414
FXUS61 KPHI 032344
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
744 PM EDT Thu Apr 3 2025

.SYNOPSIS...
A cold front associated with a strong low pressure system moves
through tonight and looks to stall near or over our area
through the start of the weekend. The cold front moves through
Sunday night followed by a stronger cold front Monday night into
early Tuesday. High pressure then builds in later Wednesday.

&&

.NEAR TERM /THROUGH FRIDAY/...
With warm front north of the area, temperatures have risen into the
60s and 70s throughout, with temperatures even around 80 in southern
portions of Delmarva. Turning humid as well with surface dew points
in the low to mid 60s, and even in the upper 60s in portions of
Delmarva.

Low pressure tracking across Canada will drag a cold front through
the region late tonight and Friday morning. Showers and scattered
thunderstorms will develop ahead of and with the passage of the cold
front. There is the possibility for some severe thunderstorms with
damaging wind gusts, but there are some limiting factors. Although
surface based CAPE will be up around 300 J/kg, MUCAPE will be much
higher, around 1000 or so J/kg. There will also be a 50 to 60 kt low
level jet that will pass through southeast Pennsylvania and southern
New Jersey, and 0-6 km Bulk Shear will be in the 45 to 55 kt range.
Despite that, BUFKIT profile soundings indicate a capping inversion
up to around 900 mb. SPC has most of the area in a Marginal Risk (1
out of 5), and has removed the Slight Risk (2 out of 5) for the
eastern shores of Maryland.

There is, however, a risk for heavy rain due the high dew points,
relatively low surface winds, and the aforementioned low level jet
that could result in localized flash flooding. PWATs will average
1.5 to 1.7 inches, and there may be some training of heavy rain
showers and possible thunderstorms across the southern Poconos,
northern New Jersey, and the Lehigh Valley. Generally on a line
north of Philadelphia, mainly from after midnight through daybreak
Friday.

Cold front works its way through the region Friday morning, although
will get hung up just south of Delmarva. The threat for convection
comes to an end, and showers taper off during the morning hours.

Highs on Friday will in the low to mid 60s for most of the region,
except in the upper 60s to around 70 in Delmarva. A much less humid
air mass also spreads south with dew points in the 30s and 40s north
of the Fall Line, and in the 40s and 50s south of the Fall Line.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As high pressure slided to our north Friday night into
Saturday, low pressure tracks up the Ohio Valley and then moves
mostly to our north through Saturday. This will pull the stalled
boundary just south of Delmarva back north as a warm front.
Some additional showers develop Friday night and Saturday,
although the focus should become more focused farther northward
with time. Onshore flow however will keep the area rather
cloudy, and the location of the front and associated warm sector
to its south will impact how warm the area gets. As of now, it
should get into the upper 60s to low 70s across much of
Delmarva with temperatures then quickly turning cooler
northward. Again, these temperatures will be highly dependent on
how far north the warm front gets. Some fog may begin to
develop Saturday night mainly along the immediate coast and the
adjacent marine area as dew points start to increase and rise
above the chilly ocean water temperatures.

Heading into Sunday, as a significant upper-level trough slides
across central to eastern Canada, it is forecast to amplify
southward with its leading edge starting to move into the
Northeast Sunday night. This trough will drive low pressure well
to our north, however a trailing cold front will arrive in our
area mostly Sunday night. The existing warm front across the
area looks to surge northward early Sunday morning, and most of
the area should get within the warm sector during the day as
southerly flow increases. This should result in high
temperatures getting into the 70s across much of the area with
even low 80s possible across portions of Delmarva and the
coastal plain. This warmth will however depend on how much
sunshine occurs as well as the timing of the cold front and
associated showers. It will feel more humid as dew points rise
through the 50s and even the low 60s for many areas ahead of the
cold front. This warm and more moist air mass may also result
in marine fog that could impact the coastal areas as well,
before it gets pushed out as the low- level flow veers more from
the southwest. While the parent trough lags well behind the
surface cold front, height falls arriving with a greater
thickness packing also arriving from the west later in the day
should result in enough forcing for ascent for showers to
develop and move in from the west especially in the afternoon
and more likely at night. The timing of the front looks to be
mostly at night which is less ideal for stronger convection,
however some thunder is certainly possible given the strength of
the incoming trough. The intensity of any convection will
depend on the available instability and shear magnitudes in
combination of any stronger forcing for ascent.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Summary...A stronger cold front moves through Monday night with
high pressure moving in for the mid-week. High temperatures
falling to several degrees below average through the middle of
next week.

Synoptic Overview...An upper-level trough is forecast to amplify
into and across the East during early next week, before starting to
lift out on Wednesday. The next upper-level trough then looks to
begin to amplify across the eastern CONUS for Wednesday night
into Thursday. At the surface, a stronger cold front moves
through Monday night. High pressure then builds in Tuesday
night before shifting offshore Wednesday night. Another low
pressure system may approach the region by Thursday.

