Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 260153
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
953 PM EDT Mon Mar 25 2024

.SYNOPSIS...
Strong high pressure is centered across the Canadian Maritimes,
however it extends southwestward across our area. This will
generally remain in place into Tuesday night. 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 TUESDAY/...
As of 930 PM, a clear sky continues across the region. A light
to calm wind combined with the clear sky and low dew points has
resulted in temperatures dropping quickly thus far across much
of the area. Made some adjustments to the hourly temperature and
dew point grids based on the latest observations and trends.
The 00z Wallops Island (KWAL) RAOB sampled a very dry atmosphere
in place. The satellite imagery however is showing some lower
clouds well offshore sliding west-southwest. It is that layer of
increased moisture that is forecast to advect to the coast and
beyond overnight and early Tuesday morning, bringing increasing
low clouds to our region.

Otherwise, strong high pressure continues to remain centered across
the Canadian Maritimes, however it extends southwestward across our
region. This remains in place through Tuesday. Plenty of subsidence
and dry air with the axis of this high which is resulting in a clear
sky across the area. This is forecast to change however overnight as
a marine layer moistens and advects inland through Tuesday morning
(aided by an easterly jet near 30 knots). The model guidance
indicates that a fairly narrow layer of increased moisture occurs
quickly overnight from east to west within the subsidence inversion.
This tends to result in marine stratus developing in place or
advecting in from the ocean. Therefore, continued with increasing
clouds overnight from west to east. No rain is expected given a thin
moisture layer and model soundings showing plenty of dry air above
the inversion. However, patchy drizzle cannot be ruled out around
daybreak especially closer to the coast, although the same model
soundings also show some dry air remaining below cloud base. Low
temperatures will mostly be in the mid/upper 30s for the coastal
plain, and upper 20s to low 30s to the west and northwest.

As we go through Tuesday, the onshore flow will continue so there
will be a mostly cloudy sky across the area. The low clouds may try
and thin and lift a little given the stronger March sun, and
assuming the moisture layer in thin. The clouds and breeze from the
northeast and east will keep temperatures on the cooler side for
late March (the higher winds closer to the coast). High temperatures
mostly near 50 degrees, cooler in the higher terrain and along
the coast.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
A weak cold front approaches Tuesday night and works its way
through the region late at night and into Wednesday morning. The
front actually washes out and becomes nearly stationary along
the coast on Wednesday, and there is not much in the way of
colder or drier air behind it, but it will touch off some
showers with its passage late at night and into Wednesday
morning.

Another area of low pressure will organize and develop over the
Southeast U.S. on Wednesday and will track along the coast late
Wednesday and Wednesday night. Rain moves into the region after
midnight, with with an approaching upper low, and interaction
with the coastal front, the low will intensify during the day
Thursday. Rain becomes moderate to heavy at times, especially
over Delaware and New Jersey, on Thursday, and another 1.5
inches or so of QPF will fall.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Coastal low pressure off the Mid-Atlantic coast Thursday
evening will track to the east-northeast during the overnight
hours and will be offshore by Friday morning. The low then
continues to track out towards the Canadian Maritimes on Friday.
Rain tapers off through the night, and then a gusty northwest
flow sets up on Friday as a tight pressure gradient develops
between the departing low and high pressure building over the
Gulf Coast states and Southeast.

A weak clipper-like system quickly passes through the Northeast
and Mid-Atlantic over the weekend. For now, will generally
carry slight chance to low end chance PoPs for Saturday and
Saturday night. High pressure then noses in from the north and
west on Sunday, but another storm system will be gearing up to
take a shot at the Northeast and Mid-Atlantic for the start of
the new work week.

Temperatures during this period will generally be near or a
couple of degrees above normal.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Tonight...VFR clear, then clouds increase overnight with a MVFR
ceiling developing. Some local IFR ceilings possible closer to
daybreak. Northeast or east-southeast winds 4-8 knots becoming
light and variable at some terminals. Low confidence regarding
the timing of the MVFR ceilings and if IFR ceilings develop.

Tuesday...MVFR ceilings, however these may lift some in the
afternoon. Some IFR ceilings cannot be ruled out for a time
especially closer to the coast (KACY). Northeast to east winds
around 10 knots overall, becoming locally east-southeast. Low
confidence regarding IFR ceilings and if ceilings improve to low
VFR in the afternoon.

Outlook...

Tuesday night through Saturday...Overall, periods of sub-VFR
conditions, mostly Tuesday night through Thursday night, first
in fog and stratus Tuesday night, and then in periods of
moderate to heavy rain late Wednesday through Thursday night.
VFR returns on Friday. Scattered SHRA may result in brief sub-
VFR conditions Saturday. Onshore flow Tuesday night through
Thursday night, generally 10 kt or less, then gusty NW winds
develop Thursday night through Saturday.

&&

.MARINE...
As of 930 PM, opted to cancel the Small Craft Advisory for the
lower Delaware Bay. While some wind gusts to 25 knots and seas
5-6 feet may linger through Tuesday around the mouth of the bay,
the conditions are anticipated to remain below advisory criteria
across most of the zone.

Large storm well offshore will meander around through Tuesday. It
will continue to produce elevated northeasterly winds and seas
through Tuesday. The Small Craft Advisory for the New Jersey and
Delaware Atlantic coastal waters continues through at least
Tuesday.

Outlook...

Tuesday night through Saturday...SCA conditions continue
Tuesday night and into at least Wednesday due to elevated seas.
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. Surge values of 2-3 feet were
expected by tonight but have not been nearly so high. Thus,
forced tidal forecasts downward across the board and replaced
all the warnings with advisories given the poor performance to
this point.

Widespread MINOR flooding still looks likely across most of the
region except for the Tidal Delaware River and 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.

Compared to the forecast along the ocean front and bay shore,
forecasts have been underdoing water levels along the tidal
Delaware River, and its possible we may need to expand coastal
flood advisories north up the river. This may be due to increase
inflow from the recent heavy rains. 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 AM EDT Wednesday for ANZ450>455.

&&

$$

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


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