Adding LWX's discussion too. Another dent in the rainfall deficit.
Therefore, widespread rain is expected across the area Sunday into
Sunday evening and it will be breezy. A line of heavier showers
and perhaps a thunderstorm will most likely accompany the
frontal passage Sunday afternoon/evening. Given the strong winds
aloft, this has the potential to mix down gusty to perhaps even
locally damaging wind gusts. One mitigating factor will be the
lack of instability that is progged in the models. It will be
difficult to get instability rooted within the boundary layer.
Therefore, certainty for damaging wind gusts is low at this
time. A soaking rain is expected given the dynamics and moisture
associated with this system. Rainfall amounts around 1-3" are
most likely. The recently dry conditions may minimize the flood
threat, but localized flooding cannot be ruled out given the
higher rainfall amounts and the fact that rainfall rates may be
heavy at times with the frontal passage.
Colder air will move in behind the front, first later Sunday
evening in the Allegheny Highlands and then Sunday night from
northwest to southeast across the rest of the area. With the
upper-level trough axis lagging behind the frontal passage by a
few hours or so, this suggests that there will be some
anafrontal characteristics to the boundary. Therefore, moderate
precipitation is expected for a few hours or so behind the cold
front before drier air eventually works its way in overnight.
There will be enough cold air for rain to change to snow in some
areas. As of now, it appears that the best chance for
accumulation will be along the ridges of the Blue Ridge, Potomac
Highlands, and Allegheny Highlands where cold air will move in
sooner. For locations along and west of the Allegheny Front, an
upslope component to the low-level flow will cause additional
snow showers to last longer behind the cold front, enhancing
potential for accumulating snow. Winter weather headlines may be
needed for the mountains. For the valleys, any chance for
accumulating snow is low, but this will continue to be
monitored.