 J/kg and aided by upslope into the Tug Hill Plateau will produce 2"/hr snowfall rates. WPC probabilities are high for 8 inches on D1, with locally more than 2 ft likely in the Tug Hill. Downwind of Lake Erie, generally south of Buffalo, and in the eastern U.P. of MI, WPC probabilities are moderate to high for 4 inches with locally 6-8" possible. Snowfall here will be slightly less due to less favorable ascent/DGZ depths. By D2, a second surge of CAA will drop southward behind a trailing shortwave, but this will also be accompanied by a shift to more northerly flow and dry advection. This will also be replaced quickly by approaching shortwave ridging from the SW with accompanying WAA. This will gradually wind down the LES, but an additional few inches of snow is possible on Tuesday. A third impulse and associated surface cold front will cross the area on D3 bringing renewed CAA and LES, but at this time additional snowfall amounts look modest. ...Northern New England... Day 1... A strong cold front crossing New England will produce an environment favorable for some scattered intense snow squalls across northern New England tonight into Monday. The instability and available moisture are modest for snow squalls, but intense 0-2 km fgen and near-0 theta-e lapse rates suggest brief periods of intense snowfall accumulating to up to 1 inch are possible. Any snow squall into Monday morning could cause travel disruptions. ...Pacific Northwest... Days 2-3... Zonal flow across the Northwest will gradually back to the SW ahead of a closed low approaching from the Gulf of Alaska D3. This will be accompanied by increasing upper level diffluence as a jet streak pushes well inland, to increase moisture and precipitation into Washington State. With the pronounced mid-level WAA ahead of the approaching trough, snow levels will climb from 4000 ft D2 to 7000 ft D3, primarily along and west of the Cascades, but will remain 3000-4000 ft to the east. Increased moisture will fall as heavy snow above these levels, and WPC probabilities for 6 inches are above 40% in the northern WA Cascades both D2 and D3, but generally above pass level. To the east, low-level cold air will be slow to erode across the Columbia Basin, so light freezing rain accumulating to as much as 0.1" is possible on D3. Weiss