-- Discussion containing changed information from previous version are highlighted. --
734
FXUS61 KPHI 222121
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
521 PM EDT Wed May 22 2024

.SYNOPSIS...
High pressure will be centered to our south and east through today
before moving further out to sea tonight. A cold front will approach
the area on Thursday before crossing through the area on Thursday
night. The front will stall to our south on Friday before lifting
back north on Saturday as a warm front. Another cold front moves
through on Sunday, with a stronger system impacting the area on
Monday into Tuesday. High pressure returns on Wednesday.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
A very warm/hot afternoon in progress across much of the region,
with the exception of locations closer to the coast thanks to a sea
breeze that is making some inland progress. The warmth and even more
on the humid side continues through Thursday.

A closed low centered just north of the Midwest and upper Great
Lakes region will gradually shift eastward through Thursday night.
Surface low pressure will also travel with it, and an associated
cold front will cross our area Thursday night. Some convection is
expected ahead of this cold front and with with a surface trough.

A lee-side trough from central Virginia into central Pennsylvania
has assisted in some convective development this afternoon. There is
also convection along a pre-frontal band in western Pennsylvania and
western New York (enhanced by an MCV). While there is MLCAPE near
1500 J/kg across our western zones this afternoon, the air mass is
on the dry side above the boundary layer, however some cumulus has
developed there especially now. Given the large scale forcing for
ascent is well to our west, convection that gets to parts of our
area tonight should be tied to how organized it is to our west (also
some isolated convection possible due to terrain influences). The
CAM guidance varies quite a bit which makes confidence lower on what
to expect, however at least isolated to scattered showers and
thunderstorms should get into our western zones this evening and
these may continue farther east although enough stabilizing of the
boundary layer may weaken or result in dissipation. Given the dry
air aloft and steep low-level lapse rates, there is some potential
for a locally stronger convective core resulting in strong to
damaging winds. The greatest potential for this is north and west of
the I-95 corridor.

Some guidance hinting at what might be a convectively induced
shortwave (or MCV) late tonight and early Thursday morning, which
results in additional convection. The placement of this is less
certain, however there is some potential for a round of some showers
and thunderstorms to start Thursday morning. This activity if it
were to be realized should be sub-severe with some decrease in the
instability and more stable boundary layer. The extent and timing of
morning convection will have an influence on the rest of Thursday as
the cold front arrives. An overall trend in the guidance is for the
modestly increased southwesterly mid level flow to occur in the
morning with this flow weakening through the afternoon. High level
winds remain stronger, however it is the lower winds that are
forecast to be weaker. The amount of instability that is forecast is
enough to sustain thunderstorm development through the afternoon,
however the main forcing is well removed from our area given the
main trough aloft is well to our north. If the morning convection
does not occur or it is much more isolated, then the model forecast
soundings show a low-level inverted-V profile developing as more
boundary layer heating will occur. At least some showers and
thunderstorms are expected throughout the day, and there remains the
potential for at least isolated severe thunderstorms. Locally
damaging winds is the main hazard, especially if storms are able to
become more organized such as in a cluster or a line segment. Given
the weaker wind field overall that is forecast, the severe
thunderstorm risk remains at Marginal or a level 1 out of 5.

Any showers and thunderstorms are expected to be weakening and/or
moving offshore Thursday night as the cold front shifts to our east.
Some drier air then arrives later Thursday night in the wake of the
cold front, however prior to that patchy fog cannot be ruled out
especially where rain occurs and if the cloud cover clears
enough.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
The cold front will continue to move offshore and stall south of the
area on Friday. A few residual showers may linger along the shore in
the morning but for the most part all precipitation should be over.
Still will mention a slight chance of a shower across the Delmarva
in the afternoon, but this is becoming increasingly less likely.
Skies will clear behind the front as dewpoints fall back into the
50s. Overall, Friday is shaping up to be a pretty pleasant day to
kick off the holiday weekend with temps in the low to mid 80s, with
shore points in the 70s.

Quiet weather will continue into Friday night with clear skies and
light winds. We should be able to radiate pretty well initially,
however clouds will increase from south to north later in the night.
This will limit the amount of cooling late, resulting in warmer
than normal lows ranging in the upper 50s to mid 60s.

