183
FXUS61 KPHI 161813
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
213 PM EDT Wed Jul 16 2025

.SYNOPSIS...
A very warm and humid airmass will be over the region through
Thursday with multiple rounds of showers and thunderstorms expected.
A frontal boundary will remain stalled across the northern portion
of the area today before lifting north of the area as a warm front
on Thursday. A cold front will pass through the region Thursday
night into Friday, with high pressure building in for Saturday.
Another cold front approaches late in the weekend and will either
move offshore or stall with high pressure trying to nudge in from
the north to start next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
A weak stationary boundary/surface trough is draped across the
region this afternoon, centered from north central NJ through
southeastern PA. With broken cumulus clouds over much of the region,
filtered sunshine has allowed the area to warm into the mid-upper
80s in most locations. Surface dewpoints are generally in the low-
mid 70s. Given that we only expect a few degrees of additional
warming, and the moisture in place is fairly deep, dewpoints will
likely hold steady into this afternoon.

With the aformentioned temperatures and high dewpoints, heat indices
across the are this afternoon are expected to be in the mid 90s,
though a few locations could approach 100. With that said, it is not
expected that we will see widespread Heat Advisory Criteria being
met.

Isolated to widely scattered showers and storms have already begun
to develop across portions of the area, and will become increasingly
widespread this evening into tonight. This afternoon, the
environment has become moderately to strongly unstable with SBCAPE
of 3000-4000 J/kg. Therefore, strong updrafts are likely. Winds
throughout the entire vertical column are quite weak, which will
limit overall storm organization. With that said, an isolated
instance of damaging wind or two cannot be entirely ruled out. As
such, the Storm Prediction Center has placed the northwestern half
of the area in a Marginal Risk (1 of 5) for severe storms this
afternoon and evening.

Of greater concern will be the potential for flash flooding.
Forecast soundings across the area indicate very tall CAPE profiles,
with near saturation extending to near 700 mb. PWATs across the area
will generally range from 1.5-2 inches. Any storms in this
environment will likely be very efficient rainfall producers. In
addition, storms will likely move very slowly due to the very weak
steering in place. We have expanded the Flash Flood Watch, which
will now be in effect across northern DE, portions of southern NJ,
and all of our eastern PA counties, from 3 pm until 11 pm. In
addition, the Weather Prediction Center has placed the western half
of our area in a Slight Risk (2 of 4) for flash flooding, with the
remainder of the area in a Marginal Risk (1 of 4).

Southwest return flow will strengthen Thursday ahead of the frontal
boundary, which will help push temperatures and dewpoints up a few
degrees from earlier in the week. Forecast high temperatures are in
the upper 80s to lower 90s across much of the area. Dewpoints will
generally be in the mid 70s, which will make for oppressively hot
and humid conditions with heat indices near 100-105 across much of
the area outside the higher elevations northwest. Even the immediate
coast and beaches will not be immune from the oppressive humidity.
Ocean water temperatures are in the mid 70s to near 80 degrees.
While temperatures may be a few degrees cooler at the coast,
dewpoints will be higher resulting in heat indices in the 100-105
degree range, especially earlier in the day before the sea breeze
gets stronger. We have not changed the Heat Advisory, which is in
place for all but Carbon and Monroe Counties where heat indices
should remain in the mid 80s to low 90s.

The environmental setup Thursday should focus convection near and
northwest of I-95, where lee side surface troughing and terrain will
act as forcing for convection ahead of the front. Drier mid level
air, steep low level lapse rates, and more modest deep layer shear
values should result in a greater severe thunderstorm threat for
Thursday than earlier in the week. PWats will remain high as well
(on the order of 2"), so locally heavy rainfall will remain a
possibility, but storms should be much more progressive, resulting
in a lower threat of flash flooding. It should be noted that there
is a great deal of uncertainty regarding timing and coverage of
convection on Thursday. Tonight`s activity could linger into
Thursday morning, which would limit any convection until much later
in the day or into the evening.
&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
The weak cold front should push into the area overnight Thursday
night into early Friday morning. This will result in a much lower
chance of convection on Friday, with 15-25% PoPs for Delmarva. Any
activity should be quite isolated in nature, and should not have any
notable severe or flash flood threats. Temperatures and especially
dewpoints/humidity will be on the decline for Friday, with dewpoints
finally dropping into the 60s for northern areas. Highs mainly in
the 80s to perhaps near 90 degrees near the coast. Friday night will
be quite pleasant by mid July standards, with dewpoints continuing
to fall under a light northerly breeze. Dewpoints in the mid 50s are
forecast northwest of I-95! Lows in the 60s to near 70 degrees at
the coast and Delmarva as the frontal stalls out across southern
Delaware.

