Special Marine Warning 68, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
325 PM EDT Sun Jul 14 2024

.SYNOPSIS...
Bermuda high pressure remains offshore through the middle of
the week. A thermal trough looks to develop east of the
Appalachians Monday and Tuesday. Excessive heat and humidity are
expected through Wednesday along with daily thunderstorm
chances. A cold front will cross the region Wednesday night into
Thursday, stalling out and lingering near or just south of the
area through the end of the week.

&&

.NEAR TERM /THROUGH MONDAY/...
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.

A shortwave trough passing through the region has resulted in
scattered shower and storm development. Given how hot and humid
it will be, SB CAPE values will be upwards of 1500 to 2000 J/kg.
0-6 km Bulk Shear will be limited. Despite this, the higher
instability and Dcape values meant that there will be a
potential for pulse type storms with downburst winds. Because
this is diurnally driven, should see storms diminish in coverage
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.

Another short wave trough will approach the region tomorrow.
Exact timing is uncertain, but at this point, it appears as if
the prime period will be late afternoon into the evening. As
with Sunday, prime concerns with any storms will be downburst
winds and heavy rain. There may be a small inversion around 800
mb (based on some model soundings), which could slightly limit
the instability, but models were depicting a similar case today,
and given the amount of heating, don't think it will make a
significant impact in limiting convective potential. None the
less, with a lack of a focus for surface convergence, do not
expect widespread storms. Rather, it should be scattered
(similar to the coverage we're seeing today.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
Excessive heat and humidity continuing, likely peaking on
Tuesday, along with daily chances for thunderstorms.

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
through the period. 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 Monday evening and Tuesday afternoon and
evening. 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.

Low temperatures Monday night will be mainly in the low to mid
70s, warmest near urban centers and across Delmarva.

The excessively hot and humid stretch continues through Tuesday
and Tuesday night. For Tuesday, temperatures increase even more
along with lower chances for convection during the daytime
period. Tuesday is still expected 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, with lows
in the mid to upper 70s in many areas, and near 80 degrees in
the urban centers. Given the latest forecast for Monday and
Tuesday's temperatures and heat indices, we've upgraded portions
of the Heat Advisory and Excessive Heat Watch to an Excessive
Heat Warning (Heat Advisory for lower Delaware and northwest New
Jersey). Additionally, a Heat Advisory was issued for Carbon
and Monroe Counties in PA, coastal Monmouth and inland Cape May
Counties in NJ (these zones did not previously have a watch in
effect).

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Summary...Excessive heat Wednesday begins to diminish as a cold
front and associated showers and thunderstorms move toward the
region late Wednesday, 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, especially by
late afternoon and evening. 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. High
temperatures are forecast to be well into the 90s yet again,
with resulting heat indices near 100-107 or so across much of
the area (especially along and south of I-78. Thus, the
Excessive Heat Watch remains in effect for Wednesday. The
arrival of convection and also the cold front will knock down
the excessive heat, and therefore Thursday is expected to be
noticeably cooler and drier than Wednesday.

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 /19Z SUNDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Scattered afternoon SHRA/TSRA with potential for
gusty and variable winds in the vicinity of any storms. Winds
prevailing out of the SW. However, 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.

Monday...Primarily VFR. Showers and storms will be possible
after 18Z, which could result in brief restrictions if they move
over a TAF site. Winds starting light and variable, but should
favor southwesterly direction for most of the day. Moderate
confidence.

Outlook...

Monday night through Tuesday night...Generally prevailing VFR.
A 20-30% chance of showers or thunderstorms, mainly northwest of
I-95.

Wednesday and Thursday...Showers and thunderstorms likely,
especially Wednesday afternoon and evening.

&&

.MARINE...
Winds and seas should stay below Small Craft Advisory criteria
through Monday. However, locally higher winds are possible in
the vicinity of any storms, especially Monday afternoon and
evening.

Patchy fog may continue through tonight, especially for waters
very close to the coast.

Outlook...

Monday night through Tuesday night...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. Areas of
fog possible.

Rip Currents...

For Monday and Tuesday, 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.

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

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

&&

.CLIMATE...
Near record breaking temperatures are forecast from Monday
through Wednesday. Records for our climate sites are listed
below:

Record High Temperatures
                          July 15
Site                  Record/Year
Allentown (ABE)           98/1995
AC Airport (ACY)         100/1995
AC Marina (55N)           99/1995
Georgetown (GED)          96/1993
Mount Pocono (MPO)        92/1954
Philadelphia (PHL)       103/1995
Reading (RDG)             96/1995
Trenton (TTN)            101/1995
Wilmington (ILG)          99/1995 & 1997

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 6 AM EDT Wednesday for PAZ060>062-
     070-071-101>106.
     Excessive Heat Watch from Wednesday morning through Wednesday
     evening for PAZ060>062-070-071-101>106.
     Heat Advisory from 10 AM Monday to 8 PM EDT Tuesday for PAZ054-
     055.
NJ...Excessive Heat Warning until 6 AM EDT Wednesday for NJZ009-010-
     012-013-015-017>020-027.
     Excessive Heat Watch from Wednesday morning through Wednesday
     evening for NJZ001-007>010-012-013-015>022-027.
     Heat Advisory from 10 AM Monday to 6 AM EDT Wednesday for
     NJZ001-007-008-014-023.
     Heat Advisory until 6 AM EDT Wednesday for NJZ016-021-022.
DE...Excessive Heat Warning until 6 AM EDT Wednesday for DEZ001.
     Excessive Heat Watch from Wednesday morning through Wednesday
     evening for DEZ001>004.
     Heat Advisory from 10 AM Monday to 6 AM EDT Wednesday for
     DEZ002>004.
MD...Excessive Heat Watch from Wednesday morning through Wednesday
     evening for MDZ012-015-019-020.
     Excessive Heat Warning from 10 AM Monday to 6 AM EDT Wednesday
     for MDZ012-015-019-020.
MARINE...None.

&&

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

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
337 PM EDT Sun Jul 14 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0240 PM     Tstm Wnd Dmg     2 S Warwick Twp         40.13N 75.76W
07/14/2024                   Chester            PA   Dept of Highways

            Tree down on 401. Time estimated from radar.

&&

SJ

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
345 PM EDT Sun Jul 14 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0305 PM     Tstm Wnd Dmg     Hillsborough Twp        40.51N 74.68W
07/14/2024                   Somerset           NJ   Public

            Large tree uprooted. Time estimated from
            radar.

&&

SJ

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
350 PM EDT Sun Jul 14 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0145 PM     Tstm Wnd Dmg     1 N Franconia Twp       40.32N 75.37W
07/14/2024                   Montgomery         PA   Public

            Large tree down onto a garage and some other
            tree damage occurred on Morwood Road in
            Franconia. Time estimated from radar.

&&

Gorse

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
410 PM EDT Sun Jul 14 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0232 PM     Tstm Wnd Dmg     1 ENE Upper Uwchlan Twp 40.08N 75.68W
07/14/2024                   Chester            PA   Public

            Trees and wires down in Chester Springs.
            Time estimated from radar.

&&

Gorse

Preliminary Local Storm Report
National Weather Service Mount Holly NJ
414 PM EDT Sun Jul 14 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0315 PM     Hail             Caln Twp                40.00N 75.75W
07/14/2024  M0.70 Inch       Chester            PA   Trained Spotter

            Dime size hail in Caln Township. Time
            estimated from radar.

&&

Gorse

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