683
FXUS61 KPHI 231400
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1000 AM EDT Mon Sep 23 2024

.SYNOPSIS...
High pressure over the Canadian Maritimes sags down into the
Northeast and Mid-Atlantic for the start of the new week before
lifting to the north and east by the middle of the week. Low
pressure approaches from the west and drags a cold front towards
the region by the middle of the week. This system clears the
region by the end of the week. High pressure builds down from
the north of the weekend and start of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
No major changes with the 10 AM update. Through the day time
today, the mid and upper level short wave ridge will weaken
slightly as a very weak short wave trough approaches from the
west.

For most, the net effect will just be cloudy or mostly cloudy
conditions. However, for some areas, scattered showers could
work their way into our region by early afternoon. Expect the
showers to be confined primarily west of the I-95 corridor.
Some high rest models are especially bullish on the extent of
shower coverage this afternoon. This seems overdone given how
weak the trough is and how robust the surface/low level ridge
will be through the day. Thus, am generally on the lower end of
guidance for PoPs.

Have higher confidence in the cloudy conditions, and thus,
temperatures being a few degrees lower today as compared to
yesterday. Highs are generally expected to range from the lower
60s in the southern Poconos to lower 70s for the 95 corridor.

Expect coverage of showers to wane after sunset with loss of
daytime heating, but clouds should stay in place. This should
be enough to preclude fog development, but dewpoint depressions
are expected to be quite low, so will be watching trends
closely.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
The base of high pressure centered over the Canadian Maritimes
will begin to pull away on Tuesday, but there should still be
enough of an influence on the Northeast and Mid-Atlantic to keep
the approaching frontal system from making too much headway.

Low pressure will be over the western Great Lakes on Tuesday
morning, and a warm front will extend out ahead of the low with
a cold front extending behind it. Low pressure lifts to the
north towards the Province of Ontario Tuesday night through
Wednesday. The warm front lifts towards the region, and showers
associated with this front will lift into far western zones
starting Tuesday afternoon, but then activity increases Tuesday
night through Wednesday afternoon. With low pressure well north
of the region, the cold front gets pulled through the region
Wednesday night, but gets hung up near the region late Wednesday
night, and almost gets washed out. There will be some
instability developing Wednesday afternoon and Wednesday night,
and this should be enough for a few thunderstorms to develop.
With increasing low level moisture, surface dew points rise into
the 60s to around 70, and this should be enough for locally
heavy rain to develop. Highest PoPs and highest rainfall will be
across the northern half of the forecast area.

PoPs have come down a bit with the latest NBM. Will go ahead
and mix some CONSALL guidance for the Tuesday night through
Wednesday night timeframe to make sure that likely PoPs are in
the forecast. Rainfall during this time will range from 0.50
inches to 1 inch for areas north of Philadelphia and otherwise
as high as 0.25 inches.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The old frontal boundary will be hung up over the area Thursday
as low pressure north of the region tracks out to sea. Some
lingering showers will taper off on Thursday as this system
departs. High pressure then builds in from the north and should
dominate through the weekend.

The fly in the ointment with this forecast is the potential
tropical system that could develop over the Gulf Coast and lift
north into the Gulf Coast states. Going into the end of the week
and weekend, this system would weaken over land, but some rain
associated with it could lift into at least southern portions of
the forecast area. The high to the north should keep most of
the rain shunted to the south and west, though. Will carry
slight chance PoPs for Delmarva for Friday through Saturday for
this potential. Confidence is low at this time.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Primarily VFR expected, though ceilings, especially this
afternoon, will be very close to the MVFR threshold. Thus, MVFR
ceilings will be possible. The period of highest risk is after
18Z, and KRDG and KABE have the highest risk to see MVFR
ceilings (though can`t rule it out at any of the TAF sites.
Rain showers possible, primarily at KRDG and KABE and primarily
after 18Z. However, there is little chance for visibility
restrictions. Easterly winds around 5-10 kt. VAD wind profile
indicates some directional shear in the lowest 2000 ft AGL.
However, expect wind speed to be primarily 10 kt or less, so
don`t expect any LLWS. Moderate confidence.

