-- Discussion containing changed information from previous version are highlighted. --
909
FXUS61 KPHI 230102
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
902 PM EDT Sat Jun 22 2024

.SYNOPSIS...
High pressure remains anchored offshore through Sunday. A cold
front comes through later Sunday, moving offshore by Monday
morning. High pressure settles in for the early part of the week
before another cold front moves in for the middle of the week.
High pressure returns for the end of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
-- Changed Discussion --
As of 900 PM, convection continues to develop from the Lehigh
Valley, Poconos east-southeastward into north-central New
Jersey. This is north of a southward moving outflow boundary.
Given the southwesterly synoptic winds perpendicular to the
outflow and also advecting the unstable airmass northward, this
is feeding the ongoing and new convective development. While
this is mostly north of the strongest downdraft instability
(DCAPE), strong elevated cores at times could support localized
strong to damaging downburst wind gusts for a while longer. This
convection is also bringing cooling relief to some areas as
temperatures drop back into the 70s. The clustering and even
some training of the convection is resulting in a corridor of
very heavy rain due to high precipitable water in place.
Therefore there is some local flash flood threat as well.
Farther south into the Philadelphia metro and even southward,
no development so far and this may remain the case. The main
adjustment with this update was to the PoPs (upward quite a bit
for a few hours across the northern areas). Also made some
adjustments to the hourly temperature and dew point grids.

Otherwise, temperatures will only cool off tonight into the low to
mid 70s with upper 70s across the urban corridor and Delmarva.
Meanwhile, dew points will remain in the 70s as well, keeping it
muggy tonight.

Oppressively hot and humid conditions remain for Sunday. Excessive
Heat Warnings were posted earlier for the urban corridor and parts
of the NJ Coastal Plain as heat indices of 105-110 are expected.
These conditions combined with the nearly week long stretch of heat,
are going to result in dangerous conditions outside for Sunday as
the effects of heat stress on the body can be cumulative. Time
outside should be limited and if you are out and about, drink plenty
of water!

With such a hot and humid airmass in place, and an approaching cold
front, there will be the chance for some severe weather. Lift will
be aided with a shortwave and pre-frontal trough coming into a moist
and unstable airmass. Deep layer shear of 30-40 kt and moderate
instability (1000-2000 J/kg of SBCAPE) will support the development
of thunderstorms capable of producing damaging wind gusts. The SPC
has updated the Day2 outlook to place much of our CWA in a Slight
risk (N/W) and Marginal risk for the shore and most of our Delmarva
area. The limiting factor is the better shear will be located
further north but still think there is sufficient shear to support
some strong to severe thunderstorms. Not overly concerned with the
flooding potential at the moment as storm motion should be steady,
though with PWATs pushing 2 inches, any thunderstorms will produce
heavy rain capable of dropping an inch or two of rain quickly.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
The cold front comes through on Sunday Night/Monday morning, knocking
down dew points a good 15 degrees or so. It will feel much more
comfortable on Monday with dew points back into the 50s and temperatures
getting into the mid to upper 80s. Monday looks unsettled though
as a series of shortwaves rotate around the base of the trough
passing by to the north. This will result in a some scattered
showers and thunderstorms, though the severe potential looks much
lower compared to Sunday. Any showers/thunderstorms will dissipate
after sunset, and it should be a quiet night overall as high pressure
moves in. Temperatures on Monday Night will get down into the 60s.
Tuesday is expected to be dry and hot as a short wave ridge traverses
the region. Temperatures are forecast to climb back into the 90s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Overview: Above normal temperatures will continue for the long-
term, however most of the week with the exception of Wednesday
will not be as oppressive as the heat this weekend.

High temperatures through most of the extended look to be in
the upper 80s/low 90s. The exception being Wednesday, as high
pressure moves offshore resulting in a southerly flow and warm
air advection. For much of the region, this will lead to
widespread 90s (with the exception of the higher terrain in the
Poconos and NW NJ and the immediate coast). May need a Heat
Advisory for some areas (especially the urban corridor), but
want to get through the current heat event before moving on to
Wednesday.

The main rain chances are Wednesday into Thursday as a cold
front approaches and again late in the week (at this point looks
like Saturday or later) as another cold front starts to approach.
Unlike the Sunday event, flooding looks like it could be more of
a concern with the Wednesday system as the front looks to be a
little on the slower side, and we will have a very warm and
moist airmass in place. With such a warm and moist airmass in
place, cannot rule out some stronger thunderstorms as well
especially a downburst/strong wind potential.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR, however some showers and thunderstorms especially
from around KABE to near KTTN on northward into the overnight
will result in a period of sub-VFR conditions. Localized fog
possible late. Southwest winds 5-10 knots, becoming locally
light and variable. Winds will become north or northeast 5-10
knots for some terminals where an outflow boundary moves through.
Low confidence on the details.

