-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 280551
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
151 AM EDT Sun Apr 28 2024

.SYNOPSIS...
High pressure will remain in control of the prevailing
conditions through early in the week with low chances of showers
and storms. Temperatures rise above normal Sunday as a warm
front lifts north of the area. A weak system will be a more
widespread chance of storms on Tuesday, and temperatures will
remain above normal through the week.

&&

.NEAR TERM /THROUGH TODAY/...
-- Changed Discussion --
Light rain/ shower activity has been a bit more spread out than
previous forecast so precip chances were increase but otherwise
no significant changes made to prior forecast.

Most of the sprinkles or light showers have tapered off and
moved offshore. Warm front continues to approach from the west,
and additional light showers are possible for the southern
Poconos and northern New Jersey, and down into eastern New
Jersey through the overnight. Lows will be in the mid to upper
40s (low 40s Poconos), with even near 50 in the more urban
spots. The warm advection and isentropic lift aloft along with
some weak mid-level vorticity advection should result in
additional isolated to scattered showers overnight. The greater
shower coverage overnight will be over northeast PA and northern
NJ, decreasing to isolated southwestward toward Philadelphia.
CAMs generally back that idea up, though are inconsistent with
regard to exact timing and coverage.

The aforementioned forcing mechanisms will shift east-northeast
away from our region Sunday morning, as an upper-level ridge
amplifies northward up the Appalachians and across the mid-
Atlantic. Surface high pressure will settle off the coast of the
Carolinas, resulting in southwesterly low-level flow bringing
the warmest temperatures since April 15th. Decreasing cloud
cover should allow for enough sunshine to allow some spots,
particularly inland from Philadelphia southward, to reach 80F.
Expect a southerly sea-breeze to keep the immediate shore
communities much cooler, but that will not make it too far
inland with the southwest to west ambient flow. Dewpoints may
make it into the mid to upper 50s for the afternoon; while not
humid by summer standards, it may be noticeable to the un-
acclimated. Meanwhile, another shortwave rotating over the
upper-level ridge may spark off a few widely scattered showers
over eastern PA, particularly from the Lehigh Valley northward
Sunday afternoon. Some CAMs suggest those could push east-
southeastward across the Delaware River into NJ, but the chance
looks quite low from Philly southward. With that activity, there
may be enough instability for a stray thunderstorm, but not
enough instability or forcing for anything severe.
-- End Changed Discussion --

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
The main story heading into early next week will be the
strengthening ridge across the East Coast. 500 mb heights look
to increase to near 580 dam by Monday, values more typical of
summertime. At the surface, high pressure will be centered
offshore of the Carolinas, helping to advect warmer and more
moist air into the region. The result will be much above normal
temperatures. A backdoor frontal boundary will sink
southwestward into the area from New England Monday night,
stalling out across the central part of the forecast area by
Tuesday.

Lows Sunday night will be about 10-15 degrees above normal,
mainly in the mid 50s to near 60 degrees with clearing skies.
Monday will be the warmest day of the stretch with high
temperatures soaring into the mid to upper 80s in most interior
locations under partly cloudy skies. Highs in the more urbanized
areas could top out closer to 90 degrees, though readings of 90
degrees or higher appear unlikely at this time. The northwest
flow will add a downsloping component to the winds and thus also
help to boost temperatures locally near the urban corridor. The
offshore wind will also allow for a notable warmup even along
the immediate coast, with highs getting to the low to mid 70s
before the sea breeze kicks in.

As the gradient flow weakens and shifts eventually to the
southwest then south, the sea breeze will likely make
significant inland progress into the I-95 corridor and perhaps
even farther inland from there during the evening. This will
cool temperatures off into the 70s and 60s by late evening.
Dewpoints will be near 60 degrees, so the Heat Index won`t be
much different than the air temperature on Monday. No heat
headlines are anticipated. Lows Monday night will also be quite
mild once again in the mid 50s to near 60 degrees. The backdoor
frontal boundary will sink into northern and central New Jersey
overnight with increasing cloud cover.

