873
FXUS61 KPHI 012018
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
318 PM EST Mon Dec 1 2025

.SYNOPSIS...
High pressure initially centered over portions of the Mid-Atlantic
and New England will begin to retreat northeastward away from the
region tonight. Low pressure will develop over the Southeast tonight
before tracking northeast towards our area Tuesday into Tuesday
night, bringing widespread precipitation to the area. High pressure
and below normal temperatures return for the middle of the week.
Another cold front will track through the region Thursday night,
with high pressure building back in thereafter. Another system may
impact the region Friday night into the weekend, before high
pressure builds back in for early next week.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
For the remainder of this afternoon into the evening hours, we will
continue to see clouds filter in ahead of our next system that
arrives late tonight into Tuesday morning. The rest of our Monday
remains dry with most of tonight being dry as well. A high pressure
system moved in today and is fast moving, so it starts to depart off
to the northeast into tonight. This will then be followed by our low
pressure system that will move out of the southeast US and off to
the northeast. Lows tonight are in the 20s for most. However, these
low temperatures actually happen earlier in the night and we warm up
heading into daybreak on Tuesday as warm air filters in with our
system arriving.

This low pressure system is the main story for the near term period
as it approaches the area tonight and then off the coast into
Tuesday, which will bring widespread precipitation to the region,
including the first accumulating snowfall to portions of the area.
This low will make its closest approach to the area Tuesday
afternoon, and begin departing to the northeast by Tuesday night.

In terms of the details with this system, there have been some
changes to the forecast. One of these changes is the arrival of the
system being a little later and precipitation may not even arrive to
the area until as late as daybreak on Tuesday. We have chance PoPs
(30-50%) currently beginning right around the early morning hours
Tuesday. Quickly after daybreak, the precipitation becomes
widespread across the area with the highest PoPs (90-100%) being
during the daytime hours tomorrow.

Due to a later arrival, and more warm air in place at the onset
of the precipitation, this has cut back on snow totals and how
far southeast they extend. At the onset, especially if it is
near daybreak Tuesday, the rain/snow line may already be near or
northwest of the I-95 corridor. By mid-morning, the rain/snow
line is inching north of I-78. During the afternoon, the
rain/snow line has the potential to reach into the Poconos and
parts of northwest NJ. There is even the potential for mixing in
the higher elevations of these areas above 1,500 feet.

Regarding more details about the precipitation accumulation, QPF has
trended lower which has also impacted snow totals with this system.
Totals are now ranging from 0.50-1.00" with localized amounts to
1.25" with the greatest across the coastal plain and least farther
inland north of I-78. Due to the later trend in precip onset, the
potential for snow looks to be little to none for the I-95 corridor.
South and east of the I-95 corridor is likely to be all rain given
the latest trends.

Through the day Tuesday, the onshore flow and warm marine influence
with the surface low drawing near will impact the temperature
profiles. Through the day Tuesday, the rain/snow line will continue
to move northwest. For perspective on this, high temperatures on
Tuesday are near or a couple degrees above freezing in the Poconos,
mid 30s to near 40 degrees northwest of the fall line, low 40s along
the I-95 corridor, and in the mid 40s to low 50s in Delmarva and
along the coastal areas. Although areas may start as snow, it does
not appear that it will last for much of the area. The southern
Poconos have the best potential at an all snow event from this
system, but even they could see some mixing with sleet, freezing
rain, or rain Tuesday afternoon.

As for snowfall accumulation, the forecast has trended lower with
this update. The probability for plowable snow (2" or more) remains
high (60-90%) in the Poconos and areas along and north of I-78. As
you head well south and east of I-78, the potential for plowable
snow quickly decreases to near 0% for the I-95 corridor. Our latest
forecast includes snowfall amounts of a few tenths of an inch for
the very NW portion of the I-95 corridor, up to an inch for areas
just northwest of there, and in the 1-3" range for the I-78 corridor
and NW NJ. Higher elevations (especially 1,500 feet and higher) in
NW NJ and across the Pocono Plateau have potential for snowfall in
the 3-6" range.

The Winter Storm Watch is now a Winter Weather Advisory for the
southern Poconos and Sussex County NJ, where probability for warning
criteria snowfall (6" or greater) has trended too low to justify a
warning for these areas.

A Winter Weather Advisory remains for much of the counties in
northern NJ and the I-78 corridor and down into the far northwestern
reaches of the Philly metro. These are the areas most likely to
experience a troublesome Tuesday morning commute, with snowfall in
the 1-3" range and there is the potential for freezing rain.