For Saturday, the stalled boundary to our south will begin to lift
back northward across the area as a warm front with the main low
pressure system tracking across the Great Lakes. Basis current
trends amongst forecast guidance, it does appear the first half of
Saturday will remain dry. However, as we progress through the
afternoon, the chance for showers and thunderstorms increase from
west to east. For locations along the shore, precip may hold off
entirely until Saturday evening, although it will be pretty cloudy
most of the day. This system will be a rather quick mover so while
Saturday night does appear to be wet, all precipitation should come
to an end by early Sunday. Aided by warm air advection, highs on
Saturday should reach again into the low to mid 80s despite cloud
cover with cooler temps along the coast. Saturday night lows will be
in the mid 50s to low 60s.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
After precip wanes on Sunday morning, a weak cold front will pass
through the area, however the front will be slowing down and
stalling either over or again just south of the area. Sunday for now
does appear to be mostly dry behind the front with partial sunshine.
Beyond Sunday, the weather pattern becomes unsettled as a stronger
low pressure system develops back over the central CONUS. Another
warm front will likely pass over the area on Monday with a
potentially stronger cold front crossing the area Monday night into
Tuesday. Will have to watch this closely in the coming days as some
of the analog based and machine learning guidance suggest severe
weather may be on the table. But this is quite a few days away.
After the cold front passes, shower chances should continue through
the middle of next week thanks to several waves/impulses aloft. For
now, will carry a chance of showers into the middle of next week.

In terms of temperatures for the long term period, Sunday appears to
be a few degrees above average, Monday and Tuesday close to average,
with Wednesday looking below average.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Rest of this afternoon...VFR. A shower or thunderstorm possible in
the vicinity of KRDG/KABE toward early evening. South to
southwest winds around 10 knots. Moderate confidence.

Tonight...VFR for much of the night, however some sub-VFR conditions
with some showers or thunderstorms possible. Greatest chance in the
KRDG and KABE areas this evening, then nearly anywhere late. South-
southwest winds around 5 knots, becoming locally light and variable.
Low confidence on timing and coverage of showers/thunder.

Thursday...Some showers and thunderstorms around resulting in a time
of sub-VFR conditions. Southwest winds 5-10 knots, becoming west to
west-northwest 5 knots or less later at night. Low confidence in
timing and coverage of showers/storms.

Outlook...

Friday through Friday night...Sub-VFR possible early, becoming VFR.
Slight chance of a shower.

Saturday through Saturday night...VFR during the day, likely
becoming sub-VFR at night. Showers and thunderstorms late in the day
into the evening.

Sunday...VFR. No significant weather expected.

Sunday night through Monday...Sub-VFR conditions probable with a
chance of showers and thunderstorms.

&&

.MARINE...
-- Changed Discussion --
The conditions are expected to remain below Small Craft Advisory
criteria through Thursday night, however a few gusty thunderstorms
will be possible especially Thursday afternoon and evening.

Outlook...

Friday through Monday...No marine headlines expected. Winds will
periodically gust up to 15-20 kt with seas around 2-4 feet. A chance
for showers and thunderstorms is expected on Saturday night and for
Sunday night into Monday.

Rip Currents...

S to SW winds will average 5 to 10 mph on Thursday along with
breaking waves around 2 feet. There is a LOW risk for the
development of dangerous and life threatening rip currents at NJ
and DE beaches for Thursday. However, showers and thunderstorms
are likely, and may be capable of strong wind gusts and hail.

On Friday, winds will once again be out of the S to SW at 5 to
10 mph with breaking waves of 1 to 2 feet. There is a LOW risk
for the development of dangerous and life threatening rip
currents at NJ and DE beaches for Friday. Although there is a
slight chance for showers, thunderstorms are not expected.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
Astronomical tides will be elevated this week with a Full Moon
on Thursday, May 23. Spotty minor coastal flooding will be
possible, especially for the back bays, around the times of the
evening high tide cycle, which will be the higher of the two
tide cycles, going into the end of this week.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...DeSilva/Gorse
NEAR TERM...Gorse
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...DeSilva/Gorse
MARINE...DeSilva/Gorse/MPS
TIDES/COASTAL FLOODING...