Special Weather Statement, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
458 AM EST Tue Jan 18 2022

.SYNOPSIS...
High pressure will build into the southeastern states today
before moving out to sea Wednesday. A cold front approaching
from the northwest is expected to arrive early on Thursday.
Frigid high pressure is anticipated to follow for Thursday night
into the weekend, when an area of low pressure may develop just
off the coast.

&&

.NEAR TERM /THROUGH TONIGHT/...
The departing deep storm, now well NE of the region, will relax
its grip on the weather today with high pressure building in
from the west. Mostly sunny skies early then some daytime SC for
most areas (especially NW through). Winds will remain gusty but
then winds will decrease thru the afternoon. Gusts 20 to 25 mph
much of the day. High temperatures will be a few degrees below
normal with highs in the 30s most areas and some low 40s for
Delmarva and some upper 20s far NW.

Tonight the ridge of high pressure passes across the region while a
front moves well NW of the region. Clouds associated with the front
will affect the northern parts of the area with mostly high and mid
clouds. Winds will be light overnight. Lows will range from the
teens and low 20s N/W to the upper 20s/low 30s for the metro areas
and Delmarva.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Busy weather pattern continues in the short term. For Wednesday, low
pressure will track by to the north of the region as it moves from
Ontario into Quebec. This will help give us a respite from the
colder weather as winds will be southwesterly as we'll be on the
warmer side of this system. As a result, most areas will see highs
reaching well into the 40s under increasing mid and high clouds.

As we go through the Wednesday night into Thursday period, the
aformentioned low will continue tracking eastward as it moves
into Atlantic Canada and this will drag a cold front through the
region from north to south. At the same time, there will be
some upper level energy rounding the base of the long wave
trough over the east and another system moving northward from
the south along the frontal boundary. The upshot of all this is
a period of rain will develop by the overnight period Wednesday
night but as the colder air moves in behind the front expect
this to change over to snow from north to south. This changeover
should occur during the overnight hours Wednesday night N/W of
the I-95 corridor and by around sunrise across the urban
corridor. The snow may continue for a few hours into Thursday
before ending as colder, drier air continues to move in on N/NW
winds. The total precipitation with this system could be on the
order of a quarter to half inch of QPF but expect that a lot of
this will occur before the changeover from rain to snow.
Experience has shown that often in these cold advection type
situations that by the time the colder air moves, heavier precip
is just about getting ready to exit. The NAM is a bit more
robust with heavier precip back into the colder air but given
the setup think this may be overdone. The upshot is that at this
time I expect snow amounts to mostly be just a light coating to
under an inch. But again, challenging forecast and if this
system is a little more robust as indicated by the NAM there
could be areas that see a couple inches of snow accumulation.

The snow should mostly wind down by mid/late morning Thursday but
could last a bit longer near the coast where some rain could also
continue to be mixed in. Otherwise it will be breezy and chilly with
temperatures not rising much due to the cold advection
pattern...mostly staying in the 20s north, 30s south. By Thursday
night, the cold front should be stalled just off to our south while
arctic high pressure settles in over the Great Lakes. This will
result in some clearing, at least over the north, with a very cold
night in store. Lows will be mostly in the single digits to even
near zero in the southern Poconos with teens farther south.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
The weather pattern remains cold and potentially quite active
through the long term period as a long wave trough continues to
dominate the eastern CONUS. For Friday, it will be quite cold as a
strong arctic high settles in to our north with highs mostly in the
20s except northern areas through the southern Poconos likely not
getting out of the teens.

Friday night into Saturday, attention will turn to the next
shortwave trough as it progresses eastward out of the Ohio /
Tennessee Valley region. The GFS and to a lesser degree the GEM
Global deamplify this wave resulting in a muted response at the
surface with the area only getting grazed by a weak low passing
south of the region. Meanwhile the ECMWF continues to be quite
robust with this wave developing it into a major coastal storm
passing just off the coast. If this solution (the ECMWF) was to
pan out, we could be looking at a significant snowstorm for the
Friday night / Saturday period. However given the continuing
model spread, forecast confidence remains fairly low so POPs are
mostly in the chance range for Friday night / Saturday. It
should remain cold enough though for whatever occurs to be a
mostly snow event unless a significant shift N/W were to occur
with the track of the low which seems less likely at this time.
Following this potential system the end of the weekend into
early next week should feature drier but continuing cold
weather. &&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

.Today... VFR conditions expected with mostly BKN sky cover N/W and
SCT for srn NJ and Delmarva. Winds will remain gusty from the W or
NW thru the day. Gusts will range mostly between 20 and 25 knots
before subsiding late this afternoon. Decreasing clouds towards
sunset. High confid.

.Tonight... VFR. Mostly just high clouds. Light W winds. High
confid.

Outlook...

Wednesday...Mainly VFR. Southwest wind increasing to 10 to 15
knots with gusts around 20 knots. High confidence.

Thursday...Rain changing to snow in the morning before ending
in the afternoon. The rain and snow should lower conditions to
MVFR/IFR with improvement to VFR in the afternoon. Northwest
wind 10 to 15 knots with gusts around 20 knots. Medium
confidence.

Friday...Mainly VFR. North wind around 10 knots. High
confidence.

Saturday...A chance of snow with MVFR/IFR conditions possible.
North wind around 10 knots. Low confidence.

&&

.MARINE...

A somewhat uncertain forecast with Gale gusts have been slow to
diminish on the waters early this morning. After watching the
latest trends, I decided to extend the Gale for the ocean out
until 10 AM since more 35 kt gusts possible. For Delaware Bay,
most of the higher gusts are probably over, so the Gale was
taken down there and replaced with a SCA flag until early
afternoon. A SCA flag will follow the remaining Gale, probably
lasting the rest of the day. The winds and seas will probably be
sub-SCA tonight, but then winds increase back to near SCA
levels by dawn Wed.

Outlook...

A prolonged period with Small Craft Advisory conditions is
anticipated.

Wednesday...South to southwest wind around 20 knots with gusts
of 25 to 30 knots.

Thursday...Northwest wind 15 to 20 knots with gusts near 25
knots.

Friday and Saturday...North wind around 20 knots with gusts of
25 to 30 knots.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Gale Warning until 10 AM EST this morning for ANZ450>455.
     Small Craft Advisory until 1 PM EST this afternoon for ANZ430-
     431.

&&

Synopsis...Fitzsimmons/Iovino
Near Term...O'Hara
Short Term...Fitzsimmons
Long Term...Fitzsimmons
Aviation...Fitzsimmons/O'Hara
Marine...Fitzsimmons/O'Hara

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