For Tuesday, the frontal boundary will stall out along a line
from near Ocean County northwest into the Lehigh Valley.
Southwest of the boundary, temperatures should warm well into
the low to mid 80s by the afternoon under partly cloudy skies.
Northeast of the boundary, temperatures will likely top out in
the 70s away from the coast under mostly cloudy skies. The upper
ridge will deamplify as a shortwave trough approaches from the
west. This wave will be weakening a good bit, so forcing won`t
be overly impressive. We should have a fair amount of diurnally
driven instability though, generally in the 500 J/kg
neighborhood southwest of the boundary. So some scattered
showers and thunderstorms are anticipated to develop into the
afternoon and evening. Shear isn`t bad, around 30- 35 kts, but
with meager forcing and instability, currently anticipate
convection to be large benign and hit or miss in nature. Have
kept PoPs near 30-50%, greatest toward the north where forcing
will be a bit stronger.

A weak cold front associated with the trough will pass through
the area Tuesday night, bringing an end to the convective
activity. This will also signal a return to more temperate
conditions for the remainder of the week, although temperatures
likely remain several degrees above normal.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Somewhat unsettled, but not overly impactful long term looks to
be on the horizon. The ensembles suggest another weaker ridge
axis could build to our west while moving eastwards with time
Tuesday night into Thursday, the overall upper-level pattern
looks to become more zonal like and somewhat slow moving Tuesday
night onwards. Otherwise, multiple rounds of shortwave energy
and perhaps some weak surface boundaries hanging around or
moving through could be in the cards, potentially supporting
some weak convective activity and varying cloud cover.

Stuck with NBM PoPS for this forecast. Slight chance or chance
of showers each day for the interior. Greatest chance for
showers and thunderstorms is the Friday/Friday night time frame
thanks to another cold front passing through. Above average
temperatures likely Wednesday through the end of the week.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through Tonight...MVFR for most TAF sites with the exception
being at ACY/MIV. Expectation is that 030 clouds will drift
towards ACY/MIV around 08z with ACY likely to be the only site
that may not prevail MVFR. A few light SHRA possible mainly for
sites south of TTN with possible VSBY restrictions but IFR is
not expected. LGT/VRB winds.

Sunday...MVFR possible early, becoming VFR through the morning
and into the afternoon. Ceilings should tend to lift and
scatter through 15Z or so. TAF sites north and west of the PHL
metro may see some pop- up shower activity in the afternoon,
possibly even a stray -TSRA. Winds mainly SW 5-10 kt.

Outlook...

Sunday night through Monday night...No significant weather
expected. Mainly VFR with winds near 5-10 kts.

Tuesday through Wednesday...Mainly VFR with winds 5-10 kts,
though some scattered showers or thunderstorms are possible late
Tuesday and Wednesday.
-- End Changed Discussion --

&&

.MARINE...
Sub-Small Craft Advisory conditions on tap for tonight and
Sunday. Another trough passing through the waters may keep wind
gusts at least periodically around 20 kt into early Sunday
morning. For the rest of Sunday, winds will generally be
northerly 10-15 KT with gusts up to 20 KT at times. Seas 3-4 ft
through this evening, highest to the lee of DE Bay, dropping to
2-3 ft for most of Sunday.

Outlook...

Sunday night through Wednesday...No marine hazards expected.
Winds 10-15 kts and seas 2-4 feet.

&&

.CLIMATE...
Near record breaking high temperatures are forecast on Monday.
Records for our climate sites are listed below:

Record High Temperatures
                           Jan 25
Site                  Record/Year
Allentown (ABE)           86/1974
AC Airport (ACY)          92/1974
AC Marina (55N)           88/2017
Georgetown (GED)          91/2017
Mount Pocono (MPO)        82/1974
Philadelphia (PHL)        90/1974
Reading (RDG)             91/1888
Trenton (TTN)             88/1974
Wilmington (ILG)          91/1974

&&

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

&&

$$

SYNOPSIS...Staarmann
NEAR TERM...Dodd/Deal/MPS
SHORT TERM...Staarmann
LONG TERM...Staarmann/Wunderlin
AVIATION...Dodd/Deal/MPS/Staarmann
MARINE...Dodd/MPS/Staarmann
CLIMATE...PHI