Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 313 PM EST Wed Feb 02 2022 Valid 00Z Thu Feb 03 2022 - 00Z Sun Feb 06 2022 ...Pacific Northwest... Days 1-3... Two shortwaves, one on Thursday and another on Friday, will drop southeast into the Pacific Northwest, separated by brief shortwave ridging Thursday night. The trailing shortwave is the stronger of the two, but both will be accompanied by diffluence at the leading edge of a Pacific jet streak to enhance deep layer ascent and spread moisture inland. The shortwaves will be embedded in otherwise mostly confluent flow, so the duration of forcing to produce snowfall should be limited as each shortwave is expected to be transient. However, briefly heavy snow is likely in the Washington Cascades both days 1 and 3, where WPC probabilities for 6+ inches peak above 60 percent. Snow levels during this time will be rather low, about 2000 ft on Day 1 and climbing to around 3000 ft by Day 3. This suggests that many of the Cascade Passes will also receive accumulating snow, with more than 6 inches likely at Snoqualmie Pass. ...Southern Rockies through the Central Plains and into the Northeast... Days 1-3... ...Several rounds of heavy wintry precipitation likely as a large scale system expands across the eastern CONUS... A large scale winter storm is ongoing this aftn and will become increasingly impactful across a large portion of the country, from the Southern Rockies through the Mid-Atlantic and Northeast. This system will occur in two waves. The first is moving across the Upper Midwest/Great Lakes today and will shift into the Northeast tonight. This first wave is associated with a northern stream shortwave moving across the Great Lakes. As this feature shits eastward, a downstream upper jet streak will intensify to place favorable RRQ diffluence overlapped with the primary mid-level height falls. This combined ascent is then likely to move atop a low-level baroclinic boundary behind a surface cold front, with the implied robust frontogenesis driving enhanced lift through the region and shifting off to the northeast. This will continue to support moderate to heavy snow, with some banded structures likely to produce snowfall rates of 1"/hr or more at times. WPC probabilities for more than 6" are above 80% from NE Indiana through western NY state. Locally more than 10 inches is possible. South of this swath of snowfall, some mixed precipitation including sleet and freezing rain is likely, but accumulations are progged to be modest during most of D1. Also on D1, a southern stream trough will amplify across the Four Corners and begin to shift east while interacting with trailing vorticity from the northern stream. As this evolves into a closed low embedded within a full latitude trough, downstream divergence will overlap with increasing upper diffluence with the RRQ of an intensifying poleward arcing jet streak. This will produce heavy snowfall across southern New Mexico including the Sacramento Mountains and nearby High Plains where upslope flow behind a surface front will drive enhanced ascent into an airmass characterized by slightly above normal PWs. WPC probabilities are high for 6 inches, with locally more than 12 inches likely in the higher terrain. As this snowfall occurs in the Southern Rockies, the developing synoptic ascent downstream will become impressive, and overlap with strongly sloping frontogenesis behind the aforementioned surface front. At the same time, a bubbling theta-e ridge both at the surface and in the mid levels will provide enhanced moisture into the region, which is likely to isentropically ascend cold surface high pressure to produce widespread and heavy precipitation. Although this deepening trough is likely to advect rapidly to the east, pronounced ascent within this increasingly moist column will produce heavy precipitation from Texas through the Ohio Valley D1, with precipitation eventually "catching" the lead wave to reduce or negate any break in precip from the lead impulse. For D1, the heaviest snow is likely from NE OK into central MO where WPC probabilities for 6 inches are 40-60%. Southeast of there, Robust WAA driving the theta-e ridge will produce a pronounced warm nose into the MS VLY and southern OH VLY producing a swath of freezing rain and sleet. There is likely to be significant accumulations of sleet and freezing rain with this event, but placement of this axis still remains somewhat uncertain. Around 0.5" of sleet is possible from eastern OK through northern AR and into the OH River Valley, with more than 0.25" of ice (and locally more than 0.5") likely from north of Dallas, TX northeast through Memphis, TN and northward to Louisville, KY. This system becomes one large sprawling complex of snow, sleet, and freezing rain D2 with precipitation spreading from Arkansas northeast to Maine. On the north edge of this swath of precip, heavy snow is likely, with some laterally translating bands of 1"/hr likely producing local maxima of more than 12 inches across Northern New England, with a large area of more than 4 inches from central Ohio northeast through Maine. South of the heavy snow, significant freezing rain is again likely as a warm nose persists but CAA begins to cool the lowest levels of the column. Across the OH VLY and into the Mid-Atlantic, freezing rain is likely to exceed more than 0.1" from eastern KY through Southern New England, with locally more than 0.25" possible, most likely in the eastern OH VLY, or in the terrain of the Poconos and Catskills. There is also increasing potential for sleet accumulating to as much as 1" where the cold depth below the warm nose causes rapid refreeze and a long duration of sleet. The best chance for this appears to be from central NY eastward through Massachusetts, including Albany, NY and Boston, MA. By D3 everything will shift offshore leaving just some light snow across Maine the first half of D3, but with limited accumulations. Weiss ~~~ Key Messages for Feb 1-3 Winter Storm ~~ -- A large, prolonged, and significant winter storm will continue to impact much of the central U.S. and move into the Northeast overnight, bringing a variety of winter weather hazards including heavy snow, sleet, and freezing rain. -- Heavy snow totals are expected over the Southern Rockies and from the south-central Great Plains through the eastern Great Lakes and interior Northeast. -- A corridor of heavy ice accumulation is likely from Texas through the Ohio River Valley, especially from eastern Arkansas northeastward to western Kentucky. This will likely result in power outages, tree damage, and dangerous travel conditions. -- Locations impacted by snow and/or ice are expected to have temperatures remain below freezing, and well below average, for at least a couple days after the wintry precipitation ends.