Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 456 AM EST Fri Jan 28 2022 Valid 12Z Fri Jan 28 2022 - 12Z Mon Jan 31 2022 ...Southern Appalachians through the Mid-Atlantic... Days 1-2... ...Significant Nor'easter likely for the Mid-Atlantic and Northeast... While some differences remain, overnight models continued to move into better agreement -- signaling that heavy snow and powerful winds are likely to develop along the Mid Atlantic coast tonight, before moving northeast across eastern New England on Saturday. Phasing shortwaves over the eastern U.S. will support surface low development east of the Carolinas by late today. As the associated upper trough begins to lift northeast, assuming a negative tilt as moves across the Mid Atlantic, the surface low will begin to rapidly intensify as it tracks north. Strong upward ascent supported by a coupled upper jet and low-to-mid level frontogenesis will promote the development of moderate to heavy snow on the northwest side of the low. Overnight hi-res guidance suggests snowfall rates of 0.5-1 inch/hour developing over southeastern Virginia, the southern Delmarva, and southern New Jersey Friday night before extending into Long Island and southern New England by early Saturday. The system will continue to strengthen on Saturday, with a closed upper low developing along the Mid Atlantic coast Saturday morning. At the surface, consensus of the deterministic models show central pressure dropping into the 960s as the low tracks east New England late in the day. As the low continues to intensify, snowfall rates are expected to increase as well, with several hi-res guidance members indicating rates of over 2 inches/hour developing across Long Island and southern New England Saturday morning and then into southern Maine by the afternoon. While this will almost certainly be a powerful system, it is expected to be fast-moving one as well. By Saturday night, the threat for heavy snow is expected to quickly fade as the low lifts into Atlantic Canada. For the 48-hour period ending 12Z Sunday, WPC probabilities indicate that widespread snow accumulations of 4 inches or more are likely from southeastern Virginia, along the Mid Atlantic coast, and through southern New England into Maine. Accumulations of 8 inches or more are likely from the Delmarva to southern Maine. WPC probabilities continue to indicate the heaviest storm totals are likely to center across eastern Massachusetts, with a significant threat there for accumulations exceeding 18 inches. Meanwhile, a frontal boundary associated with the amplifying upper trough is expected to support snow showers moving southeast from the Ohio Valley into the central and southern Appalachians later today. Favorable upper forcing along with a weak surface wave may help enhance precipitation rates over the North Carolina Piedmont into the southern Appalachians, where some locally heavy snow amounts may occur along the North Carolina-Tennessee border. ...Pacific Northwest to the Northern Rockies... Day 3... An upper low moving across the Gulf of Alaska on Saturday is expected to transition to an open wave, with energy shearing southeast across western Canada and the Pacific Northwest Sunday into early Monday. This will bring a frontal boundary and increasing moisture into the region, supporting the return of precipitation, including the potential for heavy snows across portions of the northern Cascades and Bitterroots. For days 1-3, the probability of significant icing is less than 10 percent. Pereira ~~~ Key Messages for Jan 28-30 East Coast Winter Storm ~~ -- A winter storm is likely to produce snowfall accumulations of 12 inches or more along portions of the Mid-Atlantic coast and through eastern New England Friday night and Saturday. Local maxima may exceed 20 inches. -- Heavy snow rates combined with strong winds are expected to produce blizzard conditions along portions of the Mid-Atlantic and New England coasts. Whiteout conditions could create nearly impossible travel, while strong winds will likely lead to scattered power outages and some damage. -- Significant coastal impacts are possible, including coastal flooding and beach erosion. -- Significant impacts will also likely extend south along the Mid-Atlantic coast where moderate to heavy snow and gusty winds are possible. Difficult travel is likely. -- Very cold temperatures will likely follow the storm with dangerous wind chills possible Saturday night.