Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 331 AM EST Wed Dec 04 2019 Valid 12Z Wed Dec 04 2019 - 12Z Sat Dec 07 2019 Days 1-3... ...Southern California to the Central Rockies Days 1-2... An upper low is expected to weaken and move east across California today. High elevation snow, with local amounts to a foot possible, is expected over the southern CA Sierra Nevada. Several inches are possible in the San Gabriel, San Bernadino and San Jacinto mountains in Southern California. As the system continues east, several inches are possible across the higher elevations of the southern Nevada mountains, southern UT to the southwest Colorado ranges. The wave departs CO Thu onto the Plains, so the snow duration will be limited, with just a few inches in the CO front range before the system departs and the air mass dries out. ...Northern California Day 3... Strong southerly flow ahead of an approaching low will bring a 300 mb jet maxima into northern CA with upper divergence maxima crossing the region. The persistent onshore flow results in anomalous precipitable water values. The slow movement of the area of ascent and above normal moisture is expected to result in a couple of inches liquid equivalent in favored windward terrain in Northern California on Friday and Friday night. High elevation heavy snow is expected along the Siskiyous-Shasta Cascade region. 2-3 feet of snow is possible given this will be a long duration event, which may carry over into Saturday. ...Great Lakes/Central Appalachians Days 1-3... A cold front crosses the Great Lakes, followed by cross lake Ontario and lake Erie flow. Deepening moisture and modest cold air advection aloft will support snow showers with orographic lift helping to bolster accumulations along the Allegheny and Tug Hill plateaus. 4 to 8 inches of snow are expected a few miles inland from the Lake Erie shoreline in southwest NY to northwest PA as lee shore convergence and lift this afternoon and evening persists through the night.Northwest flow will also support accumulating snows along the Allegheny Mountains, with several inches possible across the Laurel Highlands south into West Virginia. As a low level ridge approaches Thu along with dry air advection, snow should wane Thu. On Friday however as a fast moving upstream shortwave crosses the Great Lakes and New York, supporting additional light accumulations east of the lower Great Lakes. For Days 1-3, the probability of significant icing (0.25-inch) is less than 10 percent. Petersen