NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Jul 4, 2:37 PM EST, 2 hours 13 minutes earlier.
Area forecast discussion, Jul 4, 2:37 PM EST, 2 hours 13 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
337 PM EDT Tue Jul 4 2023
.SYNOPSIS...
A weak front will continue to shift just to our east through
tonight before potentially shifting back north and west during
Wednesday. A cold front moves through late Friday and Saturday,
then a few additional fronts along with weak low pressure
systems should move through Sunday through early next week.
&&
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
Latest analysis depicts a weakening frontal boundary draped
to our southeast. Upper level trough overhead is slowly pulling
northeast away from the region, but additional vort maxes
continue pushing through the area. This, combined with plenty of
lingering moisture and a notable uptick in CAPE above 2000 j/kg,
has resulted in another round of showers and storms. Focus today
is mostly further north and east, closer to the upper trough
axis. This should continue into the early evening, but as the
trough continues pulling away and we lose surface heating,
storms should rapidly dwindle near sunset, resulting in a mostly
dry night. However, the air mass will change little, so lows
will be in the upper 60s and lower 70s overall. Some patchy fog
is a concern overnight especially where it rains this afternoon.
We briefly sit under a weak ridge on Wednesday morning, but it
doesn't last long. The axis pushes just east of us in the
afternoon as a weak vort max pushes into the area. This combined
with the existing heat and humidity will provide enough CAPE for
at least some isolated to low-end scattered showers and storms
again, this time focused near and south of Philadelphia.
Otherwise, hot and humid again with highs near 90 to the lower
90s and heat indices in the low-mid 90s.
Once again, with loss of insolation, expect afternoon activity
to wane quickly tomorrow evening, with a mostly dry overnight.
However, another little shortwave then moves into the area late
at night, which could spawn a stray shower mainly south of
Philadelphia. Warm and humid again, with lows upper 60s to lower
70s.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Very warm to hot and humid conditions continue.
A leftover surface front may shift north and westward from just
offshore into parts of our region, however this front looks to
be rather weak. Meanwhile, a shortwave trough is forecast to
slide across our area Thursday and while this does not look all
that robust, an unstable atmosphere along with some local low-
level convergence should result in a few showers and
thunderstorms. This may be more favored inland from the coast
and especially across interior Delmarva to parts of eastern
Pennsylvania and northwestern New Jersey (sea breeze and terrain
influences). Locally heavy rain once again a possibility with
the moist airmass in place. The trough should quickly shift to
our east early in the evening, therefore any convection should
tend to dissipate early on. With afternoon high temperatures
around 90F for many locales (cooler along the coast with an
onshore wind), peak heat indices in the afternoon are forecast
to be in the mid 90s for many spots.
As we go through Friday, an upper-level trough is forecast to
hang back well to our west/northwest, and an incoming cold front
may slow its eastward progression. Some shower and thunderstorm
activity should accompany this front, although the overall
forcing may be on the weaker side given the trough axis
remaining so far to our west. Convective initiation may end up
being focused only near the front, therefore the highest PoPs
(high chance to likely) were placed across the western zones in
the afternoon. Convection overall should be mainly tied to
diurnal heating, therefore showers and thunderstorms should
diminish during the evening. A few stronger storms could be
possible, although this will depend on the shear, instability
and forcing magnitudes. It will be another very warm to hot day
with afternoon highs topping out in the upper 80s to 90 degrees
for many places, although once again cooler along the coast and
in the Poconos. Afternoon heat indices are forecast to be in the
low to mid 90s for much of the area given dew points around
70F.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
Summary...Humid conditions persist and it will be unsettled at
times with some showers and thunderstorms.
Synoptic Overview...An upper-level trough is forecast to remain
centered in the vicinity of Hudson Bay Canada through the
weekend, with our region on its southeastern periphery. However,
shortwaves rotating around it may sharpen a shortwave trough
across the Great Lakes, the Ohio then toward New England during
the second half of the weekend. This trough may then settle
southward with a closed low becoming centered over the Great
Lakes region into early next week. This would then result in
more of the trough settling into the East with time. At the
surface, a cold front is forecast to gradually work its way
across our area Saturday before either dissipating or stalling
to our south and east. A couple of other fronts then work their
way toward us and a few weak waves of low pressure may track
near our region into early next week.
