At the time of the Global Precipitation Measurement (GPM) Core Observatory overpass (April 1, 2017, 0550 UTC), the storm's center of low pressure was south of Long Island. At the mid-levels of the atmosphere, the circulation was centered over northeast Pennsylvania. This led to a classic overrunning, warm conveyor setup, which happened when the counterclockwise low level flow drew in cold air out of the north/northeast (hence "Nor'easter") from Canada. Higher up, warm and moist air from further south was lifted over this cold air and resulted in precipitation in the form of snow at the surface. The heavy band of snow that is visible in the GPM data resulted in 8-14 inch totals over southern Maine and New Hampshire, while totals further south in Massachusetts were limited by some mixing with rain.
Music: "Flowing with Time," Philippe Lhommet, KOKA Media