[12z GFS forecast map for early Saturday; courtesy tropicaltidbits.com]
Overview A significant coastal storm will move from the Carolina coastline early Saturday to just off the New England coastline by Saturday night and the result should be some accumulating snow in much of the I-95 corridor. This storm will undergo rapid intensification as it treks northeastward during the day Saturday. One important limiting factor for significant snow from this storm in the Mid-Atlantic region is the fact that there will be no Arctic air mass in place ahead of the system and no strong high pressure system will be located to the north during the event acting as an all-important cold air source. Nonetheless, despite a likely mixture of precipitation during this event, snow accumulations are still possible in the DC-to-Philly-to-NYC corridor given the expected storm track and rapid intensification which can "generate" its own cold air.
Another system will drop southeastward across the Great Lakes region late Sunday in much the same manner as some of the recent “clippers”. This system, however, has more potential as it will intensify in the Mid-Atlantic region on Monday and it will have a cold air mass in place as it approaches. As a result, snow is likely to be the dominate precipitation type with this system on Sunday night and Monday and accumulations are likely.
Round One Precipitation from the early weekend coastal storm should reach the DC metro region between 7 and 11pm on Friday night, Philly region between 9pm - 1am (Sat), and NYC between 3 and 6am early Saturday morning. Precipitation is likely to fall as snow at the onset and accumulations are quite likely by Saturday morning in the DC and Philly metro regions. The snow is likely to then change to rain or a mix of rain, sleet and snow on Saturday before possibly changing back to all snow later in the day. This event is likely to end in the DC metro region by early-to-mid Saturday afternoon, late afternoon-to-early evening in Philly and later in the evening in the NYC metro region. Preliminary snow accumulation estimates (still subject to change) are as follows:
1-3 inches in DC and in its N and W suburbs 3-6 inches in Philly and NYC and in their N and W suburbs Lesser amounts to the south and east of these big cities
Round Two The second storm will likely produce accumulating snow later Sunday night into Monday and it is likely to have an impact on the Monday morning commute.