113
FXUS61 KPHI 141040
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
640 AM EDT Sun Jul 14 2024

.SYNOPSIS...
Weak high pressure slides across our area today into tonight. A
surface trough may be in place Monday into Tuesday, then a cold
front approaches during the day Wednesday before crossing our
area Wednesday night and Thursday. High pressure should then
extend into our area Friday and Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Forecast is mostly on track this morning. Fog has been fairly
patchy across the area, and any lingering fog should lift and
dissipate over the next hour or so, giving way to mostly sunny
skies today. Cannot rule out patchy fog lingering along the
immediate shorelines, however.

Surface high pressure builds over the Northeast today before
sliding south of the region tonight. Zonal flow aloft sets up,
and an increasingly hot and humid airmass spreads into the
region.

Some shortwave energy will pass through the region this
afternoon, and given how hot and humid it will be, SB CAPE
values will be upwards of 1500 to 2000 J/kg, there may be some
showers and thunderstorms. 0-6 km Bulk Shear will will average
20 to 25 kt and PWATs will be 1.5 to 1.75 inches. The 06Z NAM
and the 09Z HRRR indicating convection, mainly around the I-95
corridor late this afternoon. This seems to be due to some weak
surface forcing from an approaching sea breeze boundary
interacting with that shortwave. Will carry chance PoPs, bumped
up to around 40 percent from previous forecast. Surface forcing
will not be strong, so not expecting a severe weather threat,
but a few brief downpours are possible in that highlighted area.

With highs in the low 90s and surface dew points mainly in the
low 70s, max heat index values will be around 100 degrees to as
high as 105 degrees for most of the region. The Heat Advisory
remains in effect for most of New Jersey, southeast
Pennsylvania, and northern Delaware.

Any convection ends by sunset. A warm and muggy night on tap
for tonight with lows in the 70s. Patchy fog may develop once
again, especially along the coasts.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Excessive heat probable with it peaking on Tuesday.

High pressure anchored in the western Atlantic and low pressure
across the Great Lakes will focus heat and humidity northward
across the East Coast. A more zonal flow aloft is forecast,
although with a trough and jet feature approaching gradually
with each day. Meanwhile, a convective complex (MCS) upstream
across the Midwest to the eastern Great Lakes may toss some
clouds into at least portions of our area. The trajectory for
this looks to mostly follow areas to our west and northwest,
with even a convectively induced surface low tracking near the
eastern Great Lakes to northern New York. There is some
potential this activity turns more southeastward into growing
instability, or additional development takes place on the
southward tail of the associated shortwave. The convection
should generally be favored during the afternoon and evening
time frame, mainly near and northwest of I-95 where diurnal
instability is greater. There is considerable uncertainty
however on the convective evolution and also the severe weather
risk with this setup, especially given the more zonal flow
aloft. Overall, any severe weather risk (and greater coverage of
thunderstorms) will be determined by upstream convection and
therefore the predictability in our area remains low at this
time.

The excessively hot and humid stretch continues. Temperatures
Monday will be a bit hotter than Sunday with highs mainly in the
mid to upper 90s outside of the higher terrain and away from
the coast. However, dew points should mix out a bit resulting in
peak heat indices in the upper 90s to low 100s. The Heat
Advisory continues through Monday night, although given peak
heat indices forecast to be right around 100 degrees will add
Warren, Morris and Sussex counties (NJ) to the advisory. Low
temperatures will be quite warm as well, in the 70s Monday
night, which will not offer much relief from the heat.

For Tuesday, temperatures increase even more along with lower
chances for convection. Tuesday is shaping up to be the hottest
and most oppressive of this stretch, with highs largely in the
upper 90s. Dew points remaining in the lower 70s will support
peak heat indices of 105-110 degrees across much of the area.
Lows Tuesday night will likely be the warmest of this hot
stretch. Given the extent of the heat, a shower or thunderstorm
in the afternoon and evening cannot be ruled out. The Excessive
Heat Watch continues for much of the area Tuesday into
Wednesday, however it will be expanded to include Sussex County
in New Jersey.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Summary...Excessive heat Wednesday gets knocked down by a cold
front and associated showers and thunderstorms, then
temperatures should be closer to average Thursday through
Saturday with lowered humidity.

Synoptic Overview...An upper-level trough is forecast to pivot
into and across the Northeast and Mid-Atlantic regions Thursday
into Friday. The western Atlantic ridge may try to expand
eastward again into the Mid-Atlantic Saturday, however an upper-
level trough is forecast to remain from eastern Canada down
across the Great Lakes and into the Mid-Mississippi Valley. This
may be enough to keep the main part of the ridge at bay along
with the associated hotter temperatures. At the surface, a cold
front arrives Wednesday night and gradually shifts offshore
during Thursday. High pressure should then extend eastward into
our area Friday into Saturday.

