Pretty thorough layout by LWX:
Unsettled conditions return on Friday to conclude the work week.
The mentioned closed low will track across southern Michigan on
Friday morning before settling overhead late Friday. Over the
past couple of days, this system has certainly exhibited a
faster trend. Warm advection precipitation enters the picture
before daybreak across the Allegheny and Potomac Highlands. This
shield of precipitation presses eastward through the day making
for a chilly and raw day. With a cold air damming signature
evident, have favored the colder solutions which tend to verify
better in these setups. Accordingly, have brought high
temperatures down into the low/mid 40s, with mid 30s over the
mountains.
With cold air in place, some of the precipitation will be
wintry in nature. There is a chance for a brief rain/snow mix at
the onset in the vicinity of the metros, but no accumulation is
expected. A dusting up to 0.1-0.2" are possible closer to the
Mason-Dixon Line and points westward. As usual, elevation will
be the key as temperatures are to remain colder. Models show
some wavering of the 925-850 mb freezing line which would make
for a mix of freezing rain along the Alleghenies. Through Friday
evening, a trace up to 0.05" of ice accretions are in the
forecast for such locations. Elsewhere, a cold rain is expected
through the day with up to 0.25-0.50" north of DC and lighter
amounts to the south. Light snow continues into the night along
the Alleghenies as lift is augmented by upslope flow. As the
cold front tracks through overnight, precipitation comes to an
end from west to east. If temperatures cool off enough, areas
north of the DC and Baltimore metros may see a light coating of
snow. Overnight lows will be in the low/mid 30s for most, while
20s are more commonplace west of I-81. As winds turn blustery,
wind chills are forecast to drop into the single digits to teens
along the Alleghenies.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
A deep area of low pressure is progged to be drifting offshore
Saturday. Blustery conditions are possible in its wake depending on
how strong it gets, and how close it remains to the coast; guidance
remains somewhat at odds on how both of these factors play out.
Regardless, colder than normal temperatures are expected to spiral
into the region as the low departs and high pressure briefly noses
in. High temperatures may not get out of the 40s for most (staying
in the 30s for the higher terrain). Overnight lows in the 20s seem
likely Saturday night (teens for the higher terrain).
Another trough quickly approaches Sunday into Monday. Timing and
strength differences are evident in the guidance, as is to be
expected in progressive flow at longer time ranges. There is also
uncertainty in the degree of phasing of shortwaves rotating around
the base of the large scale trough. Some cold air will be present,
so at least the higher elevations may stand another chance at some
wintry precipitation, but details are very fuzzy this far out.