494
FXUS61 KPHI 070719
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
319 AM EDT Tue Oct 7 2025

.SYNOPSIS...
High pressure will remain offshore through today. A strong cold
front will pass through the region early Wednesday, then much
cooler high pressure will build into the area through the end of
the week. The high pressure will shift offshore by Saturday,
then a coastal system may impact the region by Sunday and into
early next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Mostly clear skies encompass much of the area this morning
under a light southerly wind. As a result, not much going on at
the moment other than some instances of patchy fog, especially
in sheltered areas. This should burn off quickly though around
or shortly after daybreak as any fog is relatively shallow in
nature.

For the much of the day today, high pressure offshore will win
out yielding one more dry day. Albeit, clouds will be thickening
especially during the afternoon hours as a shortwave aloft
passes overhead and surface cold front trails back to the west.
As southerly flow ahead of the front strengthens, we should
observe a stronger push of warm-air advection, resulting in high
temps mainly in the upper 70s to low 80s despite the increase
in cloud cover. An isolated shower is possible over eastern PA
late in the afternoon, however the bulk of precip should hold
off until after sunset.

Heading into tonight, enhanced southwesterly mid-level flow
will encompass the region allowing forcing for ascent to
overspread the area. As a result, shower activity is expected to
increase in coverage through the evening hours over western
areas and eventually spread east towards the coast after
midnight. Forecast soundings continue to suggest MUCAPE values
around 500 J/kg, so a few embedded rumbles of thunder will be
possible overnight, however no severe weather is expected.
Showers may also be heavy at times, however, no flooding is
expected either due to the lack of precipitation over recent
weeks. The heaviest of precipitation will likely fall between
roughly 2 AM to 8 AM on Wednesday before beginning to taper off
from west to east by late morning into the afternoon as the cold
front sweeps through the area. In total, expect rainfall totals
to average around 0.5-1.0 inches, with localized higher amounts
possible. Skies are expected to clear out quickly during the
afternoon with a strong push of dry air following the frontal
passage. Northwest winds will also become breezy at times behind
the front where gusts up to 25-30 mph are possible.

One more mild night is in store tonight with lows ranging from
the mid 50s to mid 60s. Temperatures on Wednesday will be
noticeably cooler behind the front, with highs only in the mid
60s to low 70s.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
Much cooler and dry conditions expected toward the end of the
week following the strong midweek cold front. Widespread frost
and potential for some freezing temperatures is looking
increasingly likely for Thursday night.

Troughing from the midweek system will be shifting offshore
Wednesday night into Thursday, then shortwave ridging will
briefly pass through Thursday night through Friday. At the
surface, strong high pressure (~1035 mb) will slide in from the
Great Lakes through this period, centering itself across
portions of eastern NY, northeastern PA, and southern New
England by Thursday night. The high will then begin to shift
offshore into the daytime Friday.

Modest cold advection will be ongoing Wednesday evening as the
high pressure builds into the region in the wake of the daytime
frontal passage. Low temperatures by Thursday morning will range
from the mid to upper 30s in the higher elevations north of
I-78, to the low to mid 40s in most other places south of I-78.
Closer to 50 degrees near the coasts. The cold advection should
keep the boundary layer mixed enough to prevent any significant
frost formation in northern areas, but some patch frost is
possible in the sheltered valleys.

Thursday will be the coolest day of the season so far, with
high temperatures struggling to climb above the 60 degree mark
into the afternoon. 850 mb temperatures will fall to near 0C
during the daytime, which will significantly hinder airmass
modification despite sunny skies. A dry 10-15 mph NNE breeze
will make it feel cooler.

By Thursday night, the center of the high pressure will reside
across portions of northern NJ and northeastern PA. This is
expected to result in optimal radiational cooling conditions for
those areas and adjacent areas of SE PA and central NJ. This
will support low temperatures in the low to mid 30s for areas NW
of the I-95 urban corridor, and given the clear skies and
nearly calm winds, frost development appears increasingly
likely. Sheltered valleys north of I-78 have a good chance at a
freeze. Interior southern NJ could also see some frost
development as well, but this is less certain as winds could
remain elevated enough farther south to prevent any significant
frost development. Interior portions of Delmarva could drop into
the upper 30s, but winds should prevent any widespread frost
formation there. Frost/freeze headlines will likely be needed
northwest of I-95 in future updates for Thursday night into
Friday morning.

