814
FXUS61 KPHI 050254
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
954 PM EST Wed Dec 4 2024

.SYNOPSIS...
A low pressure system moves into the Great Lakes tonight. This
deepening low will track to our north through Thursday as a
strong cold front sweeps across our area Thursday morning. Cold
and dry high pressure will then build to our west on Friday and
remain situated to our south through the weekend. Several low
pressure systems then look to take aim at the area through the
middle of next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
10 PM update... no additional changes from the prior update at
this time.

8 PM update... no major changes at this time. Made some modest
tweaks to snowfall and pops, highlighting areas across central
and eastern NJ where latest guidance concentrates a band of
precip ovenright...this area has the best chance of snowfall
accumulations on the southeast side of I-95. Also backed off
slightly around PHL proper as this area seems pretty unlikely to
get any accumulations based on current readings and guidance.

3 PM discussion...A strong storm system will impact the region,
bringing some rain and snow showers, strong winds, and
continued below normal temperatures through Thursday. A Wind
Advisory remains in effect for Thursday from 6 AM until 10 PM
for strong westerly winds near 20-35 mph, with gusts around
40-55 mph. Greatest impacts are expected Thursday morning when
strong winds and scattered snow showers, mainly north, could
impact the morning commute with slippery road conditions.

Synoptic Overview...A deep positively tilted trough approaches
the Great Lakes tonight. The trough axis will dive quickly
southeastward across the Mid Atlantic early Thursday while
becoming negatively tilted as it shifts offshore. Height falls
quickly spread across the area tonight into Thursday morning. At
the surface, a strengthening low pressure system will pass just
north of the Great Lakes today, reaching the Canadian Maritimes
late Thursday. A strong cold front will sweep through the area
Thursday morning, likely offshore by noon. The frontal passage
will yield very strong cold advection in its wake, with 850 mb
temperatures upstream around -10C to -15C. Post frontal surface
pressure rises will be near 1 mb/hour. This is NOT a clipper
system, to be sure!

As stronger forcing for ascent arrives tonight, precipitation,
mainly in the form of scattered light rain/snow showers, should
develop within the region, with the greatest chances (60-70%)
residing mainly north and east of the Philly metro. Within the
Philly metro and south, less forcing may result in little to no
precipitation until the arrival of the front Thursday morning.
Areas along and north of the I-78 corridor will likely see
mostly snow with this activity, with a rain/snow mix farther
south and mainly rain near the coast. QPF is light, largely less
than 0.10". Any snowfall accumulation outside of the Poconos
and higher elevations of northwest New Jersey will remain less
than 1", a brief dusting at best. The higher elevations and
southern Poconos could see about an inch or two of snow tonight.
A southwest breeze will be strengthening overnight as the cold
front approaches, and especially toward daybreak to around 15-20
mph, with gusts near 25-30 mph possible. The winds, mixed
boundary layer, WAA, and cloud cover will keep temperatures
relatively mild, perhaps even rising a few degrees overnight.
Forecast low temperatures are mainly in the 30s.

For Thursday morning and through the rest of the daytime hours,
the strong cold front will quickly approach and begin passing
through the forecast area near or just after daybreak Thursday,
and should be offshore by around noon. If moisture is
sufficient, some snow showers or snow squalls could develop
along or just ahead of the frontal boundary following the
diminishing overnight precipitation. Moisture is expected to be
limited though, so it will probably be a struggle to get
anything of significance farther south. The limiting factor for
any impacts from this activity will be surface temperatures, as
most areas south of I-78 will be above freezing with above
freezing roadway temperatures. Nevertheless, a quick dusting of
snowfall could result in grassy and elevated surfaces as far
south as the coastal plain, and may cause some slippery travel
during the morning rush hour. An additional inch or two of
snowfall is forecast for the southern Poconos, resulting in
event totals of 1-3". For now, we have opted to preclude a
Winter Weather Advisory for Carbon and Monroe counties with the
intent of individually handling any snow squalls that develop
with short-fused snow squall warnings. Furthermore, any fresh
snowfall could combine with gusty winds expected during the day,
resulting in areas of blowing snow across the Pocono Plateau.
Because of this, added some enhanced wording in our forecasts to
express this possibility.

As hinted prior, the main story will the the windy conditions
expected in the wake of the frontal passage. West winds are
forecasted to be 20-35 mph with gusts as high as 40-55 mph! A
Wind Advisory remains in effect for the entire area for
Thursday. Some tree damage and isolated power outages are
possible. Any outdoor objects, including seasonal decorations,
should be secured.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As we head into Thursday night, the pressure gradient will
remain quite strong over the region as low pressure really
begins to strengthen over the Gulf of the St. Lawrence and
large/expansive high pressure builds over the Central CONUS. For
at least the first portion of the night, wind gusts around
35-45 mph are expected to continue before waning a bit into
early Friday. Skies will be mostly clear and conditions will be
dry for the majority of the area, except for the Poconos which
may have some lingering cloud cover and a chance for snow
showers. Any additional accumulation will be insignificant,
however. Lows will mainly be in the 20s.

