345
FXUS61 KPHI 181942
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
342 PM EDT Wed Jun 18 2025

.SYNOPSIS...
Bermuda high pressure sets up offshore today and Thursday. A
regime change occurs towards the end of the week as a cold front
passes through the region Thursday into Thursday night. High
pressure should then generally dominate for the end of the week
through the weekend and into early next week with a building
ridge aloft over the east coast through this period.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
A Severe Thunderstorm Watch has been issued for portions of the
area through 7 PM tonight. MLCAPE values up to 2000 J/kg,
coinciding with modest shear, in addition to the vort max
passing through aloft has primed the environment today
especially south of Philadelphia across the Delmarva where
portions of the area was upgraded to a SLIGHT risk for severe
weather. An organized area of thunderstorms are currently
tracking into the north-central Delmarva at this hour, and will
continue trekking east through the remainder of the afternoon.
Further north, an abundance of morning cloud cover has given way
to diurnal cumulus this afternoon. The atmosphere isn`t as
primed further north as instability is lower however, a few
showers and thunderstorms may be plausible for the rest of the
afternoon. With dew points in the low to mid 70s, heat indices
will be notably above air temps, so have maintained the heat
advisory as inherited for rest of today. Showers and storms
should begin to move off the coast and/or dwindle by sunset with
the loss of diurnal heating. Patchy fog may develop later
tonight, but will be far less in coverage compared to earlier
today. Lows will mainly be in the upper 60s to low 70s.

For Thursday, a more vigorous shortwave trough will be
approaching the area which will shift east towards our area by
Thursday night. At the surface, low pressure will be located
over portions of Ontario, tracking east into Quebec and far
northern New England through the day. A cold front associated
with this surface low will pass through our area during the late
afternoon and evening hours. Very warm and moist southwesterly
flow will continue across the area. Underneath mostly sunny
skies, strong surface heating is anticipated, highs in the upper
80s to low/mid 90s. There should be better mixing ongoing on
Thursday as winds will be gusting up to 20-25 mph during the
afternoon. So, even though dew points will be oppressive once
again, they may in fact be a few degrees lower compared to
Wednesday, albeit temperatures will be a few degrees warmer.
With this in mind, a heat advisory is in effect through 8 PM
Thursday for the urban corridor where heat indicies up to 100
degrees are possible.

In addition to the dangerous heat, severe weather remains a
concern Thursday afternoon and evening. Aided by background
ascent from the approaching shortwave, the cold front should
provide a focus for the development of strong to severe
thunderstorms by mid-afternoon. The environment ahead of the
cold front is expected to become unstable (MLCAPE values upwards
of 2000 J/kg). Deep layer shear on the order of 30-35 kt will
support primarily multicell clusters initially, though a
supercell or two cannot be ruled out. Forecast soundings
indicate a fairly deep mixed layer, and strong downdraft winds
appear to be the primary threat with this activity. A few
instances of marginally severe hail cannot be ruled out and
perhaps an isolated tornado. With time, storms could have a
tendency to grow upscale due to strong frontal forcing and
possible cold pool development. Should upscale growth occur, the
potential would exist for damaging winds to be somewhat
widespread, therefore this will need to be monitored closely.
The entire area is currently outlooked by SPC in a SLIGHT risk
(Level 2/5), but considering recent trends in MLP guidance,
higher probabilities may be warranted given the surrounding
atmospheric conditions. Will fine tune that out in the next
12-24 hours. PWATs will be in the neighborhood of 2" and
forecast soundings indicate tall CAPE profiles supportive of
efficient rainfall production. While widespread flooding
concerns are not anticipated, localized urban flooding is
possible.

