The new work week will begin with high pressure across the Northeast US and cold, dry dense air in place along the DC-to-Philly-to-NYC corridor. At the same time, low pressure will begin to pull out of the central Plains and make a move towards the Ohio Valley and it will be accompanied by plenty of moisture. This moisture shield, however, will tend to fall apart some by later tomorrow night and Tuesday as it pushes into areas north of the PA/MD border. The low pressure system in the Ohio Valley will tend to weaken by later tomorrow night and Tuesday as its upper-level support becomes more stretched out.
A wintry mix of snow, sleet and rain is likely to arrive in the DC metro region during the mid or late afternoon hours, but the progression of the moisture to the northeast will on the slow side. As a result, snow and/or sleet is not likely to arrive in the Philly metro region until early tomorrow night and it’ll likely hold off for New York City until early Tuesday morning. While snow accumulations will be somewhat limited in the DC-to-Philly-to-NYC corridor due to prospects for mixing and also due to the weakening nature of the low pressure system, there can be some slick spots during this event; especially, on untreated surfaces. Temperatures will remain at or below freezing for much of the time during this event and the ground is quite cold following a weekend with modified Arctic air in place. The precipitation (light freezing rain, light snow) will tend to linger into late Tuesday night and early Wednesday across PA, NJ and southern NY as the low pressure system slides quite slowly across the region.
One additional note, there is the chance for mesoscale banding during this early week event which could result in bursts of heavier precipitation and localized higher amounts of snowfall. My general thinking on accumulations for the entire DC-to-Philly-to-NYC corridor is anywhere from a coating to as much as 2 or 3 inches by Tuesday night with localized higher amounts possible due to the potential small-scale banding. The timetable of precipitation is as follows for some of the I-95 corridor metro regions:
Mid-late afternoon Monday through Tuesday morning
Early Monday night through Tuesday night
Early Tuesday morning to early Wednesday morning