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276
FXUS61 KPHI 230716
AFDPHI

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

.SYNOPSIS...
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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.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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 increasing clouds.
However, for some areas, scattered showers could work their way
into our region, 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 increasing clouds, 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.

What showers there will be will be mostly diurnally driven, so
expect coverage to wane after sunset, but will keep the low and
mid level clouds 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/...
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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.
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&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
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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.
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&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 12Z...Prevailing VFR. There are some clouds around 2K
to 3K ft AGL, which are resulting in temporary MVFR ceilings at
some sites, but impacts are brief. Still some potential for
fog/BR development, but looking less likely given the clouds in
place, so have refrained from mentioning for most TAFs. Light
winds less around 5 kt. Moderate confidence.

Today...Primarily VFR expected. As low clouds and showers build
closer to the region, MVFR ceilings will be possible after 18Z,
primarily for KRDG and KABE. Little chance for visibility
restrictions though. Easterly winds around 5-10 kt. 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.
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&&

.MARINE...
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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
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&&

.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. Although
headlines are in effect through the Monday afternoon/night high tide
cycles, additional Coastal Flood Advisories may be needed for the
Tuesday afternoon/night high tide cycles.

For the Atlantic Coast, southern Raritan Bay, and Delaware Bay,
Coastal Flood Advisories remain in effect through the Monday
afternoon high tide cycles. A Coastal Flood Advisory may be needed
for some locations for the Tuesday afternoon high tide cycle.

For the tidal Delaware River, Coastal Flood Advisories remain in
effect through the Monday evening high tide cycle for minor coastal
flooding. A Coastal Flood Advisory may be needed for some locations
for the Tuesday evening high tide cycle.

For the northeastern shore of Maryland, Coastal Flood Advisories
remain in effect through the Monday night high tide cycles for minor
coastal flooding. A Coastal Flood Advisory may be also needed for
the Tuesday night high tide cycle.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
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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 5 PM EDT this afternoon for
     NJZ012>014-020>027.
     High Risk for Rip Currents through Tuesday evening for NJZ014-
     024>026.
     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 5 PM EDT this afternoon for
     DEZ002>004.
     High Risk for Rip Currents through Tuesday evening for DEZ004.
MD...Coastal Flood Advisory until 5 AM EDT Tuesday for MDZ012.
     Coastal Flood Advisory until 2 AM EDT Tuesday for MDZ015-019-
     020.
MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ450>455.
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&&

$$

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