Upper Darby, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

598
FXUS61 KPHI 030639
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
239 AM EDT Thu Apr 3 2025

.SYNOPSIS...
High pressure over eastern Canada moves out to sea tonight.
Meanwhile, strong low pressure over the Midwest lifts into the
Great Lakes, and a warm front extending out from that low lifts
north through the region tonight through Thursday morning. A
cold front passes through Thursday night and then gets hung up
over the area through the weekend. This front will oscillate
back and forth as several waves of low pressure pass through the
region. A stronger cold front passes through Sunday night,
followed by another cold front Monday night. High pressure
returns for the rest of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Warm front continues slow progress northward. Many locations in
our region have already seen a wind shift to southerly, but that
may not be the main front as observations still show dew points
in the 40s. Watching the QLCS, which as of 2 AM is in OH and KY.
As mentioned by the previous shift, the remnants of this
convective system could arrive in our region later this morning
(likely shortly after sunrise), but given that it will have out-
run the main forcing, it should be weakening and may be little
more than showers by that point.

The center of the surface low will be moving northeastward into
Ontario and Quebec through the day. The warm front should
continue to progress northward from our area, Cloudy conditions
will somewhat limit heating today. However, still expecting high
temperatures to range from the upper 60s to upper 70s.

A cold front on the south side of the low is expected to
approach our region from the west as it occludes. As it does so,
there will be an increasing chance for showers and storms very
late today into tonight. The main area of forcing will remain
well north of our region. Additionally, the low will generally
be weakening and filling through the day. The combination of
this, plus the potential of the front occluding will mean that
by the time showers and storms approach our region, there will
be very limited large scale forcing.

There remains a marginal risk (1 out of 5) for severe
thunderstorms due to the low cape and high shear environment.
However, model soundings (even from the NAM, which tends to be a
bit more bullish than most guidance in these situations) show
very weak lapse rates below 700 mb. In fact, there may be a
robust temperature inversion around 850 mb that never erodes
until very late Thursday night. Consequently, the severe risk
will be mostly predicated on the area seeing more warming in the
low levels, than what we are currently forecasting. Given that
the front won`t be approaching our region until after sunset,
that further supports weak low level lapse rates.

That being said, if anything moves in from further west, there
is a persistent veering profile in model hodographs for many
locations in the region. Bottom line is that if any updrafts can
overcome the very limited instability, the wind shear would
support a severe risk, mostly due to damaging winds.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY/...
Conditions dry out Friday afternoon and a cooler and drier air
mass builds down into the region. Surface dew points drop into
the 40s and 50s Friday afternoon and night. Highs will generally
be in the low to mid 60s, though it will be warmer in Delmarva,
as it should be south of the cold front.

Low pressure approaches from the west and passes north of New
York State Friday night through Saturday. This will pull the
frontal boundary back north as a warm front. Another round of
showers will develop Friday night and continue into Saturday
morning. Onshore flow will keep the area cloudy. Uncertain as to
how far north the warm front will get, so it will be uncertain
as to how warm the entire area will get. Based on latest
guidance, it should get into the 70s in Delmarva, in the low to
mid 60s south of the I-195 corridor, and in the mid and upper
50s in the southern Poconos, northern New Jersey, and the Lehigh
Valley. Though those temperatures will be highly dependent on
how far north the front gets.

Another low pressure system approaches from the west, and
another round of showers is possible A few showers or an
isolated thunderstorm will be possible early this evening in
association with the thunderstorm activity currently over
western PA that will track toward the northern third of our
area.late Saturday afternoon.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Unsettled conditions on tap through the weekend as a frontal
boundary will remain over the area and several waves of low
pressure will ride along this boundary.

As one wave of low pressure passes north of the region Saturday
night, it will pull a warm front through the Northeast and Mid-
Atlantic. The region will then be in the warm sector on Sunday.
Rain lifts from south to north and tapers off late Saturday
night, and then patchy fog develops late Saturday night as
southerly winds usher low level moisture in to the region and
surface dew points rise well into the 50s. Quite warm and humid
for the start of April on Sunday with highs well in the 70s and
even low 80s in Delmarva with dew points in the 50s and low 60s.

