Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 353 AM EST Sat Jan 25 2020 Valid 12Z Sat Jan 25 2020 - 12Z Tue Jan 28 2020 ...Northwestern CONUS... Days 1-2... An initial lead shortwave crosses western WA/OR to northwest CA this morning with a band of enhanced 700 mb moisture and loft, with the band progressing steadily inland , with a break developing. The next surge of moisture and lift comes ashore in northwest CA/western OR/western WA tonight to Sun morning. Heavier snow amounts Day 1 are forecast to be in the WA Cascades due to lower snow elevations there. With the second wave of moisture and lift progressing inland Sunday across northeast OR into central and northern ID and northwest MT, several inches of snow is expected. By Monday morning the wave of moisture/lift crosses into northwest WY, so snow is expected to pick up in coverage. Several inches of snow is expected in each of these areas, but the progressive wave leads to low probabilities of a heavy snow event. The heaviest snow again is expected to be over the WA cascades due to longer duration lift and deep layer moisture persisting. Day 3... Yet another plume of Pacific moisture of tropical origin pushes into the Pac NW Monday. This raises snow levels over OR/CA back to around 6000ft. The focus of greater moisture and lift is still on the WA/OR Cascades, thus these ranges continue to have locally heavy snow predicted. Another foot with locally higher amounts is likely in higher elevations of the WA/OR Cascades. The models have different timing/amplitude of the waves producing the snow, with the Nam stronger with the incoming closed low and heavier with QPF and resultant snow in OR/ID/northwest MT. The trough that brought snow to western WY on day 2 progresses down into CO on Monday, with modest ascent leading to light totals across most of the CO and northern NM ranges. Snow should taper by Tue morning as the upper trough departs and moves east onto the Plains. ...Midwest/Great Lakes/Mid-Atlantic/Northeast... Days 1-2... The closed low drifting near southern Lake Michigan will drift across southern MI today. Snow in the mid-level deformation zone over WI/northern IL/central UP of MI will persist there through this morning. The mid level cyclonic vorticity advection progressing out of northern IL across northern IN this afternoon, and weakening as it crosses Ohio tonight. A secondary low will develop over the Mid-Atlantic in the lee of the Appalachians and take an inland track up the Eastern Seaboard through Sunday. The inland track leads to strong low-mid level warm advection across eastern NY and New England. This is turn causes a wintry mix with rapid changes from snow to sleet and freezing rain expected. This prevents heavy amounts of any one type of freezing/frozen precip. With the warm air aloft overrunning the low-level cold air, freezing rain is expected, with measurable amounts across the Catskills and Adirondacks of eastern NY and the Berkshires/Green Mtns/White Mtns/ranges of western Maine. On Sunday, the remaining ice threat is near the low in northeast Maine until the low crosses into New Brunswick, which will end the threat of mixed phase precip. Day 2-3... In the lee of the Great Lakes, cyclonic flow brings an expected period of enhanced moisture and lift across both Lake Erie and Lake Ontario. West-southwest flow results in lee shore convergence downstream from Lake Erie and Lake Ontario, and lift that is aided by topography east of Lake Ontario in the Tug Hill. Where moisture and lift coincide, several inches of snow is expected in the lee of both Lakes Erie in southwest New York and Lake Ontario in upstate New York from late Sunday into Monday. On Monday, amounts are lighter as a progressive front crosses the lower lakes, with lighter snow amounts following shorter cross lake trajectories and weaker lift. Most locations on Monday are forecast to get an inch or two, with no heavy snow areas identified. The probability of 0.25 inches of freezing rain is less than 10 percent Days 2-3. Petersen