142
FXUS61 KPHI 281331
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
931 AM EDT Fri Jun 28 2024

.SYNOPSIS...
High pressure slides across our area today before sliding offshore
this evening. A warm front lifts north across our region later
Saturday, followed by a cold front later Sunday. High pressure
returns for Monday and Tuesday, then a cold front approaches during
Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Forecast running on track. Not anticipating significant changes
to the forecast for the next 12 hours or so as high pressure
centered northwest of the region will gradually slide to the
east. Pleasant conditions on tap today. Only some high clouds
are expected in a day that will be dry and mostly sunny overall.
Temperatures will be on the cooler side for late June, topping
out in the upper 70s to low 80s across most of the region. As
the high shifts eastward, winds will gradually shift from out of
the northeast this morning to out of the southeast this
afternoon.

Heading into tonight, the high slides further eastward allowing a
surface low pressure system centered over the Great Lakes to begin
to approach the region. This movement will bring increasing clouds,
particularly after midnight. A stray shower can`t be completely
ruled out during the pre-dawn hours. However, thanks to dry air
lingering in the low-mid levels, anything substantial looks to be
unlikely. PoPs were reduced to less than 15 percent as a result.
With cloud cover providing some insulation, lows look to be 5-10
degrees warmer tonight than early this morning, falling into the mid-
upper 60s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
A central Canadian upper-level trough is forecast to pivot eastward
and amplify southward some, with a stronger shortwave sliding across
the Great Lakes region during Saturday. This will support surface
low pressure tracking well to our north across portions of eastern
Canada, however its cold front will be approaching late Saturday
night. Much of the daytime Saturday looks to be rain-free as the
overall system looks to be slower. As a warm front lifts north
across our area later Saturday, there is some resemblance of a
surface trough developing near or east of the appalachians during
the afternoon. This may support some convection mainly across our
far western zones in the afternoon. Otherwise, the main convective
development looks to occur well to our west. During the day, highs
will be in the mid to upper 80s and with increasing southerly flow,
surface dew points will rise through the 60s and therefore
it becomes more humid.

Some showers and thunderstorms are forecast to be on the increase
during Saturday night as the mid level flow increases and stronger
large scale ascent starts to arrive. This should also be tied to
more organized convection approaching from the west. Despite this
occurring at night, instability should be sufficient for a while to
maintain convection. A ribbon of strong moisture advection is
forecast to increase the precipitable water values into the 2.0-2.5
inch range Saturday night, and this will result in enhanced rainfall
rates with any stronger convection. While convection should be on
the move, heavy rain can lead to some localized flooding. While the
bulk effective shear is forecast to be about 30-40 knots,
instability may be muted some given the nighttime occurrence and
this may limit the severe thunderstorm risk. If the boundary layer
remains very warm ahead of the convection, this would hold onto some
higher downdraft instability (DCAPE) and therefore locally strong
winds cannot be ruled out especially for our western zones. It will
be a very warm and muggy Saturday night with lows generally in the
70s.

As we go through Sunday, some showers and thunder may be ongoing to
start the morning however these should decrease for a time. Cloud
cover should give way to at least some sunshine for a time and
therefore a hot and humid day. High temperatures are expected to be
in the upper 80s to low 90s for much of the region. Surface dew
points are forecast to be in the 70s, however we will have to see if
these can mix out some during peak heating. The combination of the
very warm to hot temperatures and dew points in the 70s will yield
heat indices Sunday afternoon well into the 90s with some areas
around 100 degrees. While low pressure tracks well to our north, an
incoming upper-level trough will push a cold front across our region
later Sunday. Some additional showers and thunderstorms are forecast
to develop, however a pre-frontal trough may be far enough east to
focus most of the convective development along and south/east of the
I-95 corridor. Given the heat and high humidity in place, some
storms could become locally severe with damaging winds the main
hazard, especially as some model forecast soundings show an inverted-
V low-level profile which would increase the downdraft instability
(DCAPE). The precipitable water values may start to lower during the
day although this will depend on the progression of the trough and
cold front, however locally heavy rain will be possible with any
stronger convection. The timing of the cold front will also
determine the convective coverage as the guidance does vary some
with this timing. It will dry out Sunday night in the wake of the
cold front, and dew points will also be on the decrease by daybreak
Monday.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Summary...Cooler and less humid to start then turning warm/hot and
more humid. Some convection possible, mainly Thursday.

