396
FXUS61 KPHI 171947
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
347 PM EDT Wed Jul 17 2024

.SYNOPSIS...
A strong cold front will cross the Middle Atlantic region tonight.
It will be followed by high pressure for the end of the week and
into the weekend. Another upper system and surface front will arrive
by early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
Convection is ongoing across eastern PA and into northwestern
NJ. Damaging winds have already been reported with some of these
severe thunderstorms with more expected on the way. A Severe
Thunderstorm Watch remains in effect for the northern half of
our coverage area. A new Severe Thunderstorm Watch has been
issued for extreme southern NJ and the Delmarva.

Latest mesoanalysis shows SBCAPE values have recovered with
widespread 2000-3000+ J/kg this afternoon, providing ample fuel
for convection to erupt across the region through the rest of
today and into tonight. Sufficient deep layer shear (25-30kts)
and steep lapse rates will also support rapidly developing
updrafts and severe storms. PWAT values over 2 inches across the
region will support heavy downpours leading to localized flash
flooding. The first round of storms will mainly impact the I-95
corridor and points N&W through this evening before the front
shifts ESE and brings another round of numerous to widespread
storms across southern NJ and the Delmarva through late tonight.
Storms should eventually give way to just some residual showers
before tapering off from northwest to southeast overnight as the
cold front shifts further offshore. Behind the front, light NW
winds and temperatures falling into the upper 60s to low 70s.
Some patchy fog will be possible as well.

The cold front should fully cross through the region by Thursday
morning but will begin to slow down as it passes to our south and
east. So while, the northern half of the area will begin to see some
clearing, the southern half of the area (especially near the coast),
will see cloud cover linger throughout the day. Isolated to
scattered showers and storms may hang up along the southern
Jersey shore and southern Delmarva in the afternoon. On the
bright side, this cold front will knock down temps and humidity
with highs mainly in the mid 80s.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
Front will continue slowly sliding southeastward away from the area
Thursday night. A few showers or thunderstorms may linger in the
evening across southern Delaware but it should clear out after
midnight. Lows will be in the considerably more comfortable 60s for
most of the area.

Friday looks like the most pleasant day of the forecast as
Canadian high pressure briefly builds southward into the area. Dew
points will be down into the upper 50s and lower 60s with highs only
in the mid to upper 80s with mostly sunny skies and light winds.

High pressure starts to push eastward with a lee-side trough
developing on Saturday. With winds turning back to the south, dew
points will start to creep back up. The increased moisture plus
lee side trough combined with a weak upper disturbance working in
from the southwest may be enough to bring some scattered showers and
isolated thunderstorms by afternoon, especially west and southwest
of Philly. Further north and east, dry conditions should prevail.
While dew points will be back solidly into the 60s, highs should
remain mostly in the upper 80s, so still considerably more
comfortable than recent days, but not quite as nice as Friday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The stalled front to our south will gradually creep back northward
as we head into the middle of next week. Combined with passing upper
disturbances, this should result in a general turn towards cloudier,
more showery weather, with lower temps by mid week.

At first however, Sunday should be similar to Saturday, with some
spotty convection possible mainly west and southwest of Philly. Dew
points keep creeping up, but temps remain in the upper 80s overall.

By Monday the increased moisture is more apparent, as dews start to
approach 70 and the front starts to push back north. This should
result in a slightly better chance of convection, but again, not
huge. Still mainly upper 80s for highs.

Tuesday and Wednesday are when conditions turn wetter, with the
front pushing back into the area with clouds and scattered showers/t-
storms becoming common. This will cause cooler temps as well, with
highs down into the mid 80s, but dew points rising into the low-mid
70s. Will need to monitor for any locally heavy rain risks given
high moisture and slow moving front in the vicinity, but overall
this looks like a beneficial change in the weather.


&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Rest of this afternoon...Thunderstorms in the afternoon and
into the evening could result in sub-VFR conditions beginning by
as early as around 18-20z for ABE and RDG but mainly after 21z
for the I-95 TAF sites and points south/east. TSRA coverage will
become more numerous and widespread towards the end of the
afternoon. Winds mainly out of the southwest around 10 kts.
Strong, gusty winds possible in and around any thunderstorms. Moderate
confidence.

Tonight...Sub-VFR conditions likely with numerous to widespread
thunderstorms. Some storms may be severe with locally damaging
winds. Storms should move out after 04-06Z but sub VFR cigs
likely in their wake from fog and low stratus. Winds southwest
around 10 knots early this evening veering to northwest 5 to 10
knots overnight. Moderate confidence.

Thursday...Some lingering sub VFR cigs early in the morning with
a few lingering showers possible at MIV and ACY. Some afternoon
showers and storms possible for ACY. Otherwise VFR. NW winds
around 5 to 10 knots. Moderate confidence.

Outlook...

Thursday night thru Friday night...VFR with no significant weather.

Saturday through Monday...mostly VFR with a slight chance of showers
and thunderstorms, mainly in the afternoon and evening hours.

&&

.MARINE...
Small Craft Advisory in effect through Thursday morning for all
coastal waters with SSW winds 20 knots gusting up to 25 knots
with seas around 5 feet. There will also be some storms moving
over the waters that could bring locally stronger winds
potentially gusting over 40 knots.

By Thursday, winds/seas should be sub SCA but there still could be
some lingering showers and storms over the waters.

Outlook...

Thursday night through Monday...Conditions will generally be
below Small Craft Advisory criteria. Wind gusts of 15 kt or less
with wave heights of 4 feet or less. Slight chance showers and
thunderstorms, mainly in the afternoon and evening hours.

Rip currents...

For today, the south-southwest flow will increase to around 15-
20 mph with gusts up to 25 mph. Wave heights in the surf zone
are again forecast to be around 1-3 feet with a 5-7 second
period. Therefore, a MODERATE RISK for the development of
dangerous and life threatening rip currents is in place for the
Jersey Shore and a LOW risk is in place for the Delaware
Beaches.

Late day showers and thunderstorms are possible along both the
Jersey Shore and Delaware Beaches.

Some areas of fog at times will cause reduced visibility along the
shoreline.

For Thursday, winds will turn more offshore out of the west to
northwest and decrease to around 10 mph. Wave heights will mainly
remain around 1-2 feet with a 5-7 second period. As the winds should
be weaker and directed offshore across the region, the risk for the
development of dangerous and life threatening rip currents is
forecast to decrease to LOW on Thursday for all coastal zones.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Warning until 8 PM EDT this evening for
     PAZ060>062-070-071-101>106.
     Heat Advisory until 8 PM EDT this evening for PAZ054-055.
NJ...Excessive Heat Warning until 8 PM EDT this evening for
     NJZ007>010-012-013-015>023-027.
     Heat Advisory until 8 PM EDT this evening for NJZ001-014.
     Air Quality Alert until 11 PM EDT this evening for NJZ012>015-
     017>019.
DE...Excessive Heat Warning until 8 PM EDT this evening for
     DEZ001>003.
     Heat Advisory until 8 PM EDT this evening for DEZ004.
MD...Excessive Heat Warning until 8 PM EDT this evening for MDZ012-
     015-019-020.
MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ450>455.

&&

$$

SYNOPSIS...RCM
NEAR TERM...MJL
SHORT TERM...RCM
LONG TERM...RCM
AVIATION...MJL/RCM
MARINE...MJL/RCM