By Friday, cold advection will have ceased as the high pressure
shifts offshore. This will allow for some airmass modification,
and afternoon high temperatures should easily reach into the
mid 60s under mostly sunny skies. Surface winds will shift
onshore, which could allow for some marine stratus to push in
from the coast later in the day.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
For the long term period over the weekend and into early next
week, the main feature of interest will be the development of a
coastal system near the Carolina coast along a stalled frontal
boundary. Meanwhile, high pressure will remain in place locally
through Saturday with moderating temperatures.

Another chilly night for Friday night into Saturday morning
with low temperatures in the 40s for many areas. Closer to 50
degrees near the coasts and mid to upper 30s for the usual
colder spots north of I-78. Frost potential will be much lower
compared to Thursday night. By Saturday, further modification of
the airmass is anticipated, with afternoon highs in the mid to
upper 60s. Cloud cover will be increasing due to the developing
coastal system to our south, but the daytime period should
remain largely dry.

Guidance still differs in the evolution of the coastal system
from Saturday night into early next week, but we are beginning
to see a range of potential outcomes for our area. A weaker
and/or farther south solution with the surface low would
translate to lesser impacts and lower chances of showers for our
region. A stronger and/or farther north placement of the
surface low pressure would translate to greater and potentially
more significant impacts to our area, especially along and near
the coast. This may include potential for coastal flooding,
beach erosion, and strong winds near the coast and possibly
inland across the coastal plain. Again, a lot of uncertainty
with this system, but it bears monitoring closely as it could
pack a punch if it draws close enough to our area.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 12Z...Primarily VFR. A slight chance of fog developing
at all terminals. The highest probability of observing BR/FG is
at KMIV where instances of BR have already occurred, so included
in the TAF there, otherwise, continued to keep out of the other
TAF sites for now. South-southwest winds around 5 kt or less,
becoming VRB at times. Moderate confidence.

Tuesday...VFR. Southwest winds around 10 kt with occasional
gusts up to 15-20 kt possible. High confidence.

Tuesday night...VFR early, will gradually lower to MVFR and IFR
at all terminals from west to east overnight. Showers possible
through the evening, with periods of light rain becoming likely
after midnight. Patchy fog/mist probable. South-southwest winds
around 5-10 kt. Moderate-low confidence.

Outlook...

Wednesday night through Friday...VFR. No significant weather.

Saturday...Restrictions possible in low clouds. Gusty winds
possible.

&&

.MARINE...
Small Craft Advisories have been issued for all Atlantic
coastal waters beginning as early as 4 PM this afternoon to the
north and as late as 11 PM tonight to the south. All Small Craft
Advisories are in effect until 8 AM Wednesday.

South-southwest winds around 10 kt this morning will increase
to around 15-20 kt this afternoon and continue into tonight.
Wind gusts will be around 20-25 kt through tonight as well. Seas
of 2-4 feet today will build to around 4-6 feet tonight. Fair
weather today with rain showers becoming likely after midnight.

On Wednesday, southwest winds around 15-20 kt will shift to
northwest winds follwing a cold frontal passage by early
afternoon. Seas may linger around 5 feet, before abating in the
afternoon. Further extensions of current SCA`s may be needed to
account for gusty winds up to 25 kt behind the cold front. Rain
showers likely.

Outlook...

Wednesday night through Thursday night...Small Craft Advisory
conditions likely. North to northeast winds 15-25 kts with gusts
up to 30 kts possible. Seas 4-7 feet.

Friday through Friday night...No marine hazards expected. Fair
weather.

Saturday...Winds and seas building, potential to advisory
levels. A chance of showers.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 4 PM this afternoon to 8 AM EDT
     Wednesday for ANZ450-451.
     Small Craft Advisory from 8 PM this evening to 8 AM EDT
     Wednesday for ANZ452-453.
     Small Craft Advisory from 11 PM this evening to 8 AM EDT
     Wednesday for ANZ454-455.

&&

$$

SYNOPSIS...Staarmann
NEAR TERM...DeSilva
SHORT TERM...Staarmann
LONG TERM...Staarmann
AVIATION...DeSilva/Staarmann
MARINE...DeSilva/Staarmann