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000
FXUS61 KPHI 211046
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
646 AM EDT Sun Apr 21 2024

.SYNOPSIS...
High pressure extending eastward from the Midwest to the Mid-
Atlantic will continue to build steadily eastward toward the
East Coast through Tuesday, while low pressure passes off the
Carolinas today and tonight. A cold front will swing through our
region on Wednesday, followed by another area of high pressure
pushing southeastward from the Great Lakes Thursday and Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
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Minor tweaks to the forecast were made this morning mainly to
update temps and dew points basis current observations.
RH values across N NJ and into NE PA have risen over the past
few hours above 70-80% as dew point depressions have lowered.
Accompanied by light winds less than 5 mph, this has resulted
in patchy frost developing in these areas. The Frost Advisory
for Warren/Sussex Co. NJ remains in effect until 8 AM this
morning.

Otherwise, high pressure is building over the Central Plains
with ridging extending eastward into the Mid-Atlantic. An area
of low pressure over the Southeast will move east-northeast
south of North Carolina later today. Associated with the low
are some high clouds fanning over the area, which will increase
through the remainder of the morning resulting in a mostly
cloudy afternoon. Fortunately, the northward extent of the
precipitation shield will struggle to make much progress due to
the high to the west. Still think that a few showers could make
their way into southern Delaware this afternoon but any rainfall
should not total more than a few hundredths of an inch. High
temperatures will be in the mid to upper 50s for most; with only
40s up in the Poconos.

Clouds quickly depart during the evening hours from northwest to
southeast giving way to clear skies overnight as the low moves away.
Winds are anticipated to be very light to near calm at times, so it
is expected that the boundary layer will decouple quite easily with
lows mostly in the low to mid 30s. With lower dew point depressions
tonight and expected RH values greater than 70%, areas of
patchy frost will be present early Monday morning. Greatest
confidence is across northern NJ and into the Lehigh Valley
where the growing season is now active. However, with frost
advisories currently in effect this morning, have opted to leave
any issuance of frost headlines for tonight up to the next
forecast shift.
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&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Surface high pressure centered over the lower Mississippi River
Valley with ridging extending northeastward toward the Mid-
Atlantic on Monday will shift eastward to the East Coast, with
the ridge axis pushing offshore on Tuesday. This will ensure dry
and quiet weather across our region, with stable atmospheric
conditions and mostly sunny skies. With a very dry airmass in
place along with the clear skies, nights will favor radiational
cooling and low temperatures dropping into the 30s outside of
the immediate coast and right around Philadelphia. Some patchy
frost will subsequently be possible once again early Tuesday
morning, from the Lehigh Valley north and northeastward, as well
as locally even around the Pine Barrens in southern NJ.
Meanwhile afternoons will be fairly warm with highs in the low
60s Monday rising to the upper 60s for Tuesday. That warming
will occur as a cool northwest breeze on Monday swings around
the southerly on Tuesday. Clouds will increase Tuesday night as
low pressure tracking across Quebec and northern New England
swings a sharp cold front toward our region. Showers may push
southeastward down to I-95 by dawn on Wednesday. That will
result in much milder nighttime and early morning temperatures
compared to the previous few nights, though.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Models are in good general agreement with a dynamic upper-level
trough swinging quickly east-southeastward from the Great Lakes
across the Northeast and mid-Atlantic on Wednesday. A tightly-
wound, cold late-season upper-level close low is progged to drop
in from Quebec across northern New England to the Canadian
Maritimes Wednesday night into Thursday. At the surface, this
will manifest in intensifying low pressure tracking from near
northern New York state Tuesday night to the Canadian Maritimes
by Wednesday night, with an attendant sharp cold front pushing
through our region on Wednesday. This system will lack much in
the way of moisture without a tap to Gulf moisture, and
dewpoints may struggle to even reach 50F, so do not expect much
rainfall. Perhaps less than a quarter-inch in most cases.
However, the dynamic forcing along with rather strong winds
aloft and shear may take advantage of just enough instability
for some thunderstorms. The strength and coverage of any storms
will depend somewhat on the timing of the front relative to peak
heating on Wednesday; if there isn`t much sunshine preceding
frontal passage, then that will limit the strength and coverage.
For now we just have a slight chance mainly from Philly
northward. In any case, expect breezy conditions on Wednesday
with challenging high temperatures; possibly reaching near 70F
ahead of the front from Philly southeastward (again, depending
on the timing of the FROPA), while the Poconos may struggle to
reach the low 50s.

Heading into Thursday, cool Canadian high pressure will drop
across the Great Lakes toward the mid-Atlantic, ensuring dry and
sunny weather. Temperatures will start off cool with a threat
for some patchy frost in outlying areas, then struggle to reach
60F in most spots. Highs will moderate through the 60s Friday
and Saturday, while lows stay potentially frosty in the cooler
spots. A warm front may bring some cloudy skies with showers or
just a steady light rain in on Saturday.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Saturday...VFR expected. Mostly BKN CIGs around 25000 feet in
the morning, lowering to around 7000-12000 feet after 15-16Z.
Westerly winds around 7-12 kt. High confidence.

Tonight...VFR expected. Skies scattering out becoming SKC after 04Z.
Northwest winds around 5 kt or less. High confidence.

Outlook...

Monday and Tuesday...VFR.

Wednesday...MVFR to possibly IFR conditions at times, as a cold
front brings showers and a wind shift from southerly to W/NW.

Thursday...VFR.
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&&

.MARINE...
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No marine headlines are in effect through tonight. Winds may
occasionally gust up to 20 kt early this morning, but will
generally remain around 10-15 kt through tonight. Seas around
2-3 feet.


Outlook...

Monday...NNW winds around 10 kt shifting around to southerly in
the afternoon. Seas around 2 ft.

Tuesday...SSE winds increasing to 10-15 kt in the afternoon with
some gusts around 20 kt possible. Seas 3 to 4 ft.

Wednesday...Small Craft Advisory conditions possible. Southerly
winds around 15 kt gusting to 25 kt, shifting to the W/NW later
in the day as a cold front swings through. Seas 4 to 5 ft.

Thursday...SCA possible, especially early. NW winds 15 kt with
gusts to 25 kt possible early, easing later on. Seas 3 to 5 ft.
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&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Frost Advisory until 8 AM EDT this morning for NJZ001-007.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...AKL
NEAR TERM...DeSilva
SHORT TERM...Dodd
LONG TERM...Dodd
AVIATION...Dodd/DeSilva
MARINE...Dodd/DeSilva