Damaging Wind in Delaware, July 31, 2024

Area Forecast Discussion
National Weather Service Mount Holly NJ
400 PM EDT Wed Jul 31 2024

.SYNOPSIS...
A surface trough slides across our area then stalls tonight and
Thursday. A weak system then arrives Thursday night, followed by a
stronger system Friday night and over the weekend. A weak area of
high pressure may then build toward our area early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
A weak front is slowly approaching our area with the associated
trough slowly lifting to to the north-northeast. Out ahead of the
front, some scattered showers and thunderstorms have initiated,
thanks to sufficient instability (mesoanalysis depicts 1000-2000
J/Kg of MLCAPE). However, with the stronger synoptic-scale lift
further north and weak deep layer shear less than 20 kts, strength
of any developing convection will be somewhat limited. Can't
completely rule out some localized heavy downpours but overall, this
is a low shear/moderate CAPE environment which usually does not
result in strong to severe thunderstorms. Main window for any
thunderstorms will be during the afternoon/early evening hours.
Otherwise, temperatures are climbing into the upper 80s/low 90s,
with heat index values around the I-95 corridor getting into the
upper 90s this afternoon.

Any convection weakens/moves out after sunset and it should be a
relatively quiet night overall. Some patchy fog is possible
especially in areas that see some rain this afternoon. Should have
decent radiational cooling conditions supportive of fog development
as well with skies clearing out and winds going light. Temperatures
will fall into the upper 60s/low 70s.

Despite the passage of the front, conditions on Thursday will be hot
and humid, in fact more so than today, thanks to continued
southwesterly flow with another weak shortwave approaching. No
changes have been made at this time to the Heat Advisory issued for
Thursday with max heat indicies mainly between 100-105 degrees in
the afternoon. The next wave may also again force some scattered
showers and thunderstorms during the afternoon hours with the aid of
diurnal heating. PoPs remain mainly in the 20-35% range.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
Hot and very humid with peak heat indices between 95 and 105 degrees
across the region (lowest along the coast and in the higher terrain)
Friday, then a little lower on Saturday. The Heat Advisory for
Friday has been expanded to include the rest of our southern New
Jersey counties (except Cape May County and coastal Atlantic), the
Maryland Eastern Shore and Delaware (except the Delaware Beaches).
While the dew points may mix down a little Friday afternoon, peak
heat indices are sufficient enough to warrant the advisory (plus the
heat risk is in the major category regarding impacts for most of
this area).

A few showers or thunderstorms may linger for a time Thursday night.
Otherwise, a warm and muggy night with not much relief with lows
in the low to mid 70s for much of the region.

An initially stronger upper-level trough pivots across the Great
Lakes and Ohio Valley Friday with it getting closer to our area
especially Friday night. The presence of a surface trough combined
with some increasing forcing for ascent from the approaching upper-
level trough will bring some increasing chances for showers and
thunderstorms. While the instability looks sufficient to support
some stronger thunderstorms, the deep-layer shear is forecast to be
on the weak side. If some stronger cores are able to develop and be
sustained, then a few isolated severe thunderstorms will be possible
Friday afternoon and evening with locally strong/damaging downburst
wind gusts the main threat. Some convection could linger into the
overnight period before moving offshore or dissipating. It will be
another warm and muggy night with lows in the low to mid 70s for
much of the region.

As we go through Saturday, the aforementioned stronger upper-level
trough arrives. A very humid air mass is forecast to remain in
place. Some convection is expected to develop within an unstable and
moist environment, with some increase during the afternoon and
especially the evening. Given more influence from this trough, some
additional clouds and developing convection should temper the
maximum temperatures some. The urban I-95 corridor could still be
close to Heat Advisory criteria (heat index near 100 degrees). For
now, will continue to hold off extending the advisory to include
Saturday. A high moisture content air mass will result in a locally
heavy rain/flash flooding potential especially with any more
organized or slower moving convection.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Summary...The excessive heat eases; Convective chances Sunday which
then lower some through early next week.

Synoptic Overview...An upper-level trough is forecast to be across
the region through early next week, then the flow aloft may turn
more zonal into midweek. The presence of the trough will lower the
temperatures some and the dew points should also lower some with
time. Weak high pressure from the northwest settles nearby Tuesday
into Wednesday.

