Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 204 PM EST Sun Dec 10 2023 Valid 00Z Mon Dec 11 2023 - 00Z Thu Dec 14 2023 ...Northern/Central Rockies... Day 1... Weakening atmospheric river (AR) will remain extended through the northern Rockies as weak height falls move through the region on Monday, spreading snow across the northern Great Basin to northern CO. Some enhancement is possible over the highest terrain in northwestern MT, western WY (Tetons), and along the WY/CO border (Medicine Bow Mtns and Park Range). WPC probabilities for at least 6" of snow are moderate (40-70%) in these ranges, generally above 7000ft (north) and 8000ft (south). ...Central Appalachians through the Interior Northeast... Day 1... Amplifying eastern trough, aided by an increasingly S-shaped upper jet (>150kts) will spur cyclogenesis and rapid deepening over 20mb during the period as low pressure moves across southeastern New England early Monday and lifts quickly into southeastern Canada by the afternoon and evening. Slowing surface front approaching the central/southern Appalachians today will promote strong CAA behind the front (as cyclogenesis ensues) amid a sufficiently moist column and help turn rain to snow from west to east over the central Appalachians and New York State into Monday (especially in elevations above 500ft and west of I-95). Strong NW-tilted FGEN band from northeast PA into northern New England will support snow rates >1"/hr (per WPC snowband tool and 12Z HREF probs) as the rain changes to heavy, wet snow (high snow load) especially from Northeast PA into the Catskills as well as the Adirondacks and Green Mountains. Day 1 WPC snow probabilities for >4" are moderate (40-70%+) for the WV crest of the Appalachians as well as the VA Blue Ridge at Shenandoah NP, primarily from post-frontal QPF and upslope enhancement. To the north, amounts will be higher in the colder column, strong FGEN forcing, and terrain enhancement on northerly flow. WPC probabilities for >8" are moderate (40-70%) over parts of the Catskills to the I-88 corridor, as well as over the Adirondacks (also over far northwestern Maine). Probabilities are high (>70%) over the highest elevations of the Adirondacks and into the Green Mountains/Northeast Kingdom in VT (into northern NH). Though the system will be progressive despite the negative tilt, minor fluctuations in the track of the front/low, speed of incoming cold air (rate of changeover), and precipitation focus would lead to large changes in the snowfall amounts. Spread continues in the ingredients even at this short time range. Lake effect snow in typical northwest flow snow belts off Erie and Ontario will persist on Monday before shifting westerly Monday night with additional accumulation in the Tug Hill. ...Michigan U.P. into the Tug Hill... Days 2-3... Upper low will move from Manitoba across far northern Ontario late Monday through Tuesday with a surface cold front dropping through northern MN and into the western Great Lakes. 850 temps will be colder with this wave, dropping to around -12 to -15C (into the DGZ) and supporting WNW to ESE bands post-FROPA Tuesday/Tuesday night, slowly diminishing into Wednesday. WPC probabilities for >4" are moderate to high (>40%) in WNW flow snow belts over and south of the Keweenaw Peninsula and far eastern sections of the U.P. shoreline of Superior. On Day 3, wind will veer from SW to W to WNW, favoring a resurgence in lake effect single-band snow east of Ontario into the Tug Hill as the cold front from the central Great Lakes passes through. WPC probabilities for >4" of snow are high (>70%) in the Tug Hill. Fracasso