567
FXUS61 KPHI 111127
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
627 AM EST Thu Dec 11 2025

.SYNOPSIS...
A cold front has shifted offshore early this morning. High
pressure builds over the Gulf Coast states and Southeast through
Friday before moving offshore Friday night. Several weak
disturbances will pass through the region through Saturday. Low
pressure passes through the region Saturday night through Sunday
morning, then a strong cold front moves through the region on
Sunday. Arctic high pressure builds in from the west for the
start of next week before sagging into the Southeast and Mid-
Atlantic by the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Much colder through tonight with a gusty wind. Some snow
showers and even a narrow band of lake effect snow/snow squall
probable mostly for the I-80 corridor this afternoon and early
this evening.

In the wake of a cold front, plenty of cyclonic flow through
tonight given the presence of a strong upper-level trough. A
cold west-northwest wind will be in place and areas of
stratocumulus clouds will be around. There are some early this
morning, however this should expand eastward through the day
given increased cold air advection and steepening low-level
lapse rates. Model forecast soundings show deeper mixing through
the day especially as the aforementioned low-level lapse rates
steepen. This will result in breezy to windy conditions with
peak wind gusts to 35 mph, although some gusts to 40-45 mph are
expected especially in the higher elevations. Lake effect snow
streamers off the central to eastern Great Lakes will be
strengthening during the day, and several models pull one or two
of these narrow streamers across the Poconos and into part of
northern New Jersey. The strong west-northwest flow combined
with plenty of elongated mid level vorticity within the cyclonic
flow typically assists in these streamers making it this far
eastward. Overall the I-80 corridor has the greatest chances for
a band of heavier snow showers or even a snow squall. These
could certainly put down a quick inch or so of snow along with
rapid reductions in visibility. Farther south to the I-78
corridor, some flurries or even a few snow showers cannot be
ruled out. Placed the highest PoPs (40-50 percent) along the
I-80 corridor, and held off going higher given some lingering
uncertainty on exact locations that will see a more organized
narrow streamer. Temperatures will fall through early this
morning following a cold front and increase in cold air
advection. For the coastal plain especially, today will be much
colder than yesterday. The gusty winds will also drive down the
wind chills through the day.

As we go through tonight, deep surface low pressure will
continue to move across the Canadian Maritimes as the strong
upper-level trough shifts east and northeastward. This maintains
cyclonic flow aloft across our area, although this starts to
weaken through the overnight. The center of surface high
pressure then moves across the Southeast U.S with it extending
just to our west by daybreak Friday. The tight pressure gradient
between these two systems will gradually weaken through the
overnight, and this will also result in the winds diminishing
with time. The model forecast soundings show the vertical mixing
becomes less through the night, and therefore while a breeze
will continue it should be much less especially overnight. Lows
will generally be in the low to mid 20s (teens over northwest
New Jersey and the southern Poconos), but the wind chill will
make it feel several degrees colder. Any lingering lake effect
snow streamers or snow showers across the northwest areas are
expected to end during the evening.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
High pressure off the Southeast U.S. coast will move out to sea
on Friday. Meanwhile, a deep upper trough will lie over the
Great Lakes, Ohio Valley, and Northeast, with the base of the
trough over the Mid-Atlantic area. Several shortwaves will pass
through the region Friday afternoon and Friday night. The
strongest one will pass through Friday night, and this may touch
off some snow across the Delaware Valley and Delmarva. PoPs are
fairly low, generally 20 to 30 percent, and any snow
accumulation during this time will be light.

The base of the trough flattens out on Saturday, and southerly
flow will usher some warmer air into the region. After highs on
Friday generally in the mid to upper 30s, highs will get into
the upper 30s to low 40s on Saturday.

A clipper system will dive into the Great Lakes on Saturday,
and an Arctic cold front will form behind it as Arctic high
pressure builds into the Northern and Central Plains behind it.
This clipper system will carve out a new H5 trough with strong
shortwaves that will dog down through the Ohio Valley and into
the Mid-Atlantic.

Surface low pressure will form at the base of this trough and
will pass through the region Saturday night. The details of this
system have yet to develop, but there are signals among the
00Z/11 NAM, the 00Z/11 GFS, and the 00Z/11 ECMWF that have the
low developing near the Tennessee Valley and moving towards the
Mid-Atlantic. While some rain and snow would be possible
initially over southern New Jersey and Delmarva, snow would end
up being the dominant p-type.

01Z NBM showing a 50-70% probability of greater than 1 inch of
snow in the 24 hours ending at 7 am Sunday; a 30-50% probability
of greater than 2 inches of snow in the 24 hours ending at 7 am
Sunday; and a less than 10% probability of greater than 4
inches of snow in the 24 hours ending at 7 am Sunday. The
highest probabilities are across the Delaware Valley and into
Philadelphia. Based on WPC QPF and snow-liquid ratios generally
15 to 17 inches, this yields 2 to 3 inches of snow across
Delmarva and the Delaware Valley Saturday night.

Snow tapers off Sunday morning with minimal additional
snowfall. A strong cold front passes through the region and much
colder air filters into the area with highs generally in the
mid and upper 20s north and west of the Fall Line and in the low
to mid 30s along the I-95 corridor, southern New Jersey and
Delmarva. Northwest winds increase to 15 to 20 mph with 30 to 35
mph gusts. Wind chills during the day Sunday will be in the
teens to low 20s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Cold and brisk Sunday night with northwest winds 15 to 20 mph
with 25 to 30 mph gusts. Overnight lows will be in the teens,
resulting in single digit wind chills SUnday night into Monday
morning. Still cold with highs in the 20s to low 30s. Winds will
diminish throughout the day. Another clipper system passes
north of the area, and may result in some snow in the southern
Poconos. Dry otherwise.

High pressure will be over the Southeast on Tuesday before
moving out to sea on Wednesday. Temperatures gradually moderate,
but remain well below normal levels.

&&

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

Today...VFR overall. A few snow showers possible mainly near
and north of KABE later this afternoon and early this evening,
and a PROB30 is included at KABE for this potential. West-
northwest winds 15-20 knots with gusts 30-35 knots. Low confidence
in snow shower details.

Tonight...VFR. Westerly winds 10-15 knots with gusts to 20-25
knots, diminishing through the overnight. Moderate confidence.

Outlook..

Friday through Friday night...VFR/NSW.

Saturday...VFR/NSW.

Saturday night through Sunday night...Sub-VFR in SN Saturday
night through Sunday morning. VFR thereafter. W-NW winds 15 to
20 kt with 25 to 30 kt gusts Sunday afternoon and Sunday night.

Monday...VFR/NSW.

&&

.MARINE...
Gale Warning in effect. Gale force west-northwest wind gusts,
to around 35 knots, today and then these diminish from south to
north late this afternoon and especially tonight. Hazardous
seas will gradually subside given the strong offshore flow.

Outlook...

Friday through Friday night...Sub-SCA conditions.

Saturday through Saturday night...Sub-SCA conditions. VSBY
restrictions in rain/snow Saturday night.

Sunday through Sunday night...SCA conditions developing Sunday
morning, ramping up to gales late Sunday and Sunday night. VSBY
restrictions in rain/snow Sunday morning. Freezing spray
possible Sunday night.

Monday...Gales in the morning, then SCA. Freezing spray
possible Monday morning.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Gale Warning until 6 PM EST this evening for ANZ430-431-
     453>455.
     Gale Warning until 1 AM EST Friday for ANZ450>452.

&&

$$

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