390
FXUS61 KPHI 201718
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
118 PM EDT Sat Jul 20 2024

.SYNOPSIS...
Weak high pressure is nearby today as a front remains stalled to our
south. A weak system slides by to our north tonight, then a front
settles into our area Sunday night before stalling in our vicinity
through early next week. This front may dissipate Wednesday then a
cold front should arrive later Thursday or Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Forecast on track this afternoon, just made some minor tweaks
and cut PoPs slightly for this evening, mainly in the I-95
corridor.

Overall, the near term forecast continues to feature a period of
fairly typical summer weather across the region. The main synoptic
features will be a weak surface trough passing to the north and a
stalled frontal boundary to our south. Each of these will provide
the opportunity for some showers or possibly a thunderstorm during
the afternoon/evening hours today and into the overnight hours
tonight. With the weak trough passing to the north, the primary
focus looks to be for initiation to be the west/northwest of the
region this afternoon, along the higher terrain and progressing
eastward. As a result, the most likely areas to see any
precipitation with the passage of this trough will be later this
afternoon and northwest of the Lebanon/Lehigh/Delaware Water Gap
Valleys (30-40%). CAM guidance indicates that convective activity
with this trough passage may linger into the late evening/early
overnight hours.

Precipitation riding along the stalled boundary to our south looks
to potentially push into the region late this evening and continue
through the overnight hours. The most likely areas to see any
showers or storms will be in Delmarva and southeastern New Jersey.
For areas across the central portion of the region, the near term
forecast period looks to largely be dry, but a shower or storm
drifting further south or north from the aforementioned systems
cannot be completely ruled out.

Otherwise, temperatures will be within a few degrees of normal
today. Temps look to top out this afternoon in the mid-upper 80s
across most of the region (upper 70s to low 80s at the coast and at
higher elevations). Lows tonight will be mainly in the upper 60s to
low 70s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
While temperatures are forecast to be close to average, dew points
increase some through Monday and therefore it will be more humid but
not oppressively hot.

As a large upper-level trough swings across eastern Canada it also
pivots across the Northeast. We are forecast to be on the southern
periphery of it and therefore much less forcing for ascent. A front
however will approach our area from the northwest and this may
provide enough forcing for an isolated afternoon/evening shower or
thunderstorm especially across the northern areas. Overall though,
most places should remain precipitation-free. The weak front then
should settle into our area Sunday night.

The eastern Canadian upper-level trough weakens and lifts northward
some Monday, however it also extends southwestward all the way into
the Plains as some stronger shortwave energy drops southeastward.
This places our region within southwesterly flow aloft and this will
continue to increase the moisture and therefore a more humid air
mass. Some embedded shortwaves within this flow aloft should arrive
and this should assist in focusing enough forcing for ascent for
some increase in the probability for some showers and thunderstorms
Monday afternoon and night. The precipitable water values increase
and therefore local downpours also increase at least some. May have
to watch if some training convection is able to set up given a
possible convergence area between the trough to our west and the
ridge to our east. Given some uncertainty on the evolution of the
convection, kept PoPs in the 20-40 percent range.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Summary...Humid but not oppressively hot; Increased chances for
convection at times.

Synoptic Overview...A strong ridge is forecast to be centered over
the Southeast U.S. with a trough sliding across the Pacific
Northwest with time. Meanwhile, an upper-level trough is forecast to
be positioned across the Midwest/Great Lakes and back across the Mid-
Mississippi Valley region. This trough is forecast to slowly get
closer to the East Coast Thursday and Friday. A front stalled across
our area Tuesday and Wednesday may dissipate thereafter. Low
pressure tied to the aforementioned upper-level trough in the Great
Lakes should track to our north, however its cold front settles into
our area later Thursday and especially Friday.

For Tuesday and Wednesday...The chances for especially diurnally
driven convection looks to increase as our region remains within
southwesterly flow aloft well ahead of an upper-level trough. There
looks to be a front also draped across our region and this should
provide some additional focus for some convective development. The
coverage and intensity of the convection will depend on the
available instability/shear and also the timing of embedded
shortwaves within the southwest flow aloft. It does appear though
that with a more humid air mass in place, the most coverage of
showers/storms should be each afternoon and evening. Temperatures
are forecast to be closer to average, however dew points into the
70s (not as high as last weeks excessive heat stretch) will result
in a rather humid feel. Given low enough temperatures however we are
not anticipating excessive heat levels. Increased precipitable water
values will result in stronger convection producing locally heavy
rain.

For Thursday and Friday...An upper-level trough is forecast to
gradually overspread the Northeast from the Great Lakes. This
feature may become closed off and that could tend to slow its
eastward progression at least some. The influence of this trough and
the arrival of a cold front with time will provide some forcing for
ascent and therefore some showers and thunderstorms once again.
These may be more tied again to the afternoons and evenings. A humid
air mass still in place will yield to high precipitable water and
therefore locally heavy rain with any stronger convection. The
approach of the upper-level trough should increase the deep-layer
shear some and with the arrival of the cold front with time, will
need to watch for a stronger thunderstorm risk.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Prevailing VFR. High and mid level clouds around, but
no impact to terminals. Slight chance (15-25%) of a shower or
thunderstorm, most likely at KABE and have included a VCTS
there, though the bulk of the showers/thunderstorms should
remain off to the north from there. Southerly winds around 10
kt. Moderate confidence.

Tonight...Prevailing VFR conditions expected to continue but chances
for showers increase, mainly at KACY/KMIV. However, most recent
guidance has trended lower with rain chances, and if a shower
did make it to the terminal, still expecting VFR to prevail.
Slight chance (15-20%) of a shower within the I-95 corridor this
evening, but given that any showers should be light and rain
chances are only for a three hour period, have elected to not
have any rain mentioned for the I-95 terminals. Winds become
light once again, but may favor a south-southwest direction,
particularly for the I-95 and Lehigh Valley terminals. Moderate
confidence.

Outlook...

Sunday...VFR overall. South/southwest winds at the South Jersey
terminals, with west/northwest winds elsewhere. Wind speeds will
be around 5 kt everywhere. High confidence.

Monday through Wednesday...Some times of sub-VFR conditions possible
with some showers and thunderstorms, especially Tuesday and
Wednesday afternoons and evenings.

&&

.MARINE...
No marine headlines are in effect through tonight. Mostly fair
weather expected through the day today. A few showers possible
(20- 30%) by later this afternoon, most likely for Atlantic
coastal waters south of Cape May. Southeasterly winds around
10-15 kt. Seas around 2 feet.

Tonight, chances for showers and possibly a thunderstorm increase
with the most likely areas remaining across the southern coastal
waters. Winds mainly around 5 knots with seas of 2-3 feet.

Outlook...

Sunday through Wednesday...The conditions are anticipated to be
below Small Craft Advisory criteria.

Rip Currents...

For today and Sunday, there will be a southerly wind near 10 mph with
breaking waves in the surf zone of 1 to 2 feet and a 6 to 7 second
period. There is a LOW risk for the development of dangerous rip
currents at both the New Jersey Shore and the 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
NEAR TERM...AKL/Hoeflich
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...AKL/Gorse/Hoeflich
MARINE...AKL/Gorse