685
FXUS61 KPHI 091043
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
543 AM EST Tue Dec 9 2025

.SYNOPSIS...
The center of arctic high pressure gradually weakens and shifts to
our east today. Low pressure tracks to our north during Wednesday
with its cold front crossing our region Wednesday evening. A cold
front moves through Friday night or Saturday, then low pressure
along it tracks nearby Saturday into Sunday. Arctic high pressure
centered well to our west builds into our region during early next
week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
High pressure over the area slides offshore later today. Arctic
airmass over the area results in high temperatures some 10 to
15 degrees below normal, generally in the 20s in the southern
Poconos to the low to mid 30s for most of the region, and in the
mid to upper 30s for southern Delmarva and along the Jersey
Shore. Skies clear out this morning, then high clouds build back
into the region as the afternoon progresses.

Return flow sets up behind the departing high, and after
temperatures drop in the evening, temperatures will mostly hold
steady through the overnight hours tonight generally in the mid to
upper 20s.

A clipper system over central Canada just north of the Northern
Plains will intensify as it dives into the Great Lakes tonight
through Wednesday morning. This system will move into western and
central New York on Wednesday before lifting into northern New York
by Wednesday evening.

Precipitation develops Wednesday morning initially over the southern
Poconos and the Lehigh Valley before spreading into New Jersey and
most of Delmarva. In terms of p-type, generally expecting snow over
the southern Poconos and far northwest New Jersey, and snow
precipitation will mostly be snow in the southern Poconos and far
northwest New Jersey throughout the duration of the event. For the
Lehigh Valley, precipitation will start out as snow, followed by a
brief period of wintry mix which may include freezing rain for some
spots, then rain by Wednesday afternoon. For southern New Jersey,
the I-95 corridor including Philadelphia, and into northern
Delmarva, a rain/snow mix is possible initially before changing to
plain rain late Wednesday morning. Rain then continues through the
day.

The highest snow accumulations are expected to be in the southern
Poconos, and especially the higher elevations, with as much as 2 to
4 inches. Up to an inch is likely for northern New Jersey and the
Lehigh Valley, while trace amounts are possible elsewhere. In the
wintry mix/freezing rain areas, generally a glaze of ice is possible.

Southerly flow ramps up ahead of the approaching low and with the
low passing north of the area, and this allows for strong warm air
advection. Highs warm back into the low to mid 30s for the southern
Poconos, and otherwise in the low 40s for northern New Jersey and
the Lehigh Valley. For southern New Jersey, the Delaware Valley
(including Philadelphia), and Delmarva, highs will be in the mid to
upper 40s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As as stronger upper-level through evolves across the East during
this time frame, strong low pressure will lift up across northern
New England to the Canadian Maritimes. A cold front shifts to our
east Wednesday evening and any precipitation is expected to quickly
come to an end. A notable breeze may occur as cold air advection
increases combined with enough vertical mixing.

Plenty of cyclonic flow during Thursday and Thursday night given the
presence of the upper-level trough. A cold west-northwest breeze
will also be gusty and areas of stratocumulus clouds may result.
There will be a lake response and it is possible that some flurries
and snow showers get into portions of our Pocono region and far
northwestern New Jersey at times. Temperatures continue below
average, and with the wind factored in the wind chill during the day
will be mostly in the 20s across the region. The winds should
diminish at least some at night, however wind chills look to get
down into the teens for most by daybreak Friday (single digits in
the Poconos).

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Summary...Below average temperatures with another blast of arctic
air late in the weekend and/or early next week.

Synoptic Overview...A series of stronger shortwaves sliding across
southern Canada and the northern tier of the U.S. will continue to
result in an upper-level trough as it pivots across central to
eastern Canada. This will amplify an upper-level trough more than
once across the Northeast and Mid-Atlantic regions. This will keep
temperatures on the cold side. This looks to favor mostly clipper
systems (quick moving) with their associated cold fronts crossing
our region. A stronger trough however over the weekend may result in
a surface low developing along a trailing cold front with this low
tracking near our area.

