Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 291340
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
940 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/...
Forecast running on track. No significant changes made to the
forecast.

Otherwise, a sunny, but dry, and windy day on tap.

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 /14Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

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 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 around 20-25 kts with
wind gusts near 30 kts much of the daytime period. Seas will
increase to around 4-7 feet. The Gale Warning was canceled and
replaced by a Small Craft Advisory. Gusts will remain near
20-25 kts and seas near 4-5 feet through tonight.

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.
Peak wind gusts around 25-35 mph can be expected as well. 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...Small Craft Advisory until 10 PM EDT this evening for ANZ430-
     431.
     Small Craft Advisory until 6 AM EDT Saturday for ANZ450>455.

&&

$$

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


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