Low confidence in this forecast. The American Models are still telling 2 stories, one of mostly snow and the other a mix bag of slop. So I've tried to blend them and I'll continue to do so with this update. Total liquid precip amounts are still high (from 1.5 -2.0" ending Thursday morning) so that's been consistent. The contention continues to be the near surface temperatures. The time of year and the time of day, would favor the warmer scenario however high precip rates can bring colder air down to the surface. At any rate the snow that falls will be wet and that leads to compaction when accumulating and accumulations will be dependent on the surface temperatures at any given location. I expect temperatures throughout the storm to range between 32 and 35 degrees. Today's warmth should disappear once precip begins because the atmosphere is pretty dry and the precip will evaporate at the beginning which will lead to cooling.
So precip should start this evening as a mix of rain and snow or just plain rain and gradually change to wet snow as the night progresses. Snows will accumulate mainly on grassy surfaces, car tops and roofs. With 1" or less in the cities, Charles and Calvert counties down to Fredericksburg and 1-3" for the rest of us. Streets should be just wet Wednesday morning but in Loudoun and Frederick counties there may be slushy areas. Precip will change to a mix of rain/snow b4 sunrise and then change back to all snow Wednesday afternoon. In Charles, Calvert, St Marys, Va's northern neck ( including the fredericksburg area) it will probably change to all rain in the morning b4 changing back to snow. During any period of heavy precip in the morning, the rain/snow mix may change to all snow for a time and where it's raining, snow should mix in. It all ends Wednesday evening. Once the precip changes to all snow, it may a while for it to start accumulating again.
Best guesses of total wet snow amounts ( mainly on grass, roofs, car tops );
West of Loudoun & Frederick counties: 12-18"
Loudoun & Federick counties: 6-12"
Fairfax, Montgomery, Howard & Baltimore counties: 4-8"
PG & AA counties: 3-6"
Charles & Calvert & Fredericksburg area & inside beltways: 1-3"
St. Marys down to the northern neck of Va : 0-1"
I think streets tomorrow will be mainly wet but again it's a low confidence forecast and I hoping for bust in the snowy direction....
Have a good one.