-- Discussion containing changed information from previous version are highlighted. --
140
FXUS61 KPHI 272030
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
430 PM EDT Thu Jun 27 2024

.SYNOPSIS...
High pressure builds in from the north and west before sliding
offshore by Saturday. A warm front lifts north through the
region on Saturday, followed by a cold front on Sunday and
Sunday night. High pressure returns for the start of the new
work week before departing by the middle of next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
A secondary cold front will move across the area this afternoon
into this evening, then high pressure to our west will move to
our north overnight as it shifts eastward. Winds will shift to
the north the northeast overnight, an drier/cooler air will move
in as well. Temperatures overnight will end up being close to
or slightly below normal. The stratocumulus clouds from today
will dissipate later this evening into the overnight hours for
much of the area and be replaced by high level clouds, although
southern New Jersey, southern Delaware, and southern Maryland
could hold on to the lower clouds longer.

On Friday, the high to our north will shift offshore, and winds
will shift from northeast, to east, then southeast through the
day. Temperatures will remain near or slightly below normal or
one more day. Mostly sunny to partly cloudy skies are expected,
and no rain is expected.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
Unsettled conditions on tap for the weekend. Heat and humidity
return, and there is the potential for convection.

Quiet conditions Friday night with increasing low level
moisture as surface dew points rise into the low to mid 60s.
Fairly warm with lows in the low to mid 60s, and in the upper
60s in the more urban areas. Patchy fog may develop as well, but
that is far from certain.

Low pressure moves from the Great Lakes into the Province of
Quebec on Saturday. Ahead of this low, a warm front will
approach from the west. However, most of the 12Z suite of
guidance has slowed the approach and passage of this front from
Saturday afternoon to more Saturday night. During the day, highs
will be in the mid to upper 80s and with increasing southerly
flow due to a tightening pressure gradient between the
approaching front and the offshore high, surface dew points will
rise through the 60s. This results in max heat index values
generally in the lower 90s, though the highest heat index values
will be across the southern portions of the forecast area.

Warm front lifts north through the region Saturday night.
Showers and thunderstorms develop late in the afternoon, mainly
in the far western zones, and then continue through the
overnight. With PWATs well in excess of 2 inches, possibly even
approaching 2.5", showers will be capable of heavy rainfall.
With the slower approach of the warm front, and storms
developing at night, the lack of daytime heating may be a
limiting factor in the severity of thunderstorms. MU CAPE values
will be up around 500 J/kg, and 0-6 km Bulk Shear will range
from 30 to 40 kt. DCAPE values may rise to 500 to 1000 J/kg by
daybreak Sunday, but the bulk of the activity may be over by
then. Widespread flash flooding may be limited by shear in the
30 to 40 kt range, given that storms may be moving fairly
quickly.

Uncomfortably warm and humid otherwise Saturday night with lows
generally in the 70s, though not much below 80 for the urban
corridor from Philadelphia to Wilmington and also into Delmarva.

Hot and humid ahead of an approaching cold front on Sunday,
though it will be the humidity that pushes up heat index values
as opposed to the heat. High temperatures are expected to be in
the upper 80s to low 90s. In most cases, those temperatures are
quite warm and can be borderline hot, but surface dew points
will be well in the 70s, resulting in max heat index values in
the upper 90s to around 100, and even a few spots in southern
New Jersey and Delmarva may get close to 105.

Low pressure over the Province of Quebec tracks east and
departs, it will drag a cold front through the region Sunday
afternoon. Ahead of this front, a pre-frontal trough develops
and should trigger another round of showers and thunderstorms
will develop in the afternoon and evening. With peak heating of
the day and abundant low level moisture, there is the potential
for severe thunderstorms, as well as another round of heavy
rain. Confidence is low, though, because model trends seem to
have this trough passing through the region ahead of any upper
level support. Both the 12Z NAM and the 12Z GFS seem rather
stingy with QPF in the 18Z Sunday to 00Z Monday timeframe, but
this seems unlikely given the setup ahead of the trough and
front. Will continue to carry likely PoPs for most of the area,
and chance PoPs for the southern Poconos and Lehigh Valley.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Cold front then slowly works its way south through the region
Sunday night, and showers and thunderstorms will taper off from
west to east. Rain may continue to be heavy at times, especially
in the first part of the night, and could result in localized
flooding. A drier airmass spreads into the Northeast and Mid-
Atlantic with surface dew points dropping from the upper 60s and
low 70s Sunday evening to about 10 degrees lower by daybreak
Monday.

The first half of the new work week look to be mild and
pleasant with low humidity levels. High pressure over the Great
Lakes on Monday will be right over the local area on Tuesday,
and then offshore by Wednesday. Highs will generally be in the
lower 80s on Monday, before warming into the mid 80s on Tuesday,
then into the upper 80s on Wednesday. Temperatures will also be
about 10 degrees cooler in the mountains and along the coasts
each day. In addition, surface dew points will generally be in
the 50s on Monday and Tuesday before rising into the low 60s on
Wednesday as return flow sets up behind the departing high. A
nice run, compared to the recent heatwave.

The trend for Thursday is for a return to the heat and humidity
with temperatures back in the upper 80s to low 90s and dew
points in the 60s to near 70. An approaching frontal system may
touch off some afternoon and evening showers and thunderstorms.

&&

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

Rest of Today...Stratocumulus clouds will continue through
today with VFR conditions expected with bases around 4,000 feet.
Northwest winds 5 to 10 kt, with occasional gusts 15-20 kt in
the afternoon are expected. A sea breeze may develop around
21-23Z and turn winds more south-southwesterly at KACY and
possibly KMIV. High confidence

Tonight...VFR. Northwest winds 5-10 knots, shifting to north-
northeast this evening and overnight. High confidence.

Friday...VFR. Northeast winds 5-10 knots, shifting to the east
after day break, then shifting to southeast by the afternoon.
High confidence.

Outlook...

Friday night...VFR.

Saturday through Sunday night...SHRA/TSRA will result in sub-
VFR conditions. VSBY restrictions in fog possible Saturday
night. Conditions improve late Sunday night.

Monday through Tuesday...VFR.

&&

.MARINE...
-- Changed Discussion --
Tonight-Friday...Conditions are expected to remain below
advisory levels through Friday. However, there could be
occasional gusts near 25 knots offshore of the central and
southern New Jersey waters late tonight.

Outlook...

Friday night...Sub-SCA conditions.

Saturday through Sunday night...SCA conditions likely. Showers
and thunderstorms Saturday afternoon and evening, then again
Sunday afternoon and evening, may produce locally strong wind
gusts and VSBY restrictions in heavy rain. VSBY restrictions in
fog also possible.

Monday...SCA conditions possible for occasional 25 kt wind gusts.

Tuesday...Sub-SCA conditions.

Rip Currents...

Friday...Northeast winds in the morning becoming east-southeast
winds in the afternoon around 10-20 mph. Breaking waves of 2-3
feet for all beaches. Due to an onshore component of the wind,
have maintained a MODERATE risk for the development of
dangerous rip currents for the New Jersey and Delaware beaches.

Saturday...Southeast winds around 15-20 mph with breaking waves
around 2-3 feet at all beaches. Due to similar wind and wave
conditions compared to Friday, have opted to continue with a
MODERATE risk of rip currents for both the New Jersey and
Delaware Beaches on Saturday.

For specific beach forecasts, visit weather.gov/beach/phi
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...MPS
NEAR TERM...Robertson
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...MPS/Robertson
MARINE...DeSilva/MPS/Robertson