639
FXUS61 KPHI 092316
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
616 PM EST Tue Dec 9 2025

.SYNOPSIS...
Arctic high pressure shifts offshore tonight. 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 NIGHT/...
Arctic high pressure will move quickly offshore tonight. 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 will intensify as it dives into the Great Lakes
from the upper Midwest tonight through Wednesday morning. This
system will move into the Saint Lawrence River Valley by Wednesday
evening. This will lead to a period of "warm" advection during the
day Wednesday, though we`ll really only be advecting a modified
arctic airmass. There will also still be some snowpack upstream
across southern Virginia and northern North Carolina. Thus,
temperatures will still end up a few degrees below normal across the
board.

Precipitation develops Wednesday morning initially over the southern
Poconos and the Lehigh Valley before spreading into New Jersey and
northern Delmarva. In terms of p-type, generally expecting snow
initially over the southern Poconos and far northwest New Jersey,
and precipitation will remain mostly snow in the southern Poconos
and far northwest New Jersey throughout the duration of the event.
Some mixing with rain or freezing rain may occur before
precipitation ends though. For the Lehigh Valley, precipitation will
start out as a mix, or perhaps mostly rain south of I-78. Any wintry
mix or snow here will quickly change to rain by late morning and
into the afternoon. For southern New Jersey, the I-95 corridor
including Philadelphia, and into northern Delmarva, all rain is now
expected due to slightly later onset time of precipitation. For this
area, the rain probably won`t begin until the afternoon.

The highest snow accumulations are expected to be across the Pocono
Plateau, especially elevations above 1,000 feet where roughly 1-3
inches is forecast. The Winter Weather Advisory remains in effect
for Wednesday for this area. Elsewhere across the higher elevations
of northwest New Jersey, Lehigh Valley, and northern Berks County,
generally less than 1 inch of snow is expected, if any. In these
same areas, including the Pocono Plateau, some brief freezing rain
could result in a glaze of ice from late morning or afternoon. The
probability of this is low, generally around 20-40%, and any glaze
of ice would be confined to the highest elevations and likely not
impact either the morning or evening commutes. Thus, we have not
expanded the advisory to include any of these areas at this time.

Rainfall amounts will be roughly near 0.10" or less, perhaps closer
to 0.25" north of I-78. The chance of measurable rainfall drops to
about 30-50% for far southern New Jersey and southern portions of
our Delmarva counties.

South to southwesterly flow ramps up ahead of the approaching low
and with the low passing north of the area. SSW winds will increase
to around 10-20 mph, with gusts near 30 mph possible at times. Highs
warm back into the mid 30s for the southern Poconos, and otherwise
in the upper 30s to 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,
and perhaps close to 50 degrees near the coast.

The clipper`s cold front will push through the area and offshore
quickly overnight with breezy conditions persisting overnight.
Temperatures will drop to around the mid 20s to low 30s by dawn
Thursday, producing wind chills in the teens and 20s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
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).

Daytime Friday looks to be largely dry as an axis of weak high
pressure slides across our area. Air temperatures look to be
similar to Thursday with highs in the mid 30s to near 40.
However, it will feel a bit warmer as winds continue to relax
and turn southwesterly ahead of the next approaching wave Friday
night. Apparent temps are forecast to be in the upper 20s to low
30s. A slight chance (10-20%) that some light snow and/or rain
begin to move into the area in the afternoon hours.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
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 night...A low pressure system 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 40 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 and Tuesday...As the parent upper-level low starts
to exit, the center of arctic high pressure builds into our area
during Monday and Tuesday. This will result in very cold days
with temperatures well below average, particularly on Monday.
Any northwesterly breeze should be easing as the high builds in
more and therefore erodes the pressure gradient. Another clipper
system may 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 /00Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR with increasing coverage and lowering of ceilings. SSW
winds 5-10 kts. High confidence in prevailing conditions.

Wednesday...

For the Lehigh Valley terminals...a brief period of snow, mixed
with rain will change to all rain between 15z-18z, with periods
of MVFR restrictions expected by 18z. MVFR conditions expected
to continue through the afternoon and evening. Winds will be out
of the south/southwest around 10-15 kt with gusts 20-25 kt.
Moderate confidence overall.

For the I-95 terminals...VFR to start with rain showers starting
at 18z. Conditions may drop to MVFR around 22z-23z with lower
CIGs moving in but confidence remains low on that, and some
sites, especially further south ones like KPHL/KILG may stay VFR
throughout. Winds out of the south/southwest around 15 kt with
gusts hovering near 25 kt. Low confidence.

For the South Jersey terminals...primarily VFR conditions
expected. Heavier rain and lower conditions should stay to the
north at least through 00z. Rain showers move in between 19z-20z
but should be light and CIGs/VSBYs should stay high enough to
stay VFR. Winds out of the south/southwest around 15-20 kt with
gusts 25-30 kt. Moderate confidence.

Outlook...

Wednesday night...VFR. Gusty WNW winds developing.

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

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

&&

.MARINE...
Advisory conditions developing tonight with SSW winds increasing to
20-25 kts with gusts up to 30 kts. Seas building 4-6 feet. Small
Craft Advisory remains in effect for all coastal waters for tonight.

SW winds increase further on Wednesday to 25-35 kts, with gusts up
to 40 kts at times across the Atlantic coastal waters. The Gale
Watch was upgraded to a Gale Warning, which is in effect Wednesday
through Wednesday evening. However, an additional period of gale
force wind gusts are possible during the pre-dawn hours early
Thursday morning. Some brief gale force gusts are possible across
Delaware Bay, but the probability and duration of this is too low to
warrant a Gale Warning at this time. Advisory conditions will
continue Wednesday night.

Outlook...

Thursday...Small Craft Advisory conditions continue through the
day then gradually subside at night.

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

Saturday and Sunday...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 until 6 AM EST Thursday for ANZ430-431.
     Small Craft Advisory until 6 AM EST Wednesday for ANZ450>455.
     Gale Warning from 6 AM to 10 PM EST Wednesday for ANZ450>455.

&&

$$

SYNOPSIS...AKL/Gorse
NEAR TERM...Hoeflich/MPS/Staarmann
SHORT TERM...AKL/Gorse
LONG TERM...AKL/Gorse
AVIATION...AKL/Hoeflich/Staarmann
MARINE...AKL/Staarmann