255
FXUS61 KPHI 041036
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
636 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/...
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 /12Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Any MVFR CIGs this morning will lift to VFR by 14Z,
though MVFR conditions at KACY will remain MVFR for most of
today. MVFR CIGs will spread from west to east starting at
KRDG/KABE around midday, then MVFR CIGs will spread towards KACY
prior to 00Z. SHRA arrive at KRDG/KABE prior to 00Z as well. E
to SE winds 10 to 15 kt. Moderate confidence.

Tonight...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
SHORT TERM...Hoeflich
LONG TERM...Hoeflich
AVIATION...Hoeflich/MPS
MARINE...Hoeflich/MPS