For Friday and Saturday, high pressure over the Mississippi
River Valley will slowly begin to translate east toward the
Southeast US. We`ll likely have one more breezy day though on
Friday as the pressure gradient will remain elevated across the
Mid-Atlantic. Wind gusts are expected to be in the 30-40 mph
range as model soundings suggest that we`ll mix up to around
850mb yet again. Fortunately by Friday night, the pressure
gradient will weaken, so winds will be more tame into Saturday.
Otherwise, Friday into Saturday will feature mostly clear skies
except for a few passing clouds on Friday night. It is possible
some snow showers make stream into the Poconos on Friday night
as some shortwave energy passes by, but the air may be too dry
for such to occur, so did not include in the forecast at this
time.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
High pressure off to our south will then control our weather
through Sunday night as the weather pattern begins to moderate.
Fair weather conditions are anticipated as temperatures return
back to seasonable levels.

Our attention then turns to the early and middle portions of
next week as forecast guidance suggests that the pattern will
become unsettled and a bit more active. Next week will start
with another low pressure system that is poised to cut up
through the Great Lakes region on Monday with a trailing cold
front approaching from the west. This will likely bring periods
of light to moderate rain to the region on Monday.

Beyond Monday, model guidance really begins to disperse with
regard to the progression of the front. The majority of
deterministic and ensemble members suggest that the front will
weaken as it approaches and eventually stall. Depending on where
the front stalls out, will determine what happens for the
middle portion of the week. For example, the 12Z/ECMWF stalls
the front offshore, resulting in wetter conditions toward the
coast, and drier conditions north and west. Meanwhile, the
12Z/GFS keeps the front stalled to our west, resulting in
additional lows and rain developing and riding along the front.
For this reason, have stayed very close to NBM guidance
considering the different scenarios. One thing is for certain
though, and that is we`ll return to above normal temperatures
next week with the storm track being to our north and west. So,
any precipitation that does occur will likely fall in the form
of rain.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of Tonight...VFR overall, though clouds will continue to
lower and thicken. Overnight, some rain/snow showers expected
across the region, which could cause visbys to go sub VFR at
times. Southwest winds 10-20 kts with gusts of 20-30 kts. LLWS
possible. Moderate confidence overall.

Thursday...Sub-VFR conditions possible for brief periods early
due to scattered rain/snow showers in the morning, improving to
prevailing VFR conditions by midday. Very windy with west winds
20-25 kts gusting to 35-45 kts. Moderate confidence.

Outlook...

Thursday night through Friday...VFR. Strong wind gusts up to 35
kt possible.

Friday night through Sunday night...VFR. No significant weather
expected.

Monday...Sub-VFR conditions likely with periods of rain.

&&

.MARINE...
Gale Warnings in effect through Thursday. Strong southwest
winds ahead of a cold front will gust to around 35-40 kts
tonight. Behind the frontal passage Thursday morning, west
winds will gust up to 45 kts. An occasional gust near 50 kts
cannot be ruled out. Seas will build to 8-12 feet tonight,
becoming 6-10 feet late Thursday afternoon.

A Low Water Advisory was issued for the late Thursday low tide
for Delaware Bay and adjacent Atlantic coastal waters. The
strong offshore winds will result in abnormally low water during
the Thursday late afternoon to evening low tide, which could
make navigation difficult in shallow waters. he advisory may
need to be expanded farther north toward Sandy Hook if
confidence increases in tide levels reaching -2 feet MLLW or
lower. Low water will also impact the tidal Delaware River. A
Special Weather Statement may be issued to highlight the threat
of low water there if confidence increases enough to warrant
one.

Outlook...

Thursday night...Gale force conditions are likely to continue
with wind gusts up to 40-45 kt. Seas of 5-8 feet.

Friday through Friday night...SCA conditions likely during the
day, possibly lingering into Friday night. Seas of 3-5 feet.

Saturday through Monday...No marine headlines expected, however
SCA conditions may return late on Monday.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Wind Advisory from 6 AM to 10 PM EST Thursday for PAZ054-055-
     060>062-070-071-101>106.
NJ...Wind Advisory from 6 AM to 10 PM EST Thursday for NJZ001-
     007>010-012>027.
DE...Wind Advisory from 6 AM to 10 PM EST Thursday for DEZ001>004.
MD...Wind Advisory from 6 AM to 10 PM EST Thursday for MDZ012-015-
     019-020.
MARINE...Gale Warning until 6 AM EST Friday for ANZ430-431-450>455.
     Low Water Advisory from 3 PM Thursday to midnight EST Thursday
     night for ANZ430-431-453>455.

&&

$$

SYNOPSIS...DeSilva/Fitzsimmons
NEAR TERM...MJL/RCM
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...DeSilva/MJL/RCM
MARINE...DeSilva/MJL/RCM