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000
FXUS61 KPHI 241850
AFDPHI

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

.SYNOPSIS...
A cold front will cross our region during today, 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/...
245 PM...As of this hour a cold front was moving south and
eastward into eastern PA and northern NJ with this feature
extending south and westward from an area of low pressure over
Atlantic Canada. The front, along with an associated upper level
trough combined with diurnal heating has brought a fair amount
of cloud cover due to Cu development and there are some isolated
to scattered showers around. There`s even been a few rumbles of
thunder as well over SE PA. The chance for showers will
continue through the afternoon as the front moves through with
the limiting factors for these being more widespread being lack
of moisture and that the better upper level forcing is just
about to move out. Therefor POPs are only in the 20 to 30
percent range or even a bit lower over southern parts of our
forecast area. Otherwise, breezy NW winds will continue this
afternoon with generally falling dew points as the front ushers
in drier air.

Tonight, 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.

&&

.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 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, however as the air mass
continues to moderate the temperatures should be mild enough to
keep frost not a concern at this point.

&&

.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 Tuesday. The overall pattern
though continues to suggest that a much warmer air mass will
overspread our region Sunday through early 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, 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, some increase
in moisture, plus 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. As we start to get into the warm sector, the clouds
should clear from south to north especially at night.

For Sunday through Tuesday...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. 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 may
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 to 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 Monday and Tuesday, however
the probabilities look to be on the lower side as of now.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Rest of today...Mainly VFR. A brief period of MVFR conditions
possible (10%) with some mainly isolated showers. 5% chance of a
thunderstorm across northern terminals. Northwest winds 10 to 15
gusting 20 to 25 knots at times. High confidence.

Tonight...VFR. Winds diminishing to 5 to 10 knots through the
evening and also shifting gradually to more northerly and
eventually northeasterly overnight. High confidence.

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

Outlook...

Friday...VFR.

Saturday and Sunday...A period of near MVFR ceilings possible
Saturday, otherwise mainly VFR.

&&

.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...

Friday through Sunday...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/RCM
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...Fitzsimmons/Gorse/RCM
MARINE...Fitzsimmons/Gorse/RCM