Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 051958

Area Forecast Discussion
National Weather Service Mount Holly NJ
258 PM EST Tue Dec 5 2023

A weak low will develop off the Carolina coast tonight and move
offshore through tomorrow. High pressure will build in for the
rest of the week into the first half of the weekend, though a
weak system may clip the western part of the area Thursday
morning. A strong cold front approaches on Sunday and passes on
Sunday night, with high pressure building in for the early part
of next week.


A slow moving cold front has pushed through most of the region
this afternoon and will be associated with a digging,
positively tilted upper trough that moves in overnight. A
secondary center of low pressure will develop off the coast of
the Carolinas this evening and a north to northwest pressure
gradient will tighten between it and building high pressure to
our southwest, keeping at least a light breeze in place
overnight. A shortwave embedded in the trough will cross through
just south Delmarva around midnight, and we`ll also be placed
just on the periphery of the left exit region of a departing jet
streak. This may be enough to squeeze out some precipitation in
southeast PA/Delmarva, but with forcing from the surface low
likely a good distance offshore and near surface moisture still
lacking, not expecting coverage to be too widespread. That said,
forecast soundings do show the entire profile below freezing
with surface temperatures hovering right around the freezing
mark in southeast PA, so if any wet bulb effects occur with the
near-surface dry air, some flurries/light snow showers may
result; it will be too warm across Delmarva for anything but
rain. With lingering mid-level moisture, clouds should be
around overnight though there may be some breaks as surface
ridging noses in from the southwest. Lows will bottom out in the
low to mid 30s.

Heading into the day Wednesday we could see some of the light
precip from the aforementioned shortwave trough and coastal low
linger into Wednesday morning, but impacts will remain limited.
The best chances for seeing any precip will be over Delmarva and
far southern NJ towards Philly however confidence is not high on
precip with light drizzle or a few flurries being the most
likely. With high pressure starting to build, the pressure
gradient should be modest leading to gusty winds especially
across the Shore.


High pressure will ridge northward from the Southeastern US
Wednesday night, helping clear skies and allow winds to decouple.
This favorable radiational cooling setup will allow temperatures to
drop into the 20s as a result.

Most of the region will see high pressure dominate into Thursday as
well, though a weakening shortwave embedded within an upper
level jet streak will move across southern New England and clip
the Poconos and Lehigh Valley with some light rain/snow showers
or flurries. Any precip here is not expected to become impactful
and snow accumulations, if any, should be a tenth or two of an
inch at most. Otherwise, areas outside of the Lehigh
Valley/Poconos will be dry under mostly cloudy to overcast
skies. Temperatures will remain about 5 degrees below climo
during the afternoon with highs in the mid 30s to mid 40s once

High pressure will continue to dominate into Thursday night with dry
conditions expected as skies clear out. Temperatures will be
slightly warmer due to low-level flow turning more
west/southwesterly and weak warm air advection setting up. Cloud
cover hanging around for the first portion of the evening will also
help in keeping things slightly warmer. Lows will get down into the
mid to upper 20s and low 30s.

A mid-level ridge is expected to move over the region on Friday,
which will keep the region dry and bring warmer temperatures. Should
be a nice December day to close out the week with some sun and
warmth with temperatures for the most part getting into the low to
mid 50s.


The strong ridge will continue to build in Friday Night into
Saturday. The ridge continues to amplify offshore Saturday night and
Sunday as a trough digs across the Great Lakes and Ohio Valley and
shifts eastward, taking on a negative tilt as it approaches our
area. Rather robust cyclogenesis looks to occur over the Ohio
Valley, with the quickly developing surface low traversing the upper
Great Lakes, moving into Ontario by sometime Sunday. This will drop
what looks to be a relatively strong cold front through our region
late Sunday. The trough and associated cold front is forecast to
move through the region Sunday night. What looks to be weak
transient ridging or at least zonal flow should be in place for

In terms of sensible weather or impacts, things should be fairly
benign Friday Night and Saturday with continued warming bringing
afternoon highs into the mid to upper 50s for Saturday. The
strengthening low across the Midwest and associated cold front will
begin to approach on Sunday. The 12z deterministic and ensemble
suite of guidance showed a later arrival of the cold front, and thus
PoPs were pushed back slightly. Highest PoPs at this time are late
Sunday afternoon and into the first half of Sunday Night, though
there remains some uncertainty given it is in the day 5-day 6
timeframe. Regardless, this early winter cold front could be a
bit dynamic as surface low pressure deepens over the Great Lakes
and tilting becomes negative, allowing strong warm air
advection and moisture advection to ensue.