For Sunday...As a large upper-level trough shifts eastward across
eastern Canada, a shortwave trough on its southern flank moves
across our area. A very warm and humid air mass is forecast to be in
place, although some drier air will try to advect in as the deeper
plume of moisture shifts offshore. A surface low associated with
this upper-level trough should be on the weaker side, however this
will gradually pull a cold front across our area. The forward
movement of this front will determine how long convection lasts and
also the arrival of some less humid air. Some increased forcing for
ascent with the trough will provide lift for the development of
showers and thunderstorms, especially during the afternoon and
evening. While some stronger thunderstorms are possible, the extent
of shear and instability along with forcing will determine the
details. As with any stronger convection in a moist air mass,
locally heavy rain can certainly occur (local flash flooding risk).

For Monday through Wednesday...The aforementioned upper-level trough
is forecast to weak or be absorbed into the parent Canadian trough.
This may lift north enough to result in the flow aloft turning more
zonal. The air mass is not forecast to cool a lot therefore it will
be warm/very warm. The southward push of drier air may also not be
all that strong, therefore while humid conditions look to continue
the dew points should lower at least some. The overall forcing looks
to be on the weak side especially if the trough lifts out with the
flow more zonal. A weak surface high is also forecast to build
nearby. A low chance for some convection still looks to be in place,
however all of the details will depend on the evolution of the
synoptic features.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Prevailing VFR though some scattered clouds around 3000 feet
may briefly fill in at times. Some scattered showers/thunderstorms
will move through in the afternoon. Have add a VCTS group for KPHL
and KILG as thunderstorms have developed further south while
maintain it in the TAF for KABE/KTTN. Thunderstorm activity is
expected to come to an end between 22Z and 00Z. Southwesterly winds
around 10 knots, gusts up to 20 knots possible in the vicinity of
thunderstorms. Moderate confidence in prevailing VFR for most of the
day. Low confidence in timing and extent of convection.

Tonight...Prevailing VFR though some patchy fog possible especially
at KRDG/KABE. Winds will generally be light, around 5 kt or less,
favoring a southwest direction. Moderate confidence.

Thursday...Prevailing VFR, however some scattered showers or
thunderstorms possible, most likely in the afternoon and evening.
Southwest winds around 5-10 knots. Moderate confidence.

Outlook...

Thursday night...Mostly VFR, however a few showers or thunderstorms
possible.

Friday through Sunday...Daily chances for some showers and
thunderstorms which may result in times of sub-VFR conditions.

Monday...Mostly VFR with still a chance of a few showers or
thunderstorms.

&&

.MARINE...
Conditions are expected to be below Small Craft Advisory criteria
across all coastal waters but seas may linger around 5 feet through
the remainder of the afternoon, particularly further offshore off the
coast of New Jersey. Otherwise seas are expected to continue to
decrease to 2-3 feet through Thursday. Winds will be mainly out of
the southwest, up to 20 knots this afternoon and around 10-15 knots
tonight and Thursday. Isolated showers or a thunderstorm remain
possible this afternoon and for Thursday afternoon.

Outlook...

Thursday night through Monday...The conditions are anticipated to be
mostly below Small Craft Advisory criteria. However, the seas may
build to 5 feet on the ocean zones Saturday and Sunday. Some
stronger thunderstorms are possible especially late Friday through
Sunday.

Rip Currents...

Through this evening...South to southwest winds 10 to 20 mph
with waves in the surf zone of 2 to 3 feet. As a result, there
is a MODERATE risk for the development of dangerous rip currents
for the Jersey Shore and a LOW risk for the Delaware Beaches.

Thursday...South/southwest winds will diminish to 5 to 10 mph
with wave heights falling to around 2 feet. This, combined with
an expected period of 5 to 7 seconds, will result in a LOW risk
for the New Jersey Shore and the Delaware Beaches.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 10 AM Thursday to 8 PM EDT Friday for
     PAZ060>062-070-071-101>106.
NJ...Heat Advisory from 10 AM Thursday to 8 PM EDT Friday for
     NJZ007>010-012-013-015-017>020-027.
     Heat Advisory from 10 AM to 8 PM EDT Friday for NJZ016-021-022.
DE...Heat Advisory from 10 AM Thursday to 8 PM EDT Friday for
     DEZ001.
     Heat Advisory from 10 AM to 8 PM EDT Friday for DEZ002-003.
MD...Heat Advisory from 10 AM to 8 PM EDT Friday for MDZ012-015-019-
     020.
MARINE...None.

&&

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