For Friday...As our region is on the southern side of a large upper-
level trough in central to eastern Canada, the axis of weak high
pressure slides across our area. A low pressure system however
tracks well to our north Friday night into Saturday morning with a
cold front crossing our area during Saturday. This system looks to
be moisture starved overall and therefore may not produce much in
the way of precipitation. Some differences in the guidance on this
therefore ran with the NBM guidance which has 20-40 PoPs across the
area.

For Saturday and Sunday...The cold front associated with the
aformentioned system may tend to stall to our south. The center of
arctic high pressure across the Midwest and northern Plains will
gradually build eastward. Ahead of this feature, a strong shortwave
may end up amplifying an upper-level trough across the Northeast.
This may result in a surface low developing along the trailing cold
front, which then tracks near our area. Some guidance is weaker with
this feature and therefore just has a front crossing our area, while
others have a more pronounced wave along the front. Given the rather
active upper air pattern with many moving pieces, the guidance will
likely continue to show varying solutions. As a result, did not
stray away from the NBM which paints chance PoPs (around 30 percent)
Saturday night into Sunday morning. Any snowfall will depend on the
wave developing and also tracking close enough as a rather cold air
mass heads southward. Temperatures still below average, however
Sunday looks to be several degrees colder than Saturday.

For Monday...As the parent upper-level low starts to exit, the
center of arctic high pressure builds into our area during Monday.
This will result in a very cold day with temperatures well below
average. Any northwesterly breeze should be easing as the high
builds in more and therefore erodes the pressure gradient. Another
clipper system may then start to approach Monday night, however this
feature will depend on the upper-level trough amplifying once again
as the surface high starts to weaken and shifts offshore.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. LGT/VRB winds in the morning, becoming S 5 to 10
kt by 18Z. High confidence.

Tonight...VFR. S-SW winds 5 to 10 kt. High confidence.

Wednesday...Sub-VFR in RA and/or SN, with SN most likely at
KRDG/KABE. SN changes to RA in the afternoon. S winds 10 to 15
kt with 20 to 25 kt gusts. Moderate confidence.

Outlook...

Wednesday night...Conditions improve to VFR. Southwest to wind gusts
may gust to 20 knots at times.

Thursday...VFR. West-northwest wind gusts to around 25 knots.

Friday and Saturday...A period of sub-VFR conditions possible with
snow or rain, especially Friday night and Saturday morning. Westerly
winds may gust to about 20 knots on Saturday.

&&

.MARINE...
Will cancel the Small Craft Advisories that were in effect from
Cape Henlopen DE to to Fenwick Island DE until 7 am for winds
gusting to 25 kt and seas up to 5 feet as conditions continue to
subside. Sub-SCA conditions expected thereafter, and sub-SCA
conditions on all other waters for today for north winds 10 to
15 kt, becoming south late this afternoon.

South to southwest winds increase to 15 to 25 kt with gusts up to 30
kt tonight. A SCA is now in effect for all waters for tonight.

On Wednesday, VSBY restrictions in rain expected. A Gale Watch is
now in effect for the ocean waters for Saturday as southwest winds
will range from 20 to 30 kt with gusts up to 35 kt. For Delaware
Bay, winds will range from 15 to 25 kt with gusts up to 30 kt.

Outlook...

Wednesday night...Small Craft Advisory probable. Gale force wind
gusts possible, especially during the evening, and a Gale Watch has
been issued.

Thursday...Small Craft Advisory conditions gradually subside at
night.

Friday...The conditions may remain below Small Craft Advisory
criteria.

Saturday...Small Craft Advisory probable, with gale force wind gusts
possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 6 AM to 6 PM EST Wednesday for
     PAZ054-055.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EST
     Wednesday for ANZ430-431.
     Small Craft Advisory from 6 PM this evening to 6 AM EST
     Wednesday for ANZ450>455.
     Gale Watch from Wednesday morning through Wednesday evening
     for ANZ450>455.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...MPS
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...Gorse/MPS
MARINE...Gorse/MPS