Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 248 PM EST Wed Mar 09 2022 Valid 00Z Thu Mar 10 2022 - 00Z Sun Mar 13 2022 ...Southern Rockies... Days 1-2... A potent shortwave will dive southward out of British Columbia and then race southward through the Intermountain West and amplify into the Four Corners at the end of D1 /Friday evening/. Downstream of this feature, impressive height falls and PVA will combine with WAA on mid-level SW flow and modest upper diffluence to produce heavy precipitation across the southern Great Basin and southern Rockies. This will manifest as heavy snow in the terrain, with the heaviest accumulations likely in the Wasatch, the Kaibab Plateau, the San Juans, and the Sangre De Cristos. WPC probabilities for more than 6 inches are as high as 70%, highest in the San Juans, and locally 10 inches of snow is possible before the system pulls away, leaving just additional moderate snow across the Sangre De Cristos on D2. ...Central Plains through the Mid-Atlantic and Northeast... Days 1-3.. Two significant storm systems will likely bring heavy snow to parts of this region through the weekend. The first is ongoing this aftn across the Central High Plains and into NE/KS. A cold front south of the region is leaving an elevated baroclinic zone upon which a shortwave will impinge from the west. At the same time, an upper jet streak downstream of the primary longwave trough axis digging across the Great Basin will intensify to produce enhanced RRQ diffluence for deep layer ascent. The overlap of these features will combine with an increasing LLJ and 285K-290K moist isentropic upglide to expand a shield of snowfall near the NE/KS border through Thursday, extending into NW MO including the Kansas City metro area. A band of heavy snowfall is likely as the jet streak and baroclinic gradient combine to produce some enhanced fgen, into which snowfall rates may exceed 1"/hr at times. WPC probabilities for 4+ inches are above 80% in this area, with local maxima approaching 10 inches likely as reflected by the WSE 90th percentile. This lead surge of precipitation will begin to wane over Missouri early D2 as the shortwave shifts away reducing the attendant forcing. However, as this occurs dual shortwaves, one in the southern stream over the Four Corners region, and another dropping through the northern stream out of Saskatchewan will begin to intensify. Downstream of the southern stream shortwave, impressive mid-level divergence will spread eastward downstream of this shortwave, with the impulse itself opening and ejecting into the Southern Plains Friday night. This shortwave will then likely phase with the northern stream impulse over the MS VLY Saturday, becoming an amplified neutrally-tilted longwave trough as it shifts into the Northeast late D3 and beyond. Forcing for ascent will become quite robust as this synoptic pattern evolves, with potent height falls combining with impressive coupled jet streaks, and the guidance suggests the subtropical jet streak may eclipse early March-record strength across the Mid-Atlantic and Northeast Saturday into Sunday according to the SPC sounding climatology. Where this forcing overlaps, a surface low is likely to develop and then explosively deepen from the Southeast into the Mid-Atlantic and then across eastern New England. On D2, the residual baroclinic gradient behind the aforementioned surface front will help spawn the surface low, downstream of which warm and moist advection will intensify. This should produce a swath of moderate snowfall from northern OK through southern MO and into the western Great Lakes, where WPC probabilities for more than 4 inches are as high as 40% near Springfield, MO. However, the most significant snowfall is likely beginning D3 as the surface low deepens rapidly and synoptic forcing becomes intense. As this low lifts northeast, potent CAA will commence from the NW, and this will help sharpen what should be an impressive deformation/fgen band NW of the surface low. Where this band sets up and collapse to the east, snowfall rates will likely eclipse 1"/hr, which will overcome any hostile and warm antecedent temperatures and rainfall across the TN VLY and OH VLY. While there remains uncertainty into exactly how far south this axis will pivot, and how much precipitation can fall after the changeover to snow (which may be briefly accompanied by sleet), WPC probabilities on D3 are 20-30% for 4 inches in TN, and above 70% for 4+ inches in KY. Further to the north, and especially into the terrain of Upstate New York and Northern New England, this event is likely to be all snow, and will be heavy at times. WPC probabilities are above 90% for 4 inches, as high as 50% for 12+ inches in the Adirondacks, and a widespread swath of double-digit snowfall accumulations is likely across the interior Northeast. Weiss ~~~ Key Messages for Tennessee Valley through the Northeast Winter Storm ~~~ - There is increasing confidence that a significant winter storm will develop late Friday across the Southeast and then spread heavy snow across the interior eastern United States through Saturday. - Significant impacts due to heavy snowfall rates and accumulations are possible from the Tennessee Valley through the Central Appalachians and into much of the interior Northeast. - Hazardous travel conditions are possible due to heavy snow and gusty winds. - Details in the track and timing of the storm, in addition to precipitation type and amounts, remain uncertain, but will be refined in the near future. - Extremely cold temperatures are likely behind the system this weekend. Record lows are possible across portions of the Southeast and Mid-Atlantic. Subfreezing lows are possible along the Gulf Coast and Northern Florida on Sunday.