112
FXUS61 KPHI 181100
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
600 AM EST Tue Nov 18 2025

.SYNOPSIS...
Strong low pressure will slowly move across Atlantic Canada
today. A weak low pressure system tracks eastward from the Ohio
Valley to the Mid-Atlantic late today into Wednesday. A warm
front lifts north across our region later Thursday night and
Friday, followed by a weak cold front Friday night. A secondary
cold front may move through later Saturday followed by high
pressure later Sunday into Monday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
A shortwave trough is forecast to approach our region from the west
during the day today, then slide across our area tonight before
quickly shifting to our east Wednesday morning. Much of the guidance
has trended wetter with this system and also more northward with the
associated precipitation shield over the last few days. This looks
to be due to the mid level low that is initially closed off
and maintains its strength longer as it shifts eastward.

Lingering stratocumulus north and west of I-95 continues to dissipate
northward early this morning. As the aforementioned system shifts
eastward and gets closer to our area, a 100-knot jet at 250 mb
arrives. Some lingering cold air advection at 850 mb early this
morning will become neutral and then switch to some warm air
advection later this afternoon and especially tonight. High to
mid level clouds should quickly increase through the day as a result.
It will be a chilly day with a west-northwest breeze occurring
before diminishing later this afternoon. High temperatures in
the 40s across the region. The air mass is rather dry with surface
dew points in the upper teens to low 20s this morning which will
add to the chill today.

As we go through tonight, a tricky forecast given the initial rather
dry low-level air mass in place. The incoming system aloft will
drive weak surface low pressure to our south or across Delmarva late
tonight into early Wednesday morning. As this occurs, warm air
advection increases some and moisture advection will also increase
from the southwest. The progress of this will have some impacts on
the precipitation shield especially the farther north one goes
across our area. Overall though, a chilly rain is forecast to
develop for much of the area overnight. Some of the model forecast
soundings especially from the Lehigh Valley (Berks County) northward
to the Poconos and into northwestern New Jersey indicates some
evaporative cooling takes place with the onset of the precipitation.
The precipitation intensity may be rather light initially and
therefore may not significantly cool the column, however there is
the potential for some snow to mix in with the rain or even a period
of light snow especially toward the Poconos to Sussex County, New
Jersey. The low-level warm air advection is not forecast to be all
that strong, therefore the initial cooling may result in some snow
for the I-78 corridor northward especially as some stronger 850 mb
frontogenesis overspreads the area overnight. For now, went with
more of a rain/snow mix farther south across parts of eastern
Pennsylvania into northwestern New Jersey (roughly I-78 corridor)
before going to all rain. Some guidance is colder and therefore
shows some accumulating snow (coating to an inch or so) in parts of
this zone) so something to watch considering the initial dry/chilly
air mass. The precipitation shield may struggle to get all the way
into the Poconos to Sussex County, New Jersey, but if it does a
period of light snow is certainly possible. PoPs are lowest for this
area as a result however with snow accumulations around a coating
currently forecast only for this area. Low temperatures in the 30s,
however temperatures may rise some across the southern areas overnight.

Wednesday starts out with some rain that departs quickly from about
the I-95 corridor eastward. Total rainfall amounts at this time are
forecast to be in the range of 0.10-0.50 inches, with less than 0.10
inches for the I-80 corridor. There looks to be a fair amount of
moisture lingering across much of the region within a light north to
northeast wind, therefore the cloud cover may struggle to break up
on Wednesday. Some drier air across the northern areas however
during the afternoon may result in a bit more sunshine trying to
appear there. High temperatures are forecast to be in the 40s to low
50s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
High pressure initially centered over NY state Wednesday evening
will drift eastward towards New England by early Thursday. Meanwhile
a frontal boundary will linger near Delmarva with some weak impulses
moving through aloft in the upper level flow. This will tend to keep
skies mostly cloudy however it should remain mainly dry. The
exception will be across Delmarva where there could be some spotty
drizzle. With the lingering front, overnight lows will vary from the
upper 20s over NE PA and NW NJ to the upper 30s to around 40 over
Delmarva as well as SE PA and adjacent portions of southern NJ.

