NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Aug 9, 5:15 AM EST, 3 hours 45 minutes earlier.
Area forecast discussion, Aug 9, 5:15 AM EST, 3 hours 45 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
615 AM EDT Tue Aug 9 2022
.SYNOPSIS...
A surface trough will remain in place across the region today
as a weak cold front approached from the northwest. The weak
cold front will then settle across our area tonight and
Wednesday. A stronger cold front crosses our area late Thursday,
then high pressure builds in for later Friday through Sunday
before weakening into Monday.
&&
.NEAR TERM /THROUGH TONIGHT/...
High pressure remains located over the western North Atlantic.
The circulation around the high will continue to bring very warm
and humid air into our region from the southwest and south into
this afternoon. High temperatures are again forecast to be
manily in the lower and middle 90s, except in the elevated
terrain and along the immediate coast where readings should not
get above the middle and upper 80s. Dew point values are
expected to be mostly in the lower 70s. As a result, we continue
to expect heat index values as high as 100 to 105 in the
counties covered by the Heat Advisory.
A cold front extended from northern New England to the Ohio
River Valley early this morning. The boundary will sink to the
south today and it should reach the Poconos and far northern New
Jersey late this afternoon. The boundary is then forecast to
drift through much of the remainder of our region tonight before
reaching southern Delaware and the adjacent counties of eastern
Maryland toward daybreak on Wednesday.
The front will bring and increasing chance of showers and
thunderstorms to our region from north to south during the
afternoon and evening hours. The potential for widespread
convection is greater than during the past several days as the
boundary will provide a trigger for its development.
Precipitable water values remain high, generally in the 2 to 2
1/4 inch range, so locally heavy rain is possible.
The chance of showers and thunderstorms will linger into late
tonight in parts of southern New Jersey, Delaware and eastern
Maryland, in the vicinity of the front. Meanwhile, areas to the
north should have little or no precipitation during the
overnight hours. Tonight's low temperatures should range mainly
from the upper 60s to the middle 70s with a light northerly wind
developing.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
A pattern change will start during this time frame, as we begin
to step down from the multi-day excessive heat and humidity.
Some showers and thunderstorms will accompany this change as a
couple of cold fronts move through.
An upper-level trough sliding across central to eastern Canada
is forecast to amplify across the Great Lakes, Northeast and
Mid- Atlantic. This will settle a weak cold front across our
area which may stall across our southern areas Wednesday. While
the stronger flow remains to our north and west, some gradual
influence from the incoming upper-level trough will come into
play. Ample instability will favor especially afternoon and
evening convection, however there has been some southward
shifting in much of the guidance. It appears that the initial
weak cold front Wednesday settles farther south, therefore the
greater instability may be realized across the coastal plain
including Delmarva. Given the weak flow still in place, shear
will also be rather weak. Despite this, steepening low- level
lapse rates combined with ample instability could result in
localized water-loaded downbursts. There is some potential for
some convective clustering from northern Virginia to Delmarva
later Wednesday afternoon and evening and this could expand into
southern New Jersey and even the Philadelphia metro.
Storm motions Wednesday may be somewhat chaotic given the
lighter flow, and therefore training or some backbuilding could
result especially along the weak front and/or outflows. This
will be within an environment of 2+ inches of precipitable
water, therefore slow moving convection will be capable of
producing torrential rainfall and possible local flash flooding
especially in the urban areas. The setup looks to be the
greatest from near and south/east of I-95. Given the dryness and
some southward shift in some of the guidance, opted to hold off
on any Flood Watches at this time.
It will remain warm to hot Wednesday and still humid, however
with the weak cold front in place and associated cloudiness and
some convection the temperatures are forecast to be held down
some. As a result, heat indices are forecast to fall short of
advisory criteria (100-104F for much of the area). Some
convection may continue through Wednesday night given the
presence of the weak cold front and the incoming trough,
although the environment could become worked over enough to
result in the convection dissipating overnight.
As we go through Thursday, an upper-level trough is forecast to
be amplifying across much of the East. This will take an
initial weak cold front off the coast to start the day, however
a stronger cold front is forecast to sweep through late
Thursday. Temperatures will be much closer to average given
height falls, however the humid conditions will start to ease
during the course of the day as some dry air advection gets
underway. Given the trough aloft and the secondary cold front
moving through, some showers and thunderstorms will be possible
with the greatest chances probably across the coastal plain
through about the early afternoon hours. The extent of the
convection however will depend on the timing of an impulse
exiting and then how fast the drier air moves in behind the
initial weak cold front. Much drier air then moves in Thursday
night following the passage of the stronger cold front, with
temperatures actually dropping into the 60s for much of the area
(some 50s up north).
&&
.LONG TERM /FRIDAY THROUGH MONDAY/...
Summary...A refreshing air mass settles in due to a pattern
change, which brings much cooler and less humid air.
