Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 328 AM EST Fri Feb 08 2019 Valid 12Z Fri Feb 08 2019 - 12Z Mon Feb 11 2019 ...Western U.S.... A pair of systems impacting the western U.S. are expected to produce widespread snows across the Pacific Northwest and Northern California, including lowland snows over western Washington and Oregon as well as the North Coast of California. A compact upper low off of the Pacific Northwest coast will continue to drop southeast, moving into Northern California this evening. This system will bring some significant snows to the Sierra Nevada as it weakens and pivots east across California into Saturday. Meanwhile, an anomalously deep upper low is forecast develop over southern British Columbia and drop south along the Pacific Northwest coast tonight into Saturday. The 00Z GFS shows 500mb heights more than 2 standard deviations below normal across much of western Washington and Oregon on Saturday. This will support significant snow accumulations for portions of western Washington, including the lowland areas like Seattle-Tacoma. As the low continues to drop south, snows are expected to extend south along the coastal ranges along the North Coast of California on Saturday, with snow levels dropping to as low as 500ft by Sunday morning. Models show the low transitioning to an open wave and moving east across the Northwest and Northern California on Sunday. Shortwave energy moving through the base of the associated trough will enhance lift along the trailing baroclinic zone, supporting additional heavy amounts along the Sierra Nevada. Two-day totals will likely exceed two feet for portions of the northern Sierra Nevada. As the remnant trough moves east, expect heavy snow to remain limited to higher elevations through Sunday night. ...Great Lakes... Westerly flow persists across the Great Lakes in the wake of the low departing this morning through tonight which will maintain lake effect snow, particularly east of Lake Ontario in the Tug Hill. Day 1 WPC probabilities are moderate for more than six inches near Tug Hill. A closed low off the northern California this morning will open as it tracks inland, weakly redeveloping surface low features as it spills onto the Great Plains Saturday night. Higher QPF from the 00Z ECMWF warrants an increase over all in snow potential over MN/WI with low probabilities for greater than 4 inches for Day 3. A well developed low creates a more significant snow threat to the Great Lakes early next week. ...Central and Southern Appalachians... Canadian high pressure shifts off Cape Hatteras Sunday with return flow on the back side of the high and ahead of an approaching trough over the central Great Plains will allow for overrunning precip. Enough cold air is expected to be trapped/dammed that pockets of freezing rain around a tenth inch can be expected on the eastern slopes of the Appalachians on Day 3. Moderate Day 3 WPC probabilities for a tenth inch of ice are over western VA. Jackson