127
FXUS61 KPHI 101947
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
347 PM EDT Wed Jul 10 2024

.SYNOPSIS...
A cold front will approach the area from the west this evening.
The front will then stall overhead on Thursday and remain
draped over the area through Saturday before dissipating on
Sunday. Broad high pressure builds back in for the end of the
weekend through early next week. Another frontal system then
approaches around mid- week.

&&

.NEAR TERM /THROUGH THURSDAY/...
4 PM Update: No significant changes to the forecast this
afternoon. Some isolated airmass showers have developed
northwest of the fall line. This activity should persist until
later this afternoon. Otherwise, another hot and humid day is
underway. Previous discussion follows...

The Excessive Heat Warning and Heat Advisory remain in effect
as previously issued through 8 PM this evening. Heat indices
range from near 100 to 105 degrees across much of the area away
from the coast, with some spots locally exceeding 105 degrees.
It will remain dangerously hot and humid this afternoon across
the entire region.

We continue to closely watch the remnant low of TC Beryl. The
center of the low will remain well west of our region as it
treks across the eastern Great Lakes. An associated cold front
will push across the Mid Atlantic into our region later tonight.
A few isolated showers will remain possible through the end of
the day northwest of the fall line, though no weather hazards
are expected with this activity. While we can`t rule out a rogue
thunderstorm, much of the region will stay precip- free through
about 7 PM or so. The approaching cold front and tightening
pressure gradient will continue to support fairly breezy
conditions through this evening. Southerly winds near 10-20 mph
with gusts up to 30 mph can be expected.

By 7-8 PM, the cold front and a line of thunderstorms
accompainying it will begin to push into the western forecast
zones. With the loss of daytime heating, the severe threat will
begin to diminish by the time these storms arrive, though an
isolated severe thunderstorm wind gust or a brief tornado cannot
be ruled out. Storms should reach eastern PA and eastern MD by
sunset and slowly push towards the I-95 corridor and into
Delmarva by midnight before beginning to diminish in intensity,
however scattered showers and some rumbles of thunder will
likely linger into the overnight period. The slow nature of this
frontal passage in combination with high PWat values (greater
than 2.0") will be the main driver of flooding concerns as these
storms make their way across the region. The frontal boundary
looks to stall out across the southeastern portion of the CWA
while becoming less defined over time. West of the boundary,
temperatures look to cool into the low 70s with dewpoints
dropping into the 60s. East of the boundary, still rather mild
with lows in the mid to upper 70s with humid air lingering until
Thursday morning.

With the frontal boundary settled to our south by Thursday,
somewhat drier air will filter in with southwesterly winds near
10-15 mph. Much of the area can expect mostly sunny skies
(except for southern Delaware and Cape May). Some showers or
storms may linger in southern Delaware and Cape May where the
more persistent cloud cover will be found. While we will be in a
post-frontal regime, high temperatures will still be near 90
degrees in most areas. Fortunately, the lower dewpoints in the
mid to upper 60s will yield some relief to the excessively humid
condtions that have persisted the past several days, though not
particularly comfortable. Heat indices will top out in the low
to mid 90s at best, and thus no heat headlines are expected for
Thursday.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
The stalled boundary over the area on Thursday will begin to
retreat back to the northwest gradually through Friday. This
boundary will be the trigger that initiates convection while a
tropical low moves into the Southeast US and rides northward
along the boundary while tracking through the area on Saturday.
So, while some convection is expected to develop on Thursday
night, batches of more persistent, stratiform rain with embedded
thunder will be around the area on Friday and especially into
Friday night. PWATs upwards of 2.0-2.5 inches are forecast to
surge northward on Friday night as well. In combination with the
high PWATs, high freezing levels and modest warm cloud depths
in excess of 10,000 feet, yield that any shower or storm will be
more than capable of producing heavy rainfall.

While this may bring some much needed rainfall to the region,
the larger concern is with respect to the hydro/flooding
potential. Model soundings suggest that the relative storm
motion vector is not expected to be all that fast and actually
supports either slow moving storms and training. This means that
flash flooding may be enhanced especially in areas where
training occurs. This is supported basis the latest outlook from
the Weather Prediction Center which has an area from Trenton to
Philadelphia to the Delmarva in a Slight Risk (Level 2/4) for
Excessive Rainfall, with the remainder of the area in a Marginal
Risk (Level 1/4).

Eventually, the low will ride north along the boundary on
Saturday and move north and east of our area by Saturday night.
Rain and storm chances will gradually decline through the day,
so not expecting a washout for Saturday. All precipitation
should then wane into Saturday night. In terms of storm total
rainfall, heaviest amounts will be across south Jersey and the
Delmarva with upwards of 2.0 inches (locally higher amounts
possible where training occurs). Lesser amounts are expected
further north and west.

