010
FXUS61 KPHI 292027
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
427 PM EDT Sat Jun 29 2024

.SYNOPSIS...
A warm front will lift across the region into tonight. A cold
front will then move across the area later Sunday. High pressure
builds in Monday through Tuesday before moving offshore by
Wednesday. A surface trough arrives on Thursday as a cold front
may approach from the northwest Friday.

&&

.NEAR TERM /THROUGH SUNDAY/...
The next 36 hours or so will be quite active with a variety of
weather impacts. A warm front approaches from the west this evening
and lifts north through the overnight period. A hot and humid
airmass will be in place through Sunday. A cold front then
approaches on Sunday and works its way through the region Sunday
night.

South to southeast flow ahead of the warm front continues to usher
low level moisture across the region. This will feed into showers
and thunderstorms upstream that will approach the region late
tonight. Although some spotty showers may pop up ahead of the front,
the bulk of the activity will hold off until late tonight.

Surface dew points are currently in the upper 60s to low 70s, and
will continue to rise into the mid and upper 70s behind the passage
of the warm front.

The first wave of showers and thunderstorms will pass through the
northern zones this evening into the first half of tonight, and then
a second wave of showers and thunderstorms will develop after
midnight. For the first half of the night, the biggest area of
impact will be over the southern Poconos, Lehigh Valley, and
northern New Jersey. DCAPE values in these areas will be in excess
of 750 J/kg along with SB CAPE values up around 1000 J/kg. This
suggest damaging winds are possible. Fore areas west of the I-95
corridor, SPC has a Marginal risk for severe weather (1 out of 5)
with a Slight Risk (2 out of 5) for western portions of Carbon and
Berks counties.

There is low confidence in the forecast for the second half of the
overnight period.

Models continue to be inconsistent with the development of these
showers and thunderstorms. 12Z/29 NAM has a light areas of showers
for the pre-dawn hours and into the middle of Sunday morning. 12Z/29
HRRR has an area of stronger and heavier showers passing through the
Delaware Valley and southern New Jersey. 12Z/29 WRF-ARW has a
beefier area of showers and thunderstorms passing through the
southern half of the forecast area. 12Z/29 HRW NSSL has barely
anything.

Even though heating will be limited since it will be at night, there
should be enough instability to support convection. SB CAPE values
will generally average 500 to 750 J/kg, but once surface dew points
start rising to 75 or higher, CAPE values will rise to over 1000
J/kg. Shortwave energy approaches from the west and should be enough
to trigger another round of showers and thunderstorms late in the
overnight despite inconsistencies among the models. In the areas
where convection is expected, DCAPE values will be up near 500 J/kg.
Some gusty winds are possible, but the main threat would be for
locally heavy rain. Given 0-6 km Bulk Shear will be 35 to 45 kt,
storms should be moving fast enough to prevent widespread flash
flooding, but cannot rule out localized flooding.

Given how warm and humid it will be tonight, areas of fog are likely
to develop. Lows will be well in the 70s along with surface dew
points well in the 70s.

Hot and humid on Sunday as deep southerly flow continues. surface
dew points will be well in the 70s, likely as high as 76 to 78 in
the morning for most of New Jersey, Delmarva, and southeast
Pennsylvania. There may be enough mixing in the afternoon for the
highest dew points to drop to 73 to 76. For the southern Poconos and
Lehigh Valley, surface dew points will be in the upper 60s to around
70. Highs look to get into the upper 80s to low 90s for most of the
area, but there is a chance these temperatures may be a bit too high
as widespread cloud cover may keep temperatures from getting quite
that high. Heat index values will be in the upper 90s to low 100s.
Since the eastern shores of Maryland look to be around 105, will go
ahead and hoist the Heat Advisory for the eastern shores of Maryland
for Sunday.

Pre-frontal trough develops out ahead of the approaching cold front.
Showers and thunderstorms develop with this trough, and
thunderstorms look to be severe Sunday afternoon and Sunday evening.
SB CAPE values will be in excess of 2500 J/kg, generally 2500 to
3500 J/kg, along with 750 to 1000 J/kg of DCAPE. 0-6 km Bulk Shear
will average 35 to 45 kt and PWATs will be up around 2.5 inches.
Once again, damaging winds will be likely with severe thunderstorms,
and frequent lightning and heavy rain also expected. Localized flash
flooding possible, though once again, there should be enough
steering current for storms to be moving fairly quickly.

Thunderstorms may linger over Delmarva through midnight or so.

Cold front moves across the region Sunday night, and a much drier
airmass spreads into the region with surface dew points falling into
the 50s by daybreak.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
In the wake of the cold front on Sunday, a cooler and less
humid air mass will be ushered in, leading to more pleasant and
tranquil conditions Monday and Tuesday. Broad surface high
builds in so, expect dry conditions. High temperatures are
forecast to range from the mid 70s to mid 80s across the region.
A comfortable air mass with dew points in the 50s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Summary...Less humid to start then the heat and humidity spikes
Thursday, followed by a little cooling but remaining humid. Some
convection possible late in the week. Few changes from the
previous forecast.