The main concerns appear to be strong winds and heavy rain. A
dynamic wind field with a strong low-level jet will likely be
present. Even the NBM 25th percentile (the lower end for what could
possibly occur) for maximum gusts on Sunday was showing gusts near
40 MPH across the region.  As far as rainfall, still a long way to
go and a lot of uncertainty, but worth noting that the general
ensemble mean was showing totals near an inch. Will need to continue
monitoring this system for any changes as there are signs that this
could be an impactful system. Highs on Sunday could reach into the
60s, especially if the cold front comes through on Sunday Night. As
you could probably guess from the previous sentence, this will be an
all rain event as the entire area will be firmly in the warm sector
as the front approaches. The beginning of next week will be quiet as
high pressure tries to build in from the southwest behind the
departing cold front. Temperatures will be closer to seasonal norms.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Rest of Today...VFR. CIGs will lower through the day to 4-5kft
but chances of MVFR remain low (<10%) with the exception of ABE
and RDG. Northwesterly wind 5-10 knots. Moderate confidence.

Tonight...Generally VFR. CIGs remaining in the 4-5kft range
with MVFR approaching eastern PA and the northern I95 corridor.
Briefly introduced some MVFR at PHL but don`t expect MVFR to
prevail. Light northerly wind 5 knots or less. A widely light
scattered rain or snow shower possible, mainly for
KILG/KMIV/KACY before daybreak. Moderate confidence.


Wednesday...Mainly VFR, but mostly cloudy with a few light rain
or snow showers possible in the morning. Winds mainly north to
northwest around 5 to 10 knots with some higher gusts in the
afternoon. Moderate confidence.

Wednesday Night...VFR. Northwest winds around 5-8 kt. Moderate

Thursday...Primarily VFR, though some restrictions possible at
KRDG/KABE with potential snow showers. West/southwest winds around 5-
10 kt. Moderate confidence.

Thursday Night...VFR with clearing skies. Winds favoring a southwest
direction around 5 kt or less but some spots will go calm. Moderate

Friday through Saturday...VFR. South/southwest winds around 5-10 kt.
Moderate confidence.

Sunday...Sub-VFR conditions likely. South/southeast winds around 15-
25 kt with gusts 25-35 kt possible. Low confidence.


Northwesterly wind 5-10 knots with periodic gusts to 15-20
knots possible, particularly early Tuesday morning and late
Tuesday night. Seas 3-4 feet Tuesday morning, decreasing to 2-3
feet through Tuesday night. By Wednesday winds will ramp up and
have issued an SCA beginning 18z on the Atlantic waters and 21z
on the Delaware Bay. Frequent gusts of 25-30 will be possible
through much of Wednesday afternoon into the overnight hours


Wednesday Night...A Small Craft Advisory is in effect for the
Delaware Bay until 03z Thursday and all ocean waters until 08z
Thursday as gusts will be around 25-30 kt out of the northwest. Seas
will be around 2 to 4 feet. Winds diminish after 08z to sub-SCA

Thursday through Thursday Night...No marine headlines anticipated.
Westerly winds around 10-20 kt and seas 2 to 4 feet.

Friday through Saturday Night...No marine headlines anticipated.
South/southwest winds around 10-15 kt and seas 2 to 4 feet.

Sunday...SCA conditions expected with Gales likely. Southerly winds
increasing to 25-30 kt and gusts up to 40 kt possible. Seas increase
to around 5 to 8 feet.


MARINE...Small Craft Advisory from 4 PM to 10 PM EST Wednesday for
     Small Craft Advisory from 1 PM Wednesday to 3 AM EST Thursday
     for ANZ450>455.



NEAR TERM...Brudy/Deal
LONG TERM...Hoeflich/MJL
MARINE...Brudy/Deal/Hoeflich is the U.S. government's official web portal to all federal, state and local government web resources and services.