Tonight...Ceilings are expected to lower into the MVFR category
for most TAF sites. As with Monday morning, there remains a
small chance for fog development, but this is unlikely given the
clouds that are expected to be in place. Light winds favoring
an easterly direction, but could have a variable direction if
they decouple enough. Moderate confidence.

Outlook...

Tuesday...VFR.

Tuesday night through Thursday...Periods of MVFR or IFR in
SHRA.

Thursday night through Friday...Mainly VFR conditions expected.

&&

.MARINE...
Small Craft Advisories on the Atlantic coastal waters today and
tonight, primarily due to elevated seas. On the Delaware Bay,
winds and waves should remain below SCA criteria.

Outlook...

Tuesday through Tuesday night...SCA in effect for the ocean
waters Tuesday, and the SCA is now in effect through Tuesday
night for elevated seas.

Wednesday through Thursday...SCA may be needed for elevated
seas into the middle of next week.

Friday...Sub-SCA conditions possible.

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 Tuesday. The persistent onshore flow continues
with NE winds of 10 to 20 mph along with 3 to 6 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, and will
continue to result in, a piling up of water along the coasts with
this water unable to drain within tidal waterways. Most of the
Coastal Flood Advisories are in effect through the high tide
cycles this afternoon and evening. However, some of the Coastal
Flood Advisories are now in effect through the Tuesday afternoon
and evening high tide cycles.

Details as follows.

The Coastal Flood Advisory remains in effect until 5 pm this
evening for the southern Raritan Bay, northern portions of the
Atlantic coast of New Jersey, and southern portions of the
Atlantic coast for New Jersey. These counties include Middlesex,
Monmouth, southeast Burlington, Atlantic, coastal Atlantic,
Cape May, and Atlantic Coastal Cape May.

For Ocean county, coastal Ocean county, Sussex county (DE) and
the Delaware Beaches, the Coastal Flood Advisory is now in
effect until 6 pm Tuesday to include the high tide cycle on
Tuesday. This is mainly for the back bays of Barnegat Bay as
well as the Little Assawoman Bay and the Indian River Inlet as
water continue to be slow to drain.

For Delaware Bay, the Coastal Flood Advisory is now in effect
until 6 pm Tuesday to include the high tide cycle Tuesday for
minor coastal flooding.

For the tidal Delaware River, Coastal Flood Advisories remain
in effect until 5 pm today for minor coastal flooding. A Coastal
Flood Advisory is unlikely to be needed for the Tuesday evening
high tide cycle.

For the northeastern shore of Maryland, Coastal Flood
Advisories are now in effect through Tuesday night/early
Wednesday morning high tide cycles for minor coastal flooding. A
Coastal Flood Advisory may be also needed for the Wednesday
night high tide cycle.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Coastal Flood Advisory until 10 PM EDT this evening for PAZ070-
     071-106.
NJ...Coastal Flood Advisory until 6 PM EDT this evening for NJZ016.
     Coastal Flood Advisory until 6 PM EDT Tuesday for NJZ020-021-
     026.
     High Risk for Rip Currents through Tuesday evening for NJZ014-
     024>026.
     Coastal Flood Advisory until 5 PM EDT this afternoon for
     NJZ012>014-022>025-027.
     Coastal Flood Advisory until 10 PM EDT this evening for
     NJZ017>019.
DE...Coastal Flood Advisory until 6 PM EDT this evening for DEZ001.
     Coastal Flood Advisory until 6 PM EDT Tuesday for DEZ002>004.
     High Risk for Rip Currents through Tuesday evening for DEZ004.
MD...Coastal Flood Advisory until 4 AM EDT Wednesday for MDZ012.
     Coastal Flood Advisory until 2 AM EDT Wednesday for MDZ015-019-
     020.
MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ450>455.

&&

$$

SYNOPSIS...MPS
NEAR TERM...AKL/Johnson
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...AKL/Johnson/MPS
MARINE...Johnson/MPS
TIDES/COASTAL FLOODING...WFO PHI