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000
FXUS61 KPHI 231747
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
147 PM EDT Tue Apr 23 2024

.SYNOPSIS...
The center of high pressure generally builds to our south today,
then a cold front will cross our region during mostly Wednesday
morning. High pressure then arrives from the Great Lakes Thursday
before shifting to our northeast and east during Friday. A warm
front should lift north of our area late Saturday, then a cold front
gradually approaches later Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Overall, the near term forecast remains on track. The incoming
system still over the central Plains and upper Midwest will
begin to spread some high clouds overhead today, but otherwise,
should be fairly sunny. With warm advection developing ahead of
the system on strengthening southerly flow, expect highs to rise
5-10 degrees above yesterday`s readings, mainly into the upper
60s, which will feel quite nice after the chilly morning. Winds
will be a little gusty, perhaps up to 20 mph, but not much
different from yesterday.

The approaching system will further increase clouds with a
steady southerly flow tonight. This will help keep temps much
milder, with lows likely 10-15 degrees higher than this morning,
mostly 40s and low 50s. As the system gets closer late at night,
a few showers may move into the region, but overall not
expecting much, so kept overnight POPs in the slight chance to
low-end chance range.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
An upper-level trough is forecast to swing across our region
during the day Wednesday. This will drive a cold front across
our area during mostly Wednesday morning. This system looks to
have limited moisture with it, without a tap to Gulf of Mexico
moisture, and therefore rainfall amounts are forecast to be very
light. While the main cold front shifts offshore by early
afternoon, a secondary cold front or trough (dew point front)
may arrive by late afternoon. Since the cold front continues to
look faster, more drying is forecast to be working into the area
through the afternoon. This would tend to decrease the
instability, however the model forecast soundings show some weak
instability present in the afternoon. The overall forcing
though may be on the weaker side, however the model forecast
soundings also show lowering freezing levels and steepening low
level lapse rates. If a heavy shower or thunderstorm were able
to develop in the afternoon, then locally gusty winds and small
hail will be possible. Overall though with the extent of the
drying forecast from about late morning through the afternoon,
the thunder potential looks to be on the low side. Mild
temperatures Wednesday for most of the area, however a
strengthening/gusty west to northwest wind will be in place in
the afternoon and evening. The sky will clear especially later
in the day as high pressure quickly builds southeastward from
the Great Lakes Wednesday night, across the Northeast and Mid-
Atlantic Thursday morning. If the lower levels can decouple and
winds become calm, a frosty early Thursday morning would be
quite possible especially the more favorable locations like
interior New Jersey and eastern Pennsylvania north and west of
the Fall Line.

A notable colder and dry air mass will be in place Thursday
despite a mainly sunny sky with high temperatures mostly in the
50s. An onshore wind will also keep it even cooler along the
coastal areas. Thursday night may feature more areas of frost
with temperatures dropping into the 30s for much of the area.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Summary...Cool to start then 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...As an upper-level trough shifts to our east
to start Friday, a building ridge arrives from the west as an
upper- level trough lifts across the Plains and into the Midwest
through Sunday. As the influence of the upper-level trough gets
closer Sunday night and Monday, 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 and Monday. The
overall pattern though suggests that a much warmer air mass will
overspread our region mostly during the second half of the
weekend and early next week.

For Friday and Saturday...Surface high pressure is currently
forecast to be centered across coastal New England to start
Friday, then it shifts eastward as a building ridge starts to
arrive from the west. This will initially keep a cool air mass
across our region, however better warm air advection kicks in
Saturday as more of a southerly return flow starts to set up. 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. After
a mainly sunny Friday, clouds should be on the increase some
during Saturday within the increasing warm air advection regime
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.

For Sunday and Monday...As an upper-level trough continues to
lift up across the Plains and Midwest, the downstream ridge axis
slides across our region. The influence of the trough however
may start to weaken the ridge or shift it to our east into
Monday. Surface low pressure tracks across the Great Lakes
Monday, and its associated cold front may not approach our area
until Monday night. The details however will depend on the
timing and amplification of the trough. In addition, high
pressure sliding east of Hudson Bay Canada later Sunday into
Monday may send a cold front down across New England and closer
to our area. As of now, that front should remain north of our
area given continued southerly flow ahead of the aforementioned
trough from the west. Plenty of warm air is therefore currently
forecast across the area, with high temperature for much of the
area in the 70s to even locally some low 80 degrees. There is
some chance for some showers and thunderstorms, especially
Monday however the probabilities look to be on the lower side as
of now.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through today...VFR. Southerly winds around 10 kts. Gusts of
15-20 kts possible this afternoon. High confidence.

Tonight...VFR. A few showers are possible late, but no
reductions in cigs or vsby expected before dawn Wednesday. Winds
south-southwesterly 5-10 kts. High confidence.

Wednesday...Mainly VFR. A brief period of MVFR conditions
possible (15%) with some scattered showers. Winds begin
southwesterly around 10 knots and shift to west then northwest
through the day. Gusts of 20-25 knots likely by mid-morning.
High confidence on mainly VFR conditions.

Outlook...

Thursday and Friday...VFR.

Saturday...VFR overall.

&&

.MARINE...
Today, winds start below advisory levels, but will increase
through the day and likely reach Small Craft Advisory levels on
the northern half of the New Jersey coastal waters, as well as
Delaware Bay. Therefore we have issued a Small Craft Advisory
for these areas. Tonight, the gusts on the bay diminish, but on
the oceans they should increase, so SCA`s expand to all ocean
zones after midnight. Seas will also build, reaching low-end
criteria by early Wednesday morning.

Outlook...

Wednesday...Small Craft Advisory conditions.

Thursday...Small Craft Advisory conditions possible mainly in
the morning.

Friday and Saturday...The conditions are anticipated to be
below Small Craft Advisory criteria.

&&

.FIRE WEATHER...
Though there will be some moisture advection with an
approaching system, the region will remain fairly dry today. Min
RH values across the region will be in the 25-35% range, with
southerly wind gusts in 15-25 mph range. As was done for Monday,
a Special Weather Statement for increased fire danger has been
issued for today.

&&

.TIDES/COASTAL FLOODING...
A period of southerly flow will occur into Wednesday morning
ahead of a cold front. This is forecast to result in surge
values rising to 1-2 feet above normal along Delaware Bay, the
tidal Delaware River, and Chesapeake Bay. With the full moon
occurring today, astronomical tides will be maximized around
this time as well. This should result in some areas of minor
coastal flooding with the Wednesday night high tide, although
the extent and exact areas that may experience the most impact
remains unclear at this time.

Coastal flooding is not currently anticipated along the
Atlantic coast, except for potentially Barnegat Bay.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ430-
     431.
     Small Craft Advisory until 6 PM EDT Wednesday for ANZ450-451.
     Small Craft Advisory from midnight tonight to 6 PM EDT
     Wednesday for ANZ452>455.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...AKL/RCM
SHORT TERM...Fitzsimmons/Gorse
LONG TERM...Gorse
AVIATION...AKL/Gorse/RCM
MARINE...Gorse/RCM
FIRE WEATHER...WFO PHI
TIDES/COASTAL FLOODING...WFO PHI