1) The storm is split into two parts - a vortex over the Ohio Valley and a coastal low. As the Ohio Valley storm weakens, the coastal takes over. Anytime this transfer process occurs i.e. one storm robs energy and moisture from the other, the result is often a disorganized, weak field of precipitation left in between the two systems - conincident with the D.C.-Baltimore corridor;
2) The coastal low, while intensifying, will be pulling its precipitation and energy away from the coast fairly rapidly;
3) There is no deep, subfreezing air mass to our north, and thus no feed of intensely cold air into either storm system. This has been a major reason why coastal storms have failed to produce measurable snow in our region all winter;
4) Enough mild air may be pulled in off the warm Atlantic to keep the lowest few 1000 feet of atmosphere above freezing for some of the time - thus facilitating more of a wintery mix;
5) The coldest air will be over the higher elevations to our west and northwest...and as usual this winter, these regions will likely experience the most prolonged period of all snow;
6) There is limited moisture inland in between this complex of systems, generally 0.5" of total precipitation...this does not translate into large snow accumulation particularly with rain and sleet mixing in.
Many government and private forecast agencies are starting to issue snow accumulation maps. The one I feel most comfortable with thus far, in terms of painting the general snow accumulation across the Mid Atlantic, comes from Accuweather: