793
FXUS61 KPHI 152317
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
717 PM EDT Mon Jul 15 2024

.SYNOPSIS...
A thermal trough will remain in place across the east coast through
Wednesday as Bermuda high pressure remains offshore. A cold front is
expected to move across the Mid Atlantic states Wednesday night into
Thursday, and likely stall to our south through the weekend. Weak
high pressure may briefly build into the area Friday, before
weakening Saturday into Sunday as a weakening cold front approaches
from the north. High pressure may briefly build into the region
early next week.

&&

.NEAR TERM /THROUGH TUESDAY/...
Some changes with this update, the severe threat has diminished
and not expecting severe weather for the rest of today. A very
strong QLCS with a history of significant damage will miss the
area just to the north and showers/thunderstorms that were over
the DC metro have fizzled out. With the loss of daytime heating,
not expecting any significant redevelopment, though can`t rule
out a passing shower.

The excessively hot and humid stretch continues through Tuesday
which is expected to be the hottest and most oppressive of this
stretch. Highs will largely be in the upper 90s to near 100,
most likely in the I-95 urban corridor with dew points
remaining in the lower 70s, support peak heat indices of
105-110 degrees across much of the area. Excessive Heat Warnings
and Heat Advisories are up for essentially the entire region,
with the exception of the Jersey Shore from Ocean County to Cape
May. Whichever headline you have in place, the takeaway is this:
it will be dangerously hot and humid Tuesday afternoon!

Additionally, the latest hi res guidance shows another shortwave
trough pushing across the Mid Atlantic Tuesday afternoon, which
will bring another round of thunderstorms across the region. The
timing of the storms will be during the mid afternoon through
early evening, a much more favorable timeframe for severe
weather potential. With CAPE values at least over 1500 J/kg,
sufficient shear, and steep low-level lapse rates, the
atmosphere will be primed again for strong to severe
thunderstorms with locally damaging wind gusts, heavy rainfall,
and frequent lightning. Coverage overall is expected to be more
widespread with this round as well thanks to the earlier onset
time allowing storms to persist and develop across the Delaware
Valley. A Slight Risk from the SPC is in place where the
greatest severe thunderstorms risk is (north and west of the
I-95 corridor) with a Marginal covering everywhere else.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
Another hot and humid day is expected for much of the area on
Wednesday as a thermal trough remains across the area with Bermuda
high pressure offshore. We will upgrade the Excessive Heat Watch to
a Warning for most of the area, with the exception of the Poconos
and Sussex, NJ where a Heat Advisory will be extended. This will be
a situation where portions of the area will not meet the exact
criteria, i.e. the Poconos may not reach 100 Heat Index for the Heat
Advisory, and the Lehigh Valley may not reach 105 Heat Index for the
Heat Warning, but the Heat Index will be close and the impacts of
the multi-day heat event could make it worse than usual.

In addition to the heat impacts Wednesday, we will also have a
thunderstorm threat later in the day and into the evening. With the
thermal trough in place, there will be strong instability with CAPE
values 1000-2000+ J/kg, along with an approaching short
wave/vorticity impulse, and decent shear with 30-40 knots, some
storms could be strong to severe.

The front continues to slowly move across the area later Wednesday
night into Thursday, before pushing south of the area later in the
day Thursday. There will continue to be a chance of showers and
thunderstorms through the night Wedensday into the first half of
Thursday. While the main severe threat will diminish through the
evening Wednesday, there will be a threat for heavy rain until the
front passes to the south later in the day Thursday.

Dry conditions are expected to move into the area later in the day
Thursday into Thursday night as PW values lower and high pressure
builds to our west.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
High pressure is expected to briefly affect the area Friday into
Friday night as high pressure builds into the region which will keep
dry weather across the area. However, this will only be temporary as
the high breaks down into Saturday and Saturday night, and moisture
begins to increase across the area again, which could lead to a
slight chance to chance of showers across the area. The shower
chances will continue into Sunday as a weak frontal boundary is
expected to move into the area from the north. By Monday, dry
weather could return again as high pressure again briefly builds
into the region.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Took any mention of thunder out of the TAFs as any
convection looks like it will miss all terminals. Should be VFR
through the night with a light southwest flow around 5 kt or
less. Moderate to high confidence.

Tuesday...VFR through most of the day though afternoon
showers/thunderstorms possible. Model guidance has slowed with
the progression of thunderstorms and only have thunder mentioned
in the TAFs for KRDG/KABE and KPHL. Showers/thunderstorms look
to get into the Lehigh Valley by 22z and the I-95 corridor
around 23z-00z. Winds will be out of the southwest around 10 kt,
with gusts around 20 kt. Moderate confidence in wind/prevailing
VFR through most of the day, low confidence in where convection
will develop.

Outlook...

Tuesday night...Mostly VFR. Chance of showers and thunderstorms
which could temporarily lead to lower conditions.

Wednesday-Wednesday night...Mostly VFR. Showers and thunderstorms
likely later in the day and into the evening which could temporarily
lead to lower conditions.

Thursday-Thursday night...Mostly VFR. Chance of showers and
thunderstorms which could temporarily lead to lower conditions.

Friday-Friday night...VFR conditions expected.

Saturday...Mostly VFR. Chance of showers and thunderstorms which
could temporarily lead to lower conditions.

&&

.MARINE...
Should be a mainly quiet night on the waters, though some patchy
marine fog is possible. Will keep an eye on the waters to see if
a Marine Dense Fog Advisory is needed, but will not issue one
yet. Winds out of the southwest around 10-20 kt and seas around
3 feet.

Essentially another repeat Tuesday with conditions remaining
generally below SCA criteria, but afternoon and evening
thunderstorms could bring locally heavy rain, gusty winds, and
lightning.

Outlook...

Tuesday night...Conditions likely remain below advisory levels, but
will be close with winds gusting in the low 20s and seas around 4
feet.

Wednesday-Wednesday night...Small Craft Advisory conditions possible
with wind gusts near 25 knots and seas near 5 feet.

Thursday-Saturday...Conditions drop below advisory levels early
Thursday and remain below advisory levels through Saturday.

Friday...Conditions are expected to be below SCA criteria.

Rip Currents...

For Tuesday, south to southwest flow will average 10 to 15 mph.
Gusts up to 20 mph are possible during the daytime hours. Wave
heights will average 1 to 3 feet and a 5 to 7 second period.
Therefore, there is a MODERATE RISK for the development of
dangerous and life threatening rip currents for the Jersey Shore
in Ocean, Atlantic, and Cape May counties, and a LOW risk for
the Jersey Shore in Monmouth county and Delaware Beaches.

Late day showers and thunderstorms are possible, mainly for the
Jersey Shore in Monmouth and Ocean counties.

For Wednesday, the south-southwest flow will increase to around
15-20 mph with gusts up to 25 mph. Wave heights in the surf zone
are again forecast to be around 1-3 feet with a 5-7 second
period. Therefore, a MODERATE RISK for the development of
dangerous and life threatening rip currents is again in place
for the Jersey Shore in Ocean, Atlantic, and Cape May counties,
and a LOW risk for the Jersey Shore in Monmouth county and
Delaware Beaches.

Some areas of fog at times will cause reduced visibility along
the shoreline.

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

&&

.CLIMATE...
Georgetown and Reading tied their record highs today. Georgetown
and Mount Pocono currently have tied their record warm lowest
temperature. Will see if they get below that before midnight. Near
record breaking temperatures are forecast from through
Wednesday. Records for our climate sites are listed below.

Record Warmest Low Temperatures
                          July 15
Site                  Record/Year
Allentown (ABE)           79/1995
AC Airport (ACY)          78/1995
AC Marina (55N)           80/1995
Georgetown (GED)          75/2012 & 2016
Mount Pocono (MPO)        69/2013
Philadelphia (PHL)        81/1995
Reading (RDG)             79/1995
Trenton (TTN)             78/1995
Wilmington (ILG)          78/1995

Record High Temperatures
                          July 16
Site                  Record/Year
Allentown (ABE)          101/1988
AC Airport (ACY)         100/1983
AC Marina (55N)          100/1983
Georgetown (GED)          97/1953 & 1992
Mount Pocono (MPO)        93/1988
Philadelphia (PHL)       102/1988
Reading (RDG)            100/1900
Trenton (TTN)            102/1988
Wilmington (ILG)         100/1983

Record Warmest Temperatures
                          July 16
Site                  Record/Year
Allentown (ABE)           76/1983
AC Airport (ACY)          77/1983
AC Marina (55N)           80/2013
Georgetown (GED)          80/1955
Mount Pocono (MPO)        70/1955
Philadelphia (PHL)        80/2013
Reading (RDG)             78/1955
Trenton (TTN)             78/1983
Wilmington (ILG)          77/2013

Record High Temperatures
                          July 17
Site                  Record/Year
Allentown (ABE)           99/1999
AC Airport (ACY)          99/2012
AC Marina (55N)           95/1937
Georgetown (GED)         100/2019
Mount Pocono (MPO)        91/1999
Philadelphia (PHL)       102/1988
Reading (RDG)            102/1988
Trenton (TTN)            100/1988
Wilmington (ILG)         100/1988

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Warning until 8 PM EDT Wednesday for PAZ060>062-
     070-071-101>106.
     Air Quality Alert until 11 PM EDT this evening for PAZ070-071-
     101>106.
     Heat Advisory until 8 PM EDT Wednesday for PAZ054-055.
NJ...Excessive Heat Warning until 8 PM EDT Wednesday for NJZ007>010-
     012-013-015>020-027.
     Air Quality Alert until 11 PM EDT this evening for NJZ008>010-
     012>027.
     Heat Advisory until 8 PM EDT Wednesday for NJZ001-014-021>023.
DE...Excessive Heat Warning until 8 PM EDT Wednesday for DEZ001>003.
     Air Quality Alert until 11 PM EDT this evening for DEZ001>004.
     Heat Advisory until 8 PM EDT Wednesday for DEZ004.
MD...Excessive Heat Warning until 8 PM EDT Wednesday for MDZ012-015-
     019-020.
     Air Quality Alert until 11 PM EDT this evening for MDZ012-015-
     019-020.
MARINE...None.

&&

$$

SYNOPSIS...Robertson
NEAR TERM...Hoeflich/MJL
SHORT TERM...Robertson
LONG TERM...Robertson
AVIATION...Hoeflich/MJL/Robertson
MARINE...AKL/MJL/Robertson
CLIMATE...NWS PHI