Heading into the weekend, Saturday should be a nice summer day with
the drier airmass lingering. Highs in the mid 80s and 60s dewpoints.
The stalled frontal boundary settles over the area, which could lead
to some showers and thunderstorms in the afternoon and evening,
mainly along and west of the I-95 corridor.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
A wave of low pressure rides the stalled boundary on Saturday Night,
with areas of rain and perhaps a few rumbles of thunder moving
through. This should move out by daybreak Sunday, with a lull in
precipitation coming for Sunday morning. Chances for convection ramp
back up and humidity should increase again for Sunday afternoon as
the boundary starts lifting north with return flow and another weak
cold front approaches. This will result in an unsettled Sunday
though temperatures look to be seasonable.

Overnight and the newest 12z suite of guidance have trended a bit
faster with the front and have it clearing the area, with high
pressure moving in from the north. This has resulted in a drier
forecast to start next week. However, with the front expected to be
nearby, cannot rule out some unsettled weather to start next week,
though things have trended drier. Temperatures look to be near
normal as we get into midsummer.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 00Z...Mainly VFR. Isolated thunderstorms will develop this
afternoon. This is most likely for the I-95 terminals, KRDG, and
KABE. Brief restrictions would be expected should a storm impact a
terminal. South-southwest wind 5-10 kt. High confidence overall, low
confidence on restrictions due to isolated storms at the terminals.

Tonight...Mainly VFR this evening, though scattered storms will
become increasingly likely from 01-03Z across the I-95 terminals,
KRDG, and KABE. Restrictions will be likely in any heavier storm. A
period of MVFR ceilings is increasingly likely after 03-06Z for all
terminals. South-southwest wind around 5 kt. Moderate confidence.

Thursday...MVFR ceilings will likely lift/scatter out with
prevailing VFR by around 15Z at all terminals. Scattered storms will
once again be possible during the afternoon and evening hours, with
restrictions possible in heavier storms. West-southwest wind around
10 kt, with gusts in the 15-20 kt range possible. Moderate
confidence.


Outlook...

Friday through Friday Night...VFR. No significant weather.

Saturday through Saturday Night...Primarily VFR through the day but
restrictions possible late Saturday and into Saturday Night (50-70%)
with showers and thunderstorms moving through.

Sunday through Sunday Night...Primarily VFR but restrictions
possible (40-50%) with showers and thunderstorms developing in the
afternoon.

Monday...Primarily VFR. Slight chance of a shower (15%).

&&

.MARINE...
No marine headlines are anticipated through Thursday. Today and
tonight, south-southwesterly wind of 15-20 kt with seas generally 2-
4 feet are expected. Southwesterly wind may increase some to closer
to 20 kt Thursday afternoon, with waves around 4 feet, but
conditions should remain below SCA criteria. Scattered storms are
likely this evening into tonight and again Thursday afternoon and
evening.

Outlook...

Friday through Monday...No marine headlines expected. Periods of
showers and thunderstorms expected, mainly in the afternoon and
evening most days on Saturday and Sunday.

Rip Currents...

For today, south-southwest winds around 5-10 mph with breaking
waves around 1-2 feet and a southerly swell around 7-8 seconds.
As a result, have maintained a LOW risk for the development of
dangerous rip currents all beaches.

For Thursday, southwest winds increase to 10-20 mph with
breaking waves around 1-3 feet and a building southerly 3-4 foot
swell around 7 seconds. As a result, have upgraded Cape May and
Atlantic County beaches to MODERATE due to more perpendicular
swell and have maintained a LOW risk for rip currents for the
remainder of 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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through late tonight for PAZ054-055-060>062-070-
     071-101>106.
     Heat Advisory from 10 AM to 8 PM EDT Thursday for PAZ060>062-
     070-071-101>106.
NJ...Flood Watch through late tonight for NJZ001-007>010-012-
     015>019.
     Heat Advisory from 10 AM to 8 PM EDT Thursday for NJZ001-
     007>010-012>027.
     Air Quality Alert until midnight EDT tonight for NJZ008>010-
     012-015.
DE...Flood Watch through late tonight for DEZ001.
     Heat Advisory from 10 AM to 8 PM EDT Thursday for DEZ001>004.
MD...Heat Advisory from 10 AM to 8 PM EDT Thursday for MDZ012-015-
     019-020.
MARINE...None.

&&

$$

SYNOPSIS...Hoeflich/Staarmann
NEAR TERM...Cooper/Staarmann
SHORT TERM...Hoeflich/Staarmann
LONG TERM...Hoeflich/Staarmann
AVIATION...Cooper/Hoeflich
MARINE...Cooper/Hoeflich