Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 201 AM EST Wed Feb 19 2025 Valid 12Z Wed Feb 19 2025 - 12Z Sat Feb 22 2025 ...Southern Mid-Atlantic States... Day 1... A significant winter storm will continue to spread eastward into the southern Mid-Atlantic with potentially major impacts including heavy snow and significant ice. See the latest Key Messages linked at the end of the discussion. Surface low along the Central Gulf coast will cross North Florida early this afternoon and parallel the Southeast Coast tonight. The northern stream shortwave responsible for the heavy snow in the Plains will continue eastward into the southern Mid-Atlantic, helping to spread generally light snow to the southern Appalachians, aided by some orographic enhancement. WPC probabilities for at least 4 inches are generally <30%. As the Gulf low transitions to a western Atlantic/coastal low, precipitation will progress to the VA/NC coast with snow to the north (solidly cold column over VA) and freezing rain and sleet to the south where warmer air aloft will overrun the cold surface temperatures near and just below freezing over eastern NC and into portions of eastern SC as well. Snowfall to the north will likely maximize later this afternoon and evening as the surface low starts to deepen over the Gulf Stream, with locally heavier rates >1"/hr over southeastern VA, leading to moderate/heavy amounts. WPC probabilities for at least 6 inches of snow are >50% there. There is a much larger footprint of >2" probabilities of at least 40%, extending from southwestern VA eastward, as far north as Fredericksburg, VA to Rehoboth Beach, DE, and as far south as the Raleigh-Durham metro. Into NC, several hours of freezing rain are likely starting this afternoon and continuing into the evening. Accretion will depend on rainfall rates (which limit accretion), wind, and time of day, but most of the guidance still indicates the potential for a couple tenths of an inch of ice, roughly along and east of I-95 in eastern NC. WPC probabilities for at least 0.10" ice are >40% with some areas likely seeing >0.25" ice. Precipitation will wind down overnight and end by Thursday morning. ...Great Lakes/Northeast... Days 1-2... Lake effect snow will diminish this morning as height falls over the Corn Belt move into the region, favoring widespread light snow over the Great Lakes and Midwest tonight into Thursday. WPC probabilities for at least 4 inches of snow are low (<40%) except for some lingering lake bands and/or lake enhanced snows. ...Pacific Northwest through the Central Rockies... Days 1-3... A potent but progressive Pacific system will start to move into the Northwest this morning, spanning the latitudes from NorCal up to the Canadian border. IVT will be modestly high (~90th percentile) into NorCal/southern OR/northern NV toward Idaho, supporting light to moderate snows for the terrain with snow levels near 3000ft to the north and 5000ft to the south that will rise a bit as the core of the moisture plume pushes through. The system will move steadily along which will end QPF from west to east starting as early as tonight over the Cascades and on Thursday over the Great Basin. Moisture will wane with decreasing synoptic support into Thursday, with snow confined mainly to the Unitas and higher CO Rockies by then. For the 2-day period, WPC probabilities for at least 8 inches of snow are highest (>70%) over the higher terrain above 6000ft closer to the coast, 7000-8000ft over the Great Basin, and 9000ft over CO/WY. A new system will to enter the Northwest by D3 with lighter snow into the northern Cascades. ...Southeastern Mass... Day 2... The exiting system from the Southeast/southern Mid-Atlantic will track northeastward and may clip southeastern MA/Cape Cod on Thursday on its way into Atlantic Canada. The question revolves around the speed of the incoming northern stream upper low and how much it can capture the exiting system and pump up the downstream ridge. 00Z guidance still shows at least some snow into the region, but vary on how much. The best chances for snowfall over 4 inches remains over Nantucket (~70%) as well as both Martha's Vineyard and Cape Cod (40-60%), with low probs (10-20%) from Block Island to New Bedford to Plymouth. Fracasso ...Winter Storm Key Messages are in effect. Please see current Key Messages below... https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png