796
FXUS61 KPHI 260727
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
327 AM EDT Thu Sep 26 2024

.SYNOPSIS...
An area of low pressure sliding by to the north will result in a
warm front lifting through today and a cold front moving in tonight.
The front will stall over the southern half of the area, as moisture
from Tropical Cyclone Helene moves in. An unsettled pattern will
continue for the weekend and into next week as an upper level low
meanders off to the southwest. A pattern change potentially comes by
the middle of next week as a sweeping cold front approaches.

&&

.NEAR TERM /THROUGH TONIGHT/...
A fairly complex weather pattern continues to evolve at this hour as
a warm front sits near southern Delmarva and high pressure continues
to slowly retreat to our north and east over Atlantic Canada. The
southwest extent of this ridging still extends into our region and
this has helped delay the northward push of the warm front.
Meanwhile low pressure is located well to our north moving into
western Quebec along with an associated upper level trough. Another
upper level low sits near the Tennessee Valley and then of course
there`s Hurricane Helene in the Gulf of Mexico. The upshot of all
this is that there continues to be rain/showers streaming north
through the Appalachians...largely due to the upper low however with
time some mid and upper level moisture from Helene is getting pulled
into this as well. As we go through the course of the rest of the
overnight into Thursday morning expect that some of these showers
will make it into our area as an upper level disturbance moves
through in the circulation. These showers should be confined mainly
to our eastern PA zones into NW NJ where we have the highest POPs
(around 60 percent). Otherwise, low stratus will continue to
predominate with some areas of patchy fog and drizzle.

By later Thursday morning into the afternoon, the warm front will
lift north and east through the area as we get into the warm sector.
Stratus should be lifting through this period with any showers
diminishing as well but expect it will remain a mostly cloudy day.
It will be on the warm and humid side though with highs mainly
ranging from the mid 70s north to the low 80s over much of Delmarva.
It will be a bit cooler though in the southern Poconos and NW NJ
where highs will be mainly in the upper 60s to low 70s. Dew points
will be in the upper 60s to low 70s across the region by this
afternoon.

For Thursday night, low pressure with its associated upper trough
moves from Quebec towards the Canadian Maritimes dragging a cold
front southward into the area. This could result in some additional
scattered showers and storms, mainly over eastern PA into central
and northern NJ. In fact expect the front to start to stall all
overnight as it reaches the Mason Dixon line. It will be another
warm night for this time of year with lows mostly in the 60s except
some upper 50s over the southern Poconos and NW NJ.


&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Helene is forecast to be over northern Georgia on Friday morning,
becoming absorbed into a closed upper level low over the southeast
US. This system is expected to be quite expansive, and moisture from
Helene is anticipated to move in Friday into Friday night. A stalled
boundary over the Delmarva peninsula will be the focus for
precipitation and currently where the highest PoPs are for Friday
afternoon/evening (around 60-80%), though rainfall amounts are
not overly impressive (only up to a half inch of rain at most).
Showers become more scattered to isolated the further north you
get from Philadelphia, and some areas of far northern New
Jersey could see little to no rainfall at all. Along and south
of the front, temperatures will be in the mid to upper 70s, with
upper 60s/low 70s north of the front. Overnight lows on Friday
night will be in the 60s.

Some guidance hints at a potential dry slot setting up for Saturday,
especially over Delmarva. However, onshore flow looks to continue,
bringing a cool and moist airmass. The remnants of Helene will
retrograde westward, with the expansive upper level low positioned
over Kentucky/Tennessee. With the maritime airmass in place,
and the closed low off to the southwest, a few showers could
develop, mainly in New Jersey and eastern Pennsylvania. Will not
be a washout by any means, but more of a cloudy day with some
showers around, similar to what we have seen the past few days.
With a stalled boundary still bisecting the region, temperatures
will be in the upper 60s/low 70s north of Philadelphia, and
upper 70s/low 80s from Philly on south.


&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As is the case with upper level lows, the forecast for the extended
is a bit tricky. The upper level low that will eventually absorb
Hurricane Helene will be positioned somewhere over the Ohio River or
Tennessee River Valley on Sunday with the region positioned on the
northeast quadrant of the closed low. This looks to bring some
unsettled weather, but no day will be a washout. We look to be in
for more days of clouds with periods of on and off showers until the
upper level low moves offshore or transitions to more of an open
wave. This looks to occur sometime Monday or Tuesday, though we will
not kick the clouds/showers until midweek, with guidance hinting at
a cold front coming through and a pattern change (finally).

