689
FXUS61 KPHI 050445
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1245 AM EDT Fri Jul 5 2024

.SYNOPSIS...
High pressure will remain located offshore through Friday.
Several waves of low pressure and weak fronts approach the area
through Saturday, before a cold front crosses through the area
on Saturday night. High pressure returns for Sunday and Monday
before another low pressure system approaches the area around
the middle of next week.

&&

.NEAR TERM /THROUGH TODAY/...
The showers and thunderstorms have largely ended across the
region, though an isolated shower or storm will remain possible
early in the night.

Once storms taper off, a weak frontal boundary will remain
draped across the region west to east over eastern PA into NJ
and this will extend back to a new surface low developing over
the midwestern states. Meanwhile weak impulses aloft will
continue to move through in the upper level flow. For this
reason there could be some additional showers and a few storms
overnight...mainly over eastern PA into adjacent portions of NJ.
It will otherwise be a very warm and muggy night as weak warm
advection persists. Most areas won`t see lows getting below the
low/mid 70s (except 60s over the higher terrain NW). Some areas
of fog development are anticipated overnight, especially where
appreciable rainfall occurred on Thursday. Some fog and low
stratus has already developed as of the midnight hour across
eastern PA and northern NJ. Lingering smoke from the evening
fireworks will make for ideal cloud droplet nuclei in the very
warm and humid environment with light winds, despite the broken
cloud cover overnight.

A very moist and warm to hot air mass will be in place for
Friday with dew points well into the 70s, and high temperatures
in the low to mid 90s in many spots. This will bring two main
issues... 1, the excessive heat, with heat advisory remaining in
effect starting Friday morning for I-95 corridor and Delmarva
(now extended through Saturday) and 2, the thunderstorm risk due
to increasing instability. We likely start out fairly dry,
perhaps with patchy fog/low clouds, early Friday before some
clearing brings quick warming to the low 90s for much of the
area, mid 90s possible in Delmarva. With the high dew points,
expect heat indices around I-95 to pass 100 and Delmarva to pass
105 in some spots. There isn`t a strong source of forcing for
convection, but with all the heat and instability, along with
the lingering weak front there will likely be some more
scattered showers and storms developing for the afternoon into
the early evening period, especially around and northwest of
I-95 where we`ve placed the highest POPs. With plenty of
moisture available, locally heavy rain is likely biggest
concern, but with the available instability some isolated severe
certainly looks possible.

Shower and thunderstorm chances linger Friday night as a
shortwave crosses the area, increasing forcing even as
instability decreases. While severe/flood risks likely diminish
a bit with loss of heating, will still need to be on guard after
sunset for isolated problems. Otherwise, a steamy night with
lows mostly in the 70s.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...
A similar weather story is expected on Saturday as the
extremely moist airmass continues. Although temps may be a
degree or two cooler than Friday mostly due to cloud cover
expected in the afternoon, dew points are anticipated to be at
least 2-3 degrees higher. In addition, PWATs are expected to
remain anomalously high in excess of the 95 percentile, which
essentially tells the story itself. With this in mind, the two
concerns for Saturday remain being the heat and the other being
the thunderstorm potential with approaching cold front.

In terms of the heat, it is forecast that highs will reach into
the upper 80s to low 90s across much of the area. With dew
points in the 74-77 degree range, this equates to heat indicies
around or in excess of 100 degrees for most of the immediate
I-95 corridor, with heat indicies around 105 degrees across the
Delmarva. Heat indicies in the 90s are expected up across the
Lehigh Valley and north Jersey. As a result, this warrants Heat
Advisory criteria for the same areas as Friday in addition to
Middlesex and Somerset Counties, which have been issued with
this forecast update.

In terms of thunderstorm potential, there isn`t too much
forcing present as the front does appear to rather weak. Despite
the moisture rich atmosphere, it doesn`t appear that there will
be too much of a severe threat this go around which supports
the thinking from the SPC of just a general thunderstorm risk
for the region. The main concern should be in terms of heavy
rainfall thanks to the the moisture-loaded atmosphere where any
storm will be capable of heavy rain. As a result, the WPC has
the eastern half of the forecast area in a Marginal Risk (Level
1/4) for excessive rainfall for Saturday and Saturday night.

