Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 290818
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
418 AM EDT Fri Mar 29 2024

.SYNOPSIS...
Low pressure moves up toward Nova Scotia early this morning as
cold front moves off the coast, then high pressure briefly
builds in later today. A weak clipper system passes through
late on Saturday with drying expected on Sunday. An area of low
pressure will develop over the Central Plains on Monday with a
warm front extending east into the Mid- Atlantic. This will lead
to unsettled conditions through at least the middle portion of
next week before drying out on Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
A sunny, but dry and windy day is expected.

Longwave troughing will push offshore as ridging builds to our west.
High pressure will build to our southwest today as strengthening low
pressure pushes toward Nova Scotia. Cold advection will be underway
much of the daytime period. THis combined with a modest pressure
gradient will result in deep efficient boundary layer mixing. The
result will be a dry and windy day. Northwest winds will increase
later this morning to around 15-20 mph with gusts near 30 mph. Some
peak gusts near 35 mph are possible across the higher elevations and
near the coast. Temperatures will climb well into the mid to upper
50s by this afternoon, though the dry wind will make it feel a bit
chilly despite the plentiful sunshine.

The winds will diminish this evening and shift more westerly as
boundary layer mixing wanes. There will be a persistent gradient
wind overnight near 10-15 mph though. This gradient and the winds
will prevent much radiational cooling despite the very dry airmass
and dewpoints in the 20s. We should see low temperatures mainly in
the mid to upper 30s under clear skies.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
The forecast for the weekend remains largely unchanged, with
some showers producing light rainfall on Saturday, followed by a
dry and milder day on Sunday. With weak ridging extending
northward across the Mid-Atlantic briefly Saturday morning, with
high pressure centered near Florida, we will see some sunshine
and fairly cool temperatures in the morning, warming well into
the 50s toward midday. Some low 60s will be possible around
southern NJ into the Delmarva. Model guidance continues to hone
in on a weak area of low pressure tracking across PA from the
lower Great Lakes, associated with a weak shortwave trough.
Models differ on the exact location and extent of shower
activity, but the consensus favors up to a tenth of an inch of
rainfall, mainly in the afternoon, with the `higher` amounts
across SE PA. Showers will taper off as the low passes offshore
Saturday evening. That will be followed by a fairly mild night
as some clouds and a westerly breeze keeps lows in the 40s. Mid
and upper-level ridging will expand eastward from the central US
to the East Coast on Sunday, and combined with a northwesterly
downsloping breeze off the Appalachians and partial sunshine,
highs in the 60s will result. Sunday may be the nicest day of
the entire forecast period through next week. Clouds will
thicken Sunday night with a 30-60 percent chance of showers
after midnight, especially south of ABE to TTN.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
An extended period of fairly cloudy, wet weather will commence
for the start of the new week, though Monday does not look like
a complete washout. Strong low pressure lifting out of the
Plains ahead of an upper-low ejecting out of the Southwestern US
will be the main cause of our wet weather for the week ahead.
Initially on Monday though, a weaker wave of low pressure
tracking along the tightening baroclinic zone extending
eastward from the stronger low will be the main forcing
mechanism for wet weather here. That should result in only
periodic, relatively light rainfall, and portions of the area
may just have a cloudy, occasionally drizzly day, depending on
exactly where the stronger forcing sets up near the tightening
baroclinic zone. Temperatures will remain mild, but cooler than
Sunday, with mainly 50s for highs.

Heading into later Monday night and Tuesday, as strong low
pressure heads for the lower Great Lakes or the Ohio Valley, a
warm front will attempt to lift northward through our region,
with strong isentropic lift and some steadier, heavier rain.
Guidance disagrees how far north that front will make it, before
a coastal low develops near or region heading into Wednesday.
That is clear from the wide spread in NBM temperature guidance
at PHL on Tuesday, ranging from the low 50s to mid 60s for the
25th to 75th percentile high temperatures.

Enough instability, at least of the elevated kind, may be
present for some rumbles of thunder Tuesday afternoon through
Tuesday night, particularly across the Delmarva where the warm
sector is most likely to make it through. Once the coastal low
takes over and tracks northeastward toward southern New England
on Wednesday, rain will become more showery, as the low wraps
colder and drier air into our region. Rainfall amounts from the
Monday through Wednesday timeframe look to be around 1.5 to 2
inches or so on average, but with that falling over an extended
period of time, the threat of flooding may be limited. Still,
Tuesday and Wednesday will bear watching as we get closer,
particularly if the rainfall turns more convective. Thursday
should turn drier, cooler and windy as potentially intense low
pressure wraps up off the New England coast, with perhaps still
some clouds and showers toward the Appalachians. The airmass may
turn cold enough even for some wet snow showers around the
Poconos.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE,
KRDG, KILG, KMIV, KACY and surrounding areas.

Through 12Z...VFR with clearing skies. Northwest winds 10-15 kts
with some gusts near 20 kts possible at times. North to northwest
winds near 2kft increasing to 35-40 kts may lead to some LLWS,
especially where gusty winds do not develop at the surface. High
confidence on prevailing conditions.

Today...VFR. Northwest winds increasing to 15-20 kts with gusts near
25-30 kts. High confidence.

Tonight...VFR/SKC. Winds diminishing by 00Z and shifting more
westerly for the overnight period near 10-15 kts. High confidence.

Outlook...

Saturday: Mainly VFR, with brief MVFR possible with some
scattered showers.
Sunday: VFR.
Monday: Chance of rain, Sub- VFR conditions possible.
Tuesday: Rain likely with MVFR or IFR conditions.

&&

.MARINE...
North to northwest winds will continue to increase through dawn to
around 20-25 kts with wind gusts near 30-35 kts forecast. Seas will
also increase to around 4-7 feet. Will keep the Gale Warning in
effect through this morning for all Atlantic and Delaware Bay
coastal waters. A Small Craft Advisory will be needed following the
Gale Warning through the remainder of today and perhaps even through
tonight as gusts will remain near 20-25 kts and seas near 4-5 feet.

Outlook...

Small Craft Advisory conditions may linger into Saturday morning
over the ocean with some leftover 5 ft seas and WNW gusts 20-25
kt. Otherwise expect generally W to SW winds 10-15 kt later
Saturday tending WNW on Sunday, with seas in the 2-4 ft range.
Some showers will be possible late Saturday, otherwise expect
relatively fair weather, with a pleasant day on Sunday. A warm
front will bring increasing chances for rain and lower VSBY on
Monday and especially Tuesday into Wednesday. Winds Monday and
Tuesday turn easterly 10-15 G 20 kt, potentially stronger on
Wednesday as a coastal low develops and lifts northeastward. SCA
conditions possible late Tuesday into Wednesday, and possibly a
period of gales mid to late week, especially in the wake of
that coastal low.

&&

.FIRE WEATHER...
While soils remain saturated from recent rains, gusty northwest
winds near 15-20 mph will develop today along with relative
humidity values dropping to near 25-30% across much of the area.
These conditions may result in an increased risk of fire
spread, especially this afternoon. Lighter winds near 10-15 mph,
relative humidity near 35-40%, and a chance of light rain are
forecast for Saturday.

&&


.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Gale Warning until 10 AM EDT this morning for ANZ430-431-
     450>455.

&&

$$

SYNOPSIS...DeSilva/Staarmann
NEAR TERM...Staarmann
SHORT TERM...Dodd/DeSilva
LONG TERM...Dodd/DeSilva
AVIATION...Dodd/Staarmann
MARINE...Dodd/Wunderlin
FIRE WEATHER....Staarmann


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