Upper Darby, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

781
FXUS61 KPHI 121848
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
248 PM EDT Tue Aug 12 2025

.SYNOPSIS...
High pressure will continue to be centered to our east through
Wednesday. A surface trough across our area Wednesday gives way to a
cold front crossing our area from the northwest during Thursday. The
front then settles just to our south into Friday before dissipating
by Saturday. High pressure arrives for Saturday into Sunday, then a
cold front crosses our area late Sunday into Monday. High pressure
starts to build in from the north on Tuesday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Surface high pressure remains located over the western Atlantic
through Wednesday. Fair weather ongoing this afternoon with just
some scattered cumulus and seasonably warm temperatures. A slight
chance of a shower or storm remains possible later today, otherwise
another dry day is in store.

Heading into tonight, skies will be mostly clear early with an
increase in clouds expected overnight. With light southerly flow
persisting, we`ll continue to see low-level moisture increase as
well. Hence, there likely will be another round of some low stratus
developing by early Wednesday morning with areas of localized fog,
perhaps dense at times, possible. Lows will be mild ranging from the
upper 60s to mid 70s.

For Wednesday, the prolonged stretch of dry weather will come to an
end as a shortwave approaches from the west during the afternoon. As
it does so, will begin to see an increase in cloudiness along with
the development of showers and thunderstorms. With an abundance of
moisture in place with dew points in the low to mid 70s and PWATs in
the 2.0-2.3" range, any given shower or storm will be capable of
producing very efficient rain rates. While the severe weather threat
is low, our entire area is outlooked in a MARGINAL risk for
excessive rainfall by WPC. High temperatures are expected to range
from the mid 80s to low 90s areawide. No heat headlines are
warranted though as maximum heat indicies are only expected to top
out in the mid to upper 90s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
A surface trough will shift eastward across the area Wednesday night
with lingering showers/thunder associated with it, although the
coverage is less certain. Any showers and thunderstorms should be
weakening as the night wears on as the boundary layer stabilizes due
to nocturnal cooling. It will be warm and muggy however through
Wednesday night. A weak cold front is then forecast to settle
southeastward across our area during Thursday. While the forcing and
focus for convective development looks to be weak, a very warm/hot
and humid air mass will be in place ahead of the front. Some
guidance has increased the shower chances, targeting our northern
areas more during the day Thursday before some drier air starts to
settle southward. With the assumption of some more cloud cover
across the area and at least some convection around, high
temperatures are forecast to be near 90 degrees for most of the
area. Dew points in the low to mid 70s ahead of the front should
start to gradually decrease from the north through Thursday night as
the cold front is pushed southward.

As we go through Friday, the flow aloft becomes more zonal with some
lingering ridging initially across parts of eastern Canada. This
will support surface high pressure sliding by to our north. This
should assist in pushing the weak cold front just to our south
before it starts to dissipate. We have more of the influence of the
surface high to our north, however there is no significant push of
cooler air. The dew points are forecast to come down some with
enough drier air mixing in especially during the daytime hours.
While not much of a focusing mechanism looks to be present to
initiate convection, a few showers cannot be ruled out in the
afternoon as the air mass will still be rather warm and humid
enough. High temperatures outside of the coastal areas and higher
elevations are forecast to be in the upper 80s to 90 degrees. The
dew points look to be in the 60s to low 70s (highest across the
southern areas), therefore still on the humid side.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Summary...Warm/hot with lingering humid conditions, then the start
of some cooling Tuesday. The chances for showers and thunderstorms
range from low to none.

Synoptic Overview...Our region will remain on the north part of an
east to west ridge to start the weekend. An upper-level trough
moving across eastern Canada over the weekend and early next week
should result in the ridge retreating south and westward. At the
surface, a cold front is forecast to cross our area late Sunday into
Monday followed by high pressure from the north on Tuesday.

For Saturday and Sunday...Our region is forecast to be on the
northern part of a strong west to east mid/upper level ridge to
start the weekend. An upper-level trough moving across eastern
Canada though looks to push the ridge south and westward with time.
This will result in the heights lowering some across the Northeast
into the northern Mid-Atlantic, however given the stronger part of
through is well to our north our temperatures should not be impacted
much. As a result, the warm to hot conditions are forecast to
continue with daytime highs reaching the 80s to low 90s. While the
dew points may come down some, it still looks to be on the humid
side. Heat indices are still forecast to be below heat advisory
criteria, with these values the highest on Sunday. A cold front
associated with the upper-level trough arrives late Sunday. Other
than an isolated shower or thunderstorm possible mainly well inland
and across the higher elevations each afternoon, the probability of
convection currently is looking to be very low.

For Monday and Tuesday...The aforementioned upper-level trough, most
pronounced well to our north, is forecast to push a cold front to
our south. Given that the stronger dynamics are currently forecast
to be passing by well to our north, the forcing and low-level
convergence looks to be much weaker across our area. Surface high
pressure then starts to build into our area from the north on
Tuesday. Some cooling is forecast to start taking place on Tuesday,
and at least some lowering of the dew points should occur although
to what extent will depend on the southerly push of the incoming air
mass change. Given increased uncertainty with the details/timing,
made no changes from the NBM which also includes 20-30 percent
chances for showers and thunderstorms across our area.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

This Afternoon...VFR with SCT low clouds. South-southwest winds
around 5-10 kt occasionally gusting up to 15 kt. High confidence.

Tonight...VFR for most of the night, before another round of low
stratus/fog result in a period of sub-VFR conditions. Light south-
southwest winds around 5 kt or less. Moderate confidence overall,
but low confidence with timing and magnitude of restrictions.

Wednesday...Lingering sub-VFR conditions early, should improve to
VFR by 14-15Z. Showers and thunderstorms expected during the
afternoon which may cause temporary VSBY/CIGs restrictions. Moderate
confidence.

Outlook...

Wednesday night and Thursday...Times of sub-VFR conditions mostly
due to any showers or thunderstorms.

Friday through Sunday...VFR overall.

&&

.MARINE...
No marine headlines are in effect through Wednesday. Southerly winds
around 10-15 kt are expected with occasional gusts up to 20 kt
possible. Seas of 2-3 feet. Fair weather expected through tonight,
with a chance of showers and thunderstorms on Wednesday.

Outlook...

Wednesday night through Sunday, the conditions are anticipated to be
below Small Craft Advisory criteria.

Rip Currents...

Lower winds/seas and medium period swells points to an overall
low-energy sea state. A LOW risk for the development of dangerous
rip currents is expected through Wednesday for the Jersey Shore
and the Delaware Beaches.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Air Quality Alert until 11 PM EDT this evening for PAZ070-071-
     101>106.
NJ...Air Quality Alert until 11 PM EDT this evening for NJZ008>010-
     012-015.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...DeSilva
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...DeSilva/Gorse
MARINE...DeSilva/Gorse/OHara