Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 320 AM EST Sat Mar 12 2022 Valid 12Z Sat Mar 12 2022 - 12Z Tue Mar 15 2022 ...Mid-Atlantic and Northeast... Day 1... Low pressure over central Georgia this morning will rapidly deepen as it tracks toward the Mid-Atlantic and across eastern New England today, bottoming out just under 970 mb later this evening near Nova Scotia. This quick deepening is driven by impressive height falls associated with an approaching mid level trough axis currently sweeping through the mid-MS to lower OH Valley and also a strengthening coupled jet streak. The overlap of the jet streaks with the height falls above an intensifying baroclinic zone along a surface cold front will help bomb out the cyclone. The increasing moisture and warm air advection will bring a shield of precipitation northward up the eastern U.S. while the Arctic air mass pours southeast behind the cold front. As the cyclone deepens, impressive cold air advection will lead to a rapid transition and changeover from rain to wet, heavy snow along and northwest of the low center where the frontogenesis banding is most pronounced. Within this narrow deformation band, snow rates 1-2"/hr are expected as shown by the latest HREF with the greatest snowfall rates early this morning across the TN to southern/central Appalachians then reaching the Mid-Atlantic and Northeast later this morning and New England this afternoon/evening. The trend this cycle has been for a slightly wetter solution and a nudge to the south/east with the axis of heaviest precipitation, which minor increases in snow amounts along and just west of the I-95 corridor. The greatest snow totals for the D1 period are still favored for interior Northeast locations where the latest probabilities for 6"+ remain above 50 percent and well above 80 percent for interior New England. Along the I-95 urban corridor, a difficult/challenging forecast as melting at the onset and the rapidly evolving precipitation changeover difficult to pinpoint but potential exists for a very intense 2-4 hour period where snow rates will be high enough to overcome any warm ground temperatures and combined with the gusty winds, difficult to dangerous impacts may still occur. As the core of the mid/upper level trough swings through the Great Lakes and Ohio Valley during the afternoon/evening, steepening low level lapse rates during the diurnal maximum will likely bring scattered to numerous snow showers and snow squalls as far southeast as the Central Appalachians. Gusty winds and snow rates up to 1"/hr will be possible and this could create difficult to hazardous conditions including severely limited visibility. ...Pacific Northwest... Days 1-3... A compact, potent closed low reaches the Pacific Northwest late tonight into Sunday afternoon before filling as it moves inland. The system then takes on a positive to neutral tilt as it crosses the northern Rockies. Combined with favorable upper jet dynamics, orographic lift and a favorable, modest atmospheric river, widespread precipitation is expected with heavy snow confined to the terrain areas of the Olympics and Cascades where WPC probabilities remain high for 6+ inches. Lesser probabilities for significant snow exist for the Sawtooth and Northern Rockies. Another system reaches the region late on D3 as a fast moving shortwave energy rounds the base of a closed low near the Gulf of Alaska. This opens up into a large scale trough as it swings onshore. Modest moisture combined with the favorable height falls and lift will produce widespread precipitation late Monday into Tuesday. This system is a bit warmer with higher snow levels so the greater probabilities for significant snowfall are confined to the higher elevations of the northern WA Cascades. There, WPC probabilities for 6 inches are more reach moderate to high percentages. Taylor ~~~ Key Messages for the Tennessee Valley through Northeast Winter Storm ~~~ -Snow rates of 1-2"/hr combined with wind gusts up to 50 mph will produce blowing and drifting snow at times this morning from the Central Appalachians to Mid-Atlantic and then the Northeast later this morning through the late afternoon. Severely reduced visibility and white-out conditions will make travel extremely dangerous at times. -Snow accumulations of 6-12"+ are expected over much of the interior Northeast. Closer to the coast and I-95 corridor, a burst of intense snowfall may accumulate up to a few inches in a very short period. -Strong winds and the heavy wet snow could lead to scattered power outages and tree damage. Untreated surfaces will freeze over as temperatures drop sharply. -Record cold is likely for much of the Southeast Sunday morning as temperatures fall below freezing along the Gulf Coast and through northern Florida.