Synoptic Overview...A mid/upper level ridge remains in place
Wednesday, then some influence from a Canadian upper-level
trough will push the ridge southward some Thursday and Friday.
At the surface, a warm front lifts northward Wednesday then a
trough arrives Thursday with a cold front approaching from the
northwest Friday.

Wednesday...Surface high should remain the dominant feature for
one more day, leading to one more day of tranquil conditions. As
the high shifts further off shore though, southwesterly flow
will develop, leading to increasing dewpoints, although,
guidance still shows the dew points in the lower 60s even late
on Wednesday, which is humid, but not oppressively humid.

Thursday (Independence Day) through Saturday...Southerly flow
becomes more established leading to hot and humid conditions all
three days (though Saturday is dependent on if a cold front will
stay northwest of our region. The influence of a Canadian
upper-level trough will start to approach during Thursday,
however the timing and amplitude of this trough is less certain.
As of now, the main trough is more toward the Midwest and
therefore a cold front may be slow to approach our area late in
the week. There may be a pre-frontal trough in our vicinity
Thursday into Friday and this may provide enough focus amid a
destabilizing air mass to initiate some convection.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Mostly VFR conditions through the remainder of the day.
Some lingering lower clouds on the coastal plains is resulting
in MVFR conditions at KMIV and KACY through around 20Z. Isolated
showers are present across the region, but confidence in them
affecting any one location is low, so have not included it in
the TAFs at this time. Southerly winds around 10 gusting to 20
kt. Moderate confidence.

Tonight...MVFR conditions expected, with potential for IFR
conditions. Prevailing MVFR conditions likely develop with
ceilings again around 1500-2500 feet. IFR conditions are
possible, particularly with showers or thunderstorms that are
expected to move through the region. A cluster of showers and
thunderstorms is expected to move in from the west after 01Z.
Not sure it will reach as far southeast as KACY and KMIV.
South- southwest winds around 10 knots. Low confidence on extent
of IFR conditions.

Sunday...Low ceilings should gradually lift to VFR between 15
and 18Z. After 18Z (and likely closer and after 21Z), another
round of showers and storms is likely to affect the TAF sites.
Winds should gradually shift to southwesterly through the
morning, remaining around 10 to 15 kt. Moderate confidence.

Outlook...

Monday through Wednesday...VFR.

Thursday...MVFR possible with SHRA and TSRA especially in the
afternoon.

&&

.MARINE...
Small Craft Advisory remains in effect for the Ocean for
tonight through Sunday. In addition, a Small Craft Advisory has
been issued for Delaware Bay too. South to Southeast winds will
average 15 to 20 kt with gusts up to 25 kt, though the gradient
may relax somewhat on Sunday. Seas will remain elevated at
around 5 feet on the Ocean. Across Delaware Bay a moderate chop
is expected. Winds shift to the northwest Sunday night behind a
cold front.

One round of showers and thunderstorms will develop tonight. Gusty
winds and VSBY restrictions in heavy rain biggest impacts. VSBY
restrictions in fog expected late tonight through most of Sunday
on the ocean waters. Showers and thunderstorms will impact the
waters Sunday afternoon and most of Sunday night. Damaging winds,
heavy rain, and frequent lightning expected.

Outlook...

Monday through Thursday...Winds and seas should be below SCA
criteria.

Rip Currents...

Today...Southeast winds 10-20 mph with breaking waves of 2 to 4
feet at the beaches and an 8-9 second period are expected. With
the steady onshore flow (especially in coastal Cape May,
Atlantic and Ocean counties) and increasing wave heights, there
is a HIGH risk for the development of dangerous rip currents at
the Jersey Shore. At the Delaware beaches, wind is more shore
parallel and therefore a MODERATE risk for the development of
dangerous rip currents.

Sunday...Wind turns more south/southwest, though with a shore
parallel wind and 2 to 3 foot breakers with a remaining 8 second
swell, have gone with a MODERATE risk for the development of
dangerous rip currents for coastal Cape May, Atlantic and Ocean
counties with a LOW risk for coastal Monmouth County and the
Delaware Beaches.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 11 AM to 7 PM EDT Sunday for PAZ070-071-102-
     104-106.
NJ...Heat Advisory from 11 AM to 7 PM EDT Sunday for NJZ010-012-013-
     015-017>020-027.
     High Risk for Rip Currents until 8 PM EDT this evening for NJZ014-
     024>026.
DE...Heat Advisory from 11 AM to 7 PM EDT Sunday for DEZ001.
MD...Heat Advisory from 10 AM to 7 PM EDT Sunday for MDZ012-015-019-
     020.
MARINE...Small Craft Advisory until 2 AM EDT Sunday for ANZ430-431.
     Small Craft Advisory until 7 PM EDT Sunday for ANZ450>455.

&&

$$

SYNOPSIS...Gorse/Johnson
NEAR TERM...MPS
SHORT TERM...Gorse/Johnson
LONG TERM...Gorse/Johnson
AVIATION...Johnson
MARINE...Johnson/MPS/PO