Synoptic Overview...A pattern change courtesy of a sharpening
upper- level trough that settles across the East into the
weekend. Some energy will be departing to our east to start
Friday, then surface high pressure arrives later Friday and
remains in place through Sunday before weakening. This results
in a much cooler and less humid air mass to the region, although
the dew points may start to increase a little Monday.
For Friday...The axis of a sharpening upper-level trough is
forecast to pivot across our area. This will result in
noticeably cooler and much less humid air settling into our area
under a northerly wind. Some guidance hinting at a few showers
possibly lingering in the morning for the coastal plain, however
the best moisture and lift should be offshore and therefore
opted to continue to carry a dry forecast. Surface high pressure
starts to build much closer at night with a very dry and much
cooler air mass in place. High temperatures will be in the 70s
to low to mid 80s, and low temperatures will drop into the 50s
for much of the area.
For Saturday and Sunday...While the main part of the upper-
level trough gradually lifts to our northeast and east, we
remain in an overall trough. As this occurs, surface high
pressure will be building across the area from the west with a
much more comfortable air mass in place. Despite some lingering
cyclonic flow aloft, the presence of surface high pressure and a
dry air mass will result in no precipitation. Daytime
temperatures each day are forecast to be near or below average.
For Monday...The upper-level trough is forecast to amplify some
across the Northeast and Mid-Atlantic regions. This will result
in surface high pressure weakening as it shifts offshore and a
cold front may start to approach from the northwest. A shower or
thunderstorm is possible in the afternoon and evening, and for
now went with some slight chance PoPs. Temperatures should be
near or just below the average, however the dew points should be
creeping upward some.
&&
.AVIATION /10Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Today...Generally VFR. There is a chance of showers and
thunderstorms late this afternoon, mainly around KRDG and KABE.
Southwest to west wind increasing to around 10 knots with gusts
of 15 to 20 knots. Medium to high confidence.
Tonight...A chance of showers and thunderstorms early tonight,
reducing conditions to MVFR/IFR for a time. Otherwise, mainly
VFR. Southwest to west wind 5 to 10 knots, becoming northerly 8
knots or less. Medium confidence.
Outlook...
Wednesday...VFR ceilings at varying heights, should transition
to times of MVFR/IFR conditions due to some showers and
thunderstorms especially later in the afternoon and at night.
Winds may favor light and variable due to a weak front in the
area. Low confidence with the details.
Thursday...Some lingering showers and thunderstorms possible,
especially in the morning, otherwise mostly VFR. Light and
variable winds becoming northwest 5-10 knots. Low confidence.
Friday and Saturday...VFR. Northwesterly winds around 10 knots
Friday, potentially becoming light and variable Saturday.
Moderate confidence.
&&
.MARINE...
We will discontinue the Small Craft Advisory for our ocean
waters.
High pressure located over the western North Atlantic will
maintain a southerly wind on the coastal waters of Delaware and
New Jersey for today. Wind speeds are expected to be around 15
knots on our ocean waters, and to 10 to 15 knots on Delaware
Bay.
A cold front is expected to drop southward across the coastal
waters of New Jersey and Delaware tonight, shifting the wind to
the north around 10 knots.
Wave heights should be 3 to 4 feet on our ocean waters and 2
feet or less on Delaware Bay for today and tonight.
Outlook...
Thursday through Saturday...The conditions are anticipated to
be below Small Craft Advisory criteria.
Rip currents...
A southerly wind of 10 to 15 MPH is anticipated for today.
Breaking waves should be 2 to 3 feet with a medium period south
to southeast swell. There is a MODERATE risk for the development
of dangerous rip currents along the New Jersey coast, and a LOW
risk at the Delaware Beaches today.
A north wind around 10 MPH on Wednesday morning is forecast to
become east to southeast in the afternoon. Breaking waves are
expected to be 1 to 2 feet with a medium period south to
southeast swell. There is a LOW risk for rip currents along the
coasts of Delaware and New Jersey on Wednesday.
&&
.TIDES/COASTAL FLOODING...
The full moon occurs on Thursday evening. The evening high
tides on Wednesday, Thursday and Friday will be particularly
high even without any contribution from the wind. As a result,
some localized tidal flooding is possible each evening in the
coastal counties of New Jersey and Delaware, and along Delaware
Bay.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 8 PM EDT this evening for PAZ060>062-070-
071-101>106.
NJ...Heat Advisory until 8 PM EDT this evening for NJZ001-007>010-
012-013-015>021-027.
DE...Heat Advisory until 8 PM EDT this evening for DEZ001.
MD...Heat Advisory until 8 PM EDT this evening for MDZ012-015-019-
020.
MARINE...None.
&&
Synopsis...Gorse
Near Term...Iovino
Short Term...Gorse
Long Term...Gorse
Aviation...Gorse/Iovino
Marine...Gorse/Iovino
Tides/Coastal Flooding...WFO PHI