Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 405 AM EDT Sun Mar 31 2019 Valid 12Z Sun Mar 31 2019 - 12Z Wed Apr 03 2019 ...Eastern Great Lakes and Northeast... Day 1... Surface low along the cold front will lift northeast today dragging the cold front off the coast tonight. Warm temperatures ahead of this low will keep most of the precipitation as rain, but cold advection and modest frontogenesis will allow precip to changeover to snow, especially in the high terrain of New England and the Adirondacks of New York, where a few inches are possible. WPC probabilities are low for 4 inches, and only in the aforementioned terrain. Wrap around winds from the low will allow some lake effect snow downwind of Lakes Erie and Lake Ontario today as well. Additional light accumulations are possible locally east of Lake Erie with more favorable conditions allowing moderate probabilities for four inches on the Tug Hill Plateau east of Lake Ontario through tonight. ...Colorado/New Mexico/Texas... Day 1... A shortwave trough dropping through the Four Corners will briefly close off into a mid-level low early today. This feature quickly re-opens over CO/NM as a 100+kt jet max rotates to its south kicking it to the southeast. The combination of height falls and jet level diffluence will drive synoptic ascent, and briefly increase isentropic lift atop a cold surface high pressure to the east. Despite a weakening mid-level feature, enough 1000-500mb RH tapped by this robust ascent will produce heavy snow in the San Juans and Sangre De Cristos. WPC probabilities are moderate for 8 inches in the highest terrain of these ranges, with lesser amounts more widespread above 4000 ft. Additionally, despite the rapid weakening of this feature and loss of column moisture, the jet streak racing eastward into Texas may support some light snow Sunday night as synoptic ascent combines with briefly robust frontogenesis into the elevated DGZ. The NAM suggests some light accumulations are possible, but remains a wet outlier, and WPC probabilities are less than 20 percent for 2 inches in the western Great Plains of Texas. ...Northern Rockies into Northern Plains... Days 1-2... A jet maximum diving from Western Canada will induce lift within its LFQ, aided by a modest baroclinic gradient along which a weak wave of low pressure its likely to form. This feature will move swiftly southeast from Montana into Iowa, producing a swath of light to moderate snowfall. Snow levels range from 3000 ft across MT, to as high as 6000 ft into CO, and the heaviest snow is likely in the ranges of NW WY, where WPC probabilities are moderate for 4 inches across the Big Horn, Wind River, and Absaroka Mountains. Lighter accumulations are possible into the Dakotas along the jet streak, but accumulations should generally be under 2 inches. ...Oregon/California through the Central Rockies... Days 2-3... Upper trough and associated surface reflection approach the N CA coast Tuesday morning with the upper jet and moisture plume of +2/+2.5 PWAT anomalies advecting well onshore by Wednesday. Despite snow levels being quite high Tuesday, 6-8 kft, snow will overspread the high terrain beneath robust synoptic ascent due to height falls and persistent upper diffluence. Additionally, snow levels will gradually fall as the trough axis shifts into the west, supporting heavy snow as low as 4000 ft into WY, and down to 6000 ft in CO/UT. The heaviest snow this period is likely in the ranges of ID, UT, and NW WY where WPC probabilities are moderate to high for 8 inches. Lesser amounts are likely elsewhere across the Cascades of OR, the Sierra and northern ranges of CA, as well as the Great basin and CO where probabilities are high for 4 inches. The probability for significant freezing rain (0.25 inches) is less than 10 percent all 3 days. Weiss