NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Aug 28, 3:23 PM EST, 3 hours 46 minutes earlier.
Area forecast discussion, Aug 28, 3:23 PM EST, 3 hours 46 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
423 PM EDT Wed Aug 28 2024
.SYNOPSIS...
A cold front will push south across the region tonight, then
stall south and west of the region into Friday. It will reverse
as a warm front and move back across the region Friday night
into Saturday. Another cold front will move into the region and
then wash out Saturday night with another, more potent cold
front moving through by early on Labor Day. High pressure then
returns thereafter.
&&
.NEAR TERM /THROUGH THURSDAY/...
After a weak warm front moved through this morning with clouds
and a few sprinkles, sunshine has come to dominate this
afternoon with skyrocketing temps and heat indices. Excessive
heat warnings and advisories remain in place through early
evening.
Cold front presently remains across upstate New York, just north
of the PA line, aligned almost due east-west. The front won't
likely enter the CWA til near midnight and then will push more
southwest across the region through the rest of the night into
Thursday morning, clearing our area likely by late morning
Thursday. The high pressure driving its movement will take up a
position near the northern New England coast, making the front
act more like a back-door cold front with a wedge of cooler,
somewhat maritime air pushing into the region in its wake. This
will bring a quick end to our one day heat spike, with lows
tonight in the 70s south and 50s north, and highs in the 80s
south and 70s north on Thursday.
Of course, there is the very big question about just how much
convection we get from this front. Its late passage suggests
convection will be more instability and upper-level forcing
driven, not particularly driven by the front itself, with
guidance, all though not in great agreement, generally following
the idea of scattered convection developing late this afternoon
and expanding as an approaching shortwave trough pushes into the
region through the early overnight before dwindling toward dawn
as the front and lack of insolation robs us of instability and
the shortwave moves out of the area. Given the high CAPE and
DCAPE, damaging winds look to be the main risk with storms this
evening, though can't rule out some locally heavy rain or small
hail. Most precip should be out of here by dawn, but some light
mist or drizzle may persist, along with low clouds, a fair chunk
of the day. Spotty convection developing in the warm sector west
of us may start moving in later on Thursday as well, but it
should overall weaken as it moves into the cool wedge over our
region by then.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
Surface high pressure centered north of the Great Lakes region
Thursday will move eastward with time. As this surface high shifts
eastward and offshore of the Canadian Maritimes later Friday, a warm
front is invited to approach the region. A stationary front looks to
linger south of the area into Friday before the warm front
approaches Friday into Friday night. Some weak surface low pressure
may ride along the stationary front during the time frame it remains
to our south.
Given the synoptic situation described, the short term looks
unsettled but not overly impactful. Mainly slight chance and chance
PoPs into Friday; isolated to scattered showers and thunderstorms
possible through much of the time frame. Nothing to note at this
time from WPC or SPC regarding any excessive rainfall or severe
weather potential.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
The synoptic situation is fairly straightforward for the long term.
A primary cold front looks to cross through the region sometime this
weekend (most likely Saturday night into Sunday) before a secondary
cold front crosses through thereafter (looking like Sunday night
into Monday). Surface high pressure from the west/northwest then
begins to build in to the region, migrating eastward with time.
Forecaster confidence in this synoptic evolution is high overall,
while lower confidence remains in the exact timing of features
(e.g., fronts) based on available guidance.
Overall, expect a fairly active weather weekend with a dry forecast
for the beginning of the week into midweek. Primary cold front will
likely bring widespread showers and thunderstorms to the region
Saturday into Sunday as it crosses through. The timing of the
primary cold front will need to be monitored closely as it may carry
a severe weather potential if timing is coincides with peak diurnal
heating. The secondary cold front to follow will likely be less
impactful, but will continue with a chance of showers and
thunderstorms through at least Sunday. Depending on the speed and
timing of the cold fronts, Labor Day could shape up to be a very
nice day with seasonable temperatures and low humidity. At the very
least, much of next week looks to be very comfortable with low
humidity and temperatures slightly below average.
