Models continue to show a big coastal storm to impact the Mid-Atlantic Region on Wednesday. While some model data is turning WARMER, models often overdo the warming and underestimate the strength of the “CAD” (Cold Air Damming.) If the low pressure system is closer to the coast, rain spreads father inland with ice in the Piedmont and snow or snow/sleet in the Valley. If the low is a bit further offshore by 50 miles, this will allow it to be a bit colder with more snow and ice accumulations.
Our snow and sleet map is our FIRST GUESS and *SUBJECT TO CHANGE*… We are blending in model ensemble guidance and making it a bit “colder” than the warmest models due to the “Cold Air Damming” on the east side of the mountains that should keep temperatures closer to freezing. It’s important to note that the new European model has ZERO snow accumulation for Washington, D.C., or Fredericksburg, but our current thinking is that the European model is too “amped” or aggressive. The European Ensemble is colder but not by a ton. The GFS American and GFS Ensemble guidance is colder and makes the most sense.
Snow and sleet (and even freezing rain) is expected to develop across Southwest and Southern Virginia between 5:00 a.m. and 9:00 a.m. Wednesday and slowly move into the Metro Richmond Area and US 460/360 Corridors between 8:00 a.m. and 10:00 a.m., then moving northward into Central and Northern Virginia during the late morning hours. Temperatures in these locations will begin to warm “aloft” and change the precipitation over to all freezing rain and eventually rain for some areas. IF THE PRECIPITATION ARRIVES EARLIER, MORE SNOW MAY ACCUMULATE SINCE THE AIR ALOFT WILL LIKELY BE COLD ENOUGH. This happens often, known as “Overrunning Precipitation” where the moisture rides over the colder air trapped at the surface.