004
FXUS61 KPHI 212338
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
738 PM EDT Tue May 21 2024

.SYNOPSIS...
High pressure will remain centered to our south and east through
Wednesday. A cold front crosses our area Thursday afternoon, then
stalls to our south Friday before lifting back northward some Friday
night into Saturday. A cold front moves through Saturday night into
Sunday, then a couple of systems move through Monday and
Tuesday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
The near term forecast remains on track as high pressure
located offshore the Delmarva will remain in place through
tonight. Temps are mostly in the upper 70s to low 80s with
cooler temps near the coast as a seabreeze boundary slowly makes
its way inland.

Another tranquil night is in store tonight with clear skies and
light winds. With light south-southwest winds around 5 mph tonight,
this should limit any widespread fog formation in comparison to this
morning. Hi-res guidance suggests that there may be some marine fog
that pushes inland early Wednesday morning, but overall this looks
pretty patchy and confined along the immediate New Jersey and
Delaware coasts. Lows tonight will be in the mid 50s to low 60s.

Heading into Wednesday, any morning fog should burn off rather
quickly after day break becoming clear. High pressure offshore will
begin to move further out to sea, losing its grasp of control on the
weather across the area. By the afternoon, a pre-frontal trough will
be making its way across central Pennsylvania late in the day which
may spark up a few showers and thunderstorms. MLCAPE values will be
in excess of 1000 J/kg with modest instability due to diurnal
heating as surface dewpoints will be in the mid 60s. However, the
limiting factor will be that the greatest forcing will be displaced
well to the north and west of the area. With this in mind, it is
likely any thunderstorm development will take place well to our
west, but may begin to move into and approach our northwestern
counties late in the day. This is depicted well by some of the CAMs
and as a result the Storm Prediction Center has outlined a Marginal
Risk of severe weather (Level 1/5) on a line from Reading to
Allentown to Mount Pocono for Wednesday.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
A closed low is forecast to be tracking just north of the Great
Lakes Wednesday night into Thursday. Areas of convection are
expected to be ongoing to our west with a cold front, and some of
this should reach into at least our western and northern zones
during the first half of Wednesday night. The intensity of the
storms should be on the decrease with an eastward extent as the
boundary layer starts to stabilize, however a stronger storm could
get into our far western zones before weakening some.

As the closed low remains in Canada Thursday, surface low pressure
tied to it tracks well to our north. An associated cold front
however will move across our area Thursday afternoon or Thursday
night. Prior to the cold front arriving, a pre-frontal trough may
become established nearby during peak heating Thursday afternoon.
While the main forcing is removed from our area given the main
trough aloft is so far to our north, a band of stronger
southwesterly flow in the mid to upper levels is forecast to mostly
glance our region during the day Thursday. The model guidance shows
ample instability with some increase in shear due to the
strengthening mid to upper level southwesterly flow. The model
forecast soundings show an inverted-V profile in the lower levels
given ample heating of the boundary layer. This could however be
disrupted some if some convection can initiate by late morning.
Despite the weaker forcing, a broken band of convection or some
convective clusters may accompany the pre-frontal trough Thursday
afternoon. Given the forecast environment, there is the potential
for some locally severe thunderstorms with damaging winds the main
hazard especially if storms become clustered or in a line segment.
Given the weaker forcing, convective coverage could end up somewhat
more limited. The convection should be weakening or moving offshore
Thursday night as the cold front moves through.

High temperatures Thursday are forecast to be in the 80s for much of
the area (coolest along the coast and higher elevations of the
Poconos). Dew points are forecast to be in the mid to upper 60s
ahead of the cold front, therefore a humid day Thursday.

As we go through Friday, an upper-level trough glances our region to
the north and surface low pressure is well to our north. An
associated cold front however should be stalling to our south. There
is little in the way of cold air advection, and while temperatures
will be a little cooler compared to Thursday they are forecast to be
above average. The flow looks light and therefore a sea breeze
should develop and thus keep it cooler along the coast. As the next
system moves toward the Ohio Valley, the front may start to shift
back northward Friday night aided by some warm air advection within
south to southwesterly flow.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Summary...Unsettled at times for the holiday weekend.

