312
FXUS61 KPHI 181739
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
139 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 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 THURSDAY/...
A Severe Thunderstorm Watch has been issued for portions of the
area through 7 PM tonight.

With plenty of humidity, heat indices will be notably above air
temps, so have maintained head advisory as inherited for today.
Might flirt with criteria south of the present advisory (where
criteria is higher) as well but confidence not quite there yet.
Certainly it will feel very summery for much of the region by
early this afternoon.

After that it will probably start to sound rather summery as
well as another vort max approaches, and combined with CAPE
values likely to exceed 2000 J/kg plus some modest shear, it
appears that a round of afternoon/early evening thunderstorms
will be a good bet for most of the region. We remain outlooked
for a marginal severe weather risk. Storms should be moving
along, but locally heavy rains will also be possible given
ample moisture.

After the storms dwindle, with the front possibly hung up near
NYC, northeastern areas could see a return of some patchy
fog/mist/drizzle, but unlike tonight, the majority of the region
should just be warm and humid. Lows near or above 70 for most.

A shortwave axis will be located over the Ohio Valley on
Thursday morning, shifting eastward towards our area by the
evening hours. At the surface, low pressure will be located over
portions of Ontario Thursday morning, tracking eastward into
southern Quebec and far northern portions of New England through
the day. A cold front associated with this surface cyclone will
pass through the area during the late afternoon and evening
hours.

Ahead of the aforementioned cold front, very warm and moist
southwesterly flow will continue across the area. Underneath
partly to mostly sunny skies, strong surface heating is
anticipated, with temperatures generally climbing into the upper
80s to near 90 across eastern PA and northern NJ, and into the
lower 90s near/southeast of the I-95 corridor.

With quite a bit of moisture in place (surface dewpoints in the
lower 70s), it will feel quite hot. Heat indices will climb
into the upper 90s southeast of the Lehigh Valley and away from
the immediate coastal strip. Due to the potentially dangerous
heat impacts, a heat advisory will be in effect for the urban
corridor through 8 PM Thursday.

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 scattered thunderstorms
by mid-afternoon across western portions of our area, tracking
east into the late afternoon and evening hours. The environment
ahead of the cold front is expected to become moderately
unstable (MLCAPE values of 1500-2000 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 during the relatively early stages of convective
evolution. 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. Similar to today, 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 cannot be ruled out with any stronger
storms.

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

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

Tonight...Showers/storms early should diminish and we may
actually stay VFR for most terminals all night as south-
southwesterly flow remains dominant, though still 5-10 kt.
Moderate confidence.

Outlook...

Thursday through Thursday night...VFR in the morning. Scattered
showers and storms during the afternoon and evening hours could
lead to periods of sub-VFR conditions. Improvement back to VFR
is anticipated overnight Thursday night.

Friday through Monday...VFR.

&&

.MARINE...
A Marine Dense Fog Advisory is now in effect through 3 PM from
Sandy Hook to Greaet Egg Inlet due to areas of dense fog with
visibilities 1 nautical mile or less.

Otherwise, no wind/sea hazards are in effect through tonight.
Showers and thunderstorms for this afternoon. South-southwest
around 10-15 kt later today into tonight. Seas of 3-4 feet.

Outlook...

Thursday through Thursday night...Conditions may briefly
approach SCA criteria during the afternoon, with southerly wind
of 20-25 kt and wave heights of 4-5 ft. Scattered showers and
storms could also lead to locally rough seas during the
afternoon and evening.

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

Rip Currents...

For today, 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 today 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 until 8 PM EDT Thursday for PAZ070-071.
     Heat Advisory from 11 AM to 8 PM EDT Thursday for PAZ104-106.
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...Dense Fog Advisory until 3 PM EDT this afternoon for
     ANZ450>452.

&&

$$

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