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327
FXUS61 KPHI 041812
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
212 PM EDT Sat May 4 2024

.SYNOPSIS...
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High pressure over New England will maintain an onshore flow
through the weekend. A series of cold fronts approaches from
the west, 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.
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&&

.NEAR TERM /THROUGH SUNDAY/...
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Latest analysis depicts a backdoor cold front extending from the
Virginia capes northwestward toward western Pennsylvania and
north across the eastern Great Lakes. Another cold front moving
southeast from Canada is washing out over the eastern Great
Lakes. A third cold front is pushing southeast across the
western Great Lakes and north/central Plains. Aloft, a ridge
straddles our region north to south, but several weak shortwaves
are located over the upper Ohio Valley and southeastern US,
with more further west over the central Plains.

Weak warm advection above the cool marine layer will allow
showers to continue through Sunday, but the main mid and upper
level forcing will remain mostly to our west in central PA.
Thus, expect relatively dry conditions near the immediate coast,
with the bulk of precip near Chesapeake Bay and across western
Chester, Berks and the Poconos through Sunday afternoon. That
said, enough shortwave energy finally pushes eastward over the
region by then to allow more organized showers to cross much of
the remainder of the region, so have POPs maxing out Sunday
afternoon, but even then, still keep them below categorical from
I-95 south and east. QPF looks relatively light given the long
duration as well, with less than an inch area-wide and less than
a half inch from I-95 corridor on south and east, with almost
nothing near the coast. All that being said, it still won`t be
very nice, as the persistent easterly flow will keep skies
cloudy and temps cool, mostly 40s to near 50 at night and 50s
and 60s during the day. The warm front does try to lift
northward late on Sunday, so that gives areas from Philly south
the opportunity to approach (but not reach) normal, but it`ll
be a struggle.
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&&

.SHORT TERM /SUNDAY NIGHT 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 SATURDAY/...
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 /18Z SATURDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of today...VFR to MVFR with spotty showers. Best conditions
around KTTN where showers will struggle longest to reach. Winds
easterly 5-10 kts. Moderate confidence.

Tonight...dropping to IFR cigs most of the area, but not much
reduction in vsby except in showers. Showers common western
terminals, minimal if any eastern terminals, but low cigs likely
regardless. Winds remaining mostly east 5-10 kts. Moderate
confidence.

Sunday...IFR cigs most of the day, with IFR or low MVFR vsby
likely by afternoon esp where showers most common, which will be
western terminals. Winds remaining mostly east 5-10 kts.
Moderate confidence.

Outlook...

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.
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&&

.MARINE...
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Sub-Small Craft Advisory conditions through Sunday. Ocean waves
2-4ft with easterly winds 10-15 kts and a few gusts up to 20
kts. Intervals of reduced vsby in spotty showers.

Outlook...

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

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

&&

$$

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