506
FXUS61 KPHI 131754
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
154 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 and continues into the beginning of 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 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 threat especially with stronger cores aloft enhancing
the downburst potential. Freezing levels look 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, with this
potentially the most focused across northern New Jersey.

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 SATURDAY NIGHT/...
High pressure builds in from the north and west on Saturday,
ushering a rather tranquil weekend. Highs during the afternoon
will be in the low-to-mid 80s with nighttime lows dipping into
the mid 50s to right around 60.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Behind the cold front the synoptic pattern sets up with a
building ridge through the weekend. Heights will quickly rise
across the Mid Atlantic with a mid level ridge dominating
through at least the early portion of next week. While the
surface high will start to push offshore, all that does is setup
southerly return flow leading to warm temperatures being
advected north for several days in a row. While global guidance
is still rather spread out with just how hot it will get across
the region next week, guidance across the board has been fairly
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 (10-15%) due to
the very weak forcing from these shortwaves. At this point, a
large number of ensembles show the ridge starting to deamplify
but still holding on till late in the week. This would allow for
some weakening in max temps during the day but not much.

&&

.AVIATION /18Z 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 possible for a time, 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 Monday...VFR.

&&

.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 Monday...No marine headlines expected. Winds
up to 10-15 kts with seas 2-4 feet. Fair weather.

Rip Currents...

Southwest flow 5-10 mph becomes south 10-15 mph with occasional
gusts up to 20 mph today. Breaking waves will average 1 to 2
feet. Primarily a 1-2 ft 7-8 second short period swell from the
E-SE. As a result, there is a LOW risk for the development of
dangerous rip currents today.

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 northern New Jersey and Delaware. That
said, strongest winds will be across northern New Jersey.
Additionally, guidance shows a 1 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 once again
average 1 to 2 feet.

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

&&

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

&&

$$

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