Outside of potentially the Poconos and perhaps the higher elevations
in NW NJ, the snow that falls will then be melting through the day
with the change to all rain and warm air moving further inland.
During the transition period from snow to rain, some sleet is
possible briefly. Due to the stronger signal of warmer air advecting
in, the transition zone from snow to rain may not be as clean.
There is now the potential for a light accumulation of ice from
freezing rain in the areas where a Winter Weather Advisory is in
place. The ice accumulation looks to be a light glaze. The
areas that see all rain or a change to rain will have a good
soaking all-day type of rain. A few precipitation and/or
snowfall records could be challenged. See the Climate section
below for more details on the records.

Once the low departs Tuesday night, a high pressure system will
build in from the southwest. This will lead to drier conditions
through Tuesday night. Lows Tuesday night are in the 20s for most,
which may lead to some black ice issues where any slushy snow melt
refreezes on roadways (especially north of I-78).

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
By Wednesday morning, the axis of the H5 trough that will lead to
Tuesday`s widespread precipitation will be in the Gulf of Maine
vicinity, rapidly lifting northeast away from the area. A subtle
upper-level ridge axis will shift eastward across the area through
the day Wednesday. Wednesday night into Thursday, enhanced
southwesterly flow aloft will begin to overspread the area as a
trough digs southeastward over portions of Ontario and eventually
Quebec. The trough axis will pass to the north/glance the region
Thursday. Subtle height rises will follow with flow aloft becoming
zonal Thursday night. At the surface, high pressure will build in
from the west on Wednesday. A surface low will pass well to the
north of the area on Thursday with a strong trailing cold front
moving through by Thursday evening.

Wednesday should be a partly to mostly clear day. Highs will range
from the mid 30s across eastern PA and northern NJ to the low 40s
across southern NJ and the Delmarva. Wednesday night will feature
increasing clouds from northwest to southeast as the cold front
begins to approach the region. Lows will be in the low-mid 20s
across most of eastern PA and NJ, with upper 20s to near 30 for the
coastal plain, urban corridor, and Delmarva.

Thursday will be partly to mostly cloudy ahead of the front. While
not explicitly mentioned in the forecast at this time, a couple of
snow showers could occur with the frontal passage across the
Poconos. If this were to occur, amounts would be light. Otherwise,
it looks to remain dry. Will defer to future shifts on potential
inclusion of PoPs for this region. Highs will generally be in the
30s northwest of I-95 and 40s southeast. Skies should clear behind
the front, but breezy northwest winds will ensue, so it will be
quite chilly.

With the cold post-frontal airmass in place, decreasing winds, and
partly to mostly clear skies, the stage will be set for a very cold
Thursday night. Lows are expected to be in the single digits across
the Poconos and into far northwestern NJ, the teens across the
remainder of eastern PA and NJ, and the low 20s across the
Delmarva.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Friday looks to start with high pressure centered over our area
under zonal flow aloft. Deterministic guidance still shows the
potential for a weak impulse aloft to track through the region
Friday night into Saturday, but the overall trend has been for a
much less amplified pattern. The surface high will shift eastward
and off the coast Friday night into Saturday. Ensemble guidance
still suggests the possibility of surface cyclone formation, though
the trend has been weaker and farther south. As a result of these
trends, the potential for a significant storm system this weekend
appears to be decreasing. With that said, still have chance (30-50%)
PoPs across most of the area for Friday night, with PoPs near 60%
for southern DE and far southeastern NJ. These ultimately may
continue to come down, but trends will be monitored in the coming
days as this potential storm system gets closer in time. The airmass
in place will be cold enough that any precipitation that does fall
across the area with this system would have the potential to be of
the wintry variety.

Regardless of precipitation chances for Friday night into Saturday,
the pattern favors well below average temperatures. In fact,
temperatures may remain below freezing on Friday for most of eastern
PA and northern NJ, and only reach the mid 30s across the Delmarva
and into southern NJ. Saturday and Sunday look to remain below
average, though slightly warmer than Friday. Another cold front
could bring at least low precipitation chances and a renewed shot of
cold air Sunday night into Monday.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of Today (through 00z)...VFR. North/northwest winds around
5-10 kt with gusts near 20 kt through 19z-20z and diminishing
quickly thereafter. High confidence.

Tonight...Primarily VFR. Chance (20-40%) of MVFR conditions
after 10Z as rain and snow begin to move in though things come
down more towards daybreak and after. East-northeast winds
around 5 knots or less. Moderate confidence.

