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644
FXUS61 KPHI 241910
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
310 PM EDT Fri May 24 2024

.SYNOPSIS...
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A weak front continues to settle to our south through tonight, then
it lifts back to the north as a warm front during Saturday. A cold
front moves through Saturday night into Sunday, then a stronger
system and cold front arrives for Monday. A secondary cold front
crosses our area Tuesday night into Wednesday, then high pressure
should build in during Thursday and Friday.
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&&

.NEAR TERM /THROUGH SATURDAY/...
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Isolated convection across far southern Delaware and nearby
Maryland continues this afternoon in response to a mid-level
shortwave moving eastward across the Delmarva.

Otherwise, surface high pressure over the Great Lakes gradually
builds in from the north and west, bringing in a drier airmass
through this afternoon. Tranquil weather will continue tonight
with clear skies and light winds initially. We should be able
to radiate pretty well leading to some patchy fog development
over Delmarva and southern New Jersey. However, clouds will
increase from south to north later in the night as a weak front
to our south begins to lift back north. This should limit the
amount of cooling late, so expecting lows in the mid 50s to
lower 60s with mid 60s around Philadelphia.

Other than patchy morning fog over the Delmarva, Saturday
morning should be fairly tranquil. A warm front will push north
of the area with the main forcing for some afternoon showers
occuring late in the day over the Lehigh Valley and Poconos. The
showers will progress eastward to the Delaware Valley by
Saturday evening. Temperatures are anticipated to rise into the
mid 80s with low 70s along the shore.
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&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
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As an upper-level trough moves across portions of Eastern Canada, it
is forecast to weaken as is the surface low tied to it. An
associated weakening cold front is forecast to arrive into our area
Saturday and then shift offshore or dissipate near our area Sunday.
While the main forcing for ascent weakens with time and even shifts
mostly to our north and west, convection with it well to our west
initially may become organized enough and therefore making it into
our western zones during Saturday night. It may then tend to weaken
with an eastward extent, however there is some hints in the guidance
of a possible embedded MCV (convectively induced shortwave). This
may invigorate the convection eastward, although with some weak
ridging starting to develop overhead a weakening trend should occur.
PoPs were held at chance or lower as a result. Some ridging remains
in place then for Sunday with weak surface high pressure nearly
overhead. While it should mostly be dry Sunday, may have to watch a
few pop-up showers or storms during peak heating. It will be warm
Sunday with highs in the 80s for most places, although the flow
looks light and therefore supporting sea breeze circulations and
cooler temperatures closer to the coast. A warm front looks to start
arriving Sunday night with some increased lift, therefore some
increase in showers/thunder will be possible.

As we go through Monday, it looks increasingly unsettled as a
stronger system and cold front arrives from the west. As an upper-
level trough moves across the Great Lakes and adjacent Canada, the
southern part of it will start to approach our area Monday
afternoon. Despite surface low pressure once again tracking well to
our north, a warm front will be lifting northward across our area.
This may not clear our entire area, however increasing low to mid
level flow will aide in stronger moisture transport northward and
also increase the warm air advection. This results in the
precipitable water values increasing to 1.5-2.0 inches. There should
be some showers and perhaps thunder in the morning and this would
tend to hold the instability down, although convection is expected
to increase through the afternoon with more forcing for ascent
arriving.

While there is some severe thunderstorm risk with at least
some locally damaging wind potential, this could be limited due to
instability being on the lower side if showers/storms are more
widespread earlier in the day. The model guidance does vary at least
some on the degree of instability, however the low-level flow is
forecast to exhibit some veering with height and therefore
strengthening shear profiles. The high moisture content will result
in areas of heavier rain, and with the potential for some repeated
convection in some areas, there is some flash flooding risk with
higher hourly rainfall rates associated with stronger convective
cores especially for the urban areas centered on the I-95 corridor.
The convection shifts eastward and then offshore later Monday night
as a cold front works its way through our region.
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&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
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Summary...Potentially unsettled at times especially to start with
also some cooling.

Synoptic Overview...An upper-level trough is forecast to amplify
eastward into the the Mid-Atlantic and Northeast Tuesday and
Wednesday. The trough may then linger and even become closed off as
we go through the end of the week, however there are differences
among the model guidance regarding this scenario. At the surface, a
cold front should be shifting offshore to start Tuesday with a
secondary cold front possibly moving through Tuesday night into
Wednesday. If the upper-level trough ends up weaker and moving
along, then high pressure looks to build in during Thursday and
Friday.

For Tuesday and Wednesday...As an upper-level trough amplifies
eastward into the Northeast and Mid-Atlantic regions, surface low
pressure is forecast to track north of northern New England. A
trailing cold front should be offshore to start Tuesday taking any
showers and thunderstorms with it. As the main portion of the upper-
level trough moves into the Northeast Wednesday, some showers or a
thunderstorm will be possible into our area especially during peak
heating. This may occur ahead of or with a secondary cold front
arriving into our area Tuesday night into Wednesday. Coverage in our
area may be limited due to the deeper moisture plume offshore.

For Thursday and Friday...The aforementioned upper-level trough
looks to remain in place during this time frame, although the
strength of it varies among some of the model guidance as some close
it off across the Northeast. If the closed low scenario does not
become realized, then surface high pressure should be building
toward and into our area during this time frame. At this point,
cannot rule out some mostly diurnally driven showers especially on
Thursday. Given the influence of the upper-level trough,
temperatures should be cooler and closer to average.
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&&

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

This afternoon...VFR. Scattered showers in southern Delaware
early this afternoon. Light winds becoming northwest around 5
knots, then becoming west. A sea/bay breeze will develop along
the New Jersey and northern Delaware coasts in the afternoon.

Tonight...Clear skies and calm winds. Fog may form in southern
New Jersey and Delmarva after 06Z with visibility 3-5SM.

Saturday...VFR. Widely scattered showers and thunderstorms late
in the day in the Poconos and Lehigh Valley.

Outlook...

Saturday night...A period of sub-VFR conditions with some showers
and a thunderstorm possible.

Sunday...VFR overall.

Monday and Tuesday...Sub-VFR conditions probable with showers and
some thunderstorms Monday, then conditions improve on Tuesday.

Wednesday...VFR overall.
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&&

.MARINE...
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The conditions are expected to remain below Small Craft Advisory
criteria through Saturday. Isolated showers and thunderstorms
Delaware coastal waters this afternoon.

Outlook...

Saturday night through Wednesday...Southerly winds could gust to 25
knots later Monday, otherwise the conditions are anticipated to be
below Small Craft Advisory. Some thunderstorms Monday afternoon and
evening could produce locally gusty winds.

Rip Currents...

For this afternoon, winds S to SW at 5-10 mph with breaking
waves of 1 to 2 feet. There is a LOW risk for the development of
dangerous rip currents at NJ and DE beaches.

The LOW risk for the development of dangerous rip currents is
expected to continue for Saturday.
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&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...Franklin/MJL
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...Franklin/Gorse/MJL
MARINE...Franklin/Gorse/MJL