Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 270803
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
403 AM EDT Wed Mar 27 2024

.SYNOPSIS...
High pressure will recede away from the area toward the
northeast today. A frontal boundary will gradually approach our
region from the west tonight, then a wave of low pressure will
track northeastward off the coast on Thursday resulting in a
period of unsettled weather. A weak clipper system may move
through on Saturday, otherwise dry and seasonable conditions
will prevail over the weekend. Another rain making system will
impact the region early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
The day will start off with high pressure still generally in
control, centered over the Canadian Maritimes, with ridging
still extending southwestward across the Mid-Atlantic. By the
end of the day, low pressure developing along the coast of the
Carolinas will begin taking aim at our region, as high pressure
gives way. This low will be triggered in part by a deep upper-
level trough approaching from the Midwest, with a slowing cold
front trailing a surface low lifting north of the Great Lakes.
As colder air pushes across the Appalachians tonight with that
front, frontogenetic forcing will increase along a tightening
baroclinic zone, as the low to the south advects warmer, moist
air northward along the coast. That combined with additional
forcing mechanisms in the form of vorticity advection ahead of
the upper-level trough, and upper-level divergence at jet-stream
level, will result in steadier rain developing, especially late
tonight from the I-95 corridor southeastward.

Prior to that steadier rain developing, today will start off
with just a few showers clipping areas north and west of the
Lehigh Valley, while onshore flow will continue to bring
overcast skies to our entire area. While yesterday turned out
surprisingly sunny and mild, there is much more confidence that
will not be the case today, as the cloud layer is more well-
established with a strong inversion and very light winds in the
lower atmosphere to aid in any mixing or erosion of the layer.
That said, it is a milder start to the day, with lows mainly in
the low 40s this morning, so most places should still see us
reach the low 50s this afternoon outside of the immediate shore
and the Poconos. Those showers will gradually spread eastward,
becoming more numerous across SE PA by this afternoon, with
scattered light showers spreading across much of the rest of our
area for the second half of the day. Expect only a tenth or two
of an inch at most northwest of the I-95 corridor through early
evening, with less to the southeast. Later tonight, with the
aforementioned steadier rain, amounts of a half-inch to one inch
can be expected from I-95 southeastward, with lighter amounts
northwest as better forcing and deeper moisture focuses along
the coastal plain. Winds today and tonight will be very light,
even calm at times.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Troughing shifting eastward toward the East Coast will amplify
by late Thursday. Some subtle jet dynamics will be at play with
a developing low pressure system, which will have implications
on direct sensible impacts we receive from the system Wednesday
through Thursday night. Surface low pressure located near the
Carolina coast early Thursday will lift northeastward and
eventually offshore later Thursday along a baroclinic zone in
place due to a stalled frontal boundary. There remains a notable
amount of spread and lack of discernible consensus in the
deterministic and ensemble guidance regarding where the heaviest
axis of QPF will be located. The synoptic forcing modeled does
not really support a far eastward solution as some guidance has
suggested. Thus, we`ve held the QPF forecast fairly close to the
previous update.

The strongest forcing with this system will arrive 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 evening. Currently, QPF ranges from
0.25-0.5" in the far interior areas of eastern PA and northwest
NJ, to 1-1.5" along I-95 and the interior coastal plain, to near
2" along the coast. This forecast is still 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, however the likelihood of any significant
flooding with this event is low (10-20%).

Winds will settle out of the north to northwest on Thursday and
increase into Thursday night to near 15-25 mph by Friday 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 for low temperatures through Friday night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
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 mostly cloudy skies, however it will not be
the washout last Saturday was and the system overall does not
look very impactful. More widespread rain and a period of
unsettled weather looks likely as early as Monday, as most of
the deterministic guidance has an upper level low diving down
from Canada. A lot of timing and impact discrepancies with this
system but it bears watching over the next several days.

