This forecast is for the second part of the two-part rain/snow event. What I have is not too different from what the models show now, save for some lesser amounts in northern MD. The changeover from rain to snow and the surface temperatures will be the biggest players in inhibiting snowfall totals. The models have probably underforecast the warmth in MD on Monday before the front makes its way through from north to south. However, once the changeover is made, moderate to heavy snowfall after a brief period of moderate sleet could lead to decent totals from DC northwards through central PA. The best combination of colder air and intense snowfall seems to be in southwestern PA, where a band of 4-8″+ is possible.
I also included a small area of 8-12″ for upsloping and cooler surface temperatures in the Appalachians in southern PA. The band of higher totals could shift north/south a bit depending on the placement of the low as it passes over the region.
EDIT: I may have to make some last minute changes to it if the temperatures stay colder in northern MD today. The 2-4″ and 4-8″ contours could creep further south!