Sunday...Some showers and thunderstorms in the afternoon will result
in times of local sub-VFR conditions and gusty winds. Southwest
winds increasing to 10-15 knots with gusts 20-25 knots. Moderate
confidence.

Outlook...

Sunday night...Restrictions likely with showers and thunderstorms
(60-80%).

Monday...Mainly VFR. Restrictions possible with a chance of
showers/thunderstorms (30-40%) the first half of the day.

Monday night...VFR.

Tuesday...VFR.

Wednesday into Thursday...Sub-VFR conditions possible (40-50%)
in the afternoon and overnight with showers and thunderstorms.
-- End Changed Discussion --

&&

.MARINE...
No headlines expected through tonight. Seas 3 feet will begin to
build into early Sunday morning. For Sunday, a SCA goes into effect
at 8 AM as winds and seas will build to the low-end of SCA criteria.
Some showers/storms develop late in the afternoon and continue
Sunday night.

Outlook...

Sunday night...SCA conditions are expected on the ocean waters. S to
SW winds gusting up to 25 to 30 kts. Seas 4 to 7 ft. Showers and
thunderstorms likely.

Monday...Winds are expected to relax, but a residual swell will
remain. SCA conditions are possible. W winds 10 to 15 kts with gusts
up to 20 kts. Seas 4 to 5 ft. A chance of showers and thunderstorms.

Monday night...NW winds 5 to 10 kts. Seas 3 to 4 ft.

Tuesday...W winds 5 to 10 kts, becoming S in the afternoon. Seas 2
to 3 ft.

Wednesday...No marine headlines expected.

Wednesday night into Thursday...Wave heights may get close to 5
feet and gusts close to 25 kt on the Atlantic Coastal Waters.

Rip Currents...

Sunday...With south winds 15 to 25 mph, breaking waves in the 3
to 5 foot range, and a 5 to 7 second wave period, we are
running with a HIGH risk for the development of rip currents for
Cape May/Atlantic/Ocean County and a MODERATE risk for Monmouth
and Sussex, DE beaches. Low tide is mainly in the mid
afternoon.

Monday...Winds relax a bit and back offshore, but wave periods
are forecast to increase. This said, with west winds 10 to 15
mph (maybe some gusts up to 20 mph across the northern beaches),
breaking waves in the 2 to 4 feet range, and a 6 to 8 second
wave period, we are running with a HIGH risk for the
development of rip currents everywhere. Low tide is mainly in
the mid to late afternoon.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.CLIMATE...
Record high temperatures Sunday.

Location          Record High (6/23)

Philadelphia, PA      97/1888
Allentown, PA         95/1965
Reading, PA           96/1908
Mount Pocono, PA      90/1908
Trenton, NJ           97/1894
AC Airport, NJ        98/1988
AC Marina, NJ         91/1909
Wilmington, DE        100/1894
Georgetown, DE        100/1988

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Warning until 8 PM EDT Sunday for PAZ070-071-
     102-104-106.
     Heat Advisory until 8 PM EDT Sunday for PAZ054-055-060>062-101-
     103-105.
NJ...Excessive Heat Warning until 8 PM EDT Sunday for NJZ010-012-
     013-015>020-027.
     Heat Advisory from 6 AM to 8 PM EDT Sunday for NJZ014-021>026.
     High Risk for Rip Currents from Tuesday morning through Tuesday
     evening for NJZ014-024>026.
     Heat Advisory until 8 PM EDT Sunday for NJZ001-007>009.
     High Risk for Rip Currents from Monday morning through Monday
     evening for NJZ024>026.
DE...Excessive Heat Warning until 8 PM EDT Sunday for DEZ001.
     Heat Advisory from 6 AM to 8 PM EDT Sunday for DEZ002>004.
     High Risk for Rip Currents from Tuesday morning through Tuesday
     evening for DEZ004.
MD...Heat Advisory from 6 AM to 8 PM EDT Sunday for MDZ012-015-019-
     020.
MARINE...Small Craft Advisory from 8 AM Sunday to 6 PM EDT Monday for
     ANZ450>455.

&&

$$

SYNOPSIS...Hoeflich/Johnson
NEAR TERM...Gorse/OHara
SHORT TERM...Hoeflich/Kruzdlo
LONG TERM...Hoeflich/Johnson
AVIATION...Gorse/Hoeflich/Johnson/MJL/OHara
MARINE...Hoeflich/Johnson/MJL/OHara
CLIMATE...PHI