It certainly will be feeling like fall with cloudy and cool
conditions expected for the end of the weekend and into next week.
Temperatures will be a few degrees below normal for late
September/early October, with upper 60s/low 70s for highs. Overnight
lows may actually end up a few degrees above normal with limited
diurnal ranges continuing with an abundance of cloud cover in place.


&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of overnight...Between scattered showers, stratus, and fog,
generally expect the lower trend of conditions to continue with most
sites seeing IFR by morning or at least times of IFR. Winds
generally SE 5 to 10 knots. High confidence in overall trend but low
confidence on specific details/timing of cig changes.

Thursday...Conditions will be slowly transitioning through the day.
Most of the morning will feature IFR conditions for most sites. MVFR
in the afternoon. A brief period of VFR is possible later in the
day. SE to S winds 5 to 10 mph. Moderate confidence.

Thursday night...Cigs lowering once again with MVFR likely by the
early overnight period and IFR likely by the predawn hours. Winds
backing to E/NE around 5 knots as a cold front pushes south into the
area. Moderate confidence.



Outlook...

Friday through Friday Night...MVFR/IFR conditions likely (80-
90%) with periods of rain moving through.

Saturday through Saturday Night...Sub-VFR conditions expected at
times, potentially as low as IFR, though stretches of VFR possible,
mainly from KPHL on south.

Sunday through Monday...sub-VFR conditions possible with 20-40%
chance of showers and low clouds hanging around in between periods
of rain.


&&

.MARINE...
Small Craft Advisories remain in effect for all the ocean waters
through the rest of the overnight, and then for tomorrow, for our
waters south of Cape May. Primarily for 5 ft seas. SE to S winds
will generally average 10 to 20 kts.

Sub-SCA conditions for Delaware Bay. Mainly SE winds around 10 to 15
kts.

All of our Marine zones are expected to be headline free by Thursday
night.

Outlook...

Friday through Friday Night...No marine headlines expected.

Saturday through Saturday Night...Small Craft Advisory conditions
possible (30-40%), mainly for the New Jersey coastal waters as seas
get near 5 feet.

Sunday through Monday...Small Craft Advisory conditions possible
(50%) with seas around 5 feet and gusts nearing 25 kt.

Rip Currents...

For Thursday...South-southeast winds around 10-15 mph. Breaking
wave heights of 3-4 feet with an 11-12 second period. For this
reason, have opted to upgrade to a HIGH risk of the development
of dangerous rip currents for both the Jersey Shore and Delaware
Beaches.

For Friday...East-southeast winds around 5-10 mph. Breaking wave
heights of 2-3 feet with a 10-11 second period. Due to lighter
winds and lower wave heights, have opted to go with a MODERATE
risk of rip currents for both the Jersey Shore and Delaware
Beaches.

Rip currents occur often in the vicinities of jetties and piers and
the speed of the currents are generally maximized at low tides.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.TIDES/COASTAL FLOODING...
Tides and water levels continue to decrease as onshore flow
weakens and we move away from the full moon.

A Coastal Flood Advisory remains in effect through Thursday
evening`s high tide for Ocean County, NJ and Sussex County, DE
as the back bays remain in minor flood stage, even during low
tide. Although onshore flow has weakened, the east-southeast
wind direction will continue to keep water trapped in the back
bays.

Some spotty minor flooding remains possible along the Eastern
Shore of Maryland with tonight`s high tide, but tidal flooding
should subside thereafter.

Otherwise, no upcoming tidal issues are expected on the
Delaware Bay, tidal Delaware River, nor the New Jersey coast
outside of Ocean County.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory until 11 PM EDT this evening for NJZ020-
     026.
     High Risk for Rip Currents through this evening for NJZ014-024>026.
DE...Coastal Flood Advisory until 11 PM EDT this evening for DEZ003-
     004.
     High Risk for Rip Currents through this evening for DEZ004.
MD...None.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for
     ANZ450>453.
     Small Craft Advisory until 6 PM EDT this evening for ANZ454-
     455.

&&

$$

SYNOPSIS...Hoeflich
NEAR TERM...Fitzsimmons
SHORT TERM...Hoeflich
LONG TERM...Hoeflich
AVIATION...Fitzsimmons/Hoeflich
MARINE...Fitzsimmons/Hoeflich
TIDES/COASTAL FLOODING...Hoeflich