For Wednesday and Thursday...As an upper-level trough arrives,
a cold front will approach during the day Wednesday before
crossing our region Wednesday night and Thursday. A pre-frontal
trough may also develop on the leeward side of the mountains.
This combined with increasing forcing for ascent and greater
effective shear should result in showers and thunderstorms
developing and becoming more widespread with time. The
convective organization may be more tied to the pre-frontal
trough as it shifts eastward later Wednesday, and given ample
instability and enough shear some thunderstorms could be strong
to severe Wednesday afternoon and evening. The details however
remain a bit unclear. The highest PoPs are included Wednesday
afternoon and evening, however the PoPs remain at least in the
chance range Thursday for most of the region as the front may be
slow to clear our area. The arrival of convection and also the
cold front will knock down the excessive heat, and therefore
Thursday is expected to be noticeably cooler than Wednesday. The
Excessive Heat Watch continues for much of the area Wednesday
(Sussex County in New Jersey now included).

For Friday and Saturday...The main part of the upper-level
trough should be lifting up across the Canadian Maritimes later
Friday, however this trough (weaker form) may extend
southwestward across the Great Lakes and into the Mid-
Mississippi Valley. Pending that the front clears our entire
area by Friday and drier air advects in, precipitation chances
then drop off during this time frame. Surface high pressure
centered near the Midwest should then extend eastward with time
and into our area. This should promote a more light northerly
flow, although may result in a sea breeze both days, and
therefore temperatures much closer to average and also lowered
humidity.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Scattered afternoon SHRA/TSRA, but confidence is
too low that a given storm will pass over a given terminal to
warrant including in the TAF. Terminals that could be impacted
are the I-95 terminals, including KPHL, and generally in the 19Z
to 00Z timeframe. LGT/VRB winds early, becoming SW 5 to 10 kt.
Afternoon sea breezes will turn winds S first at KMIV/KACY, then
at the I-95 corridor terminals late in the afternoon.

Tonight...VFR initially. MVFR or lower VSBYs in fog possible
after 06Z. Highest potential for VSBY restrictions in fog will
be at KMIV/KACY. LGT/VRB winds. Moderate confidence.

Outlook...

Monday...A chance of some showers and thunderstorms later in
the afternoon and at night.

Tuesday...VFR overall.

Wednesday and Thursday...Showers and thunderstorms.

&&

.MARINE...
Sub-Small Craft Advisory conditions today and tonight. South to
southwest winds 5 to 10 kt. Seas 2 to 4 feet.

Not really seeing much in the way of marine dense fog, so will
cancel the Marine Dense Fog Advisory. Will keep a mention of
patchy fog on the ocean for today and tonight, and fog may
redevelop on Delaware Bay late tonight.

Outlook...

Monday and Tuesday...The conditions should be below Small Craft
Advisory criteria. Some fog possible at times.

Wednesday and Thursday...A Small Craft Advisory may be needed,
especially Wednesday. Showers and thunderstorms develop Wednesday
afternoon with some continuing into Thursday.

Rip Currents...

For today and Monday, south to southwest flow will average 10
to 15 mph with wave heights only 1 to 3 feet and a 5 to 7 second
period. Therefore, there is a LOW risk for the development of
dangerous and life threatening rip currents for both the New
Jersey Shore and the Delaware Beaches.

Fog at times will cause reduced visibility along the shoreline
through this afternoon.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 10 AM this morning to 6 AM EDT Tuesday for
     PAZ060>062-070-071-101>106.
     Excessive Heat Watch from Tuesday morning through Wednesday
     evening for PAZ060>062-070-071-101>106.
NJ...Heat Advisory from 10 AM this morning to 6 AM EDT Tuesday for
     NJZ009-010-012-013-015>022-027.
     Excessive Heat Watch from Tuesday morning through Wednesday
     evening for NJZ001-007>010-012-013-015>022-027.
     Heat Advisory from 10 AM Monday to 6 AM EDT Tuesday for NJZ001-
     007-008.
DE...Heat Advisory from 10 AM this morning to 6 AM EDT Tuesday for
     DEZ001.
     Excessive Heat Watch from Tuesday morning through Wednesday
     evening for DEZ001.
     Excessive Heat Watch from Tuesday morning through Wednesday
     evening for DEZ002>004.
MD...Excessive Heat Watch from Tuesday morning through Wednesday
     evening for MDZ012-015-019-020.
MARINE...None.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...MPS
SHORT TERM...Gorse/Staarmann
LONG TERM...Gorse/Staarmann
AVIATION...Gorse/MPS
MARINE...Gorse/Hoeflich/MPS