Upper Merion, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

604
FXUS61 KPHI 040123
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
923 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/...
920 PM update...
So far the evening has been quite quiet and tranquil, with warm
and humid conditions prevailing. However, still expect
widespread showers and scattered thunderstorms to move in
overnight with wave of low pressure and cold front approaching,
so have not altered the forecast significantly. In fact, have
raised POPS overnight into early morning Friday. Otherwise, no
major changes at this time.

3 PM discussion...
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 could 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. The warmth will also 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 /01Z 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 have not been particularly strong over the waters, but
seas are still expected to increase, so Small Craft Advisories
remain in effect for the ocean waters. Latest guidance holds
elevated seas even later into Friday, so extended the SCAs into
the morning. Winds may 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 midday Friday. For the bay, sub-SCA conditions should
prevail.

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 after midday 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/RCM
SHORT TERM...AKL/Gorse
LONG TERM...AKL/Gorse
AVIATION...AKL/Cooper/Guzzo/MPS
MARINE...AKL/MPS/RCM