For Saturday...As an upper-level trough is forecast to hang
back well to our west/northwest, a cold front working its way
across our area may stall in our vicinity or dissipate. Showers
and thunderstorms should redevelop with this weakness, although
much of this may be more to our west closer to an incoming
shortwave trough. Convection should be mostly tied to diurnal
heating, therefore the afternoon and evening time frame appears
to have the better chance of occurrence. Depending on the shear,
instability and forcing magnitudes with an incoming shortwave
trough, some stronger thunderstorms will be possible especially
across the western areas. The details will ultimately depend on
the timing specifics of the weakening cold front and magnitude
of forcing for ascent.
For Sunday through Tuesday...The main upper-level trough
initially centered in the vicinity of Hudson Bay Canada should
then settle southward and a closed low becomes centered over the
Great Lakes. This will eventually place more of a trough in the
East with time. Another cold front looks to arrive later Sunday
into Monday, plus this energy may assist in developing some
ripples of energy along the front. Incoming energy associated
with the incoming trough plus weak surface lows and a boundary
would result in some uptick in forcing for ascent and therefore
the chance for showers and thunderstorms. The evolution of this
is of lower confidence especially with the timing and
amplification of the aforementioned upper-level trough and
embedded impulses. Therefore, PoPs are mostly in the chance
range.
&&
.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Through tonight...VFR with isold/sct TSRA/SHRA. Instances of
MVFR vsby and a few wind gusts up to 30-35 kts possible. Winds
otherwise mainlyl W to NW 5-10 kts. Will need to watch for
patchy fog development late tonight especially outlying
terminals. Winds light and variable. Moderate confidence.
Wednesday-Wednesday night...VFR overall. Patchy fog a concern
early Wednesday and again late Wednesday night. ISOLD/SCT
TSRA/SHRA again possible Wednesday afternoon with MVFR vsby
possible. Moderate confidence.
Outlook...
Thursday...A few afternoon and evening showers and
thunderstorms possible which could locally result in
restrictions, otherwise mainly VFR. Southeast winds 10 knots or
less. Moderate confidence.
Friday...Some afternoon and evening showers and thunderstorms
with brief sub-VFR conditions. Southeast winds 5-10 knots,
becoming light and variable at night. Low confidence.
Saturday and Sunday...Mainly some afternoon and evening showers
and thunderstorms possible with times of sub-VFR conditions.
Southerly winds 5-10 knots. Low confidence.
&&
.MARINE...
Main concern will be thunderstorms into early this evening and
again Wednesday afternoon producing potential gusty winds.
Otherwise, Light winds westerly, then northerly, and finally
easterly 5-10 kts. Seas 2-4 ft.
Outlook...
Thursday through Sunday...The conditions are anticipated to be
below Small Craft Advisory criteria. Some thunderstorms are
possible especially over the weekend.
Rip currents...
For today, there is a LOW risk for the development of dangerous
rip currents for the New Jersey and Delaware beaches. The wind
should be from a southerly direction around 10 mph. Breaking
waves are forecast to be around 2 feet with a medium period
south to southeast swell. The risk for the development of
dangerous rip currents is expected to stay LOW for Wednesday.
&&
.TIDES/COASTAL FLOODING...
The evening high tide cycles will be elevated along the ocean
and into Delaware Bay through the middle of the week. Tide
levels will generally be +0.6 to +1.0 feet above normal, and
minor coastal flooding thresholds will be touched. This will
result in spotty minor tidal flooding around the evening high
tide cycles.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.
&&
SYNOPSIS...Gorse
NEAR TERM...RCM
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...Gorse/RCM
MARINE...Gorse/RCM
TIDES/COASTAL FLOODING...PHI