Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 357 PM EST Sat Jan 15 2022 Valid 00Z Sun Jan 16 2022 - 00Z Wed Jan 19 2022 ...Ozarks to the Tennessee and lower Ohio Valleys... Days 1... An upper low centered over Oklahoma and North Texas this afternoon is expected to continue to dig southeast into the lower Mississippi Valley this evening. Still some concerns for the potential for heavy snow development along the western edge of the associated deformation zone as it evolves across northern Arkansas this evening. Indications of a well-defined TROWAL may support heavy snowfall rates, especially from the Ozarks eastward into the Mid South this evening. Latest HREF guidance shows a brief window where snowfall rates may reach above an inch/hr in some locations. Latest WPC probabilities have increased, indicating that accumulations of 2-4 inches are likely across north-central to northeastern Arkansas. Given the forcing, there is significant potential for locally heavier accumulations. As the upper low continues to pivot east, the western edge of the deformation precipitation shield is expected to move through the Mid South overnight and into the Tennessee and lower Ohio valleys on Sunday. Guidance indicates rain changing to snow in many locations as the low continues to deepen and track east. Due in part to model uncertainty with respect to thermals and where heavier precipitation will develop, probabilities for heavy snow have decreased across the area. However, cannot discount the potential for at least locally heavy accumulations, especially from Middle Tennessee into the Cumberland Plateau. ...Southern Appalachians through the Interior Northeast... Days 1-3... Overall, not much change to the previous forecast, with heavy snow expected from the southern Appalachians northward into the interior Northeast and significant icing likely for the southern Piedmont. As the low continues to move east, low-to-mid level frontogenesis/warm air advection will support precipitation spreading from the Southeast into the southern Appalachians and Mid Atlantic Sunday morning. A strong arctic high centered over the Northeast will ridge south, setting the stage for a significant freezing rain event over the southern Piedmont on Sunday. With the ridge expected to hold well into the day, heavy ice accumulations are expected. WPC probabilities indicate that ice accumulations of 0.10 inch or more are likely from Upstate South Carolina to the southern Virginia Piedmont. Within this area, locally heavier accumulations of 0.25 inch or more can be expected, especially across portions of Upstate South Carolina into central North Carolina, including the Charlotte Metro. Farther west, heavy snow is still expected for the southern Appalachians, with 8-12 inches likely and locally heavier amounts expected for the North Carolina mountains. By late Sunday as the system begins to lift ahead of an approaching northern stream trough over the Upper Midwest/Great Lakes, the low is expected to begin to track rapidly north along the Mid Atlantic coast Sunday night and through the interior Northeast on Monday. Overall, not much change in the larger scale picture -- with the track favoring snow changing to rain along the I-95 corridor. Heavy snow is still expected from the central Appalachians northward into the interior Northeast. Strong forcing, coupled with low-to-mid level frontogenesis is expected to support heavy snowfall rates (up to 2 inch/hr) moving north from the central Appalachians into the upper Ohio Valley and eastern Great Lakes region Sunday night, before reaching into northern New England by Monday morning. Snow totals of 8-12 inches are likely across this region, with locally heavier amounts expected, especially in the lee of the eastern Great Lakes, where a period of lake effect behind the departing system will likely bolster totals. ...Upper Midwest... Day 3... Alberta clipper will dive southeastward across North Dakota early Tues (D3) in association with a mid level shortwave and weak jet streak aloft. Moisture will increase to about 1-1.5 standard deviations above climatology (near 0.50") ahead of the system with warm advection snow spreading quickly across northern MN by Tuesday afternoon. Quick movement will limit snowfall potential but modest moisture and frontogenesis will support several inches along and south of the Canadian border. WPC probabilities for at least four inches of snow increase from south to north to around 50-60% near International Falls. Farther west, tail-end of the cold front will sink southward into western Montana where upslope snow will increase around Glacier National Park. Pereira ~~~ Key Messages for Winter Storm Affecting the Mid Mississippi Valley and Ozark Region to the Eastern U.S. January 15-17 ~~~ -- Heavy snow rates greater than 1"/hr are possible across portions of the Tennessee Valley and along and just west of the Appalachians Sunday into Monday. Significant impacts to travel are likely. -- Ice accumulation will expand from northeast Georgia through the interior Mid-Atlantic states on Sunday. The most damaging icing is likely across the Piedmont of the Carolinas, including Charlotte, NC and Greensboro, NC, which will result in dangerous travel, power outages, and tree damage. -- Heavy snow is expected along the Appalachians into the interior Northeast. Significant snow totals are likely across western North Carolina northward through western Pennsylvania and New York into Northern New England. -- Along the Atlantic coastline, strong winds and coastal flooding are likely. Some locations may reach moderate flood levels, with inundation affecting some coastal roads and structures.