Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 413 PM EST Wed Feb 19 2025 Valid 00Z Thu Feb 20 2025 - 00Z Sun Feb 23 2025 ...Mid-Atlantic and Carolinas... Day 1... Major winter storm continues into tonight for southern Mid- Atlantic with heavy snow and notable icing. See the latest Key Messages linked at the bottom. Developing surface low ahead of southern stream wave is off SC/GA border this afternoon. This coastal low strengthens as it shifts northeast off Cape Hatteras through tonight. Heavy snow bands will persist over southeast VA into northeast NC through this evening where Day 1 snow probs for an additional >4" after 00Z are 40-70%. Snow bands shift offshore after midnight. A wintry mix of mainly freezing rain will persist over southern and eastern NC through this evening. Day 1 ice probs for an additional >0.1" after 00Z are 40-70% over portions of the MHX and ILM CWAs. The northern stream upper low is currently over Iowa and will track to Ohio through tonight before pushing over the northern Mid- Atlantic Thursday. Generally light snow is expected from this upper low over the Ohio Valley tonight and over the central/ southern Appalachians into the DC metro area Thursday morning. Day 1 snow probs for >2" are 40-70% over the WV Highlands and the Great Smokies. ...Great Lakes/Massachusetts Cape and Islands... Days 1-2... Lake effect snow reinvigorates over Lake Michigan tonight into Thursday on the back side of the aforementioned upper low. NNWly flow brings single band LES to far southwest MI into northern IN through Thursday where Day 1 snow probs for >4" are 40-60%. NWly flow late Thursday brings lake enhanced snow downwind of Erie despite the lake being nearly frozen over. However, fetch from Lake Huron will aid snowfall. Day 1.5 snow probs for >4" are around 20% near Erie, PA. The system developing off the Mid-Atlantic coast Thursday tracks up off Nova Scotia Thursday night. This will bring the precip shield with bay/ocean enhanced snow to southeastern MA/Cape Cod and Islands Thursday afternoon/evening. Day 1.5 snow probs for >4" are 40-70% for the Cape and Islands. ...Pacific Northwest through the Central Rockies... Days 1-3... A potent but progressive Pacific system over the PacNW coast early this afternoon will dig south as it moves inland with the base of the trough reaching CO by late Thursday. Snow levels drop to 3000ft over the WA Cascades through this evening before precip cuts off with Day 1 snow probs for >4" 40-80% at and above pass level. Snow levels over the northern Rockies are around 4000ft and closer to 6000ft over CO through Thursday as this trough approaches. Moderate elevation snow can be expected with Day 1 snow probs for >6" 40-80% around the Bitterroots on the ID/MT border, northeastern NV ranges, the Wasatch, Uinta and Tetons. Snow continues over the CO Rockies through Thursday night with Day 2 snow probs for >6" 30-60% across central and northern CO ranges. The next wave pushes into the Queen Charlotte Sound Friday evening with another atmospheric river pushing across WA Friday afternoon, expanding south through OR Sunday. Snow levels at onset are around 4500ft in the WA Cascades Friday, increasing to 5000ft Friday night and 6000ft over WA (and 8000ft over OR) on Saturday. Day 3 snow probs for >6" are 30-40% over the only higher WA Cascades with the very high snow levels over OR precluding snow probs for the isolated higher Cascade peeks at this time. Jackson ...Winter Storm Key Messages are in effect and linked... https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png