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000
FXUS61 KPHI 301929
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
329 PM EDT Tue May 30 2023

.SYNOPSIS...
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High pressure remains anchored over the Northeast through mid-week
while weakening low pressure off the coast of the Carolinas
will linger into Thursday. The low will continue to bring some
scattered showers to the Delmarva Peninsula, but dry weather
should prevail overall with increasing temperatures through the
end of the week. A back-door cold front passes through on
Saturday and introduces a cooler airmass for the weekend.
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&&

.NEAR TERM /THROUGH WEDNESDAY/...
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High pressure south of the Canadian Maritimes will sag to the south
and east tonight through Wednesday. Meanwhile, upper low over the
Mid-Atlantic continues to dissipate.

The other aspect to this forecast is smoke and haze from wildfires
in Nova Scotia will spread into the region. More on that in a bit.

In terms of sensible weather, onshore flow will continue tonight
through Wednesday. Some light rain showers may continue to move into
far southern portions of Delmarva with minimal, if any, QPF prior to
this evening. Another round of light rain showers may impact these
areas, again with minimal QPF, Wednesday afternoon.

With onshore flow and increasing low level moisture spreading into
the region, patchy fog and drizzle is likely for coastal areas and
areas just inland from the coast late tonight through Wednesday
morning. In addition, a stratus deck will spread farther inland.

Clouds scatter out Wednesday morning, giving way to hazy sunshine in
the afternoon.

Lows tonight will be in the mid and upper 40s to low 50s. Highs on
Wednesday will top off in the upper 70s to low 80s inland, and in
the upper 60s to low 70s along the coast and just inland.

Smoke from wildfires in Nova Scotia will then spread west into the
region from the northeast. Latest HRRR and RAP vertically integrated
smoke forecasts have one wave spreading into the region into this
evening, and then another wave on Wednesday. Will go ahead and carry
a wide swath of haze across much of New Jersey and southeast
Pennsylvania this evening, and then a wider swath of haze across
southeast Pennsylvania, most of New Jersey, and northern Delmarva.
HRRR is also indicating the potential for smoke to mix down to the
surface. Will go ahead and carry "patchy smoke" for parts of New
Jersey and southeast Pennsylvania, including Philadelphia. Keep an
eye out for any Air Quality Alerts that may be issued, and be
prepared for the smell of smoke.
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&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
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A strong upper ridge will remain overhead for the short term period
while upper troughing digs across the Southwest. The flow will be
quite meridional aloft and the resultant blocking pattern will hold
strong through the end of the week. At the surface, high pressure
remains in control while a weak surface low spins off the coast of
the Carolinas.

Weak onshore flow Wednesday night will introduce a marine layer
with low stratus/fog/light drizzle as moisture is trapped
underneath a subsidence inversion around 900 mb. Further inland
(Lehigh Valley to the Poconos) expect mostly clear skies and,
with wind going light to calm, efficient radiational cooling,
though warm advection will work to offset the cooling and lows
will be a few degrees warmer than Wednesday night in the low
50s. In addition, expect that some haze/smoke will still be
around into the early overnight, so maintained the patchy smoke
mention.

Temperatures will rebound quite quickly on Friday as the NBM is
still holding firm with highs in the upper 80s and low 90s, while
cooler along the coast. Latest guidance has continued the slight
increase of 850 mb temperatures to around 17-19C which is very close
to supporting highs in the 90s. NBM prob MaxTs are indicating a >60%
chance of MaxTs >90F primarily along I-95 and west, though MOS
guidance is still not budging from the upper 80s. Regardless, we`ll
be seeing above average temperatures across the board. Forecast
soundings show a very deep, dry boundary layer, so do expect that
dew points will mix out in the afternoon and apparent
temperatures should remain around actual air temperatures. A
sea breeze should develop in the afternoon and will drop
temperatures some as it progresses inland.
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&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
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The forecast still remains more uncertain going into the weekend.
The deterministic suite of guidance indicates a potent shortwave
diving south out of New England and a back door surface front coming
onshore on Saturday. Meanwhile, an area of surface low pressure will
be sliding up the Atlantic coast, and both the GFS and ECMWF show
the shortwave aiding in the low`s development before quickly
evolving into a closed low itself.

