Southeastern, Pennsylvania Weather Forecast Discussion

327
FXUS61 KPHI 110958
AFDPHI
Area Forecast Discussion
National Weather Service Mount Holly NJ
558 AM EDT Thu Sep 11 2025
.SYNOPSIS...
High pressure sliding across portions of eastern Canada today will
extend southward into our area through Friday. The high then shifts
eastward and gradually weakens over the weekend. A cold front
crosses our area later Sunday into Monday, then high pressure builds
to our north Tuesday into Wednesday.
&&
.NEAR TERM /THROUGH TONIGHT/...
High pressure centered over eastern Canada sinks southward towards
the northeastern United States through the near term forecast
period. As a result, dry conditions are expected throughout the
period.
Winds will be lighter today as the pressure gradient relaxes with
the offshore low pressure system continuing to move out to sea.
Northerly winds up to around 10 mph are expected. Otherwise, skies
will become mostly clear, outside of some passing cirrus during the
day today. High temperatures this afternoon look to top out in the
upper 70s to low 80s.
Skies look to be clear tonight with winds becoming light and
variable as the center of the high moves closer. Overnight lows will
be mainly in the low-mid 50s, with temps bottoming out closer to 60
in the heart of the Philly metro and along the coasts of New Jersey
and Delaware.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
A gradually weakening upper-level trough is forecast to cross our
area during Friday, then an upper-level trough across portions of
eastern Canada amplifies southward into the Northeast Saturday and
Saturday night.
Surface high pressure building across New England Friday and
extending into our area will gradually shift eastward and weaken
through late Saturday. The presence of a trough aloft is expected to
result in at least some clouds, with this perhaps more pronounced
during the daytime hours. There is some hints in the guidance that
nocturnal cooling Friday night into early Saturday morning results
in more moisture pooling beneath an inversion. This could result in
some low clouds and/or fog development for a time. A dry forecast is
maintained given the influence of surface high pressure, although
given cloud development especially during the day Friday, could
result in an isolated shower or a few sprinkles. A lighter flow is
expected to result in a light northerly wind becoming more easterly
during Friday, then southeasterly on Saturday. This will keep it
cooler along the coast.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Summary...Temperatures around average, although these could end up
below average next week depending on the evolution of a trough or
closed low.
Synoptic Overview...An upper-level trough is forecast to amplify
across the Northeast and the Mid-Atlantic Sunday into Monday. Some
guidance continues with this becoming a closed low in the Mid-
Atlantic Monday, which then meanders through Tuesday before slowly
weakening and shifting eastward Wednesday. At the surface, high
pressure weakens across our area Sunday as a cold front crosses our
region late Sunday into Monday. A weak area of low pressure may be
off of our coasts Tuesday as high pressure builds across the Great
Lakes and then more into our area through Wednesday.
For Sunday and Monday....The evolution of an eastern Canadian upper-
level trough will determine our sensible weather. There remains
differences among the model guidance regarding the development of a
closed low with the core of it dropping southward and over the Mid-
Atlantic region including our area. The ensemble guidance from the
GFS however still has several members that are much weaker with this
trough including no closed low. The Canadian ensembles also have
some variability with some members having a closed low, however
these are mainly much weaker than the ECMWF model. Speaking of the
ECMWF, the 00z run has backed off of the strong closed low idea with
this now much weaker and developing much farther south than some
previous runs. Either way, a cold front looks to cross our area
later Sunday into Monday and there is some chance for a few showers
and thunderstorms. These chances are on the low side currently as
deeper moisture may be lacking ahead of the cold front. If a
stronger trough, or even closed low, evolves then stronger forcing
may tend to bring a higher chance of convection. In addition,
guidance that has a more pronounced closed low shows low pressure
developing off our coast which could enhance shower activity into
our area. Given the continued uncertainty with the details, shower
chances and thus PoPS are challenging. Based on this uncertainty,
did not deviate from the NBM output. Temperatures at this time look
to be about average, although a closed low overhead would result in
temperatures below average.