The cold front slowly crosses the area on Saturday night with
drier air gradually filtering into the region in its wake.
Overall, this should lead to a pretty nice day on Sunday under a
mix of sun and clouds as high pressure builds in from the north
and west. Although afternoon temps will reach into the upper
80s to around 90 degrees, it will feel a bit drier compared to
Saturday as dew points fall into the mid 60s. Mostly clear skies
are expected to continue into Sunday night as high pressure
persists. Lows for Saturday and Sunday night will both be in the
mid 60s to low 70s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
High pressure remains in control through Monday with above
normal temps continuing. A slight chance of a shower or
thunderstorm may approach our western counties late in the day
as the next weather system approaches toward the middle portion
of next week. An upper trough will be located over the Great
Lakes on Tuesday and Wednesday as some shortwave energy
spreading east into our neck of the woods. Due to uncertainty of
timing and spread amongst model guidance, heavily based the
forecast on NBM guidance. This generally yields a 30-50% chance
of showers and/or thunderstorms each day through Thursday. This
is not an indication that any one day will be a washout, instead
there will likely be some shower activity around each day as
variability exists amongst current forecast guidance. Temps for
the middle portion of the week are expected to remain seasonable
to a few degrees above normal.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Through 12z...MVFR conditions in BR/stratus likely during the
overnight hours, especially at RDG/ABE/TTN where rainfall
occurred earlier. For the remaining terminals, could end up
being more stratus rather than fog. Winds diminish to around 5
kts or less, favoring a southerly direction. Overall lower than
average confidence given the uncertainty regarding both the
convection and timing/degree of overnight restrictions.

Friday...Lingering restrictions in the morning should give way
to VFR by around midday, with further restrictions possible by
later in the day due to more showers/storms. South to southwest
winds 5 to 10 knots. Moderate confidence.

Outlook...

Saturday through Saturday night...Sub-VFR probable with a
chance of showers and thunderstorms. Locally gusty winds
possible in thunderstorms.

Sunday through Monday...VFR. No significant weather expected.

Monday night through Tuesday...Sub-VFR conditions possible. A
slight chance of a shower or thunderstorm.

&&

.MARINE...
No marine headlines anticipated through the overnight.
Southerly winds 10 to 20 knots with seas 2 to 4 feet. Scattered
showers and thunderstorms possible during the evening hours, but
otherwise fair weather is expected.

Conditions should stay Sub SCA for Friday but by Friday night
both winds and seas could approach Small Craft Advisory levels.

Outlook...

Saturday through Saturday night...SCA conditions likely due to
seas around 4-6 feet. Winds are likely to remain below 25 kt
during this period, however. A chance of thunderstorms possible.

Sunday through Tuesday...No marine headlines expected. Winds
are expected to remain below 20 kt and seas of 2-4 feet. Fair
weather through Monday, with a slight chance of a thunderstorm
on Tuesday.

Rip Currents...

Friday and Saturday...A New Moon will occur on Friday. Winds
will be around 10-15 MPH out of the south both days, with an
onshore component to the wind in some spots. There is a MODERATE
risk for rip currents for Cape May, Atlantic, Ocean counties in
NJ, and a LOW risk for Monmouth NJ and the Delaware Beaches.
Breaking waves of 2 to 4 feet within the moderate risk and 1 to
3 feet within the low risk.

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

&&

.TIDES/COASTAL FLOODING...
With the New Moon to occur Friday, some locations may see some
spotty minor coastal flooding during the next few high tide
cycles.

With continuing S/SE flow and the approach of the New Moon,
some guidance has areas of Cumberland County NJ seeing advisory
minor coastal flooding with the upcoming evening high tide
cycle. Though guidance may be running a bit high, a short-fused
coastal flood advisory may be needed later on.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for
     PAZ070-071-102-104-106.
NJ...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for
     NJZ010-012-015>019.
DE...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for
     DEZ001>003.
MD...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for
     MDZ012-015-019-020.
MARINE...None.

&&

$$

SYNOPSIS...DeSilva
NEAR TERM...Fitzsimmons/MPS/Staarmann
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...DeSilva/Fitzsimmons/MPS/Staarmann
MARINE...Fitzsimmons/Hoeflich
TIDES/COASTAL FLOODING...Wunderlin