Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 411 AM EST Fri Mar 11 2022 Valid 12Z Fri Mar 11 2022 - 12Z Mon Mar 14 2022 ...Mid-Mississippi Valley through the Mid-Atlantic and Northeast... Days 1-2... A surface cold front will stall as a stationary front across the Mid-South/TN Valley late Friday while a secondary arctic front approaches from the NW. Along the lead front, a southern stream shortwave moving out of the Desert Southwest will shift eastward while weakening, but will likely interact/phase with a northern stream shortwave digging out of Alberta to form a neutrally tilted longwave trough near the Ohio Valley. At the same time, downstream jet streaks will intensify to near or above record strength according to the SPC sounding climatology, and form an impressive coupled jet structure lifting northeast across the eastern CONUS. Spread in the location and intensity of this overlap of features is decreasing, and it is likely a surface low will develop near the Gulf Coast and then move relatively quickly northeast while explosively deepening. Northwest of this track, heavy snow is likely. On D1, as the surface low begins to deepen and eject northeastward with the coupled jet structure strengthening downstream of the phasing longwave trough, an expanding area of precipitation will likely spread from the southern Tennessee Valley as far north as northern New England as WAA increases. Initially, the column will be too warm for snow except in northern New England and the far NW portion of the TN and OH Valley. However, rapid CAA will quickly cool the column, while at the same time leading to tightening fgen overlapping the strengthening deformation axis. This will cause rain to change quickly to snow from west to east, and snowfall will likely become heavy within a narrow band from central TN through eastern KY and farther north into WV, PA, and Upstate NY. The guidance is in good agreement in this band occurring, and some of the models suggest folded theta-e collocated with -EPV favorable for CSI or even upright convection, and snowfall rates reaching 2"/hr. This convective snowfall could quickly overcome the hostile antecedent conditions, and WPC probabilities for more than 4 inches are as high as 10% as far south as Huntsville, AL, and above 50% from eastern TN through western MD and into much of Upstate NY and northern New England. More than 8 inches of snow is likely in Upstate NY and northern New England where most of the event should be cold enough for heavy snow, and more than 12 inches is likely across portions of the Green and White Mountains where upslope flow is maximized. By D2, this low quickly pulls away to the northeast while continuing to deepen into Canada, and residual heavy snow will linger into Maine and far northern NH/VT early D2 before pivoting off to the northeast. WPC probabilities for 8+ inches are high in Canada D2, and storm total snowfall may reach 18 inches in parts of the Adirondacks and northern New England. Along the I-95 corridor from Washington, D.C. to Boston, MA, snowfall is likely to be much less. However, the guidance overnight has continued to trend a bit more progressive and colder. This colder solution combined with the impressive CAA/fgen that will cause a rapid transition from rain to snow has led to a continued increase in snowfall probabilities on Saturday for the urban areas of the Northeast. Heavy snow rates which could reach 1"/hr will likely overwhelm antecedent warm/rain, and WPC probabilities for at least 1 inch of snow are as high as 70% for the I-95 corridor from Washington, D.C. to NYC, with slightly lower probabilities into Boston, MA. Along that same stretch from D.C. to NYC the WPC probabilities for 4+ inches have increased to 5-10%, while just west of I-95 those probabilities are as high as 20-30%. ...Pacific Northwest... Days 2-3... A potent closed low dropping out of the Gulf of Alaska will approach the Pacific Northwest coast Saturday night and lift onshore as far east as the Northern Rockies while filling on Sunday. This feature will be accompanied by a robust Pacific jet streak and WAA ahead of a cold front which will help spread moisture onshore while snow levels rise to 3000-5000 ft. Above these levels, heavy snow is likely as the shortwave advects eastward enhancing deep layer ascent which will be aided by upslope flow as mid-level winds nearly orthogonally intersect some of the terrain. WPC probabilities for more than 6 inches of snowfall are high in the Olympics and both WA and OR Cascades, with lesser accumulations likely into the Sawtooth Range and Northern Rockies. Light to moderate snowfall accumulations are likely at the Cascade Passes across WA and OR on Sunday. Weiss/Churchill ~~~ Key Messages for the Tennessee Valley through Northeast Winter Storm ~~~ - A significant and impactful winter storm is likely for portions of the Tennessee and Ohio Valleys, through the interior Eastern United States late tonight through Saturday. - Snow rates of greater than 1"/hr combined with gusty winds will produce blowing and drifting of snow and severely reduced visibility. This will create difficult to hazardous travel conditions. - The greatest snow accumulations are likely across portions of the interior Northeast where totals in excess of 8 inches are likely. This could lead to scattered power outages due to the heavy and wet nature of the snowfall. - In the wake of the storm system, much colder air will spread across the Southeast and Mid-Atlantic with lows likely below freezing along the Gulf Coast and northern Florida Sunday morning.