Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 400 AM EST Fri Jan 21 2022 Valid 12Z Fri Jan 21 2022 - 12Z Mon Jan 24 2022 ...Western/Southwestern U.S... Days 1-3... Strong mid-level shortwave trough moving through the Great Basin will dig south-southeastward and close off over the Desert Southwest tonight. This weekend, the closed low is forecast to dip into northern Mexico and turn east, eventually pushing into far west Texas by the end of Day 3 (12Z Mon) as it starts to weaken. Sufficient moisture and forcing is favored over Colorado day 1, coupled with orographic enhancement, yielding locally heavy snowfall accumulations for areas of the central Rockies with as much as 6 to 12 inches of new snowfall and isolated heavier amounts, especially over the Sangre De Cristo range. Nearer to the track of the upper low, more favorable dynamics will capitalize on limited moisture to produce a few inches of snow over the higher peaks in eastern Nevada. By days 2 and 3, sufficient forcing may allow for some light snowfall accumulations to occur over the Mogollon Rim of AZ as the upper low turns toward the east. ...South Texas/Gulf Coast to the Southern Mid Atlantic... Days 1-2... Cold air filtering into/through the South/Southeast behind an arctic front with overrunning precip will support a continuation and/or blossoming of wintry ptypes through South Texas and along the Gulf Coast from Louisiana eastward to southern Alabama this morning before ending this afternoon as temperatures warm. Farther east, slowly-moving boundary astride the Gulf Stream will carry an area of low pressure northeastward with a gradient of rain to ice to snow on its northwest side. Isentropic ascent atop sub-freezing temperatures will support a significant icing threat for areas of eastern NC and northeastern SC. Potential exists for 0.10-0.25" ice accretion over a large area of the Carolinas with locally higher amounts into early Saturday. This could cause serious impacts to areas that receive more than 0.25" ice. The farther east/suppressed trend has largely stopped and the recent guidance is now wavering on how far northwest to take the precip shield (snow) via the surface front as well as the approaching upper vort max progged to move through the southern Appalachians ~06Z Sat. This may enhance some snowfall back toward Charlotte, NC but heavier totals will be farther northeast near Virginia Beach. There, WPC probabilities of at least four inches of snow is moderate (about 40-50%), but smaller-scale banding may enhance snow totals here with the north-northeast flow off the Atlantic. ...Upper Midwest/Great Lakes... Days 1-3... Fast cyclonic flow around the upper vortex in Canada will take three clipper systems across the Upper Midwest and Great Lakes through the period. Each will have some warm advection snow preceding it with a resurgence of lake effect snow post-FROPA on variable northwesterly flow. Lead system will spread a couple inches across central/northern Minnesota as the front pushes through while the second and third systems may see a stripe of modest snow of a few inches from northwest to southeast along each's area of low pressure. Cold airmass will support SLRs in the 15-20:1 range. Three-day totals may exceed six inches over some areas outside the lakes while favored lake areas will see higher amounts through multi-band setup. Downwind of the eastern lakes, several inches of snow is expected days 2-3 with lighter amounts over the Midwest day 3 as the second system moves through. WPC probabilities of at least four inches over the three-day period was highest over Minnesota (30-70%) as well as over the lake belts (>80%). ...Eastern Massachusetts... Days 1-2... Northeast flow off the Atlantic into the cold airmass over New England will support ocean effect snows into eastern Massachusetts, generally south/southeast of Boston, and over Cape Cod. Exiting system to the south may enhance some snowfall with some banding potential per some higher res guidance day 2 before the flow becomes unfavorable and QPF ends. Several inches of snow is possible in some localized areas should the flow align and maintain over the route 3/3A corridor. Fracasso ~~~ Key Messages for Winter Storm Impacting Portions of the Southeast and Mid-Atlantic Jan 20-22 ~~~ -- Snow, sleet, and freezing rain will spread across areas of the Southeast through the southern Mid-Atlantic states today. -- Significant ice accumulations are expected in parts of the Carolinas, resulting in dangerous travel conditions and scattered power outages. -- Moderate to locally heavy snow is forecast from northeastern North Carolina through the southern DelMarVa Peninsula tonight.