876
FXUS61 KPHI 131617
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1217 PM EDT Tue Aug 13 2024

.SYNOPSIS...
High pressure will gradually build closer to our area through
tonight, then slide over our area Wednesday and Thursday before
shifting to our east. Low pressure and an associated warm and
cold front are forecast to arrive over the weekend, with the
cold front shifting offshore during Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
12:15PM...No major changes to the forecast at this time; quiet
conditions persist across the region.

Tranquil weather conditions with below normal temperatures
continuing today and through tonight. Troughing aloft remains
just offshore with weak subsidence in place across the entire
region. At the surface, expansive high pressure will be centered
across the Great Lakes, extending its reach toward the East
Coast.

The pressure gradient will be a bit lighter today than it was
Monday, and this should favor sea and bay breezes developing
into the afternoon. Elsewhere, north to northwest winds near
5-10 mph can be expected. 850 mb temperatures will be a degree
or two cooler today than Monday, so high temperatures should
also be a couple degrees cooler in the upper 70s to low 80s. The
drier air aloft and subsidence should help mix out the
dewpoints quite well into the mid 50s this afternoon. This will
translate to an usually pleasant mid August day across the area.
Can`t entirely rule out a shower popping up over the higher
terrain or on a sea breeze, but thinking subsidence and limited
diurnal instability will preclude any mention of this in the
forecast. We should see pretty extensive fair weather cumulus
development this afternoon though.

The column starts moistening up a bit into tonight, and with us
still on the fringes of the surface high, radiational cooling
won`t be quite as good tonight. Nevertheless, low temperatures
will still be below normal in the mid 50s to low 60s (mid 60s
for the coasts and urban corridor).

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
While the axis of an upper-level trough is forecast to be
positioned to our east Wednesday, we continue to be under
cyclonic flow aloft. Some shortwave energy sliding southward
across our area will team up with daytime heating to result in
cumulus development. The model forecast soundings overall show
dry air below cloud base and also drier air in the mid levels,
however instability increases through the afternoon. While the
shear is low, a couple of showers or a thunderstorm cannot be
ruled out across parts of the area Wednesday afternoon to early
evening. The coverage looks to be low and therefore maintained
some slight chance PoPs (15-20 percent) for parts of the region.
Outside of any spotty rain, the dew points should lower some
during peak heating given plenty of drier air within the
boundary layer (blended in the CONSAll guidance for dew points
to better reflect the mixing down especially during peak
heating). High temperatures are forecast to be near average. Any
showers dissipate in the evening with lingering cumulus
flattening and then dissipating as well.

As we go through Thursday, it looks similar to Wednesday
although we start to lose some of the influence of the upper-
level trough. Some additional shortwave energy sliding southward
on the western side of the departing trough may touch off a
shower or thunderstorm during the afternoon before the mid level
flow starts to become less cyclonic. Some warming aloft however
may temper some of the cumulus development and therefore any
showers, however kept a slight chance PoP (15-20 percent) for
parts of the area during the afternoon. A sea breeze each day
may also try to focus a few afternoon showers. The dew points
during peak heating may lower a bit again given enough dry air
within the boundary layer.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Summary...An increase is shower chances associated with a slow
arriving system.

Synoptic Overview...An upper-level trough is forecast to
amplify into the East from the Great Lakes region during the
weekend, then remain in place early next week. At the surface,
low pressure across the Great Lakes Friday tracks to our north
with a warm front lifting north across our area Saturday. A cold
front then crosses our area late Sunday and Monday.

For Friday...Weak high pressure initially across our area
shifts east and offshore at night. This is in response to a weak
mid level ridge that arrives ahead of the next system. An
increase in warm air advection and the approach of a warm front
may provide enough lift and forcing for ascent for some showers
to develop or arrive from the west and southwest. This looks to
be mostly late in the afternoon and especially at night,
therefore the PoPs reflect this current thinking. The dew points
are forecast to increase some, although not to very humid
levels.

For Saturday through Monday...A more unsettled pattern is
forecast as an upper-level trough gradually settles into the
East. While there still remains some uncertainty especially with
the timing, the overall theme is for increasing chances for
showers and some thunder. As of now, surface low pressure tracks
across the Great Lakes region and then to our north over the
weekend. A warm front lifts into or just north of our area
during Saturday, then a trailing cold front works its way across
our area during Monday. This entire process could be slower
especially if the parent upper- level trough becomes closed
which some guidance/ensembles suggest. A more humid air mass is
forecast to get pulled up ahead of the cold front, and with
increased warm advection for a time temperatures will warm some
outside of any more organized showers/thunder. The intensity of
thunder at this time is uncertain as this will depend on the
timing of the forcing, extent of the showers and cloud cover and
magnitude of the instability. The PoPs are mainly in the 30-60
percent range, but do decrease during Monday based on the cold
front shifting east as of now.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR with SCT cumulus developing by 18Z. North to
northwest winds 5-10 kts. High confidence in prevailing
conditions.

Tonight...Prevailing VFR conditions expected. Winds diminishing
to 5 kts or less, favoring a north to northwesterly direction.
High confidence.

Outlook...

Wednesday through Friday...VFR overall, however a few showers
or a thunderstorm possible mostly Friday night.

Saturday...Times of sub-VFR conditions possible with the chance
of showers and some thunderstorms.

&&

.MARINE...
Conditions are forecast to remain below advisory conditions
through tonight. Winds 10-15 kts from the north to northwest
this morning (land breeze) shifting southerly this afternoon
(sea breeze), then back to a land breeze again tonight. Seas 1-2
feet. Fair weather.

Outlook...

Wednesday through Friday...The conditions are anticipated to be
below Small Craft Advisory criteria.

Saturday...Small Craft Advisory conditions possible on the
Atlantic coastal waters as southerly winds increase and seas
build.

Rip Currents...

For Today...Northerly winds around 5-10 mph in the morning,
will become south-southeast in the afternoon. Breaking waves
around 1-2 feet with a 7-8 second period. Have maintained a LOW
risk for the development of dangerous rip currents at the Jersey
Shore and the Delaware Beaches.

For Wednesday...Similar wind and breaking wave conditions are
expected with an 8-9 second period. For this reason, have opted
to continue with a LOW risk for rip currents for both the Jersey
Shore and the Delaware Beaches.

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

&&

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

&&

$$

SYNOPSIS...Gorse
NEAR TERM...Staarmann/Wunderlin
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...Gorse/Staarmann
MARINE...Gorse/Staarmann