Both deterministic and ensemble guidance remains spread on the
timing of the backdoor front as well as the strength and track
of the surface low. The GFS and Canadian favor a very early
Saturday morning passage with the ECMWF later. Ultimately, the
setup is favoring a post-frontal cooldown on Saturday after a
quite warm Friday with thickness values falling and cold
advection with northeasterly onshore flow. Held with NBM which
introduces some PoPs (20-40%) with frontal passage on Saturday,
though moisture may be overall lacking with the front. Cool high
pressure is expected to build in on Sunday with mostly dry
conditions and high temperatures in the low to mid 70s.

The beginning of next week looks to stay dry overall for now, but
there is quite a bit of model spread regarding where this closed
coastal low will end up. Current ensembles keep it a good distance
offshore and mostly unimpactful to our area, though a surface
boundary may sag south across the area sometime Monday. Run-to-
run fluctuations continue essentially after the frontal passage
Saturday, so stuck close to the consensus/NBM forecast here
until we can narrow down possibilities over the next several
days.
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&&

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

Rest of this afternoon (through 00Z)...VFR. Hazy skies with no
restrictions possible for KTTN/KPNE/KPHL. E winds 10 to 15 kt with
gusts up to 20 kt, diminishing to 5 to 10 kt by 00Z. Moderate
confidence.

Tonight (00Z through 12Z)...VFR initially, then MVFR CIGs likely to
develop at KTTN/KPNE/KPHL/KILG and IFR CIGs with MVFR VSBYs in fog,
stratus, and drizzle will develop at KMIV/KACY after 09Z. E winds
around 5 kt. Moderate confidence.

Wednesday (12Z through 00Z)...Any sub-VFR conditions will give way
to VFR. HZ develops in the afternoon. Cannot rule out VSBY
restrictions in smoke, but probabilities are low. E-NE winds 5 to 10
kt, increasing to around 10 kt in the afternoon. Moderate confidence.

Outlook...

Wednesday night...Sub-VFR conditions expected with low stratus and
fog, especially at I-95 terminals and KACY/KMIV. Some haze and
patchy smoke at mid-levels through the early overnight. Variable
wind less than 5 knots. Moderate confidence.

Thursday...Some early morning fog/low stratus may continue sub-VFR
conditions early, otherwise expect VFR for the remainder of the day.
Northeasterly wind 5-10 knots becoming southeasterly in the
afternoon. Moderate confidence.

Friday...VFR. Northeasterly wind 5-10 knots. Moderate confidence.

Saturday...Sub-VFR conditions possible with passage of a cold front.
Northeasterly wind increasing to 10-15 knots with gusts to 25 knots
behind the front. Low confidence.

Sunday...VFR. Northeasterly wind 5-15 knots. Low confidence.
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&&

.MARINE...
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NE winds 10 to 20 kt with gusts up to 25 kt will diminish through
this evening and will be 10 to 15 kt after midnight. On Wednesday,
winds will be NE 10 to 15 kt with gusts up to 20 kt. Seas of 5 to 7
feet will subside to 3 to 5 feet tonight through Wednesday.

Small Craft Advisory for Lower DE Bay will end at 7 pm, and sub-SCA
conditions then expected for DE Bay through Wednesday. Seas remain
elevated on northern NJ ocean waters through tonight, then seas will
be below 5 feet through Wednesday. For southern NJ and DE ocean
waters, seas remain around 5 feet through Wednesday, and SCA remains
in effect through Wednesday.

Outlook...

Thursday...No marine headlines expected. Northeasterly wind 5-10
knots. Seas 3-4 feet.

Friday...No marine headlines expected. Southeasterly wind 5-10
knots. Seas 2-3 feet.

Saturday...Small Craft Advisory conditions possible. Northeasterly
wind 5-10 knots in the morning increasing to 15-20 knots with gusts
to 25-30 knots in the afternoon. Seas 2-3 feet building to 5-7 feet
from north to south.

Sunday...Small Craft Advisory conditions possible. Northeasterly
wind 15-20 knots with gusts to 25 knots and seas 5-7 feet in the
morning. Conditions may improve later in the day.
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&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...High Rip Current Risk until 9 PM EDT this evening for NJZ014-
     024>026.
DE...High Rip Current Risk until 9 PM EDT this evening for DEZ004.
MD...None.
MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ431.
     Small Craft Advisory until 6 AM EDT Wednesday for ANZ450-451.
     Small Craft Advisory until 8 PM EDT Wednesday for ANZ452>455.

&&

$$
SYNOPSIS...Brudy
NEAR TERM...MPS
SHORT TERM...Brudy
LONG TERM...Brudy
AVIATION...Brudy/MPS
MARINE...Brudy/MPS