For Tuesday and Wednesday...The details during this time frame also
depend on the evolution of the aforementioned upper-level trough and
whether a closed low occurs. It is possible this time frame starts
on the more unsettled side, although this will be tied to a closed
low or not and where it tracks. A stronger trough occurring would
place weak low pressure off our coast Tuesday before it shifts
farther offshore Wednesday. As this occurs, ridging across the Great
Lakes into adjacent Canada would support surface high pressure from
the Great Lakes and into the Northeast. This high then extends into
our area with time. Given the uncertainty at this time range, opted
to run with the NBM guidance which is basically dry for our area
(for now). Temperatures are currently forecast to be on the mild
side, although there is some potential for lower temperatures if the
stronger trough/closed low idea ends up occurring.
&&
.AVIATION /10Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Today...VFR with mainly clear skies and northerly winds around
5-10 knots. High confidence.
Tonight...VFR with mainly clear skies. Light and variable winds,
favoring a northerly direction. High confidence.
Outlook...
Friday and Saturday...A low chance for some sub-VFR conditions
occurring later Friday night and early Saturday morning due to some
low clouds and/or fog, otherwise VFR.
Sunday and Monday...A few showers or thunderstorms possible that
could result in times of sub-VFR conditions.
&&
.MARINE...
Small Craft Advisory remain in effect for the Atlantic Ocean zones
through 11 AM due as seas gradually decrease from 5-6 feet. Sub-SCA
conditions are expected for the remainder of the period beyond the
current SCA.
Northerly winds 10-15 knots with gusts up to 20 knots this morning.
Winds turn easterly this afternoon and decrease to around 10 knots,
then become light and variable tonight.
Outlook...
Friday through Monday...The conditions are anticipated to be below
Small Craft Advisory criteria.
Rip Currents...
A HIGH RISK OF RIP CURRENTS CONTINUES THROUGH THIS EVENING.
For today, north to east winds 10-15 mph. Breaking waves in the surf
zone of 3-5 feet are forecast. An easterly swell around 8 seconds
will persist as the rough surf conditions improve, especially this
afternoon. A HIGH risk for development of dangerous rip currents has
been maintained at all beaches, however this risk may lower some
this afternoon as wave heights subside some more.
For Friday, north to east-southeast winds around 10 mph. Breaking
waves in the surf zone of 2-3 feet are forecast. An easterly swell
around 7 seconds is forecast as the surf conditions improve. As a
result, there is a MODERATE risk for development of dangerous rip
currents at all beaches. This risk may lower some especially in the
afternoon.
For specific beach forecasts, visit weather.gov/beach/phi
&&
.TIDES/COASTAL FLOODING...
Northerly flow today will be weaker and it should become more
easterly this afternoon. The astronomical high tides are still on
the higher side and with an onshore wind component, minor tidal
flooding is expected to continue at most of our tide gauge sites. A
Coastal Flood Advisory remains in effect through later this
afternoon to cover the high tide cycles today for the Jersey Shore,
Delaware Coast and also along the coast of Delaware Bay.
For the tidal Delaware River, some minor tidal flooding is forecast
with today`s high tide cycles. Much of this looks to be below minor
advisory level and given lower confidence will continue to hold off
on a Coastal Flood Advisory for now.
Some minor tidal flooding may continue into Friday, however the need
for another advisory is less certain at this time.
No tidal flooding is expected along the northeast coast of
Chesapeake Bay.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory until 5 PM EDT this afternoon for
     NJZ016.
     Coastal Flood Advisory until 4 PM EDT this afternoon for
     NJZ012>014-020>027.
     High Risk for Rip Currents through this evening for NJZ014-024>026.
DE...Coastal Flood Advisory until 5 PM EDT this afternoon for
     DEZ001.
     Coastal Flood Advisory until 4 PM EDT this afternoon for
     DEZ002>004.
     High Risk for Rip Currents through this evening for DEZ004.
MD...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for
     ANZ450>455.
&&
$$
SYNOPSIS...Gorse
NEAR TERM...AKL
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...AKL/Gorse
MARINE...AKL/Gorse
TIDES/COASTAL FLOODING...WFO PHI

NWS PHI Office Area Forecast Discussion