&&

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

Today...Ceilings are leveling off between 007-012 this morning
for most of the area; locally lower along the immediate coast.
Some modest improvement can be expected later this morning
through early afternoon, but would not expect higher than 020
for the vast majority of our region. VSBY is mainly
unrestricted, and that should continue to the case into the
early evening, even as some light showers spread eastward toward
I-95 by this afternoon. Very light winds, tending easterly but
variable or calm at times. Moderate confidence.

Tonight...CIGs will lower into the IFR category this evening,
with potential for occasional LIFR toward midnight. VSBY will
initially be VFR but should also lower to IFR in most locations
by dawn as steadier rain develops after midnight, especially
from I-95 southeastward. Winds remain very light. Moderate
confidence.

Outlook...

Thursday...MVFR and IFR conditions likely with rain. North to
northwest winds 10-15 kts. Moderate confidence.

Thursday night through Sunday...Mainly VFR. Northwest to west
winds during this period, strongest on Friday with gusts near
30-35 kts possible. Light rain possible Saturday or Saturday
night.

&&

.MARINE...
Onshore flow will persist today, but winds are settling down to
around 10 kt from the NE this morning, and will only tend to
ease further later today, tending easterly at times. Winds
remaining NE 4-8 kt tonight. Seas are still 5-7 ft with a
lingering easterly swell, resulting in an ongoing Small Craft
Advisory for all ocean zones. That may drop below 5 ft and end
the advisory toward the predawn hours on Thursday.

Outlook...

Thursday...No marine headlines anticipated. Rain will restrict
visibility to 1-3 NM.

Thursday night through Friday...North to northwest winds
increasing with gale force wind gusts possible. A Gale Watch is
in effect for this period.

Saturday and Sunday...Some gusts near 25 kts possible early
Saturday, otherwise no marine headlines anticipated.

&&

.TIDES/COASTAL FLOODING...
The low pressure system that is lingering well off the coast
resulting in an extended duration of long period swells, rough
surf, and widespread minor tidal flooding impacting the Atlantic
coast is finally losing its influence on our coastal areas.

Coastal Flood Advisories remain in effect for the tidal
Delaware River as widespread minor flooding is expected with the
high tide early this morning. A Coastal Flood Advisory goes
into effect for the Chesapeake Bay communities within the
Eastern Shore of Maryland for this morning`s high tide as
widespread minor tidal flooding is expected there as well.

Tidal surge anomalies have started to recede due to the
lessening influence of the offshore storm and moving further
away from the full moon. Following the early morning high tide
cycle, coastal flood impacts will cease for the most areas. The
exception will be for the back bays in Ocean and Sussex (DE)
Counties, where it will take some time for the water to drain.
The advisory was extended into this afternoon for these areas.
Additionally, there is some potential for lingering minor tidal
flooding near the times of high tide through the week along the
tidal Delaware River. An additional advisory may be needed for
the early Thursday morning high tide. But otherwise, no further
impacts/threats are expected.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Coastal Flood Advisory until 7 AM EDT this morning for PAZ070-
     071-106.
NJ...Coastal Flood Advisory until 4 PM EDT this afternoon for
     NJZ020-026.
     Coastal Flood Advisory until 7 AM EDT this morning for
     NJZ017>019.
DE...Coastal Flood Advisory until 4 PM EDT this afternoon for
     DEZ003-004.
MD...Coastal Flood Advisory from 8 AM this morning to noon EDT
     today for MDZ012.
     Coastal Flood Advisory until 10 AM EDT this morning for MDZ015-
     019-020.
MARINE...Gale Watch from Thursday evening through Friday afternoon for
     ANZ430-431-450>455.
     Small Craft Advisory until 6 AM EDT Thursday for ANZ450>455.

&&

$$

SYNOPSIS...Staarmann
NEAR TERM...Dodd
SHORT TERM...Staarmann
LONG TERM...Hoeflich/Staarmann
AVIATION...Dodd/Staarmann
MARINE...Dodd/Staarmann
TIDES/COASTAL FLOODING...Staarmann


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