Just read Mt. Holly's take. Thought it was a really good breakdown of the situation as it stands. Worth a read, especially the first paragraph.
In the long term, all eyes are on the end of the week as a potential
storm takes shape off the US East Coast. The Arctic high pressure
from midweek remains in control through Thursday. From there, the
range of possible outcomes diverges wildly. With strong ridging
present in the West, a deep trough will dig into the Southeast, with
a strong shortwave embedded within the base. This trough will
gradually tilt from positive to neutral or negative as it moves
towards the Southeast coast. This will spur offshore cyclogenesis,
with its strength and placement dependent on how fast the trough
begins to tilt negative. In addition, the developing storm appears
likely to eventually phase with a northern stream shortwave dropping
out of Canada, which would yield further intensification as it moves
north or northeast. The track of this developing low will then
determine potential impacts for the Northeast and mid-Atlantic.
Based on the potent nature of the shortwaves involved and with
unusually strong baroclinicity likely to be present, this has the
potential to be a strong storm. Certainly cannot ignore the number
of various ensemble system members and occasional deterministic runs
showing sub-970mb cyclones along or within striking distance of the
Northeast and mid-Atlantic coasts. At this early stage, a multi-
cycle consensus of model guidance favors a glancing blow for our
region, with potentially greater impacts towards New England or
Atlantic Canada. However, this system does have some of the
hallmarks of previous high impact storms where medium range models
displayed a right of track (ROT) bias. And ensemble spread has
generally been favoring the left side of the means and deterministic
runs. So we are definitely not out of the woods, but we also have
several days to watch this, and it will likely be some time before
we can definitively say whether there will be any impacts locally.