378
FXUS61 KPHI 281849
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
249 PM EDT Fri Jun 28 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
move across the east coast Sunday into Sunday night. High
pressure builds out of the Great Lakes region Monday, and across
the Mid Atlantic region Tuesday, then offshore by Wednesday. A
cold front is expected late in the week next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Broad high pressure centered over New York state, but
encompassing much of the Northeast, will slide east into this
evening. This high will be east of Cape Cod by Saturday morning
before moving out to sea during the day.

Pleasant conditions into this evening. Persistent southeast
flow sets up behind the departing high, and with a warm front
approaching from the west, low level moisture will increase over
the area. Surface dew points will rise into the mid and upper
60s by daybreak Saturday. Stratus develops over the area late
tonight and should persist into Saturday morning. As a result of
the increasing moisture and developing cloud cover, lows
tonight 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 on Saturday. 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 /SATURDAY NIGHT 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 /19Z FRIDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of Today...VFR conditions continue. East winds 5-10 knots,
shift to southeast through this afternoon. Occasional gusts
15-20 knots. High confidence.

Tonight...VFR conditions for much of the night. MVFR ceilings
expected to develop late in the night and toward daybreak
Saturday. IFR conditions possible at RDG, ABE, ILG. Southeast
winds 5-10 knots. High confidence.

Saturday...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 10 kt tonight, increasing to around 15 kt with gusts15
up to 20 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...

Today...Northeast winds in the morning becoming east-southeast
winds in the afternoon 10-20 mph. Breaking waves of 2-3 feet for
all beaches. Due to an onshore component of the wind, have
maintained a MODERATE risk for the development of dangerous rip
currents for the New Jersey and Delaware beaches.

Saturday...Southeast winds 10-20 mph with breaking waves of 2-3
feet at all beaches. Due to similar wind and wave conditions
compared to Friday, have opted to continue with a MODERATE risk
for the development of dangerous rip currents for both the New
Jersey and 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.
DE...Heat Advisory from 11 AM to 7 PM EDT Sunday for DEZ001.
MD...None.
MARINE...Small Craft Advisory from 6 PM Saturday to 7 PM EDT Sunday for
     ANZ450>455.

&&

$$

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