Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 340 PM EST Sun Mar 03 2019 Valid 00Z Mon Mar 04 2019 - 00Z Thu Mar 07 2019 ...Northern Mid-Atlantic to New England... Day 1... ...Hazardous overnight travel conditions expected over the northern Mid-Atlantic and New England through Monday... A shortwave over the TN Valley will swing around a cold core low centered over Ontario and swing across the Mid-Atlantic this evening and off New England Monday, riding behind a 130kt jet streak. Meanwhile a surface low over the southeast will lift over the southern Mid-Atlantic coast this evening and rapidly develop off the northern Mid-Atlantic coast late tonight and push past Maine Monday afternoon. On the northern side of the moisture plume ahead of the trough, snow will continue to intensify as the surface low develops. Snow this evening will quickly shift northeast from the central Appalachians and southern PA across the northern Mid-Atlantic coast and southern New England tonight. The 12Z consensus of the HREF/ECMWF/GFS is a bit heavier and farther west than the 00Z consensus. The highest snow accumulations are forecast along and just NW NYC to Boston tonight, and along the coast of Maine Monday morning. WPC Day 1 probabilities are moderately high for 6" in this corridor with high probabilities for 8" in far east Maine. A 4-8 hour window exists where snowfall may approach or exceed 1"/hr where low level frontogenesis and mid-level deformation overlap, making for overnight travel impacts over northern portions of the northeast urban corridor. Snow looks to linger over Boston around sunrise, ending earlier south of there. Snow rates will decrease over eastern Maine Monday afternoon as the low lifts across Nova Scotia. A narrow swath of sleet and freezing rain is likely on the southern periphery of the heaviest snow swath, but accretion is expected to be light and WPC probabilities are less than 20 percent for 0.1 inches over the northern Mid-Atlantic and southern New England. ...Great Basin across the Central and Southern Rockies to the southern High Plains... Day 1... Weak shortwave disturbances will continue to push east from CA on a strong Pacific Jet max over 130kt that shifts east tonight. A narrow swath of precip from northern California will continue to push across Colorado, with the best overlap of left front quadrant diffluence and low-level confluence between a Pacific airmass and Canadian airmass along a slowly drifting south cold front will occur across Colorado this evening. Snow elevations along this front range from 4000 to 5000ft. Heavy snow is expected at higher terrain in this narrow corridor with high Day 1 probabilities for 8" confined to the Wasatch and San Juans, where low probabilities for 12" exist. Mid-level forcing from the shortwave activity tonight is strong enough to create lift over the cold surface air and produce bands of snow on the southern High Plains. Moderate probabilities for two inches extend over southeastern CO across the OK and northern TX Panhandles and even into west-central OK. ...California... Day 2... A mid-level ridge axis crosses the CA coast late Monday, cutting off moisture inflow and making about 24hrs of precip relief until the next low approaches the CA coast with much above normal moisture Tuesday. A narrow atmospheric river reaches the central CA coast Tuesday afternoon with very elevated snow levels of 7000 to 8000ft over the Sierra Nevada. Day 2 WPC probabilities are moderate for 8" in the southern Sierra Nevada. ...The West... Day 3... The low reaches the northern CA coast Wednesday with a now expansive Pacific moisture plume spreading across CA/OR the Great Basin to the northern and central Rockies. Snow elevations will remain elevated; around 4000ft in OR/ID/WY and 5000 to 8000ft over CA/NV/UT/CO. Heavy snowfall is likely above 7000 ft in the Sierra where Day 3 WPC probabilities feature a high risk for 18" inches with 30" in 24hrs possible. Moderate to high probabilities for 8" are also across higher terrain of the northern CA and southern OR Cascades, the Great Basin and across UT/CO. Jackson