We are now within 12 hours of this time period of wintry weather starting, and we have a much better idea of what will happen than we did yesterday. However, there are a few things we do not know, and that we probably won't know until the event starts. Nevertheless, I think after this storm, we will be done with winter.
What we do know is that a weak area of low pressure, referred to as a clipper, is currently moving out of the Midwest and into the lower Ohio River Valley and Mid-Atlantic. As it moves closer towards the Mid-Atlantic, and surge of moisture will overspread the area around 5pm (give or take a hour or two). This initial surge of moisture should be all rain. If temps can drop quick enough, that surge of moisture may be able to end as some snowflakes around 10pm or so, but don't bet on it. It's during this time that areas north and west of DC should see most, if not all, of their accumulations. There will then likely be a little bit of a lull once that round of precip ends around midnight.
As that weak area of low pressure, moving out of the Midwest, dies off, a coastal storm (which is already developing), will take over. That coastal storm will move northward throughout the night, and bring in our next surge of precip into the area, which should be mostly snow.
What we don't know mainly concerns the coastal system. The biggest question is, "How far north and west does it track?" The further northwest it is, the more snow we could see. Right now, it appears that the coastal storm should stay far enough to our southeast to spare us of a significant snowfall, but it should come close enough to give us some snow.
Another worry I have concerns the temperatures during this event. Temps will only be marginally cold enough for snow (31-34). However, if the storm can come far enough northwest, we will see heavier precip, which would overcome the temps and cool our atmosphere. Temperatures will also determine what sticks. We'll need temps to be closer to 32, or below, to really pile anything up. Roads should be fine. Our snow totals will be dependent on how low the temps get and how heavy the precip is (which is dictated by how far NW the coastal storm can come).
Currently, we have a Winter Weather ADVISORY up for a large chunk of the Mid-Atlantic for the possibility of at least 2" of snow. Again, the totals NW of DC are dependent on the first round of moisture, and I'm not sure that will have enough of a punch with that to bring more than an inch or maybe two to most locations. I think that most areas southeast of DC should be able to meet the advisory criteria of 2" with the coastal storm.
Impacts across Southern Maryland should be minimal to moderate. Right now, I do expect delays and a few closings for area school districts (refer to the School Odds below). Expect a few slick spots on the way to work tomorrow morning as well. For federal and military employees, I don't think you will get a delay (I'd place it a 30% chance), but I could see Liberal Leave/Telework being an option that is offered.
If this coastal storm tracks further south and east, and we don't see the snows we're expecting, everyone should go to school on time, and there would be no issues with the AM commute. If the storm comes a little further north and west than expected, then the chances of closings and delays goes up along with impacts in the morning. Remember, this time of year, it is hard to accumulate snow on the roads. With this storm, it's more so the timing, than the amount.
The Bottom Line is that snow looks likely tomorrow morning. An initial area of precip will move through tonight giving the NW DC suburbs their snow, while we should get rain. A coastal storm will then head northward, before going out to sea, which should give us our accumulating snow in the morning. Remember, this time of year, it is hard to accumulate snow during the daylight hours. We could see more snow if this coastal storm moves further NW than thought (25% chance) and we could see less if it stays further to our SE (20% chance). If my forecast verifies, as I think it will, there will be a few issues tomorrow morning with some slicks spots. However, because of the timing we could see area schools opt to delay or cancel classes. Temps warm to near 40 in the afternoon, so any snow should be gone by then! Stay with JB Weather for continuing coverage.