589
FXUS61 KPHI 171045
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
645 AM 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 TONIGHT/...
As of early this morning, the warm front which will ever so
gradually shift north of the region over the next 24-36 hours
remains south of the region closer to Norfolk VA. Expect it to
push northward significantly today, reaching near Philadelphia,
before stalling again tonight. A final push northward which will
bring it clear of our region is expected Wednesday morning.

For areas north of the front, it will be a struggle to get rid
of the showery/drizzly/misty weather we`ve been seeing, and
temps will struggle to rise. Allow much of the area to push into
the 70s today, but this may ultimately depend on where the front
ends up, and given high uncertainty about its ability to pass
north of Philly, its possible northern areas such as the Lehigh
Valley and northern/central NJ will see temps fail to reach 70.
Further south, with the front likely to clear most of Delaware
and eastern Maryland, temps shouldn`t have much difficulty
blasting past 70 and stand a chance of reaching 80.

Tonight, as the front potentially stalls again for a time,
expect some patchy fog/drizzle esp. mainly north and east of
Philly. Lows will be mostly in the 60s, with low-mid 60s north
and east of Philly and upper 60s to near 70 south and west.

Through the entire period, we`ll continue to need to watch for
spotty showers from dying convection approaching from the south
and west. Overall this mainly impacts locations north and west
of Philly/I-95 corridor, but a few might make it further
southeast. First band of these will move through early this
morning, then potentially several more during the afternoon and
evening today.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Broad mid-level southwesterly flow will overspread the area
through the day on Wednesday, with a subtle shortwave axis
likely to shift northeastward across southeastern portions of
the region into the afternoon hours before sliding offshore
sometime in the evening.

Surface pressure will be fairly high to start the day Wednesday
due to the influence of the strong Bermuda High over the
Atlantic. However, gradual pressure falls are anticipated
through the day as a surface cyclone tracks through the Great
Lakes and the influence of the Bermuda High lessens some.

While there will not be a particularly tight pressure gradient,
the surface pattern will support warm and moist southwesterly
flow at the surface. While at least some cloud cover is likely,
temperatures will still warm up quite a bit during the
afternoon, particularly along and southeast of the I-95
corridor.

There are two primary concerns with Wednesday`s forecast:

The first is dangerous heat. Afternoon highs look to generally
be in the low-mid 80s across eastern PA and northern NJ,
however, temperatures could climb to near 90 across the Philly
metro, southern NJ, and the Delmarva. Dewpoints will generally
be in the low 70s, although some mixing is likely in areas that
see the strongest surface heating. Regardless, the combination
of temperatures near 90 and high relative humidity could lead to
heat indices in the mid-upper 90s across these areas.

The second is the potential for isolated to scattered strong to
severe thunderstorms Wednesday afternoon and evening. While
forcing for ascent will be somewhat nebulous, the combination of
the passing weak shortwave and strong surface heating should be
enough to allow for widely scattered storms to develop during
the afternoon hours. Deep layer shear will support storm
organization into multicells and perhaps transient supercell
structures. The extent of severe weather potential will depend,
in part, on the degree of vertical mixing that takes place
during the afternoon. Regardless, forecast soundings across the
area indicate that the environment will be at least moderately
unstable and wind fields will be strong enough to support a
threat for damaging wind gusts and perhaps marginally severe
hail with any stronger storms. In addition, high PWATs exceeding
2" will be present, so any storms will likely be efficient
heavy rainfall producers.

While the exact timing of the shortwave passage is uncertain,
the convection is still expected to be strongly diurnally
influenced. Storm coverage should decrease fairly rapidly after
sunset Wednesday night. Partly cloudy skies are likely after
storms diminish with continued warm and moist southwesterly
flow. Wednesday night will likely be quite warm and muggy, with
lows ranging from the upper 60s across eastern PA and northern
NJ to the low-mid 70s across the Delmarva.

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 Thursday afternoon and
evening.

Ahead of this cold front, another day of dangerous heat is
likely. 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.

Scattered convection is also likely to develop along the cold
front Thursday afternoon and evening as it tracks eastward
across the area. While the overall ceiling for severe weather
potential appears higher on Thursday than for Wednesday, some
questions remain. Model discrepancies exist regarding the timing
of the shortwave, surface cyclone, and cold front. While these
discrepancies are generally not significant for being two days
out, they will be consequential in determining the spatial and
temporal details of the severe weather threat. For now, it
should be noted that the environment ahead of the cold front is
expected to be supportive of strong to severe thunderstorms,
with the primary hazards being damaging winds and sporadic
instances of marginally severe hail.

After the cold front clears the area Thursday night, a slight
decrease in temperatures is expected, with temperatures
generally falling into the low-mid 60s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
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.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Today...LIFR/IFR conditions expected through the morning,
lifting to IFR/MVFR in the afternoon. Periods of mist expected
early, with a slight chance of showers during the afternoon.
Northeast winds will gradually become south-southeast around 3-8
kt. Low- moderate confidence.

Tonight...Intervals of IFR/LIFR in fog, stratus, and scattered
SHRA. Low-moderate confidence.

Outlook...

Wednesday through Wednesday night...Sub-VFR conditions in the
morning will likely give way to primarily VFR by the afternoon.
Isolated to scattered showers and storms during the afternoon
and evening could lead to brief periods of sub-VFR conditions.
Expect VFR areawide Wednesday night.

Thursday through Thursday night...Mainly VFR. Scattered showers
and storms during the afternoon and evening could lead to brief
periods of sub-VFR conditions. Expect VFR areawide Thursday
night.

Friday through Saturday...VFR.

&&

.MARINE...
Periods of showers, drizzle, and mist to continue through
tonight. Visibility near the coast is now down to 1 mile or less
as of early this morning, so have issued a marine dense fog
advisory until midday.

No marine wind/sea hazards are in effect through tonight. Winds
will gradually turn from northeast to southeast today around
5-10 kt. Seas of 3-4 feet.

Outlook...

Wednesday through Saturday...In general, Sub-SCA conditions are
anticipated through the period with winds below 25 kt and seas
below 5 ft. Isolated to scattered showers and storms on
Wednesday and Thursday afternoon could briefly cause higher wind
gusts and rough seas.

Rip Currents...

For today, winds turn to be a bit more east-southeasterly and
decrease to around 10 MPH. Swell remains onshore but the number
of swell groups look to consolidate with the period decreasing
to 6-7 seconds. Breaking waves in the surf zone look to decrease
to 2-3 feet as a result. The combination of these factors look
to lead to a decreasing risk for the development of rip
currents, so at this time a LOW risk is forecast for the beaches
south of Atlantic City and MODERATE for the northern Jersey
Shore beaches.

For Wednesday, winds increase to 10-15 mph with the swell period
remaining around 6-7 seconds. However, winds and swell turn to
become more shore parallel out of the south-southwest. As a
result, breaking waves in the surf zone look to decrease to
mainly 2 feet or less. Therefore, a LOW risk for the development
of rip currents is forecast for all beaches on Wednesday.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Dense Fog Advisory until noon EDT today for ANZ430-431-450>455.

&&

$$

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