Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 405 PM EDT Thu Oct 17 2019 Valid 00Z Fri Oct 18 2019 - 00Z Mon Oct 21 2019 ...Northeast... Day 1... A powerful cyclone over New England will gradually weaken as it tracks into Atlantic Canada overnight. Cold air advection on the backside of the system will support a changeover from rain to snow, with accumulations of 6-inches or more possible across the higher summits of the Adirondacks and White Mountains late Thursday into early Friday. ...Pacific Northwest to the Northern Rockies... Days 1-3... An amplifying shortwave diving southeast toward Vancouver Island will support organized, heavier precipitation across western Washington and the northern Rockies Thursday night. Expect shortwave ridging to provide a relative lull early Friday, before the next shortwave and another round of organized precipitation moves into the Pacific Northwest Friday afternoon and evening. Snow levels across the Olympics and much of the northern Cascades will drop below 5000ft, with heavy locally heavy accumulations likely along the higher summits. As a upper level shortwave continues to amplify over the Northwest, precipitation will continue through Friday night into Saturday, with additional heavy accumulations likely across the Washington Cascades early Saturday. Locally heavy snows are also expected to extend further south into the Oregon Cascades later as the day the mid-upper level wave moves onshore and snow levels drop. Meanwhile, locally heavy amounts are also expected to extend farther east into the northeastern Oregon ranges as well as the northern Rockies from northern and central Idaho to western Montana and western Wyoming. Mid level energy embedded within strong northwest flow will support additional snow showers with locally heavy accumulations possible from the northern into the central Rockies Saturday night and Sunday. Although showers will continue, the heavy snow threat is expected to wane across the Northwest as strong upper level ridge begins to build along the coast on Sunday. The probability of significant icing is less than 10 percent Days 1-3. Pereira