180
FXUS61 KPHI 290549
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
149 AM EDT Sat Jun 29 2024

.SYNOPSIS...
High pressure moves out to sea tonight, then a warm front will
lift across the Mid Atlantic area on Saturday. A cold front will
then move across the East Coast Sunday into Sunday night. High
pressure builds out of the Great Lakes region Monday, across
the Mid Atlantic region Tuesday and then offshore by Wednesday.
A cold front may arrive late next week.

&&

.NEAR TERM /THROUGH TODAY/...
Broad high pressure offshore of New England will continue to
move slowly eastward early this morning. Conditions remain
pleasant overall as low level moisture has been a bit slower to
increase. However, with a strengthening southeast flow behind
the departing high, and with a warm front approaching from the
west, we are still expecting moisture to increase with surface
dew points rising 8 to 12 degrees from last evening over many
areas by daybreak this morning. Stratus develops over the area
early this morning too and should persist into the post daybreak
hours this morning. As a result of the increasing moisture and
developing cloud cover, lows early this morning will be fairly
warm, generally in the low to mid 60s, though in the 50s in the
southern Poconos and northern New Jersey. Patchy fog is
possible, but the developing stratus should mitigate fog
formation.

Warm and humid during the daytime today. The warm front will be
east of the region and will slowly approach from the west. Any
convection looks to hold off until late in the day, and even
though, mainly focused on the far western zones. Highs will
generally be in the mid to upper 80s, though in the 70s along
the coasts and in the southern Poconos. With surface dew points
in the upper 60s to around 70, max heat index values will be in
the upper 80s to low 90s, though in the mid to upper 80s across
Delmarva.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
An upper trough over central Canada digs down into the Northern
Plains and upper Great Lakes on Saturday. Surface low pressure
out ahead of it will moves into eastern Canada, and this will
lift a warm front north through the region Saturday night.
Showers and scattered thunderstorms will develop with the
approach and passage of the front, and with abundant low level
moisture over the area, PWATs will be around 2.5 inches.
Thunderstorms will be capable of heavy rain and localized
flooding. Although 0-6 km Bulk Shear will range from 20 to 30 kt
in the evening, it will rise to 35 to 40 kt through the
overnight hours. As a result, flow should be strong enough for
storms to move quickly and mitigate widespread flash flooding.
PWATs may even rise to 2.7 inches through the overnight. A warm
and humid night on tap with lows in the low to mid 70s for most
of New Jersey and southeast Pennsylvania, but in the mid to
upper 70s along the I-95 corridor from Philadelphia to
Wilmington, and across Delmarva.

Although some storms may produce locally strong and gusty winds
in the evening for the far western zones, the bulk of the
activity will occur during the overnight hours. As a result, the
severe threat should be mitigated by lower instability. MU CAPE
values will be 500 to 750 J/kg in the evening, rising to 1000
J/kg by Sunday morning. However, by then, the bulk of the
activity will be tapering off.

The warm front will be north of the area Sunday morning, and a
hot and humid airmass spreads into the region on Sunday. Surface
dew points will rise well into the 70s with highs in the upper
80s to low 90s. There may be enough cloud cover over the area to
keep high temperatures tampered down and from getting even
higher. Max heat index values will be in the mid to upper 90s
for most of southeast Pennsylvania and portions of northern New
Jersey, and in the upper 90s to around 100 elsewhere. This is
enough to warrant a Heat Advisory for the I-95 corridor counties
and portions of southern New Jersey, which will be issued with
this forecast package.

This sets the stage for a potential severe weather outbreak
Sunday afternoon and evening. A cold front approaches from the
west and a pre-frontal trough develops out ahead of it. Showers
and thunderstorms will develop with that trough in the afternoon
and continuing through the evening. Instability thresholds will
be off the charts, with SB CAPE values upwards of 3000 J/kg,
and 35 to 40 kt of 0-6 KM Bulk Shear. SCAPE values in excess of
1000 J/kg indicate the potential for damaging wind gusts. PWATs
will be in excess of 2 inches, which indicates potential for
heavy rain. However, the strong steering current aloft should
mitigate widespread flash flooding. This does not rule out
localized flash flooding.