A deep upper trough will dig through the central U.S. and low
pressure will develop at the base of the trough over the
Southeast and Mid-Atlantic, and this low lifts north through the
region Sunday night. As it departs, the front over the area
will move through as a cold front late Sunday night through
Monday morning. Showers and isolated thunderstorms develop
Sunday afternoon and persist through the night, tapering off
from west to east Monday morning. Based on the setup, which
includes an airmass with 60 or so degree dew points ahead of the
front and 30 to 40 degree dew points behind it, there is the
potential for severe weather, but there will be a lack of
heating with the frontal passage occurring at night, so
instability may be limited.

Turning much cooler and dryer on Monday. Another cold front
passes through Monday night through Tuesday morning, resulting
in a reinforcing shot of colder and drier air into the region
for Tuesday and Wednesday. There may even be some rain and/or
snow showers with the passage of this front on Tuesday. High
pressure builds in from the west for the mid-week period.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through today...Expect prevailing MVFR and IFR conditions
(mostly due to low ceilings) through at least 18Z. Many sites
could see a brief improvement to VFR centered around 21Z.
Isolated showers possible between 12 and 18Z. Wind either SE or
S less than 10 kt through 12Z, becoming southwest around 10-15
kt with gusts up to 25-30 kt. Moderate confidence on the overall
pattern, but low confidence on details especially timing of
flight category changes.

Tonight...Another round of scattered showers and isolated
thunderstorms possible between 00 and 09Z (coverage of
thunderstorms is expected to be too limited to include in the
TAFs at this time). If any sites are VFR to start the evening,
expect conditions to once again lower to MVFR or IFR (again
mostly due to low ceilings). SW winds 10 to 15 kt to start the
night, but should see a wind shift to northwesterly after 06Z.
Low confidence.

Outlook...

Thursday night...Sub-VFR in SHRA and scattered TSRA.

Friday through Friday night...Improving conditions in the
morning, then sub-VFR in SHRA in the afternoon and at night.

Saturday through Saturday night...Sub-VFR conditions early,
then VFR for the middle of the day. RA develops in the afternoon
and evening with sub-VFR conditions. Sub-VFR in patchy fog and
low clouds Saturday night.

Sunday through Sunday night...Improving conditions from late
morning through the afternoon, then sub-VFR in SHRA and isolated
TSRA Sunday afternoon and night.

Monday...Sub-VFR in SHRA Monday morning, then VFR.

&&

.MARINE...
A Small Craft Advisory will be in effect beginning tonight for
the Atlantic coastal waters, with the Delaware Bay beginning
early Thursday morning. Southeast winds will become south winds
around 20-25 kt with gusts up to 25-30 kt through the day on
Thursday. Seas will also build to 5-7 feet. Fair weather
expected tonight with a chance for showers and thunderstorms on
Thursday. Dense marine fog is also possible beginning on
Thursday too.

Outlook...

Thursday night...SCA conditions continue on the ocean waters.
Winds will gust to 25 kt until midnight or so, and seas will
subside from 5 to 7 feet to 3 to 5 feet. VSBY restrictions in
showers and isolated thunderstorms.

Friday through Friday night...Sub-SCA conditions. Lingering
showers and thunderstorms in the morning, then another round of
showers possible Friday night.

Saturday through Saturday night...Generally sub-SCA conditions,
though seas may build to 5 feet late Saturday night. VSBY
restrictions in rain and fog in the morning, then again in the
afternoon and at night.

Sunday through Sunday night...SCA conditions possible for wind
gusts up to 25 kt and seas building to 5 to 7 feet. VSBY
restrictions in showers and isolated thunderstorms late in the
afternoon and at night.

Monday...SCA conditions possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 AM this morning to 6 PM EDT this
     evening for ANZ430-431.
     Small Craft Advisory until 6 AM EDT Friday for ANZ450>455.

&&

$$

SYNOPSIS...MPS
NEAR TERM...Johnson
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...Johnson/MPS
MARINE...DeSilva/Hoeflich/MPS