Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 260746
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
346 AM EDT Tue Mar 26 2024

.SYNOPSIS...
Strong high pressure is centered across the Canadian Maritimes,
however it extends southwestward across our area. This will
remain in place through tonight. Meanwhile, low pressure
continues to meander around well offshore. A cold front is
forecast to cross our region Tuesday night, then it becomes
nearly stationary along the coast. Low pressure tracks northward
along this front Thursday and Thursday night before moving out
to sea on Friday. A weak clipper system may move through on
Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure centered over the Canadian Maritimes, with a
ridge extending southward along the East Coast to the Carolinas
will remain in control of our weather today. This will join
forces with an upper-level ridge also amplifying along the East
Coast, to result in continued dry and stable conditions through
sunset.

However, a surge of shallow low-level moisture circulating
around cut-off low pressure well offshore is pushing onshore,
manifesting in the form of a layer of marine stratus. This will
quickly pass I-95 toward sunrise, and may only allow for a
couple hours of partial sunshine toward the Lehigh Valley
northwestward before clouds advance westward. While this cloud
layer may lift a little today, and should not carry any
precipitation aside from a few drips of drizzle right along the
coast, do not expect it to go anywhere for the rest of today.
This will result in a slightly cooler day, with afternoon highs
across most of our area in the upper 40s to low 50s. Winds will
be fairly light and onshore, but will add to a bit of a chill
along the coast.

As we head into tonight, low pressure lifting across Lake
Superior will send a cold front toward the Appalachians by
Wednesday morning, while the trailing end of a weak warm front
will near northwestern portions of our region. CAMs and the NAM
are more bullish with at least some light showers pushing in
during the predawn hours Wednesday, perhaps amounting to a few
hundredths of an inch of rain by sunrise from northwest of
Reading to Allentown. As ceilings lower and boundary layer
moisture increases with continued light onshore flow, some
patchy mist or light fog may develop in spots toward morning,
but visibility should stay at or above 1 to 3 miles. It will be
a mild night, with lows staying in the 40s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Troughing across the Southwest will amplify and shift eastward
this week toward the East Coast by late Thursday. Some subtle
jet dynamics will be at play with a developing low pressure
system, which will have implications on direct impacts we
receive from the system Wednesday through Thursday night.
Surface low pressure should develop across the Southeast
Wednesday and then lift northeastward and eventually offshore on
Thursday along a baroclinic zone in place due to a stalled
frontal boundary. The latest trend in some of the deterministic
and ensemble guidance was for a farther eastward and thus drier
solution. However, the synoptic forcing modeled does not exactly
support this trend. There was no significant changes to the
forecast with this update aside from some adjustments to the
PoPs.

Some areas of light rain should develop on Wednesday, primarily
inland where PoPs are higher during the daytime. This will be
in response to the initial height falls and diffluence aloft.
Stronger forcing will arrive late in the night and especially by
early Thursday as the surface low begins making its closest
pass to our area. This is when more widespread, steadier/heavier
rain is currently anticipated. The system and rain will depart
late Thursday and Thursday night. Currently, QPF ranges from
0.5-1" in the far interior areas of eastern PA and northwest NJ,
to 1-1.5" along I-95, to near 2" along the coast. This forecast
is subject to change though, given the aforementioned subtle
synoptic features at play. This will have implications on an
impacts due to flooding as soils remain very saturated from the
weekend rain. This rain may lead to additional rises on creeks,
streams, and river across the area.