Synoptic Overview...An upper-level trough is forecast to be shifting
to our east Monday, then a mid/upper level ridge arrives Tuesday
into Wednesday. Some influence from a Canadian upper-level trough
will start to glance our area during Thursday. At the surface, high
pressure builds in later Monday and Tuesday before shifting to our
south and east into Wednesday. A warm front lifts northward
Wednesday then a cold front approaches during Thursday.

For Monday and Tuesday...As an upper-level trough departs Monday, a
ridge arrives into Tuesday. A cooler and less humid air mass will be
ushered in under a north to northeast wind as surface high pressure
builds in. High temperatures Monday are forecast to be into the low
80s for many places, then with some warm air advection starting
highs Tuesday will be a few degrees warmer. The surface flow however
turns more southeast Tuesday resulting in some cooling along the
coast. A comfortable air mass both days with dew points in the 50s.

For Wednesday and Thursday...The ridge aloft is forecast to
gradually weaken and shift southward some and this will take surface
high pressure with it. A more south to southwest flow will become
established as a result, and this will also boost the warm air
advection. A warm front should also be lifting on by Wednesday with
a hotter air mass overspreading our region. The influence of a
Canadian upper-level trough will start to approach during Thursday,
however the timing and amplitude of this trough is less certain. As
of now, the main trough is more toward the Midwest and therefore a
cold front may be slow to arrive into our area. There may be a pre-
frontal trough in our vicinity and this may provide enough focus
amid a destabilizing air mass to initiate some convection. Given the
uncertainty at this time range, kept PoPs on the lower side
Thursday. High temperatures are forecast to rise into the low 90s
for many places Thursday and with dew points into the lower 70s,
hot and humid conditions are forecast.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Northeast winds 5-10 knots, shifting to the east
this morning, then shifting to southeast by the afternoon. High
confidence.

Tonight...VFR to start. However, late at night low clouds may
develop and bring cigs down to MVFR, perhaps even IFR in a few
spots. Winds southeast 5-10 kts. Low confidence.

Outlook...

Saturday and Sunday...VFR overall. Some showers and thunderstorms
mainly Saturday night and Sunday can result in areas of sub-VFR
conditions for a time.

Monday and Tuesday...VFR.

&&

.MARINE...
Through Tonight...Conditions are expected to remain below advisory
levels. Prevailing winds shift from the northeast this morning
to the southeast this afternoon. Seas of 2-4 feet throughout the
period.

Outlook...

Saturday and Sunday...Small Craft Advisory conditions possible. Some
thunderstorms Saturday night and especially Sunday may produce
locally strong winds.

Monday...Small Craft Advisory conditions possible, especially early.

Tuesday...The conditions are anticipated to be below Small Craft
Advisory criteria.

Rip Currents...

Today...Northeast winds in the morning becoming east-southeast
winds in the afternoon 10-20 mph. Breaking waves of 2-3 feet
for all beaches. Due to an onshore component of the wind, have
maintained a MODERATE risk for the development of dangerous rip
currents for the New Jersey and Delaware beaches.

Saturday...Southeast winds 10-20 mph with breaking waves of 2-3
feet at all beaches. Due to similar wind and wave conditions
compared to Friday, have opted to continue with a MODERATE risk
for the development of dangerous rip currents for both the New
Jersey and Delaware beaches.

For specific beach forecasts, visit weather.gov/beach/phi

&&

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

&&

$$

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