Now that New York City and Boston have received significant snowfalls, what about DC and Philly where there hasn’t been a major snowstorm in a couple of years?  The overall weather pattern (neg SOI values, neg NAO, MJO) is setting up to give DC and Philly their best shot in quite awhile during the next two or three weeks. 

Specifically, the southern branch of the jet stream has become active (as suggested by the negative SOI) and this will very likely produce additional coastal storms in the next few weeks.  Also, there is the best chance for some decent blocking in quite awhile as the NAO is forecasted by both the 12Z Euro and 12Z GFS Ensemble (maps below from raleighwx.com web site) to stay in negative territory over the next couple of weeks. 

Finally, the MJO moves from phase 1 (cold) to phase 2 and/or 3 (still cold) over the next couple of weeks (map below).  In fact, we have two threats for accumulating snow in the Mid-Atlantic region between mid-week and the latter part of the weekend. 

The first threat for the DC-to-Philly-to-NYC corridor comes later Wednesday into Wednesday night as a storm rolls out of the southeast US towards the Mid-Atlantic coastline.  The air will be marginally cold for this first system; therefore, precipitation should begin in the form of rain across the DC metro region and possibly even as far north as Philly and NYC.  However, once the low scoots by to the coast, colder air will move in and change the rain to snow and accumulations are possible Wednesday night. 

There is even more potential for the weekend event as a widespread cold air outbreak will take place in the eastern US.  A large long wave upper level trough of low pressure will set up near the east coast on Saturday allowing for cold air to plunge from the Arctic Circle way down into northern Florida and this pattern should also help to spawn a coastal storm, but exactly where it forms is still to be determined. 

The timetable for accumulating snow in the Mid-Atlantic from this potential weekend coastal storm would be late Saturday into early Sunday.  The “precipitation-type” this weekend will likely not be an issue in the I-95 corridor as it will be with the mid-week system since cold air should be well established in the region by then.

Paul Dorian/Meteorologist

The SI Organization, Inc.

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