Winds will be light on Wednesday favoring an easterly
direction. As the departing system strengthens and high pressure
pushes into the area, winds will then settle out of the north
to northwest on Thursday and increase into Thursday night to
near 15-20 mph with gusts up to 35 mph possible. Temperatures
will remain mild in the 40s and 50s for much of this period,
although the cold advection beginning Thursday night will drop
us back into the mid to upper 30s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Long wave ridging building across the central CONUS should
result in seasonable temperatures and relatively benign weather
conditions this weekend into Monday of next week. A quick moving
shortwave trough may impact the area Saturday with a 20-30%
chance of rain and increasing clouds, however it will not be the
washout last Saturday was. The next system looks to impact the
area late Monday into Tuesday with more widespread rain
possible.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Through 12Z...MVFR ceilings around 020-025 will continue to
advance westward to past I-95, but may not reach RDG and ABE
until a little later this morning. Surface VSBY under the
stratus layer will remain mainly unrestricted, with dry boundary
layer air remaining in place. Winds mainly ENE 3 to 6 kt. High
confidence.

Today...MVFR ceilings, possibly lifting to low VFR in the
afternoon at least away from the coast. ACY may drop and even
remain below 020 today. VSBY should remain mainly unrestricted.
Winds E/NE 5-10 kt. Moderate confidence.

Tonight...MVFR ceilings likely dropping below 020 in the
evening, and probably down to IFR by Wednesday morning. Some
light rain showers possible at ABE/RDG after 06Z. VSBY may drop
into the MVFR range toward morning in light BR, especially
outside of the I-95 sites. Moderate confidence.

Outlook...

Wednesday through Saturday...Overall, periods of sub-VFR
conditions, mostly Wednesday through Thursday evening in periods
of moderate to heavy rain late Wednesday through Thursday. VFR
returns on Friday. Scattered SHRA may result in brief sub- VFR
conditions Saturday. Light east winds on Wednesday becoming
10-20 kts and gusty from the north to northwest Thursday through
Saturday.

&&

.MARINE...
Some gusts to around 20 kt or so may continue early this
morning around the mouth of Delaware Bay, but conditions will
remain below Small Craft Advisory criteria today. Meanwhile,
winds will continue to gust to 25 kt or so through early this
morning across the open ocean, but gradually ease through this
evening.

However, a large storm well offshore will meander today. Along
with the elevated, albeit lessening northeasterly winds, a
substantial easterly swell will persist today, with seas of 8-10
ft much the day, only gradually lowering into the 5-7 ft range
later tonight. Small Craft Advisories will remain up as a
result.

Outlook...

Wednesday through Saturday...SCA conditions continue into at
least Wednesday due to elevated seas, then seas diminish
Wednesday night. A storm will develop and lift along the coast
Wednesday night through Thursday night, departing on Friday.
Strong NW winds develop Thursday night and continue into
Saturday. SCA conditions expected with marginal gales possible
on Friday.

&&

.TIDES/COASTAL FLOODING...
A low pressure system lingering well off the coast will result
in an extended duration of long period swells and rough surf
impacting the Atlantic coast. Widespread minor flooding has
occurred with the nighttime high tide, including the tidal
Delaware River. This may be due to increase inflow from the
recent heavy rains.

Widespread MINOR flooding still looks likely across most of the
region except for the Chesapeake Bay shore, though even there
spotty minor is possible. It does look like it may linger
through Tuesday evening`s cycle as well, so the new advisories
go until after midnight Tuesday night.

Additionally, the bottling of water up at the mouth of the
Chesapeake may be holding water in there, and that may be
increasing the minor flood risk across our portions of the bay
as we head into Wednesday. Will be watching that closely as
well.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory until 4 AM EDT Wednesday for NJZ016.
     Coastal Flood Advisory until 2 AM EDT Wednesday for NJZ012>014-
     020>027.
DE...Coastal Flood Advisory until 4 AM EDT Wednesday for DEZ001.
     Coastal Flood Advisory until 2 AM EDT Wednesday for DEZ002>004.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT Wednesday for ANZ450>455.

&&

$$

SYNOPSIS...Gorse/MPS
NEAR TERM...Dodd
SHORT TERM...Staarmann
LONG TERM...Staarmann
AVIATION...Dodd/MPS/OHara
MARINE...Dodd/MPS/OHara
TIDES/COASTAL FLOODING...WFO PHI


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