-- Discussion containing changed information from previous version are highlighted. --
264
FXUS61 KPHI 251553
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1153 AM EDT Wed Sep 25 2024

.SYNOPSIS...
High pressure over Atlantic Canada will gradually retreat eastward
through today as a warm front approaches. Low pressure associated
with this warm front will move eastward today and 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. This
set up looks to continue into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
For the midday update, I made some tweaks to the temperature
(lowered afternoon highs) and PoP (pushed highest PoPs further
west) grids.

Rather complex synoptic pattern is setting up with a splitting
trough moving in from the west and a ridge off the coast of the
Outer Banks. As the trough approaches, rather deep southwesterly
flow aloft will set up with a few shortwaves moving through the
flow aiding in lift for some developing showers. Most of the
showers and resulting higher rainfall amounts will be north and
west of the I-95 corridor with the ridge near the Outer Banks
having some influence, bringing subsidence over southern areas.
Precipitation mainly looks to come in two waves, the first
moving in for the mid to late morning and into the afternoon,
with another moving through tonight as a warm front lifts
through. With some elevated instability moving into the Lehigh
Valley and Poconos, cannot rule out a few rumbles of thunder,
though no severe weather is expected.

In between rounds though, some light showers remain possible. Low-
level onshore flow will bring continued low clouds and overcast
conditions through tonight. As a result, expecting another cool day
with temperatures in the mid to upper 60s north and west of the
Philly metro, with low to mid 70s along and south of the I-95
corridor. There won`t be much of a diurnal range with lows tonight,
with temperatures only falling into the 60s.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
The forecast will continue to be a bit unsettled through the short
term period. Thursday through Thursday night, an area of low
pressure and an associated upper level trough will move eastward
from Quebec into the Canadian Maritimes. This will push a trailing
cold front south into the area arriving in our northern zones by
late day Thursday and then pushing south into the area Thursday
night. Along and ahead of this feature there will continue to be
some showers and even the chance of some thunderstorms
Thursday...especially over our NE PA zones into NW NJ where POPs are
as high as 60 to 70 percent. Farther south, for areas near and south
of the urban corridor, any showers will be more scattered and
short lived with POPs here only around 30 percent. Otherwise expect
mainly cloudy skies for Thursday with warm and humid conditions
ahead of the front as highs will be mainly in the upper 70s to low
80s.

For Thursday night, there will continue to be some scattered showers
and storms around as the cold front pushes south into the area. This
front should eventually tend to stall out as it gets into Delmarva
and southern NJ. It will be a mild night with lows mainly in the
60s.

The forecast continues to be a bit tricky for Friday, Friday night,
and beyond as there will be competing factors at play. To our north,
low pressure and it`s associated upper level trough will be
departing over the Canadian Maritimes with high pressure building in
in its wake over southern Quebec. This setup will try to advect
cooler and drier air south through New England towards the Mid
Atlantic. However to our south, there will be a large upper level
low centered near the Gulf coast in the lower Mississippi Valley.
This feature will wrap in and merge with large Tropical Cyclone
Helene as it moves northward while weakening. What this means for
our area is that the cold front discussed above is likely to remain
stalled over Delmarva into southern NJ with some moisture from the
weakening storm to our south advecting northward bringing at least
some rain/showers into our area. The best chances for this look to
be late day Friday into Friday night over SE PA, southern NJ, and
points southward where POPs have been increased to 50 to 60 percent
(compared to 20 to 30 percent farther north through NE PA into NW
NJ). Otherwise expect overcast skies with east winds persisting with
highs Friday mainly in the 70s and lows Friday night mainly in the
60s.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
There continues to be more uncertainty than normal for the long
range forecast. However the overall trend has been shifting towards
and an increased chance of the weekend being overcast and wet for at
least parts of our area.

