Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 442 PM EDT Tue Mar 25 2025 Valid 00Z Wed Mar 26 2025 - 00Z Sat Mar 29 2025 ...Eastern Great Lakes/Northeast... Day 1... An upper low over northern MI this afternoon shifts east over New England through Wednesday evening. Low level westerly flow will continue over the eastern Great Lakes through Wednesday morning before veering northerly into Wednesday evening. PVA ahead of the upper low center will aid lift on this favored flow across Lakes Erie and Ontario and help produce lake enhanced snow and upslope snow on New England mountain ranges. Day 1.5 snow probs for >4" are generally 30-50% for the Tug Hill, Greens, Whites, and northwestern Maine. ...Upper Midwest/Great Lakes... Day 3... A flattening upper ridge over the northern Great Plains and lee- side surface cyclogenesis centered over South Dakota Thursday night allows some warm air advection precip to form along and north of the ND/MN border early Friday and possibly blossom toward Lake Superior later Friday. Antecedent cold air and a warm nose look to bring a (most likely light) wintry mix to northern ND/MN/WI and the U.P. Day 3 ice probs for >0.1" are 20-50% centered around Duluth and up the North Shore. ...Cascades into the northern Sierra Nevada... Days 2-3... An anomalously deep, cold core low approaches the OR Coast Wednesday evening before occluding in place off WA through Friday. Strong ridging over the West now means high snow levels at onset (>8000ft) Wednesday afternoon, but will quickly drop to around 4500ft Wednesday night. These lower snow levels are maintained through Thursday as the upper low approaches the coast, then drops even further, to around 4000ft Thursday evening as precip rates increase again with some heavy rates likely. Day 2 snow probs for >8" are 30-60% for the highest Klamath and OR/WA Cascades only. However, the lower snow levels and increased precip rates make Day 3 snow probs for >8" more expansive with 40-90% probs from the northern Sierra Nevada, Klamath, and along the spine of the OR Cascades and WA Cascades. Jackson