With plentiful of cloud cover around for much of the short term
period, temperatures will be much cooler during the day time
compared to earlier this week. Highs will mostly be in the 80s
with lows in the 60s/70s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Unfortunately, for those that do not like the heat and humidity
then the long term forecast is not for you. High pressure will
once again set-up offshore, resulting in another prolonged
period for southerly flow, aiding the return of high heat and a
humid airmass. Temperatures for the most part again look to be
well above normal with highs in the mid 90s each day with
dewpoints in the 70s. It is certainly plausible for another
round of heat headlines to be expected for next week.

Overall, there does not look to be a period of consistently wet
weather though. There does not appear to be any fronts nearby
so forcing will be relatively weak. However, diurnal heating
should aid in at least a slight chance for showers/thunderstorms
to develop each afternoon into the early evening. The next
frontal system eventually approaches near mid-week.

&&

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

Through 00Z...VFR with SCT to at times BKN clouds. Aside from
an isolated shower, no impacts anticipated to the terminals
through 00z. Winds prevailing from the south around 10-15 kts
with some gusts to around 20-25 kts. High confidence on the
overall pattern.

Tonight...VFR likely to start, but a line of thunderstorms is
expected to impact terminals from west to east from around
00z-06z. Maintained SHRA and VCTS to signal when storms are most
likely, including TEMPO groups for briefly lower conditions in
heavy rain. Some abrupt wind shifts to the west possible.
Stratus development behind the showers and storms could be MVFR
around 2-3kft, however confidence on this is low (have included
mainly VFR for now). Winds southerly ahead of the front with
gusts 15-20 kts turning SW behind the front and diminishing to
around 10 kts. Moderate confidence overall.

Thursday...After any lingering restrictions early, VFR
conditions expected. Southwest winds near 10 kts. High
confidence.

Outlook...

Thursday night through Saturday...Sub-VFR conditions probable
developing from southeast to northwest on Thursday night into
Friday. Chances for showers and thunderstorms expected through
Saturday.

Saturday night through Monday...Primarily VFR expected with a
slight chance of a rain or thunderstorm.

&&

.MARINE...
Southerly winds near 15-25 kts with gusts near 30 kts are
expected across all waters, including Delaware Bay, and seas
approaching 5-6 ft are expected on the Atlantic Ocean waters.
The Small Craft Advisory remains in effect through tonight for
all coastal waters.

Some patchy fog with lower visibility will remain possible into
tonight. Scattered showers and thunderstorms will pass offshore
after midnight, otherwise fair weather is expected through
today.

On Thursday, southerly winds remain near 15-20 kts with gusts
up to 25 kts possible at times and seas lingering near 4-5 feet
across the Atlantic waters. The Small Craft Advisory remains in
effect through Thursday for the Atlantic coastal waters.

Outlook...

Thursday night...SCA conditions likely to continue on ocean
waters due to seas lingering around 5 feet.

Friday through Monday...No marine headlines anticipated. Winds
are forecast to generally remain between 10-15 kt occasionally
gusting up to 20 kt with seas of 2-4 feet through the period.


Rip Currents...

Southerly winds will continue to increase through midweek and
will generally be around 15 to 20 mph for both Wednesday and
Thursday. This will result in waves around 2 to 3 feet in the
surf zone. Given the wind component and some higher breaking
waves developing, there is a MODERATE risk for the development
of dangerous rip currents through Thursday for the New Jersey
Shore. Due to somewhat lower waves for the Delaware Beaches, we
went with a LOW risk for the development of dangerous rip
currents both days.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Warning until 8 PM EDT this evening for
     PAZ060>062-070-071-101>106.
     Heat Advisory until 8 PM EDT this evening for PAZ054-055.
NJ...Excessive Heat Warning until 8 PM EDT this evening for
     NJZ007>010-012-013-015-017>020-027.
     Heat Advisory until 8 PM EDT this evening for NJZ001-016-021-
     022.
DE...Excessive Heat Warning until 8 PM EDT this evening for DEZ001.
     Heat Advisory until 8 PM EDT this evening for DEZ002-003.
MD...Heat Advisory until 8 PM EDT this evening for MDZ012-015-019-
     020.
MARINE...Small Craft Advisory until 2 AM EDT Thursday for ANZ430-431.
     Small Craft Advisory until 6 AM EDT Friday for ANZ450>455.

&&

$$

SYNOPSIS...DeSilva
NEAR TERM...MJL/Staarmann
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...DeSilva/MJL/Staarmann
MARINE...DeSilva/MJL/Staarmann