Showers and thunderstorms may linger through Sunday night. Cold
front works its way through the region after midnight, and
conditions gradually dry out with surface dew points falling
into the 50s by Monday morning.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
The first half of the long term forecast is expected to be
rather tranquil as high pressure builds out of the Great Lakes
region on Monday, across the Mid Atlantic region on Tuesday,
then offshore on Wednesday. Temperatures will warm each
successive day Monday through Wednesday, but not reach excessive
levels through at least Wednesday.

On Thursday, temperatures continue to rise, and will likely
reach at least the low to mid 90s for much of the area as a pre-
frontal/thermal surface trough develops ahead of an approaching
cold front. This will likely be the warmest day of the upcoming
week, and some areas might approach advisory levels for some
locations.

The cold front is expected to move into the area on Thursday,
and could linger near the area Friday and into part of the
weekend. There will be a chance of showers and thunderstorms for
at least Thursday and Friday.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.


Early this morning...VFR conditions continue but MVFR ceilings
expected to develop toward daybreak (09Z-10Z) this morning,
mainly for terminals near and northwest of the I-95 corridor.
IFR conditions possible but not certain about which sites have
the best chance for this. Kept KILG lower CIGS for now.
Southeast winds 5-10 knots. High confidence except for
occurrence/timing of IFR conditions.

Today...MVFR, or IFR in a few spots, to start the day,
improving to VFR later in the morning into the afternoon.
Southeast winds 5-10 knots, become southerly through the morning
into the afternoon, with gusts 15-20 knots. High confidence
overall, moderate confidence on timing of improving conditions.

Outlook...

Saturday night...MVFR/IFR in SHRA/TSRA. Heavy rain at times.

Sunday through Sunday night...VFR initially. Sub-VFR conditions in
SHRA/TSRA with potentially damaging winds and heavy rain Sunday
afternoon and night. Conditions gradually improve from west to east
late Sunday night.

Monday-Wednesday...VFR conditions expected.

&&

.MARINE...
Sub-Small Craft Advisory conditions tonight through Saturday.
SE around 8 to 12kt tonight, increasing to around 15 kt with
gusts to low 20`s (kt) on Saturday. VSBY restrictions in fog
developing on the ocean waters on Saturday.

Outlook...

Saturday night through Sunday night...A SCA is now in effect
for Saturday night through Sunday. S winds will increase to 15
to 20 kt with gusts up to 25 kt with seas around 5 ft. Winds may
diminish a bit on Sunday, but seas remain elevated. Showers and
thunderstorms Saturday night with VSBY restrictions in heavy
rain. Another round of showers and thunderstorms Sunday
afternoon and evening with potentially damaging winds, VSBY
restrictions in heavy rain, and frequent lightning. VSBY
restrictions in fog also possible Saturday night and Sunday.
Conditions improve Sunday night.

Monday-Wednesday...Sub Small Craft Advisory conditions
expected, although winds could gust around 20 knots on Monday
and Wednesday, and seas could be near 4 feet on Monday.

Rip Currents...

Saturday...Southeast winds 10-20 mph with breaking waves of 2 to 4
feet at the beaches and an 8-9 second period are expected. With the
steady onshore flow (especially in Cape May/Atlantic/Ocean County)
and increasing wave heights, have elected to with a HIGH risk for
rip currents at the Jersey Shore. At the Delaware beaches, wind is
more shore parallel. Thus, a MODERATE risk for rip currents is in
place.

Sunday...Wind turns more south/southwesterly, though with a shore
parallel wind and 2 to 3 foot breakers with a remaining 8 second
swell, have elected to go with a MODERATE risk at Cape
May/Atlantic/Ocean County with a LOW risk in Monmouth County and the
Delaware Beaches.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 11 AM to 7 PM EDT Sunday for PAZ070-071-102-
     104-106.
NJ...Heat Advisory from 11 AM to 7 PM EDT Sunday for NJZ015-017>020-
     027.
     High Risk for Rip Currents from 9 AM EDT this morning through this
     evening for NJZ014-024>026.
DE...Heat Advisory from 11 AM to 7 PM EDT Sunday for DEZ001.
MD...None.
MARINE...Small Craft Advisory from 6 PM this evening to 7 PM EDT Sunday
     for ANZ450>455.

&&

$$

SYNOPSIS...Robertson
NEAR TERM...AKL/MPS
SHORT TERM...MPS
LONG TERM...Robertson
AVIATION...AKL/MPS/Robertson
MARINE...MPS/Robertson