176
FXUS61 KPHI 300841
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
441 AM EDT Mon Sep 30 2024

.SYNOPSIS...
Unsettled pattern continues through Tuesday night as the upper level
low off to the southwest lingers, eventually becoming an open
trough. The trough passes overhead on Tuesday night. A cold front
approaches for Wednesday and passes by Wednesday evening, ushering
in a pattern change. High pressure builds in for the end of the
week. Another cold front passes on Friday night, with high pressure
building in for the weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
The main story through Tuesday is the mid and upper level low
currently over middle Appalachia will weaken and fill as it
starts to make slow progress eastward. At the surface, a few
weak low pressure systems will traverse along the remnant
stationary front to our south. At the same time, a surface high
is building towards our region from the north.

The net result of most of this is generally more of the same
from what we`ve seen the last few days. Cloudy conditions with
some light rain. Most of the rain will be south of our
region, closer to the front. However, northern Delmarva could be on
the northern fringe of measurable rain. Even there, rain amounts are
expected to be generally less than a quarter of an inch.

For the rest of the region, some modest dry air advection as the
surface high builds closer will generally mean a decrease in
rain chances.

As for temperatures, highs will generally be a few degrees below
normal, while low temperatures will be a few degrees above
normal. Thanks to the continued persistent cloud cover and
onshore flow, the diurnal range in temperatures remains
relatively small.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
Showers move out on Tuesday Night with the trough axis moving
overhead and offshore. There could be a lingering shower, though
PoPs are only around 15-20% areawide. A spread of 50s is expected
for overnight lows.

Wednesday looks to be mainly a dry day, though the cool maritime
airmass will remain in place with onshore flow persisting ahead of
the cold front. The cold front will come through Wednesday
afternoon/evening, and it should be a dry frontal passage for most,
though some showers remain possible north and west of Philadelphia
(only a 15-30% chance though). Cloudy with seasonable temperatures
expected for Wednesday with low to mid 70s.

The front comes through by Wednesday evening ushering in a pattern
change and kicking the maritime airmass and onshore flow out. Much
drier air begins to move in by Wednesday night in the wake of the
front with westerly flow at the surface. Clouds don`t look to move
out until Thursday however. Another night of temperatures in
the 50s is expected, though it should be dry.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Rather progressive pattern coming in for the extended portion
of the forecast. However, we are looking high and dry through
the end of the week as ridging builds in aloft with high
pressure moving in and overhead by Friday. Looking at a period
of above normal temperatures both Thursday and Friday with mid
to upper 70s both days with overnight lows in the 50s.

Ridging moves offshore on Friday with a trough moving in from the
northwest. At the surface, a cold front approaches on Friday night,
which will knock down temperatures for the weekend. Only expecting
some widely scattered light showers at the moment (15-20% PoPs)
ahead of the front though it should mainly be a dry frontal passage
for most. The front quickly moves through, with another expansive
area of high pressure building in for Saturday/Sunday. More
seasonable temperatures expected for Saturday-Sunday (generally
upper 60s/low 70s).

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through Today...Ceilings should generally continue to slowly
improve through 18Z, though exact timing of improving to
the next higher category is uncertain. Additionally, as we have
already seen with some sites, ceilings may waver right around
category thresholds for a few hours. That being said, expect most TAF
sites to have a period of VFR generally between 15 and 21 Z.
KMIV and KACY are the exception as the onshore winds are likely
to keep ceilings in MVFR throughout the day (and can`t rule out
brief IFR conditions as well. Winds out of the northeast at 10kt
with higher gusts especially at KACY. Moderate confidence overall,
but low confidence on timing details.

Tonight...Low clouds may move back in over the TAF sites, but
not confident on the westward and northward extent (especially
for KTTN, KABE, and KRDG). Elsewhere, expect mostly MVFR
ceilings when the low clouds build back in (exact timing of that is
uncertain, but most guidance depicts this happening by 06Z. Can`t
rule out some visibility restrictions in fog after 06Z, particularly
at KACY, but confidence is very low and if the low clouds build in
as early as some guidance is depicting, it should limit fog
development. Northeasterly winds 5 to 10 kt. Low confidence.

Outlook...

Tuesday...potential for MVFR ceilings with low clouds.

Tuesday night...MVFR/IFR expected with low clouds and showers
around.

Wednesday...IFR in the morning could lift back to MVFR or even VFR.
Some light showers possible at KRDG/KABE/KTTN.

Wednesday night...Primarily VFR though some MVFR CIGs possible (20-
30% chance).

Thursday through Friday...VFR. No significant weather.

&&

.MARINE...
We are currently in a lull of Small Craft Advisory conditions, seas
are expected to build from south to north starting after sunrise,
leading to SCA conditions on the Atlantic coastal waters. The
elevated seas, and even gusts to 25 kt are expected to be at their
highest during the day on Tuesday.

On the Delaware Bay, winds and seas should stay below SCA criteria
through tonight.

Outlook...

Tuesday Night...Small Craft Advisory was issued for all ocean
zones as seas will be around 5 to 7 feet. A few gusts to 25 kt
are possible on the outer waters.

Wednesday...An extension to the SCA is possible as seas should be
diminishing, but cannot rule out 5 foot seas on the ocean hanging
through the daytime.

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

Rip Currents...

For today, the final day of our seasonal SRF forecast, onshore
winds will be around 10-20 mph out of the east/northeast for
all beaches, with breaking waves around 2 to 4 feet and a 6 to 8
second period. As a result, went MODERATE for the New Jersey 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

The last issuance of the SRF Product for 2024 came this morning.
This section in the forecast discussion will be deleted when the
full afternoon forecast package is released.

&&

.TIDES/COASTAL FLOODING...
Onshore flow has resulted in some minor tidal flooding. A
Coastal Flood Advisory was issued for Kent County, DE as minor
tidal flooding is expected with tonight`s high tide. A Coastal
Flood Advisory remains in effect for Sussex County, DE for
tonight`s high tide.

For the New Jersey coast and New Jersey side of Delaware Bay,
only spotty minor tidal flooding is expected currently, but an
advisory may be needed for tonight`s high tide.

No tidal flooding is forecast for the tidal Delaware River or
along the Chesapeake Bay in the Eastern Shore of Maryland.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...Coastal Flood Advisory from 6 PM this evening to midnight EDT
     tonight for DEZ002.
     Coastal Flood Advisory until midnight EDT tonight for DEZ003-
     004.
MD...None.
MARINE...Small Craft Advisory from 6 AM Tuesday to 6 AM EDT Wednesday
     for ANZ450.
     Small Craft Advisory from 8 PM this evening to 6 AM EDT
     Wednesday for ANZ451-452.
     Small Craft Advisory from 8 AM this morning to 6 AM EDT
     Wednesday for ANZ453>455.

&&

$$

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