High pressure will weaken and continue moving off to the north and
east through Thursday. This will set up a weak warm advection
pattern by later in the day well ahead of the next system as it
starts to approach from the midwest. As a result, it will remain
mostly cloudy with a chance for some spotty drizzle around over
Delmarva and eastern PA. This shouldn`t really amount to anything if
it occurs and so we stayed with NBM POPs for Thursday which has
chances for measurable precip at less than 15 percent across the
area. Temperatures will continue to be a bit on the cool side for
this time of year with highs ranging from the 40s over NE PA and
northern NJ to the low to mid 50s over Delmarva and adjacent
portions of southern NJ. The greater Philadelphia area should see
highs within a couple degrees either side of 50.

The warm advection pattern starts to strengthen some for Thursday
night as the next system continues to approach and its warm front
starts to lift north. This will bring in chances for some light rain
by the overnight period, especially over eastern PA, northern
Delmarva, and the northern half of NJ. Overnight lows will remain
above freezing as they will generally range from the mid to upper
30s north to the low to mid 40s south.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
A frontal system associated with a progressive upper level low /
trough will affect the region Friday and Friday night with some
light rain. Temperatures will also moderate for Friday with highs in
the 50s to low 60s as the area briefly makes it into the warm
sector. A cold front will follow by Friday night into early
Saturday. Overall, rain amounts do not look to be very significant
and POPs for any given 12 hour period only max out around 30 to 50
percent. That said, this is due in part to differences in exact
timing between the different models and most areas should see at
least a little bit of rain at some point between Friday morning and
Saturday morning.

Differences in the forecast guidance increase as we go through the
weekend period with some guidance keeping a dominant long wave
trough over central and eastern Canada with an upper level low held
at bay over the SW CONUS. Meanwhile some of the ensembles depict a
more progressive trough lifting out through the weekend as the
upper level low initially over the SW starts to move eastward.
Overall, our forecast stayed close to the NBM and leans towards
the former of the two scenarios just described. This should
lead to generally decreasing POPs through the weekend however
it`s possible one more impulse could move through by later
Saturday into Saturday night bringing some light rain mainly to
the southern half of the forecast area. Confidence is low on
this though so our POPs are only around 30 percent or less.
Otherwise, temperatures this weekend should return to around
average for this time of year.

The beginning of next week looks to feature generally dry and
seasonable weather dominated by high pressure.

&&

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

Today...VFR with increasing and gradually lowering clouds
through the day. West-northwest winds 5 knots or less increasing
to 8-12 knots through this morning, then becoming west-southwest
later this afternoon and diminishing. Moderate confidence.

Tonight...VFR ceilings lower to MVFR after about 05z then to IFR
between about 06z-10z. Rain develops from west to east, mostly
in the 03z-06z timeframe. The rain should be rather light to
start with no visibility restrictions, then visibilities lower
overnight. Some snow may mix in at KRDG and KABE overnight, and
given low confidence just included a PROB30 for now. Winds becoming
light and variable overall. Low confidence in the timing details
and if snow occurs at KRDG and KABE.

Wednesday...IFR or MVFR ceilings in the morning improve to VFR. Some
rain mostly from around the KPHL area ends during the morning. Light
and variable winds becoming northeast to north 5-8 knots. Low
confidence.

Outlook...

Wednesday night through Thursday...Low stratus may result in MVFR
cigs.

Friday and Saturday...Sub-VFR conditions and some rain possible.

&&

.MARINE...
As of 6 AM, the winds continue to slowly diminish across the
southern coastal waters and therefore this portion of the Small
Craft Advisory was allowed to expire at 6 AM. The Small Craft
Advisory remains in effect until 10 AM for the northern New
Jersey coastal waters due to lingering wind gusts to around 25
knots. Once this advisory ends, the conditions are anticipated
to be below Small Craft Advisory criteria through Wednesday.

Outlook...

Wednesday night through Saturday...The conditions are anticipated to
be below Small Craft Advisory criteria.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 10 AM EST this morning for ANZ450-
     451.

&&

$$

SYNOPSIS...Fitzsimmons/Gorse/Guzzo
NEAR TERM...Gorse
SHORT TERM...Fitzsimmons
LONG TERM...Fitzsimmons
AVIATION...Fitzsimmons/Gorse
MARINE...Fitzsimmons/Gorse