For Monday and Tuesday...This time frame starts as more of a day in
transition on Monday as the first cold front is offshore and we
await a secondary cold front tied to the amplifying upper-level
trough. This second front may end up moving through our area Monday
night with little in the way of precipitation as the deeper
moisture is shoved offshore with the earlier cold front. Given
the strength of the incoming upper-level trough however, cannot
ruled out some additional rain showers with the second cold
front mainly Monday night or early Tuesday. This could also be
in the form of some wet snow across the higher elevations of the
Poconos if enough moisture remains. High temperatures Monday
should be closer to average. The second cold front should be
offshore to start Tuesday with strong cold air advection
underway. There will be a tightened pressure gradient in place
between departing low pressure well to our northeast and
incoming high pressure from the Midwest to the Ohio Valley. This
will translate to a gusty wind on Tuesday before diminishing
some at night. High temperatures Tuesday look to be several
degrees below average. It will be cold Tuesday night with most
if not all areas dropping below freezing. There may be to much
wind for frost formation, however a freeze warning may be needed
where the growing season has started (most of our Delmarva
zones).

For Wednesday...The strong upper-level trough is currently forecast
to be lifting out with time. This will result in surface high
pressure building into our area before it starts to shift offshore
at night. There may still be a gusty wind in place before a
tightened pressure gradient relaxes as the the center of the surface
high builds closer. High temperatures will be several degrees below
average once again, and the wind will determine how cold it gets at
night despite the air mass especially aloft starting to modify. A
clear sky with dew points at or below freezing would typically yield
a cold night especially if the wind is able to completely decouple.
As a result, there is some risk for frost and/or freeze (the growing
season has started for most of our Delmarva zones).

For Thursday...The next upper-level trough looks to begin
deepening across the Eastern US and a surface low may begin to
approach the region as a result. However, this will be dependent
on the strength of the developing low relative to the departing
high, so much of Thursday may end up remaining dry. Temperatures
do look to begin to moderate though as southerly flow returns.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR to MVFR with brief periods of IFR possible.
Scattered showers and isolated thunderstorms are possible
between 03Z and 12Z. Expect mainly MVFR ceilings in this
activity, but IFR visibilities will be possible in the heaviest
storms. Some LLWS is possible between 03Z and 10Z at KACY and
KMIV. Southwest wind around 10 kt, shifting to northwest after
06Z at 5-10 kt. Low confidence in the timing and placement of
heaviest storms and lowest flight categories.

Friday...Showers and isolated thunderstorms taper off around
15Z and conditions improve. Ceilings lift to VFR, with perhaps
some lingering MVFR ceilings at KMIV and KACY. Northwest wind
5-10 kt with a few gusts around 15 kt. Moderate confidence.

Outlook...

Friday night and Saturday...Sub-VFR conditions probable along
with some possible showers.

Sunday...IFR possible in the morning due to low clouds and/or fog,
then some improvement however sub-VFR probable at times along with
showers and possibly a thunderstorm in the afternoon and especially
at night. Southwesterly wind gusts up to 25 knots possible during
the day.

Monday...Sub-VFR conditions possible with a slight chance for
showers.

Tuesday...VFR with no significant weather.

&&

.MARINE...
Winds are finally ramping up behind the warm front. Small Craft
Advisories remain in effect for the ocean waters through tonight.
Winds will be gusting to 25 kt or so for much of the night, and even
when gusts are less than 25 kt, seas will be above 5 feet.
Conditions subside to sub-SCA criteria on the ocean by daybreak
Friday. For Delaware Bay, the SCA remains in effect until 7 pm.

SW winds 15 to 20 kt with gusts up to 25 kt will become NW 10 to 15
kt with gusts up to 20 kt Friday morning. Sub-SCA conditions
expected on Friday.

VSBY restrictions in showers and scattered thunderstorms tonight. A
few thunderstorms may be capable of wind gusts in excess of 40 kt.
Fog will develop late tonight as well.

Outlook...

Friday night...The conditions are anticipated to be below Small
Craft Advisory criteria.

Saturday...The conditions should be mostly below Small Craft
Advisory criteria. Some visibility restrictions possible due to some
fog in the afternoon and especially at night.

Sunday...Small Craft Advisory conditions possible. Visibility
restrictions possible due to some morning fog, then showers and
isolated thunderstorms late in the afternoon and especially at
night.

Monday and Tuesday...Small Craft Advisory conditions possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until noon EDT Friday for ANZ450>455.

&&

$$

SYNOPSIS...AKL/Gorse
NEAR TERM...MPS
SHORT TERM...AKL/Gorse
LONG TERM...AKL/Gorse
AVIATION...AKL/Cooper/Guzzo/MPS
MARINE...AKL/MPS