-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 242254
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
654 PM EDT Wed Apr 24 2024

.SYNOPSIS...
A cold front will cross our region this afternoon and evening,
then high pressure arrives from the Great Lakes later tonight
and Thursday before shifting to our northeast and east during
Friday. A warm front should lift north of our area later
Saturday, then a cold front gradually approaches later Monday
before moving across our area later Tuesday.

&&

.NEAR TERM /THROUGH THURSDAY/...
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Any showers out there continue to taper off, and all should be
over by 8 pm. Cold front continues to work its way through the
region. Otherwise, Canadian high pressure builds southward
reinforcing the cool, dry air mass pushing southward. It should
become mainly clear over NE PA into NW NJ with still some
lingering cloud cover farther south. A Freeze Warning is in
effect for the Lehigh Valley into NW NJ where temperatures are
expected to fall to around or below freezing and the growing
season has started. Meanwhile a Frost Advisory is in effect for
Berks, Upper Bucks, and Hunterdon Counties where lows will be
mainly in the mid 30s. Winds and relatively drier air could
limit frost from being too extensive but decided to err on the
side of caution with the advisory.

For Thursday, high pressure will dominate over the mid Atlantic
and northeast. A notably colder and dry air mass will be in
place though despite a mainly sunny sky for most with high
temperatures mostly in the 50s. An onshore wind will keep it
even cooler along the coastal areas.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
An upper-level trough is forecast to be across the Northeast and Mid-
Atlantic regions through Thursday night, then it shifts to our east
to start Friday. Strong surface high pressure centered over the
Great Lakes Thursday builds eastward through Thursday night, then
shifts off the New England coast during Friday.

As the center of surface high pressure slides to our north but
extends over our area Thursday night, a cold night is forecast
with little to no wind and a dry air mass. Much of the area will
drop into the low to mid 30s with some potential for some
locations getting a little colder. Areas of frost are probable,
and frost and/or freeze headlines are quite possible.

After a cold start Friday morning, the surface flow should
start to become more southeast to even south-southeast. This
will still keep some marine influence across the area, however
the air mass is forecast to start modifying and therefore high
temperatures will be in the upper 50s to low 60s, a bit higher
compared to Thursday. It will still be cooler though closer to
the coast given the onshore flow. Another chilly night Friday
night, though slightly warmer compared to Thursday night as well
with low temperatures in the upper 30s to low 40s. This would be
sufficiently warm enough to mitigate widespread frost
development, but patchy frost remains possible.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Summary...A significant warm-up probable over the weekend and early
next week. Some shower chances later in the weekend and/or early
next week.

Synoptic Overview...A building ridge arrives from the west as an
upper-level trough lifts across the Plains and into the Midwest
through Monday. As the influence of the upper-level trough gets
closer late Monday and Tuesday, the ridge shifts to our east. The
timing of this however is less certain as the upper-level trough in
the Plains may become a closed low which tend to be slower moving
(may be two separate systems). This will also have an impact on our
precipitation chances Sunday through Wednesday. The overall
pattern though continues to suggest that a much warmer air mass
will overspread our region Sunday through the middle of next
week.

For Saturday...A building ridge starts to arrive from the west and
this will initially keep a cool air mass across our region. However,
some warm air advection starts as more of a southerly return flow
starts initiates. In addition, a warm front should lift to our north
later Saturday. While a few showers cannot be ruled out with this
warm front, mainly northwest of the I-95 urban corridor, the
probability looks to be on the low side at this point. Cloud
cover should dominate the sky during at least a portion of
Saturday due to some increasing warm air advection and some
increase in moisture ahead of and with the warm front. The
timing of this warm front looks to be driven by a lead upper-
level trough or closed low that lifts across the Midwest which
also has a surface low with it.

For Sunday through Wednesday...As an upper-level trough
continues to lift up across the Plains and Midwest, the
downstream ridge axis slides across our region Sunday and Monday
before shifting offshore into Tuesday. While the initial
trough looks to continue to lift to the northeast across
eastern Canada, if the secondary trough forms, it may not push
through our area until Wednesday. Surface low pressure tracks
across the Great Lakes and into adjacent Canada Monday into
Tuesday, and its associated cold front approaches our area
Monday night. The actual cold front looks like it will not slide
across our area until later Tuesday. The details however will
depend on the timing and amplification of the trough. In
addition, high pressure sliding east of Hudson Bay Canada Monday
into Tuesday may send a cold front down across New England and
closer to our area. While this front may settle into at least
our northern areas Monday night into Tuesday, it should not get
too far south given the continued southerly flow ahead of the
aforementioned trough from the west. Plenty of warm air with
increasing dew points are therefore currently forecast across
the area, with high temperatures for much of the area in the 70s
to even some low to mid 80s. The surface flow however looks
more south or even southeast at times and this will keep it
several degrees cooler at the coastal communities compared to
farther inland. There is a chance for some showers and
thunderstorms, especially Tuesday and Tuesday night, with PoPs
mainly in the 30-50% range during this period. With the
possibility of a secondary front, slight chance PoPs (15-25%)
linger into Wednesday.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Tonight...VFR. NW winds 10 to 15 kt with gusts up to 20 kt,
becoming NE around 10 kt through the overnight. High
confidence.

Thursday...VFR. Northwest winds generally 5 to 10 knots before
diminishing late day.

Outlook...

Thursday night and Friday...VFR.

Saturday...A period of near MVFR ceilings possible, most likely
Saturday night, otherwise mainly VFR.

Sunday and Monday...VFR conditions anticipated.
-- End Changed Discussion --

&&

.MARINE...
Seas will remain elevated through tonight before slowly
starting to come down through Thursday. For this reason, the
Small Craft Advisory was extended to 16z Thursday for our
northern ocean zone off the coast of Monmouth County with it
running until 22z Thursday for the remaining ocean zones.
Northeast winds will increase later tonight to a brief period of
SCA levels of 15 to 20 gusting up to 25 knots but should
otherwise be sub SCA.

Outlook...

Thursday night through Monday...The conditions are anticipated
to be below Small Craft Advisory criteria.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Freeze Warning from 3 AM to 9 AM EDT Thursday for PAZ061-062.
     Frost Advisory from 3 AM to 9 AM EDT Thursday for PAZ060-105.
NJ...Freeze Warning from 3 AM to 9 AM EDT Thursday for NJZ001-007-
     008.
     Frost Advisory from 3 AM to 9 AM EDT Thursday for NJZ009.
DE...None.
MD...None.
MARINE...Small Craft Advisory until noon EDT Thursday for ANZ450.
     Small Craft Advisory until 6 PM EDT Thursday for ANZ451>455.

&&

$$

SYNOPSIS...Fitzsimmons/Gorse
NEAR TERM...Fitzsimmons/MPS/RCM
SHORT TERM...AKL/Gorse
LONG TERM...AKL/Gorse
AVIATION...AKL/Fitzsimmons/MPS/RCM
MARINE...AKL/Fitzsimmons/RCM