In the big picture, there will be ridging building in to our north
through the course of the weekend. Meanwhile a large upper level low
containing what will be by this time the remnants of Helene will be
to our south. There are still differences between our different
computer model guidance but the overall trend has been for the
ridge to our north to be weaker allowing the remnants of Helene to
make it farther northward. This could bring some rainfall to at
least southern parts of our forecast area (SE PA, southern NJ,
Delmarva) during the course of Saturday and Sunday along with mainly
cloudy skies and persistent east winds. Given the trends, we nudged
POPs up a bit from NBM guidance to around 30 percent for Saturday
for the aformentioned southern parts of our forecast area while
keeping POPs around 20 percent farther north and east. Again, still
a lot of uncertainty in the forecast but another thing that needs to
be noted is that the overall weather pattern will continue to be
slow moving meaning that any rain that makes it in for Saturday
could linger right through much of Sunday and Monday. Eventually by
next Tuesday an approaching upper trough and associated cold front
arriving from the west should kick the system out to the east but
will bring with it its own chances of showers. In terms of total
rain amounts for the weekend, it`s a bit early to specify any
amounts with much confidence but most likely this would be
beneficial rains with any flooding rains staying to our south.

Temperatures through the long range look to be close to average for
this time of year with highs mostly in the 70s.

&&

.AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas...

Today...Pushed back timing and extent of showers, with the bulk
of the rain falling over the Lehigh Valley. This will result in
IFR CIGs and reduced visibility as rain moves through today.
Low confidence forecast for the I-95 corridor as those terminals
will be right on the edge of the more widespread showers. If
showers make it that far east to the I-95 corridor, conditions
likely will get down to IFR with low clouds, with some MVFR
VSBYs possible. For the South Jersey terminals, showers mainly
stay off to the north and west, though MVFR CIGs expected to
hang around through the day. Winds out of the east/southeast
around 10 kt. Moderate to high confidence in the forecast for
KRDG/KABE, low confidence in the forecast for
KTTN/KPNE/KPHL/KILG, moderate confidence in the forecast for
KMIV/KACY.

Tonight...Some showers and stratus around resulting in a mix
for MVFR/IFR CIGs with some lower visibilities in heavier
showers, which will be around KABE/KRDG. High confidence in
restrictions occurring, low confidence in extent of
restrictions. Winds out of the southeast around 5-10 kt.

Outlook...

Thursday through Thursday night...Sub VFR conditions possible
Thursday morning and again overnight Thursday night due to low
stratus and showers.

Friday through Sunday....Mainly cloudy with periods of sub VFR
conditions possible along with some rain, especially from around
PHL southward. Low confidence forecast.

&&

.MARINE...
A Small Craft Advisory is in effect through tonight for all ocean
zones as seas will be around 5 to 6 feet. No marine headlines for
Delaware Bay. Winds will be out of the east/southeast around 10-20
kt.

Outlook...

Thursday...Seas may continue to linger around 3-5 feet. SCA
possible.

Thursday night-Sunday...The conditions should be sub-SCA Thursday
night and Friday before winds and seas ramp up Friday night into
Saturday potentially to SCA levels (20-25 kt gusts and 4-6 foot
seas). This may persist through Sunday.

Rip currents...

Today...East-southeast winds around 10-15 mph. Breaking wave
heights around 3-4 feet with a 9-10 second period. As a result,
have maintained a HIGH risk for the development of dangerous rip
currents for both the Jersey Shore and Delaware Beaches.

For Thursday...South winds around 10 mph. Breaking waves heights
around 2-3 feet with a 11-12 second period. With winds becoming
more parallel to shore and breaking wave heights a bit lower,
have opted to go with a MODERATE risk for rip currents for both
the Jersey Shore and Delaware Beaches.

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...
Tides and water levels continue to decrease as onshore flow
weakens and we get away from the full moon.

Some spotty minor flooding remains possible along the Eastern
Shore with tomorrow night`s high tide, but tidal flooding should
subside beyond Wednesday Night.

A Coastal Flood Advisory remains in effect through Thursday
evening`s high tide for Ocean County, NJ and Sussex County, DE
as the back bays remain in minor flood stage, even during low
tide. Although onshore flow has weakened, the east/southeasterly
wind direction has kept water trapped in the back bays.

For Delaware Bay, tidal Delaware River, and the New Jersey coast
outside of Ocean County, no further tidal issues are expected.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory until 11 PM EDT Thursday for NJZ020-026.
     High Risk for Rip Currents until 8 PM EDT this evening for NJZ014-
     024>026.
DE...Coastal Flood Advisory until 11 PM EDT Thursday for DEZ003-004.
     High Risk for Rip Currents until 8 PM EDT this evening for DEZ004.
MD...None.
MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ450>455.

&&

$$

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