050
FXUS61 KPHI 172113
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
513 PM EDT Tue Jun 17 2025

.SYNOPSIS...
A slow moving warm front will gradually lift northward
across the region through tonight. Bermuda high pressure sets up
offshore Wednesday and Thursday. A regime change occurs towards the
end of the week as a cold front passes through the region Thursday
afternoon and night. High pressure should then generally dominate
for the end of the week through the weekend into early next week
with a building ridge aloft over the east coast through this period.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
Have started to see some improvements today with some brightening
skies across southern areas and mostly dry conditions for most.
Still a few showers are ongoing across the Lehigh Valley and
Poconos, but overall, improvements compared to the last 3-4 days.
Temperatures are mainly in the 60s/70s this afternoon.

For tonight, the warm front that we are eagerly waiting for to clear
out this dreary weather will be on our doorstep. Latest guidance
indicates that the positioning of the front should be located near
the Delmarva early this evening, moving up towards the vicinity of
Philadelphia after midnight, then clearing north of the area by day
break on Wednesday. Until the front passes by, intervals of patchy
mist, drizzle, and fog will continue. We`ll also have to keep an eye
on dying convection to our west early this evening which will be
tracking north of east. For the most part, guidance generally keeps
this threat focused on the Lehigh Valley, Poconos and northern New
Jersey, however a few showers cannot be ruled out elsewhere. Will
have to keep an eye on potential hydro threats as PWATs are in
excess of 2 inches, but any showers should be moving at a pretty
decent clip tonight. All in all, a mild, and muggy night is in store
with lows in the mid 60s/low 70s.

For Wednesday and Wednesday night, we`ll have two primary concerns:
Strong to severe thunderstorms and increase in heat and humidity.

1) Strong to severe thunderstorms: Broad mid-level southwest flow
will overspread the area as a subtle shortwave tracks northeast
across portions of the area on Wednesday afternoon. While the
greatest forcing remains displaced to our west, the combination
of clearing skies and diurnal heating along with the shortwave
forcing should be enough for isolated thunderstorms to develop once
convective temperatures are reached. Latest soundings indicate
that we`ll have 35-40 kt of bulk shear, 1500-2000 J/kg of
MLCAPE, PWATs between 2.00-2.25 inches, and strong surface
heating with dew points in the low to mid 70s. Despite a
marginally conducive environment, these factors support the
potential for wet microbursts to occur, so damaging wind gusts
will be the primary threat. SPC currently has most of our area
in a MARGINAL risk for severe weather (Level 1/5) mainly for
areas south of the I-78 corridor. In addition, WPC currently has
the entire area in a MARGINAL risk for excessive rainfall
(Level 1/4) as seasonably high PWATs will allow any areas of
convection to produce heavy rain rates. Storms should begin to
wane into the evening hours as the loss of diurnal heating will
prevent the threat from continuing into Wednesday night.

2) Heat and Humidity: High temperatures on Wednesday are forecast to
top out in the mid 80s to low 90s across the coastal plain with
upper 70s to low 80s across higher elevations. Although this is not
uncommon, we will have seasonably high dew points, maxing out in the
low to mid 70s. Factoring the warm temperatures with the soupy
airmass in place, this will result in heat indicies in the 90-100
degree range. Since our criteria for heat advisories is 96 degrees
or higher only in the urban corridor prior to June 30th, have opted
to issue our first heat headlines of the season for New Castle
County in DE, Delaware and Philadelphia Counties in PA, and NW
Burlington, Gloucester, and Camden Counties in NJ.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
A more prominent shortwave axis will shift eastward across much of
the Northeastern US on Thursday. A surface cyclone will track
northeastward from the Great Lakes into Ontario and eventually
Quebec by afternoon. A cold front will trail this cyclone and pass
through the region late Thursday afternoon into the evening.

Ahead of this cold front, another day of dangerous heat is expected.
Temperatures will likely be a few degrees warmer Thursday than
Wednesday areawide, and consequently a broader area of apparent
temperatures rising into the mid-upper 90s is expected. In fact,
heat indices could exceed 100 across portions of the Delmarva.

Showers and thunderstorms are expected to develop along and ahead of
the cold front Thursday afternoon and evening as it tracks eastward
across the area...best chances appear to be focused in the 4-10 PM
time frame with earlier timing in our N/W zones and later timing
towards the coast. It appears the environment will be quite
favorable for severe weather as ML CAPEs are progged to max out in
the 1500-2500 j/kg range with deep layer shear of 30-35 knots. We
are also noting the mixed boundary layer should be quite deep (to
around 800 mb) with inverted V type soundings likely setting up.
What`s more, the flow near the top of this layer will be around 30-
40 knots which is fairly strong flow for this time of year. This
indicates the potential for a higher end severe weather day where
there could potentially be numerous instances of damaging winds.
Still, this is a couple days away and how exactly this plays out
will come down to the details regarding the strength of the
shortwave and upper level flow and how this lines up timing wise
with the surface cold front. So confidence is still only in the
moderate range. In addition to damaging winds, large/severe hail
will be possible.