&&
.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Through tonight...VFR to start with little chance of issues
until 23Z or so, by which time scattered TSRA will likely start
developing in the area/moving into the region from the
northwest. These linger until near midnight, dwindling to
showers thereafter but likely remaining scattered in coverage.
Backdoor cold front will then usher in some MVFR cigs across
most terminals by dawn. Winds could be gusty in storms, but
otherwise generally 5-10 kts, northwest early then becoming
northeast late. Low confidence.
Thursday...MVFR cigs likely persist a fair chunk of the day as
back door cold front stalls to our southwest, with northeasterly
to easterly winds 5-10 kts. Cigs may lift to VFR in places at
times during the afternoon. Mostly dry though an isolated shower
is possible, especially out towards KRDG. Moderate confidence.
Outlook...
Thursday night through Friday night...Mainly VFR with some stray
showers possible. No significant weather expected.
Saturday through Monday...Should primarily remain VFR, with
intervals of sub-VFR conditions due to shower and thunderstorm
potential, most notably Saturday into Sunday.
&&
.MARINE...
Generally sub-advisory winds and seas through most of tonight,
outside of any gusty thunderstorms which may necessitate special
marine warnings tonight. With strong north to northeast push
behind passing cold front late tonight through Thursday, winds
will be near 25 kts with seas building to 5-6 feet. Thus have
issued Small Craft Advisory for ocean zones starting Thursday
morning, though further south it may not begin until later in
the day.
Outlook...
Thursday night...A Small Craft Advisory is in effect through
Thursday night for the Atlantic coastal waters due to seas
lingering around 5 feet. No headlines warranted for the
Delaware Bay.
Friday through Monday...No marine headlines anticipated. Showers and
thunderstorms possible through the period, most likely Saturday into
Sunday.
Rip Currents...
Tonight into tomorrow, winds will become northeasterly and
increase. This will be directly onshore for the coast line from
LBI northward. Consequently there is a MODERATE risk for those
areas, while a LOW risk is expected for the rest of the coast
line. We will continue with this same forecast for Friday as
there will be little in the pattern as onshore flow persists.
For specific beach forecasts, visit weather.gov/beach/phi
&&
.CLIMATE...
Temperatures Wednesday afternoon will rise into the mid to
upper 90s, but likely fall short of challenging record highs for
the day.
Record High Temperatures for August 28th
SITE RECORD/YEAR
Allentown (ABE)........97/1973
AC Airport (ACY).......97/1973
AC Marina (55N)........96/1973
Georgetown (GED).......98/1948
Mount Pocono (MPO).....90/1953
Philadelphia (PHL).....99/1973
Reading (RDG)..........99/1948
Trenton (TTN)..........98/1973
Wilmington (ILG)......100/1973
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 8 PM EDT this evening for PAZ060>062-
101>103-105.
Air Quality Alert until 11 PM EDT this evening for PAZ070-071-
101>106.
Excessive Heat Warning until 8 PM EDT this evening for PAZ070-
071-104-106.
NJ...Heat Advisory until 8 PM EDT this evening for NJZ007>010-012-
013-016-020>023-027.
Air Quality Alert until 11 PM EDT this evening for NJZ012>027.
Excessive Heat Warning until 8 PM EDT this evening for NJZ015-
017>019.
DE...Heat Advisory until 8 PM EDT this evening for DEZ001>003.
MD...Heat Advisory until 8 PM EDT this evening for MDZ012-015-019-
020.
Air Quality Alert until 11 PM EDT this evening for MDZ012-015-
019-020.
MARINE...Small Craft Advisory from 9 AM Thursday to 6 AM EDT Friday for
ANZ450>455.
&&
SYNOPSIS...DeSilva/RCM
NEAR TERM...RCM
SHORT TERM...DeSilva/Wunderlin
LONG TERM...DeSilva/Wunderlin
AVIATION...DeSilva/RCM
MARINE...DeSilva/RCM
CLIMATE...