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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 141754
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
154 PM EDT Sun Apr 14 2024

.SYNOPSIS...
High pressure will briefly be in control through this morning before
an area of low pressure passes to the north of the region and drags
a cold front across the Mid-Atlantic region tonight into Monday.
High pressure builds back in by late Monday into Tuesday,
before a series of frontal boundaries and low pressure systems
affect the east coast Wednesday through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 140pm...Latest guidance stays in line with the previous
forecast with a high shear, low CAPE environmental setup. Round
of showers with some small hail did push through northeast PA
earlier this afternoon. It will be interesting to see how these
showers may influence the mesoscale environment ahead of the
line of storms expected this evening. One one hand, these
showers may have created a more favorable environment with
additional low-level moisture the models may have not accounted
for. On the other hand, increased cloud coverage and any
lingering outflow boundary may limit convective development
later or even relocate the area of convective initiation.
Nonetheless, we will be keeping an eye on the sky.

Previous forecast...The entire area will get into the warm
sector, with temperatures getting into the upper 60s and low to
mid 70s. A cold front will approach from the northwest, with
showers and thunderstorms developing out ahead of it, taking on
a linear mode. The highest instability will be to our west,
though with good forcing and relatively high shear, especially
in the low- levels, some organized convection will likely make
it into our area. The limiting factor is the instability over
our region, roughly 300-500 J/KG of MUCAPE. The steepest lapse
rates will also be well ahead of the better dynamics. Most of
the CAM guidance also has the line of storms coming in right
around sunset or even later.

Overall, everything really isn`t lining up perfectly for a
widespread severe event, and the thinking is that it will be more
localized due to the relatively limited instability. The Storm
Prediction Center now has a SLIGHT risk for the southern
Poconos and portions of the Lehigh Valley and northwest New
Jersey. The threat diminishes significantly the further south
you go as guidance has the line fizzling rather quickly once the
sun goes down. Delmarva and far southern New Jersey actually
will likely stay dry. The main threat is damaging wind gusts as
a 50-60 kt low level jet will be overhead around the time the
line of storms make it to our area which could mix down with any
stronger storms. Cannot rule out a tornado as well with good
low-level shear and SRH in the 0-1 km layer.

The cold front passes overnight and any showers should dissipate by
midnight or so. Temperatures will drop into the 50s overnight with
upper 40s in the Poconos/northern New Jersey.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The main forecast challenge for Monday will be a cold front that
will still be our vicinity. There is some uncertainty regarding how
quickly it will move through with the NAM and GFS clearing it south
through the area Monday morning into the early afternoon while the
GEM Regional is several hours slower. The upshot of this is that we
did add in a 20 percent chance of showers and thunderstorms for
Monday afternoon for our Delmarva Counties into southern NJ as these
areas will be the last to see the front clear and so will have at
least a slight chance of seeing some afternoon convection. It will
be another warm day with most areas seeing highs in the 70s except
cooler near the coast and over the southern Poconos.

High pressure builds in for Monday night and Tuesday bringing fair
weather under mainly clear to partly cloudy skies. Lows Monday night
will be mainly in the 40s to low 50s with highs Tuesday mainly in
the low 70s except once again cooler right near the coast and over
the southern Poconos. The high will start to retreat to our north
and east as we head into Tuesday night as the front to our south and
west starts advancing back towards the area as a warm front. This
will bring an increase in cloud cover with a few showers possible by
Wednesday morning, especially over Delmarva into SE PA.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
In the big picture, the weather pattern will become more unsettled
once again as a large upper level trough with a closed off low
gradually moves eastward from the Canadian Prairies into into Ontario
and Quebec through the mid to late week period. An associated
surface low will also consolidate over the Great Lakes region and
then move into northern Ontario during this period. This will put
our area in a moist deep layer SW flow which will overrun a frontal
boundary at the surface that will remain stalled near Delmarva much
of this period. The upshot of this is that it will be mostly cloudy
with chances for rain/showers each day Wednesday through Friday. The
best chances for widespread showers look to be late Wednesday into
early Thursday and it is for this time period where we have likely
POPs in the forecast. The cloud cover and showers will keep it
cooler compared to this weekend and earlier in the week although
temperatures will actually be fairly close to average.

The upper level trough with its associated frontal system at the
surface should finally swing through the area Friday night into
Saturday with one final round of showers before there should be a
drying trend through next weekend.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Rest of Sunday (through 00Z)...VFR expected at all terminals.
SW winds 10-15 kt with gusts reaching up to 25-30 kt. Showers
and scattered thunderstorms will approach the north and west
terminals (ABE/RDG), but likely stay away through sunset.

Sunday night...Some showers and scattered thunderstorms are
anticipated to move in during the late afternoon/early evening,
mainly for KRDG/KABE. Sub-VFR conditions are possible within any
thunderstorm that does occur. Any lingering sub-VFR conditions
Sunday night will lift to VFR once the cold front comes through.
LLWS concerns for a few hours ahead and along the frontal
boundary, diminishing after 05-06Z. Moderate confidence
overall.

Outlook...

Monday and Tuesday...VFR conditions expected with fair weather.

Wednesday and Wednesday night...Sub-VFR conditions possible (30-40%)
with showers. SSE winds around 10 kts to start, gradually increasing
to 15 kts by late afternoon with gusts up to 20 kts at night.
-- End Changed Discussion --

&&

.MARINE...
Winds and seas will remain below SCA criteria for all Atlantic
Ocean coastal waters until this afternoon when wind gusts and
seas will increase once again to 25-30 knots and 5-7 feet
respectively. As a result, an SCA has been issued beginning at
2 PM EDT this afternoon and continuing through tonight until
early Monday morning.

For the Delaware Bay, sub-SCA conditions are expected through
Sunday night.

Outlook...

Monday and Tuesday...Seas may still be near 5 feet early in the day
Monday but otherwise sub SCA conditions expected for this
period.

Wednesday and Wednesday night...Winds and seas gradually build as
the next storm system approaches. SCA conditions possible by
Wednesday night.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 8 AM EDT Monday for ANZ450>455.
-- End Changed Discussion --

&&

$$

SYNOPSIS...AKL/Fitzsimmons/MJL
NEAR TERM...AKL/DeSilva/Hoeflich/MJL
SHORT TERM...Fitzsimmons
LONG TERM...Fitzsimmons
AVIATION...AKL/Fitzsimmons/MJL
MARINE...AKL/Fitzsimmons