There was a noticeable gap early this morning in the precipitation field along much of the I-95 corridor as the initial northern stream surface low pressure system was beginning to transfer its energy to a secondary developing coastal storm. Also, an upper level low at 850 mb is strengthening near the North Carolina coastline and this will actually gradually pull colder air into the Mid-Atlantic in the upper part of the atmosphere as the day progresses. That gap seen earlier in the radar loops is now filling in and snow has broken out within the last hour across the western (Virginia) suburbs of DC (Chantilly, Reston, Tysons). Snow and graupel (snow pellets) has been quite intermittent so far in the Philly metro region, but the snow will become steadier and heavier late this morning and continue throughout much of the afternoon mixed with sleet at times. The steadier snow will spread into the NYC metro region during the mid-day hours.
A general 2-4 inch snowfall is expected in the northern and western suburbs of Philly with isolated higher amounts and lesser amounts in the city of Philly and its southeastern suburbs of interior South Jersey due to some mixing. Farther south, the western and northern suburbs of DC should end up in the coating to a couple of inches range with lesser average amounts in the District and points south and east due to some mixing. The entire NYC metro region should see a general 2-4 inch snowfall with isolated higher amounts and there is the chance for more than that in nearby places like Long Island as the coastal storm really gets cranking late today and early tonight just off the Mid-Atlantic coastline. In fact, farther up the coastline in the corridor between Providence, RI and Boston, MA, there will likely be quite a significant snowfall from this developing coastal storm. Stay tuned for updates.