Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 418 AM EST Sat Nov 30 2019 Valid 12Z Sat Nov 30 2019 - 12Z Tue Dec 03 2019 ...California to Great Basin and Rocky Mountains... Days 1-3... ...More heavy snow for the ranges of central to northern California... An upper low centered west of Oregon will retrograde SW to a position off the northern California coast Sunday. A prolonged and robust Pacific jet will advect copious moisture into California, noted by PWAT anomalies of more than 2 standard deviations above the mean. The period of surging 700 mb moisture advection and ascent is Sat into early Sunday across the ranges of northern and central CA, with heavy snow resulting in the Siskiyous and Shastas down to the northern Ca Sierra Nevada mountains. The lift continues as the moist inflow persists through Sunday across the Sierra Nevada while a break occurs in the ranges of northwest CA. A second wave of low pressure approaches with renewed lift from the wave in northwest CA overnight to early Mon. The day 2 higher snow totals are forecast across the central CA Sierra Nevada mountains, where 2-3 feet of snow is expected at higher elevations. Moisture streaming inland combines with more modest ascent across Oregon and into Idaho/Nevada where light snows are expected on day 2. On Monday the strength of the 700 mb lift weakens with time, so the early period continuing snow in the CA Sierra Nevada finally taper as drier air aloft moves around the circulation into northwest CA. The heaviest snow for the 3 day period is likely in the CA Sierra Nevada, where 3-day totals may exceed 4 feet in places. ...Central/Northern Plains into the Great Lakes... Days 1-2... ...Major Winter Storm Moving from the northern Plains to Upper Midwest and upper Great Lakes... A 700 mb low is forecast to move from Nebraska east across Iowa to northern IL tonight. Warm air advection around the low leads to a mixed phase precipitation event across southeastern SD and southern MN, southern WI, and southern lower MI. Much of western and central SD an southeast ND are projected to have heavy snow, continuing across northern central MN and northern WI. Snowfall rates may exceed 1"/hr at times, and there is confidence in a swath of snow exceeding 12 inches as noted by WPC probabilities over 70% in the SD Black Hills and across portions of southeast ND and areas of MN near the Lake Superior shoreline, where upslope flow produces an extended period of snow. On the north side, dry air from Canada limits how far north snow extends to the US/Canadian border, with amounts tapering in northern ND/northern MN, and the northeastern UP of Michigan. On Sunday, the low will continue to move across southern lower MI. In central MI, the in situ cold air leads to mixed sleet and freezing rain, which eventually becomes snow in northern lower MI and into the UP of MI. Probabilities are moderate to high for 8 inches in the UP of MI across to the northern lower MI. In the northern L.P., lake enhancement may paid in producing higher local maxima near Lake Huron. The event ends as the low departs and drier air aloft moves across MI Sunday night into Mon. ...Mid Atlantic/Northeast... ...Prolonged Snow Event in interior Eastern New York and Interior New England... Days 2/3... Low-mid level warm advection occurring as a high moves east across the northeast and low pressure approaches from the Ohio Valley results in a mixed sleet and freezing rain event across southwest NY to PA along and east of the Allegheny Mountains, and then into the southern tier of NY into southeast NY. WPC probabilities are moderate for 0.25" of accretion. Sleet accumulations are expected to reduce snow amounts in southern NY and northern PA. Higher snow amounts are possible in areas bordering Lake Ontario into the Tug Hill and down the Mohawk Valley to the Catskills, Capital District, and Berkshires. On Monday, low pressure redevelops off the Mid-Atlantic coast and lifts slowly E/NE off the New England coast. The track allows cooling to occur west of the 850 mb low to allow mixed precip to change to snow over northeast PA to southeast NY and the Metro New York area. The track south of New England will advect moisture westward into the cold air over New England and New York. This allows for a long duration snow event inland from the Catskills across the Capital District to the Berkshires and southern Green Mountains and Monadnocks of southern NH. WPC probabilities are high for 6 inches or more across much of eastern upstate NY, as well the Berkshires and Worcester Hills of Massachusetts. The proximity of the low near the New England coast lowers snow probabilities due to mixed precip types along the MA/NH/ME coasts. The 00z NAM had heavier QPF in northern NJ to metro New York due to slower forward progression of the low and was given the least weighting. More weighting was given to the GFS, ECMWF, UKMET, and SREF Mean. The probability of greater than a quarter inch of freezing rain is less than 10 percent day 3. Petersen