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000
FXUS61 KPHI 240655
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
255 AM 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 TONIGHT/...
Latest analysis depicts the approaching cold front as extending
from south of Chicago northeastward across southern Michigan and
into southern Ontario and southern Quebec. This front will make
steady progress southeastward today, reaching our region this
evening and clearing the area after midnight tonight. Ahead of
the front, modest warm advection will result in plenty of clouds
early this morning, perhaps with a few sprinkles or very
isolated showers, but low levels remain quite dry and the system
is overall moisture-starved, so not expecting much. After the
initial clouds break, we should warm up to within a few degrees
of 70 across most of the region this afternoon, but there will
be just enough instability ahead of the upper trough and surface
front to promote some mainly isolated showers to develop during
the afternoon. There could be just enough instability for a very
isolated thunderstorm, mainly Lehigh Valley and Poconos/NW NJ.
For sure, shower coverage will be a bit higher in the Poconos
compared to the rest of the region, but still scattered at best.
Despite the front not arriving until evening, winds for much of
the day will already shift to west to northwest as early as
midday, with gusts increasing up to 20-25 mph. Overall, not a
bad day, but not as nice as yesterday aside from yesterday`s
chilly morning.

Tonight, Canadian high pressure builds southward and reinforcing
cool, dry air mass pushes southward. Think winds staying up and
the dry air limit frost potential, but temps may still reach
freezing in parts of northern NJ where growing season is active,
so have maintained freeze watch there for the time being. Lows
overall will be chilly, with 40s warmest spots, most areas 30s,
and coldest locales 20s.

&&

.SHORT TERM /THURSDAY 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.

A notably colder and dry air mass will be in place Thursday 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. 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 TUESDAY/...
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 /07Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Through Today...Mainly VFR. A brief period of MVFR conditions
possible (10%) with some mainly isolated showers. 5% chance of a
thunderstorm across northern terminals. Winds begin
southwesterly around 10 knots and shift to west then northwest
through the day. Gusts of 20-25 knots by the afternoon. High
confidence on mainly VFR conditions.

Tonight...VFR. Winds NW 5-10 kts with gusts up to 20 kts early.
High confidence.

Outlook...

Thursday and Friday...VFR.

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

&&

.MARINE...
Winds across the Delaware Bay will subside around daybreak.
Winds diminish across the coastal waters through the morning,
but remain gusty around 20 kts during the afternoon. Seas will
continue to build, however, peaking around 5-7 feet this
afternoon. These likely remain near 5 feet thru tonight, hence
the SCA continues on the ocean zones through tonight.

Outlook...

Thursday...The Small Craft Advisory may need to be extended through
much of the morning mainly for the Atlantic coastal waters, as the
winds/seas diminish through about midday.

Friday through Sunday...The conditions are anticipated to be
below Small Craft Advisory criteria.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Freeze Watch from late tonight through Thursday morning for
     NJZ001-007-008.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 7 AM EDT this morning for ANZ430-
     431.
     Small Craft Advisory until 6 AM EDT Thursday for ANZ450>455.

&&

$$

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