935
FXUS61 KPHI 132024
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
424 PM EDT Thu Jun 13 2024

.SYNOPSIS...
Weak surface high pressure centered offshore will still remain
in control through tonight. A cold front crosses our region
Friday afternoon into Friday night. High pressure then builds
in over the region bring a stretch of dry and increasingly hot
conditions that will likely last well into next week.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
A closed low centered across Hudson Bay Canada will gradually shift
eastward tonight and especially Friday and Friday night. One of the
shortwaves embedded with this trough should amplify some Friday from
the Great Lakes into the Northeast. This system will drive a cold
front across our area Friday afternoon and evening. Meanwhile, weak
surface high pressure centered offshore but extending across our
area this afternoon will shift farther away tonight into Friday.
Increased low-level moisture from south to north has resulted in a
decent amount of cumulus this afternoon. This is expected to dwindle
through the evening with the loss of daytime heating. Sea and bay
breezes will also keep temperatures lower closer to the coasts into
this evening, and the KDOX radar shows a narrow convergence boundary
across Delaware due to flow off the Delaware Bay running into a more
south to southwest wind to its west.

A weak shortwave trough is forecast to arrive from the west late
this afternoon and this evening. Some guidance, especially the high-
resolution ones, show some isolated showers mainly across our
western zones that develop off the higher terrain into this evening
and again overnight. The forcing is rather weak with this system and
the probability of precipitation is so low and therefore opted to
keep the forecast dry. An isolated shower however still cannot be
ruled out. Temperatures will drop back into the 60s for most areas.

As we go through Friday, an upper-level trough is forecast to arrive
in the afternoon and evening. While the parent trough is farther
north, the southern portion of it has stronger shortwave energy and
is timed during peak heating across our region. At the surface, a
cold front will work its way across our region from west to east
during the afternoon and evening. Since the stronger winds look to
lag to the west of the cold front, the flow is strongest in the
upper levels with it weakening in the mid to lower levels, and this
all decreases especially in the lower levels the farther south and
east across our area. As a result, the stronger shear is positioned
across our northern and western zones. There is ample instability
forecast to be in place (MLCAPE up to 1500 J/Kg) given air
temperatures forecast to be in the 80s with even some lower 90s and
dew points in the 60s. The model forecast soundings show a well
mixed and warm boundary layer in the afternoon and early evening.
This results in an inverted-V profile in the lower levels and thus
increasing the downdraft instability (DCAPE).

Given the flow profiles and incoming frontal forcing, convection is
forecast to develop to our northwest and west and then propagate
east and southeastward during the afternoon and evening. While
coverage and timing does vary some among the guidance suite,
convection should organize into a few clusters or a broken line as
it shifts into and across our area, with this possibly weakening
near and especially south and east of I-95. This will depend on the
timing as southerly flow ahead of the convection and front will
bring some marine influence into portions of the coastal plain.
Given convection in a cluster or linear mode, locally damaging winds
are the main severe weather threat especially with stronger cores
aloft (along with some mid level dry air) enhancing the
downdraft/downburst potential. Freezing levels look to be on the
higher side, however some hail cannot be ruled out with some
stronger convective cores. The precipitable water values are
forecast to be approaching 2 inches for a time ahead of the cold
front, and therefore high rainfall rates should occur with the
strongest convection for a time. The flash flooding risk however
looks to be low overall as storms should be on the move, however
there is a non-zero risk focused across mostly our northern and
western zones.

The convection looks to be shifting offshore or weakening during the
evening hours with the severe thunderstorm risk ending. Some drier
air then starts to arrive from the northwest in the wake of the cold
front by later Friday night with at least some partial clearing also
starting to arrive.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
High pressure builds in from the north and west on Saturday,
ushering a rather tranquil weekend. The high looks to become
centered over our region on Sunday before passing offshore
Sunday night. Conditions will be dry throughout the weekend with
plenty of sunshine to go around. Those who do not enjoy the heat
will want to try and get outside this weekend as temperatures
will be marginally cooler in the low- mid 80s across most of
the region. Upper 70s are expected near the shore and at higher
elevations. Nighttime lows are forecast to dip into the mid 50s
to right around 60 Saturday night then upper 50s to low 60s
Sunday Night.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Accompanying the high pressure into the region over the weekend
will be a building ridge. Rising heights will be seen across
the Mid Atlantic with the mid level ridge dominating through at
least the middle of next week. While the center of the surface
high pressure looks to be offshore by the start of the long term
period, all that does is setup southerly return flow leading to
warm temperatures being advected north for several days in a
row. Little change has occurred with this latest forecast cycle
as global guidance is still rather spread out with just how hot
it will get across the region next week. However, that also
means that guidance across the board remains consistent with
the building high pressure and increasing heat through the week
with a high likelihood of temperatures lingering well into the
90s for a number of days. At this point, it is certainly not too
early to start thinking about your cooling options for next
week. For anyone hoping for temporary relief from precipitation
chances, at the moment, chance for this remain rather low. While
there are some pieces of shortwave energy tracking through the
region during the week, the overall chance for showers is fairly
capped (10-20%) due to the very weak forcing from these
shortwaves. The relatively higher chances of 15-20% look to come
Thursday at the earliest as it is at this point, that some
ensemble members begin to show the ridge weakening over our
region. However, southwesterly flow looks to remain in place so
relief from the heat looks unlikely through Thursday at this
time.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of this afternoon...VFR. South to southwest winds around 10
knots (south-southeast winds for a time at KACY and KILG). Some
local gusts to 20 knots, especially at KACY. Moderate confidence.

Tonight...VFR. South-southwest winds diminishing to near 5 knots,
with it becoming light and variable at some terminals. Moderate
confidence.

Friday...VFR for much of the time, however some times of sub-VFR
conditions later in the afternoon and evening as some showers and
thunderstorms move through with a cold front. South to southwest
winds around 10 knots, becoming west later in the afternoon at KRDG
and KABE. Low confidence on the timing details.

Outlook...

Saturday through Tuesday...VFR with no significant weather.

&&

.MARINE...
Through Friday, the conditions are anticipated to remain below Small
Craft Advisory criteria. Southerly winds should be the strongest at
times across the northern New Jersey coastal waters and possibly up
Delaware Bay. However, given much warmer air moving over the cooler
waters, mixing should be more limited and since it looks marginal
opted to keep the conditions below advisory criteria. Some showers
and thunderstorms should arrive late Friday afternoon and Friday
night, and some storms could produce locally gusty winds.

Outlook...

Saturday through Tuesday...No marine headlines expected. Fair
weather.

Rip Currents...
On Friday, south winds increase to around 15 mph with 20 to 25
mph gusts. The flow will be a bit more onshore for most of New
Jersey as opposed to Delaware.  Additionally, guidance shows a
2 ft 9-10 second longer period swell from the SE to SSE
developing by the afternoon. As a result, there is a MODERATE
risk for the development of dangerous rip currents for New
Jersey beaches where the coastline is more perpendicular or
oblique to the longer period swell. LOW risk for the development
of dangerous rip currents for the Delaware beaches. Breaking
waves will be around 2 to 3 feet.

Winds turn offshore for Saturday, with a LOW risk for rip
currents everywhere.

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

&&

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

&&

$$

SYNOPSIS...AKL/MJL
NEAR TERM...Gorse
SHORT TERM...AKL
LONG TERM...AKL
AVIATION...AKL/Gorse
MARINE...AKL/Gorse/Hoeflich