The cold front will clear the area from west to east Thursday
night. Behind the front, skies are expected to clear out with a
cooler and drier northwest wind. Lows Thursday night are
expected to range from near 60 for the Lehigh Valley and
northward to the mid-upper 60s across the Delmarva.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
Behind the cold front that exits Thursday night, we see some cooler
and drier air filter in for Friday. This means temperatures will be
in the upper 70s to mid 80s on Friday which is lower than Thursday`s
high temperatures. The drier air drops dew points as well for Friday
with them mainly hovering around 60. Overall, this will help lower
heat index values for Friday compared to Wednesday and Thursday. Our
main weather feature for Friday will be an expansive area of high
pressure which leads to a sunny day. We stay dry and quiet with a
mainly clear sky Friday night. Lows Friday night will be in the
upper 50s to upper 60s.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
During the long term period, an expansive area of high pressure will
be our main weather feature at the surface with an upper-level ridge
also building in. A weak disturbance may rotate through over the
weekend leading to a slight chance for showers and thunderstorms
mainly Sunday. Overall, the weekend looks pretty dry. Saturday will
be mostly sunny with Sunday being mostly to partly sunny. Dry
weather and sunshine then continues into the beginning of next week.

The main concern during this period is the potential for dangerous
heat, specifically Sunday into the beginning of next week. Saturday
will be warmer than Friday with highs in the 80s across the area.
Dew points on Saturday are in the 60s which keeps heat index values
in the 80s.

By Sunday, we start to see the heat and humidity build leading to
the potential for dangerous heat. On Sunday, highs are in the mid
80s to low 90s with dew points hovering close to 70. This leads to
heat index values of around 95-100 degrees. The heat and humidity
continues to build for Monday and Tuesday. High temperatures both
days will be in the 90s area wide and dew points will range from the
low to mid 70s. Heat index values will potentially reach 95-105
degrees. The only exceptions will be the Poconos and the coastal
areas where it will be slightly cooler.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of Today...VFR. Showers and scattered thunderstorms during
the afternoon will be possible, causing potential sub-VFR
ceilings to develop. South-southwest winds around 5-10 kt.
Moderate confidence.

Tonight...VFR. Showers and thunderstorms should diminish by
early evening, yielding partly cloudy skies over night.
Southwest winds around 5 kt or less. Moderate confidence.

Thursday...VFR. Showers and scattered thunderstorms to develop
from west to east especially after 18Z which may cause temporary
vsby/cigs restrictions. West-southwest winds around 10-15 kt
with gusts up to 20-23 kt possible. Moderate confidence.

Thursday night...VFR and clearing skies. Southwest winds around
5-10 kt becoming northwest overnight. High confidence.

Outlook...

Friday through Monday...VFR.

&&

.MARINE...
No marine headlines are currently in effect through Thursday
night. South-southwest winds around 10-15 kt through tonight
will increase to around 15-20 kt with gusts up to 22-24 kt
possible on Thursday into Thursday night. Seas of 3-4 feet,
possibly up to 5 feet. Due to marginal conditions, have held off
on a SCA for the Atlantic coastal waters at this time, however,
a SCA may become warranted if further confidence is reached.

Otherwise, two rounds of showers and thunderstorms are expected
to occur, one later this afternoon into this evening and the
other Thursday afternoon and evening. Also, patchy areas of
dense marine fog are possible to re-develop again later
tonight, especially for the Atlantic coastal waters offshore of
New Jersey.

Outlook...

Friday through Monday...Sub-SCA conditions are anticipated with
winds below 25 kt and seas below 5 ft.

Rip Currents...

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 NJ beaches Thursday
while for the Delaware beaches we have a LOW risk.

For Friday, the winds shift to offshore and the wave heights
diminish however it looks like there will be some longer period
swell groups. For this reason, we will continue with a MODERATE
risk for the development of dangerous rip currents for the NJ
beaches with a LOW risk for the Delaware Beaches.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 8 PM EDT Thursday for PAZ070-071.
     Heat Advisory from 11 AM to 8 PM EDT Thursday for PAZ102-104-
     106.
NJ...Heat Advisory until 8 PM EDT Thursday for NJZ017>019.
     Heat Advisory from 11 AM to 8 PM EDT Thursday for NJZ015.
DE...Heat Advisory until 8 PM EDT Thursday for DEZ001.
MD...None.
MARINE...None.

&&

$$

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