Synoptic Overview...A weak shortwave trough looks to slide by
Saturday into Sunday. Another upper-level trough may lift across the
Great Lakes and adjacent Canada Sunday into Monday, with another one
sliding across the Plains to the mid-Mississippi Valley into
Tuesday. At the surface, a front is forecast to lift northward some
into Saturday before a cold front moves through Saturday night into
Sunday. Some additional impulses of energy track across or nearby
early next week.

For Saturday...A front initially to our south may lift back
northward some as a shortwave trough slides across with weak low
pressure. Some of the guidance has shifting northward with the track
of the surface low, which would pull the front farther northward.
The low-level flow is now forecast to be more southeast to south,
and this will still result in some cooling especially for the
coastal areas. Some showers and perhaps thunder should move through
as a weak shortwave trough arrives followed by a cold front at night.

For Sunday through Tuesday...As the aforementioned shortwave trough
departs to the east to start Sunday and a trough remains across
portions of eastern Canada, weak surface high pressure builds in as
a cold front is offshore. This may be enough to result in dry
weather for Sunday. The next upper-level trough in the Plains should
eject energy northeastward, with weak low pressure making a run at
our area Sunday night and Monday. The combination of synoptic lift
and moisture should result in some showers occurring on Memorial
Day. Depending on the location of the warm sector, thunder cannot be
ruled out however this is much less certain this far out in time. An
associated cold front should be east of our coast to start Tuesday,
however at least some guidance shows some trailing energy in the
Tennessee Valley. This could get some showers into parts of our area
Tuesday, however it is possible this system is slower or tracks
farther south. Given the uncertainty, kept PoPs no higher than the
chance range.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Tonight...VFR with clear skies. A few low clouds and patchy fog will
be possible at KACY/KMIV, although not expecting any significant
restrictions. South-southwest winds decreasing to around 5 kt
or less. Moderate confidence.

Wednesday...VFR expected with increasing high clouds during the
afternoon. Slight chance (15%) of a late day thunderstorm at
KRDG/KABE. South-southwest winds around 10-15 kt. High
confidence.

Outlook...

Wednesday night and Thursday...Sub-VFR conditions possible at times
with some showers and thunderstorms possible, mostly north and west
of KPHL Wednesday night then all areas Thursday afternoon and
evening.

Friday...VFR overall.

Saturday...A period of sub-VFR conditions and some showers possible.

Sunday...Mostly VFR.

&&

.MARINE...
No marine headlines are in effect through Wednesday. South-southwest
winds around 10-15 kt with occasional gusts up to 20 kt possible.
Seas around 3-4 feet. Patchy dense fog will be possible tonight into
early Wednesday morning.

Outlook...

Wednesday night through Sunday...The conditions are expected to be
below Small Craft Advisory criteria.

Rip Currents...

For the afternoon update, the Monmouth County, NJ beaches and
the Delaware Beaches were dropped to a LOW risk for rip currents
as wind direction will be more shore-parallel with only 2 to 3
foot breaking waves and an 8 second period. A more onshore
component of the wind will exist for Ocean/Atlantic/Cape May
beaches, where a MODERATE risk for the development of rip
currents remains.

For Thursday, the wind direction goes more southwesterly
(offshore). Breaking waves will only be around 2 feet with a 6
to 8 second period. All beaches will have a LOW risk for the
development of rip currents.

&&

.TIDES/COASTAL FLOODING...
Astronomical tides will be elevated this week with a Full Moon
on Thursday, May 23. Spotty minor coastal flooding will be
possible, especially for the back bays, around the times of the
evening high tide cycle, which will be the higher of the two
tide cycles, going into the end of this week.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...AKL/DeSilva
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...AKL/DeSilva/Gorse
MARINE...DeSilva/Gorse/Hoeflich
TIDES/COASTAL FLOODING...