Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 403 PM EST Fri Feb 14 2025 Valid 00Z Sat Feb 15 2025 - 00Z Tue Feb 18 2025 ...Rockies... Day 1... The upper trough over the west will continue to dig through the Four Corners tonight before ejecting east over the southern Plains through Saturday. NWly jet on the back side of the trough will shift over the Rockies Saturday. Generally moderate snow continues over the Utah and CO Rockies tonight through Saturday with Day 1 snow probs for >8" generally 50-80% with snow levels dropping from 6000ft to 4000ft. ...Central Plains/Midwest/Great Lakes/Northeast... Days 1-3... ...Winter storm shifts east through this weekend, with heavy snow from the central Great Lakes through the interior Northeast with areas of freezing rain for much of the Appalachians, northern Mid- Atlantic and southern New England. See Key Message link below... Shortwave impulses ejecting ENE on strengthening SW flow are providing lift above a developing inverted surface trough over the east-central Plains. Thump of snow from WAA ahead of this inverted trough has brought a swath of light to moderate snow over IA/MN that will lift over much of WI and northern IL this evening and much of the L.P. of MI overnight. Enhancement of precip is expected in banding as the jet approaches with local snowfall rates reaching 0.5"/hr. Some narrow banding is likely to develop farther southwest from eastern CO through Neb and central IA. Day 1 snow probs for >4" are over 10% from northeast Neb through much of WI and MI with over 30% probs for >6" over the southern half of WI, increasing to around 60% by the western shore of Lake MI. Potent surface low development is expected over the Mid-South on Saturday with well above normal moisture (see the WPC excessive rainfall outlook for further info there and a developing comma head over the Midwest Saturday night that further develops as it tracks over the Northeast Sunday. Heavy snow bands can be expected in this comma head north and on the back side of the low pressure system. Warm air advection brings a wintry mix of snow to sleet to freezing rain to some areas going plain rain over the Northeast Saturday through Sunday. Saturday morning expect some freezing rain in the central Appalachians at precip onset that may linger over WV/VA through Saturday afternoon. Greater coverage of ice is expected over much of PA and NY Saturday/Saturday night before spreading over southern New England Sunday. Day 1.5 probs for >0.25" ice are around 20% in the Allegheny Highlands of VA into WV and 50-70% over west-central PA over the Laurels and Allegheny National Forest. For Day 3 these probs for >0.25" are 20-60% over the Poconos, Catskills, Berkshires and even Worcester Hills in MA. Heavy snow is most likely to persist over far northern NY, central Mass and north through the Greens/Whites and much of Maine all over 50% for >6" on Day 2.5 with values over 80% along the northern NY border and across the northern half of Maine for Day 3.. ...Pacific Northwest/Rockies/Central Plains... Days 2-3... The next multi-vorticity lobe upper low in the northeast Pacific will send a cold front into the Pac NW late Saturday. Snow levels around 3000-4000ft for the WA/OR Cascades and Pacific moisture will give light to moderate snow to the passes that continue through Monday as the trailing main upper low finally reaches the coast. Westerly flow spreads moisture across the northern Rockies with low level northerly flow over the Plains from a 1040mb high shifting south from the Canadian Prairies. Day 2 snow probs for >6" are 50-80% over the Cascades and northern Rockies to the Tetons. Day 3 snow probs for >6" expand down the OR Cascades, much of the ID Rockies, western WY, and northern CO with 50-90% values. Jackson ...Winter Storm Key Messages are in effect with a shift to the Northeast this weekend... https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png