891
FXUS61 KPHI 041420
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1020 AM EDT Sat May 4 2024

.SYNOPSIS...
High pressure over New England will maintain an onshore flow
through the next few days. A series of cold fronts approaches
from the west through the weekend, with the second (and stronger
of the two) front stalling out nearby by early next week. The
stalled front lifts north as a warm front at some point in the
Tuesday/Wednesday timeframe, bringing a return to above normal
temperatures.

&&

.NEAR TERM /THROUGH TONIGHT/...
10 AM update...Made some tweaks to forecast based on latest
guidance, but not a whole lot changed, just nudged temps down,
cloud cover up. POPs are tricky given showers seem to be
progressing a bit faster than most guidance, with the GGEM being
somewhat closer to reality it would appear. Even the GGEM has
the first band dying out over southern NJ in the next few hours,
so won`t get too aggressive with POPs today just yet, especially
given its quite light rain. That said, if this trend continues,
might have to make some more upward adjustments across the area
as the rain doesn`t seem like its too eager to stop moving
northeast.

Previous discussion...
Scattered showers continue over portions of Delmarva, though
lightning has ended, and showers are not producing the brief
downpours they did earlier. These showers will continue to wind
down this morning.

The base of high pressure centered over New England extends
down into the Mid-Atlantic. An old warm front lies over the
Appalachians, and a cold front is moving through the Great Lakes
and into the Ohio Valley. High pressure slowly lifts to the
north and east throughout the day today and into tonight.
Several shortwaves will approach from the west, pushing those
frontal boundaries towards the local forecast area.

Some marine stratus will continue to spread over portions of
New Jersey and southern Delaware. That stratus will dissipate
later this morning, but skies remain cloudy through the day as
showers continue to develop well west of the region. Those
showers will slowly track east, not making it into the far
western portions of the forecast area until late in the
afternoon and early evening. A cool day with highs in the 50s to
low 60s, which will be some 10 to 15 degrees below normal for
this time of year.

Best chances for showers will be during the overnight period
tonight, mainly for inland areas as those frontal boundaries
wash out as they approach.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
A cold front approaches from the west on Sunday. With a slower
approach, showers will mainly be north and west of the Philly
metro through the morning, before pushing over the rest of the
area through the afternoon and evening. The marine airmass in
place will keep things stable, and really not expecting much in
terms of thunder or heavy rainfall Sunday/Sunday night. Rainfall
amounts will generally be around a quarter to three quarters of
an inch of rain, spread out over a rather large period, so not
expecting much in terms of hydro concerns. Temperatures will be
in the upper 50s/low 60s, though some spots in the Delmarva will
get into the upper 60s/low 70s. Temperatures won`t drop much on
Sunday Night, likely staying in the 50s.

For Monday, temperatures moderate as a weak west/southwesterly
flow takes over. The first of several shortwaves next week is
expected to traverse the area, with some showers and
thunderstorms potentially developing in the afternoon and
evening. Some of the model soundings show decent instability
with marginal shear, so can`t rule out a strong to severe
thunderstorm late Monday. However, not expecting the threat to
be widespread at all. Will continue to monitor as we get in
range of CAM guidance. Best chance to see any convection will be
over Delmarva and southern New Jersey. Temperatures will be in
the upper 70s/low 80s on Monday with mid to upper 50s/low 60s on
Monday Night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Unsettled conditions are expected for most of the week as a
rather progressive pattern will be in place. Several shortwaves
are expected to pass over the region. Lift will also be aided by
a stalled boundary bisecting the area that will meander for the
middle and end of next week. The front looks to venture
northward on Tuesday into Wednesday, resulting in a period of
above normal temperatures with upper 70s/low 80s expected. With
a relatively warm and moist airmass in place, incoming
shortwaves could potentially spark some showers and
thunderstorms Tuesday/Wednesday PM. Wednesday afternoon/evening
looks to be the most active in terms of convective weather,
though too early to see if severe weather is on the table.

The stalled boundary retreats southward towards the end of the
week with onshore flow likely taking over, at least along the
coastal plain. Depending on where this stalled boundary sets up
will have implications on temperatures and thunderstorm
potential on Thursday/Friday. Areas near and east of the front
will be under the influence of the marine layer with cooler and
more stable air, while areas west of the boundary are more
unstable with warmer temperatures. A deepening trough will begin
to move into the Mid- Atlantic, with a series of
shortwaves/frontal systems moving through both Thursday/Friday.
Both days will feature temperatures near/below normal, depending
on where this lingering boundary sets up.

Important to note that there remains a lot of uncertainty with
the long-term forecast as models tend to struggle with a
progressive pattern like this, and the placement of this
boundary that will hang around through next week. As mentioned
before, where that boundary sets up will have large implications
on the forecast. We look to potentially shake this unsettled
pattern once a sweeping cold front comes through late next
week/early next weekend.

&&

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

Rest of Today...Most CIGs have lifted to VFR, though MVFR/IFR
conditions at KACY will remain MVFR/IFR for most of the day.
Slowed progress of MVFR return, but will need to watch progress
of rain as there are lower cigs further west where rain has
been falling longer, though guidance mostly indicates this first
round should dissipate toward midday. MVFR CIGs will spread
from west to east starting at KRDG/KABE tonight. E to SE winds
10 to 15 kt. Low confidence.

Tonight...MVFR/IFR conditions in stratus/BR/SHRA tonight. E
winds 5 to 10 kt. Low confidence.

Outlook...

Sunday through Sunday Night...MVFR/IFR conditions expected with low
ceilings. Reduced visibility likely with showers.

Monday through Monday Night...Conditions gradually improve as the
day goes on, likely back to VFR, though some showers/thunderstorms
develop for the afternoon/evening, with restrictions possible if any
storms move over the terminals.

Tuesday through Tuesday Night...Primarily VFR though some
restrictions possible with 20-40% chance of SHRA.

Wednesday...Sub-VFR conditions possible (30-50%) with scattered
showers/thunderstorms expected, especially in the
afternoon/evening.

&&

.MARINE...
Sub-Small Craft Advisory conditions on tap today and tonight with E
to SE winds 10 to 15 kt with gusts up to 20 kt and 3 to 4 ft seas.
There is the potential for localized marine dense fog early this
morning for areas south of Little Egg Inlet. Otherwise, mostly
cloudy. Some showers may result in VSBY restrictions tonight.

Outlook...

Sunday through Wednesday...No long-fused marine headlines
anticipated, though periods of showers/thunderstorms possible on the
waters.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Hoeflich
NEAR TERM...MPS/RCM
SHORT TERM...Hoeflich
LONG TERM...Hoeflich
AVIATION...Hoeflich/MPS/RCM
MARINE...Hoeflich/MPS/RCM