Storms should clear the coast by the late evening / early overnight
period as the cold front moves off the coast. In the wake of the
cold front, drier air will move in overnight on west winds with lows
by Friday morning mostly in the 60s. Friday will then feature
sunshine with highs in the 80s and comfortable humidity levels.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Significant mid-level ridging will begin to take shape to our
southwest across central and southeastern portions of the US heading
into the weekend. It is not out of the question that northwesterly
flow on the periphery of this expanding ridge could have a weak
impulse or two provide parts of the area with low precipitation
chances this weekend. Overall, however, high pressure will become
firmly in control. The primary story in the extended period looks to
be very warm temperatures during the late weekend and into early
next week. For next Monday and Tuesday, forecast highs for much of
the region are forecast to be in the middle to high 90s with heat
indicies forecast to exceed 100. The exception will be along the
coast and in the Poconos where it will be a bit cooler.

&&

.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of Today...Mainly MVFR ceilings expected for the rest of the
afternoon with temporary periods of IFR and even VFR ceilings at
times. Other than a stray shower, should remain dry.
Southeast winds around 5-10 kt. Moderate confidence overall.

Tonight...MVFR/IFR ceilings early, will lower through tonight down
to LIFR/IFR for all terminals. Scattered showers expected overnight
with intervals of mist and possible fog. Southeast winds will
gradually turn more southerly around 5 kt or less.
Low-moderate confidence.

Wednesday...Lingering IFR ceilings in the morning, should
drastically improve to VFR ceilings by the afternoon. Showers and
scattered thunderstorms during the afternoon will be possible,
causing potential sub-VFR ceilings once again. South-southwest winds
around 7-12 kt. Moderate confidence.

Outlook...

Thursday through Thursday night...Mainly VFR in the morning.
Scattered showers and storms during the afternoon and evening could
lead to brief periods of sub-VFR conditions. The storms could also
bring strong winds and hail. Becoming VFR overnight Thursday night.

Friday through Sunday...VFR.

&&

.MARINE...
A Marine Dense Fog Advisory is in effect through 7 AM Wednesday from
Sandy Hook to Great Egg Inlet due to visibilities 1 nautical mile or
less. Further expansions may become warranted basis trends and later
observations.

Otherwise, no wind/sea hazards are in effect through Wednesday
night. Intervals of showers, drizzle, mist, and fog re-develop
tonight, with a separate round of showers and thunderstorms for
Wednesday afternoon. South-southeast winds around 5-10 kt
tonight, becoming south-southwest around 10-15 kt on Wednesday
into Wednesday night. Seas of 3-4 feet.

Outlook...

Thursday through Sunday...In general, Sub-SCA conditions are
anticipated through the period with winds below 25 kt and seas below
5 ft. However there will be some showers and storms moving over the
waters Thursday evening and some of these could produce locally
strong winds.

Rip Currents...

For Wednesday, winds become south-southwesterly and increase to
10-15 mph. Swell initially begins onshore before also turning to
the south-southwest, becoming more shore parallel with the
swell period remaining around 6-7 seconds throughout. As a
result, breaking waves in the surf zone look to be around 2-3
feet for the central and northern Jersey Shore and 2 feet or
less southwards of there. Therefore, a MODERATE risk for the
development of rip currents is forecast for Jersey Shore beaches
from Atlantic City northwards on Wednesday with a LOW risk for
the Cape May shore and Delaware Beaches.

For Thursday, winds and swell remain oriented south-
southwesterly. However, winds increase to 15-20 mph with seas
increasing to around 4 feet. As a result, breaking waves in the
surf zone of 2-3 feet look to occur across all beaches.
Therefore, a MODERATE risk for the development of rip currents
is forecast for all beaches on Thursday.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 11 AM Wednesday to 8 PM EDT Thursday for
     PAZ070-071.
     Heat Advisory from 11 AM to 8 PM EDT Thursday for PAZ104-106.
NJ...Heat Advisory from 11 AM Wednesday to 8 PM EDT Thursday for
     NJZ017>019.
     Heat Advisory from 11 AM to 8 PM EDT Thursday for NJZ015.
DE...Heat Advisory from 11 AM Wednesday to 8 PM EDT Thursday for
     DEZ001.
MD...None.
MARINE...Dense Fog Advisory until 7 AM EDT Wednesday for ANZ450>452.

&&

$$

SYNOPSIS...Cooper/Deal/Fitzsimmons/RCM
NEAR TERM...Cooper/DeSilva
SHORT TERM...Cooper/Fitzsimmons
LONG TERM...Cooper/Fitzsimmons
AVIATION...DeSilva/Fitzsimmons
MARINE...AKL/DeSilva/Fitzsimmons