Tuesday...IFR/LIFR conditions develop between 11z-15z. High
confidence in all rain at KACY/KMIV. The trend as of this
morning has been warmer and slower with precipitation moving in.
This will result in pretty much all rain for KILG/KPHL and have
taken snow out of the TAF for now. Cannot rule out a few
flakes/mix at onset, but would expect a quick flip to rain once
precipitation begins. For KPNE/KTTN, expecting a longer period
of snow and/or mix, but a flip to all rain should occur by
12z-14z. A period of all snow expected at KRDG/KABE from about
10z-16z before mixing occurs and eventual flip to all rain after
18z. High confidence in at least IFR through the morning with
the potential (25-35%) in prevailing LIFR. Moderate confidence
in timing of precipitation type changes. Winds will be out of
the east/northeast around 5-10 kt, expecting to shift to
north/northwest between 18z-21z. Moderate confidence in timing
of wind shifts.

Outlook...

Tuesday Night...Conditions gradually improving though MVFR/IFR
expected to start, with VFR anticipated later in the night. Rain
showers taper off as the night goes on.

Wednesday through Wednesday Night...VFR. No significant weather.

Thursday...VFR. Gusts near 20 kt expected out of the
west/northwest

Thursday Night through Friday...VFR. No significant weather.

Friday Night through Saturday...Restrictions possible (40-60%)
with rain and snow showers expected to move through.

&&

.MARINE...

No marine hazards are anticipated through tonight with seas 2-3
feet and winds out of the east to then southeast gusting to
10-20 knots.

Winds and seas will increase Tuesday morning with the Gale Watch
being converted to an SCA for the ocean zones starting at 10AM.
For the Delaware Bay, the SCA starts at 3PM. Winds will gust to
25-30 knots out of the north to northwest. Occasional gusts to
35 knots are possible on the ocean zones. Seas will reach 6-8
feet Tuesday night. The Small Craft Advisory continues for
Tuesday night.


Outlook...

Wednesday...SCA conditions could linger into the first part of the
day. While winds are expected to have subsided, seas of 4-7 feet are
possible in the morning, decreasing to 2-4 feet through the day.

Wednesday night...No marine headlines are anticipated with winds
below 25 kt and seas below 5 feet.

Thursday through Thursday night...SCA conditions are possible with
northwest winds 15-25 kt and seas 3-5 feet.

Friday through Saturday...No marine headlines are anticipated with
winds below 25 kt and seas below 5 feet.

&&

.CLIMATE...
Widespread moderate to heavy precipitation is expected on
Tuesday, December 2nd. A few daily precipitation and/or snowfall
records could be challenged. Records for our climate sites are
listed below:

Record Precipitation (Rainfall)
                       December 2
Site                  Record/Year
Allentown (ABE)        0.86"/1934
AC Airport (ACY)       1.03"/1996
AC Marina (55N)        1.18"/1929
Georgetown (GED)       1.11"/1974
Mount Pocono (MPO)     3.56"/1996
Philadelphia (PHL)     1.48"/1986
Reading (RDG)          1.29"/1981
Trenton (TTN)          2.13"/1986
Wilmington (ILG)       1.27"/1991

Record Snowfall
                       December 2
Site                  Record/Year
Allentown (ABE)         3.6"/1952
AC Airport (ACY)           T/2019*
Philadelphia (PHL)      2.0"/1903
Reading (RDG)           6.0"/1929
Trenton (TTN)           3.0"/1903
Wilmington (ILG)        1.0"/1952

*Multiple years with a Trace.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 4 AM to 1 PM EST Tuesday for
     PAZ060>062.
     Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for
     PAZ101-103-105.
     Winter Weather Advisory from 4 AM to 6 PM EST Tuesday for
     PAZ054-055.
NJ...Winter Weather Advisory from 4 AM to 7 PM EST Tuesday for
     NJZ001.
     Winter Weather Advisory from 4 AM to 1 PM EST Tuesday for
     NJZ007-008.
     Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for
     NJZ009.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 3 PM Tuesday to 4 AM EST Wednesday
     for ANZ430-431.
     Small Craft Advisory from 10 AM Tuesday to 4 AM EST Wednesday
     for ANZ450>455.

&&

$$

SYNOPSIS...Cooper/Guzzo/Staarmann
NEAR TERM...Guzzo
SHORT TERM...Cooper
LONG TERM...Cooper
AVIATION...Hoeflich
MARINE...Cooper/Guzzo
CLIMATE...WFO PHI