On Sunday night and Monday, this initial low pressure system over the Ohio Valley should then weaken and give way to a developing storm near the Mid-Atlantic coastline and this second system will become the dominant player. The exact timing of the transfer of energy from the initial low to the secondary system and the speed at which the coastal storm intensifies will play important roles as to how much snow (and/or rain) can fall in the DC-to-Philly-to-NYC corridor. It does appear increasingly likely that accumulating snow is a real threat in the Mid-Atlantic region on the front end of this winter storm event (later Sunday into early Monday) that will be associated with the (initial) Ohio Valley system. There is a chance that some areas see a changeover from snow to rain and/or sleet by early next week; especially, in areas south of the PA/MD border such as in the DC metro region.
Shortly after the second storm develops off the Mid-Atlantic coastline, it is likely to encounter a pretty strong blocking pattern in the part of the atmosphere over the eastern Canada and this will inhibit its movement to the north and east. As a result, the precipitation time period from this second (coastal) system could extend all the way into early Tuesday in the Mid-Atlantic region and an influx of colder air on its back side could result in a change back to snow in some of those areas that do indeed turnover to rain and/or sleet earlier in the event (such as in those areas south of the PA/MD border).
Stay tuned…lots of details to be ironed out in coming days for this complex storm threat.
Meteorologist Paul Dorian