922
FXUS61 KPHI 240850
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
450 AM EDT Tue Sep 24 2024

.SYNOPSIS...
High pressure over Atlantic Canada will gradually retreat eastward
through the course of Tuesday and Wednesday as a warm front starts
to approach. Low pressure associated with this warm front will move
eastward Wednesday through Thursday as it passes by to our north
moving from Ontario and Quebec into New England. By the weekend, the
area will be situated between high pressure to the north while low
pressure will be to our south.

&&

.NEAR TERM /THROUGH TONIGHT/...
A weak shortwave rippling through the upper level flow is resulting
in some light sprinkles mainly south of Philadelphia this morning.
As high pressure, centered over eastern Canada, nudges in from the
northeast, showers will gradually dissipate, most likely by
daybreak. Cannot rule out some patchy fog, mainly in the Lehigh
Valley and northern New Jersey, as well with dewpoint
depressions shrinking as temperatures decrease.

For today, high pressure continues to nudge from the northeast. This
will result in a dry day overall, though with continuing onshore
flow, a mostly cloudy to overcast day is expected. With a cool and
moist maritime airmass remaining in place, temperatures will only
get into the upper 60s/low 70s with low 60s in the Poconos.

A digging trough moving through the central US will eventually
cutoff near the Mississippi River with a split flow pattern
developing. The result will be southwesterly flow aloft with weak
positive vorticity advection beginning tonight. Additionally, weak
warm air advection will set up tonight as a warm front
approaches, and with a moist airmass already in place, some
showers will begin to move in. However, the bulk of the rain
should come in during the day on Wednesday (more on that below).
Overnight lows will be in the upper 50s/low 60s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
It will be a bit unsettled for parts of the short term period as a
system brings parts of the area some much needed rainfall.

For Wednesday, an upper level trough will be digging southward into
the Great Lakes along with an associated trough at the surface. This
will help push a warm front towards the area keeping skies mostly
cloudy with some showers around. Expect that these showers will be
heaviest and most persistent N/W of the urban corridor and more
scattered to isolated farther south/east. In fact the coast may not
see anything. Highs will range mostly from the upper 60s to mid 70s
except a bit cooler over the Pocono Plateau.

The trend will be for showers to generally diminish with time
throughout the course of Wednesday night and Thursday with any
lingering showers by Thursday being confined mainly to areas near
and especially north of the urban corridor. This will occur as low
pressure moves eastward from Quebec into eastern New England while
high pressure starts to build back in over Central into western PA.
Total rain amounts will be very minimal near the coast with a tenth
to a quarter inch possible near the urban corridor and a half to
three quarters inches possible over parts of NE PA into NW NJ.
Expect skies to overall be partly to mostly cloudy Thursday with it
being warmer and more humid compared to Wednesday as we will be in
the warm sector. Highs will be mainly in the upper 70s to low 80s
with dew points mainly in the mid to upper 60s. Weak surface ridging
should try to build east into the area Thursday night keeping it
mainly dry but with lingering cloud cover. Lows are expected to
range from the mid 50s north to the mid 60s south.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
There is more uncertainty than normal for the long range period as
the pattern will be quite complex over eastern North America. To
start the period early Friday, there will be an upper level low over
the Canadian Maritimes with another upper low near the Gulf coast.
Meanwhile upper level ridging will be over the Great Lakes with a
surface high over PA. Finally, by this time the upper low near the
Gulf coast will have likely pulled in the tropical cyclone which
should be situated by this time somewhere over the SE CONUS. The
main uncertainty hinges around whether some of the moisture to our
south will be able to move northward bringing the area some rain
this weekend or whether the ridging to our north will suppress it
south. The latest guidance has generally trended toward bringing
some decaying remnants of the system to our south a bit farther
north suggesting an increased chance for rain this weekend along
with more in the way of cloud cover. Given the continuing
uncertainty in the forecast, we stayed close to the NBM which
generally brings the area POPs of around 20 to 30 percent by late
Friday and again for the day Saturday and Sunday.

If the upper level low to our south is able to move far enough north
to bring us rain for this weekend, this unsettled weather could
linger into early next week as the upper level pattern will be quite
blocky. As far as temperatures, they should be close to seasonal for
the long range period with highs mostly in the 70s.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Rest of Tonight (thru 12z)...Most sites start VFR but some stratus
begins to move in around/just before daybreak, reducing ceilings
down to MVFR. Some terminals could stay VFR through the night before
coming down later this morning. High confidence in prevailing
VFR/MVFR, with low to moderate confidence in timing of restrictions.
Winds out of the east/northeast around 5 kt.

Tuesday... MVFR to start with stratus, but ceilings should
lift/scatter out a bit for the afternoon at most sites. Not exactly
high confidence though, and changes could come with the 12z TAF
package keeping MVFR ceilings through the day as an easterly onshore
wind could reinforce stratus. Model guidance is having trouble
handling this setup overall. Winds out of the east around 10 kt.
High confidence in wind speed/direction, low confidence in extent of
restrictions and timing of improvement to VFR.

Tuesday Night...Scattered showers move in with ceilings coming down
gradually, first to MVFR by the mid-evening, potentially down to IFR
early on Wednesday morning. Winds out of the east around 5-10 kt.
Low confidence.

Outlook...

Wed thru Wed night...Some showers along with low stratus could bring
sub VFR conditions at times, especially for RDG and ABE.

Thu thru Sat... Mostly VFR.

&&

.MARINE...
A Small Craft Advisory is in effect for all ocean zones as seas
will be around 3 to 6 feet through Wednesday. On Delaware Bay,
no marine headlines are expected as winds will be out of the
east around 10-15 kt.

Outlook....


Outlook...

Small Craft Advisory level conditions are expected to continue
through Wednesday...mainly due to seas 4 to 6 feet. Conditions
should finally diminish below Small Craft Advisory conditions
through Wednesday night. The sub-SCA may last thru Fri night with a
possibility of another SCA Sat or Sunday. Scattered showers Tue
night thru Wed night.

Rip currents...

There is a HIGH risk for the development of dangerous and life
threatening rip currents at the Jersey Shore and at Delaware Beaches
through Wednesday. The persistent onshore flow continues with
easterly winds of 10 to 20 mph along with 3 to 5 ft breaking waves.

Rip currents occur often in the vicinities of jetties and piers and
the speed of the currents are generally maximized at low tides.

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

&&

.TIDES/COASTAL FLOODING...
A prolonged period of onshore flow has resulted in a piling up
of water along the coasts with this water unable to drain within
tidal waterways.

Coastal Flood Advisories are in effect today for Ocean County,
NJ and Sussex County, DE mainly for minor and spotty moderate
flooding in the back bays-Barnegat Bay in NJ, and Little
Assawoman Bay and the Indian River Inlet in Delaware. Thought
about extending the Advisory as some of the back bay tidal
guidance keeps minor flooding through Wednesday, but will wait
to see how today`s high tide cycle goes.

For Delaware Bay, a Coastal Flood Advisory is in effect for Kent
County, DE and Cumberland County, NJ for minor tidal flooding
with this afternoon`s high tide. Following this afternoon`s high
tide, no further advisories are anticipated.

For the Eastern Shore of Maryland, a Coastal Flood Advisory
remains in effect through tonight for minor tidal flooding
around tonight`s high tide. May need to extend for one more high
tide following tonight but will wait for more guidance to come
in and see how high the evening high tide gets.

Some spotty minor flooding remains possible along the southern
New Jersey coast, with no tidal issues expected along the
northern New Jersey coast (Monmouth and Middlesex County) and
along the tidal Delaware River.



&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory until 6 PM EDT this evening for NJZ020-
     021-026.
     High Risk for Rip Currents through Wednesday evening for NJZ014-
     024>026.
DE...Coastal Flood Advisory until 6 PM EDT this evening for
     DEZ002>004.
     High Risk for Rip Currents through Wednesday evening for DEZ004.
MD...Coastal Flood Advisory until 5 AM EDT Wednesday for MDZ012.
     Coastal Flood Advisory until 2 AM EDT Wednesday for MDZ015-019-
     020.
MARINE...Small Craft Advisory until 6 PM EDT Wednesday for ANZ450>455.

&&

$$

SYNOPSIS...Fitzsimmons
NEAR TERM...Hoeflich
SHORT TERM...Fitzsimmons
LONG TERM...Fitzsimmons
AVIATION...Fitzsimmons/Hoeflich
MARINE...Fitzsimmons/Hoeflich
TIDES/COASTAL FLOODING...Hoeflich