Areal Flood Warning 23, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
438 PM EDT Fri May 20 2022

.SYNOPSIS...
A mid level disturbance will move across the area this evening.
A Bermuda high pressure pattern will develop for Saturday and
Sunday with the Mid Atlantic region on the northwestern
periphery of the high. A strong cold front will move through
Sunday night as low pressure passes to our northwest, with the
front slowly settling offshore on Monday. High pressure builds
in for Tuesday and Wednesday, then a frontal system may approach
the area later next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A mesoscale convective vortex was passing over our region late
this afternoon. Showers and thunderstorms developed ahead of the
feature and will continue to move across eastern Pennsylvania,
and central and northern New Jersey into this evening.

We have been able to cancel the Tornado Watch for areas to the
west and south of Philadelphia based on radar trends. The watch
remains in effect for Bucks County, Pennsylvania, and for parts
of central and northern New Jersey until 7:00 PM.

The CAPE values are lower in central and northern New Jersey
than they were in areas to the west and southwest. However, the
thunderstorms have some momentum as they advect into those
areas. There continues to be a decent amount of shear and the
storms were rather organized. We have been receiving numerous
reports of hail will localized strong wind gusts.

The precipitation will remain to the north of much of eastern
Maryland, Delaware and far southern New Jersey.

The mid level short wave trough associated with the convection
is forecast to pass overhead this evening and off the coast by
about 10:00 PM, bringing and end to any lingering showers in our
region. High clouds are expected to linger overnight.

A fog bank developed over the coastal waters of New Jersey and
Delaware today. It may expand inland tonight. A warm front is
anticipated to lift northward through our region late tonight
and it may cause some of the fog over land to dissipate toward
daybreak.

A south to southeast wind 10 to 15 MPH into this evening is
forecast to become light and variable tonight. Low temperatures
are expected to be in the 60s and lower 70s with muggy
conditions.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
The warm front will move well north of the area during the day
Saturday, while a thermal trough will develop across the east
coast by the afternoon. Saturday is still forecast to be very
hot across the area with high temperatures in the mid to upper
90s for most areas. Heat index values will likely reach around
100 degrees for portions of southeast Pennsylvania, central and
southern New Jersey, as well as Delaware and eastern Maryland.
The Heat Advisory remains in place where it was previously as
these areas have the lower heat index criteria of 100 degrees,
while areas south of the advisory have criteria of 105, and we
are not expected to reach that high there. For areas north and
west of the advisory, temperatures may end up being a few
degrees lower than in the advisory and southward as they will be
north and west of the developing surface thermal trough and
thicknesses will be slightly lower farther north and west.
Nevertheless, it will still be a hot day!

Saturday and Saturday night should remain dry as any
showers/thunderstorms should develop to our west, west of the
thermal trough and closer to a passing short wave/vorticity
impulse aloft. Saturday night will be a muggy night as
temperatures may not drop below 70s for some areas, and barely
into the 60s for most other places.

Sunday will likely be another hot day, although not at hot as
Saturday as thicknesses lower some across the area. Plus there
will likely be some cloud cover ahead of an approaching cold
front which could limit how high temperatures get.

The cold front will approach the area Sunday afternoon, but
likely not get here until Sunday evening. The timing of the
front could play into how many thunderstorms we get, and how
strong their potential will be. Guidance continues to indicate
showers and scattered showers developing late in the afternoon
into the evening as the cold front moves through, before
diminishing as the front moves eastward. Instability is
increases as CAPE values could reach 1000-2000 J/kg, while shear
is not very strong, only 20-30 knots due to weak mid level
flow, DCAPE values of 600-700 J/kg could lead to a some isolated
damaging wind gusts.

As the front moves offshore overnight, any precipitation will
end overnight and cooler/drier air will move in overnight. Winds
could become occasionally gusty overnight as well.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
A much cooler pattern relative to the weekend heat develops for
next week. Synoptically, following the Sunday night cold
frontal passage, the upper level pattern does not change
dramatically, with considerable positive height anomalies
remaining in place over the East. However, an expansive surface
high pressure center will build from the Great Lakes into
northern New England from Monday through midweek. This will act
to turn the winds northerly, then easterly, drawing cooler air
into the region despite the warmer look to the upper air
pattern. High temperatures into the 70s will be common for much
of next week, and "cooler coast" will be a common theme as well.

Regarding rain chances, the week does not appear too rainy
overall. NBM PoPs in the Monday through Wednesday range
generally depict 30% or less. This is agreeable based on latest
guidance and the synoptic pattern of strong high pressure to the
north. While this still leaves some mentions of showers, expect
most if not all of the first half of the week to be dry. Better
rain chances should arrive later in the week as a frontal
system approaches in response to a slow moving trough pushing
into the Great Lakes.

Dailies...

Monday-Monday night... Most indications are that the cold front
should be offshore by Monday morning. However, it will be
slowing down as it moves through, and there is still a chance it
comes to a near stall over the coast or just offshore. As such,
there is a slight chance to chance for some residual showers
especially over the southern half of the area, and a good deal
of cloud cover may linger through the day. But by and large, the
story will be the more seasonable temperatures, with daytime
highs in the 70s and overnight lows in the 50s.

Tuesday-Wednesday... Some additional cooling is expected into
midweek as high pressure centers itself to our north and turns
the winds onshore. High temperatures look to favor the low 70s
on these days, but only in the 60s closer to the coast. Do have
a slgt chc of showers for most of the area with chc showers
further south mentioned Tuesday. However, given the strong high
pressure to the north, a fully dry day Tuesday remains possible.
On Wednesday, PoPs increase a little more to the north as a
frontal system possibly begins to approach from the southwest.
But am still not too enthused on rain chances Wednesday either,
and have a feeling that day will probably be dry as well.

Thursday and Friday... By Thursday, a frontal system appears
likely to approach the area as a slow moving trough, and
possibly a closed low, track towards the Great Lakes. While
confidence in details remains low, the overall pattern should
support an increase in rain potential by the latter half of next
week. Temperatures should start to recover also by Thursday as
a southwest flow develops, and we may get back to around 80 in
some places both Thursday and Friday.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...A mix of VFR and MVFR conditions are expected tonight
after the showers and thunderstorms move through. With an
abundance of low level moisture, restrictions in visibility are
likely overnight. South to southeast winds around 5 kts.
Moderate confidence.

Saturday...VFR after some morning fog. Southwest winds 5 to 10
kt. High confidence.

Outlook...

Saturday night...VFR conditions will continue across the area.
Some fog is possible near the coast including ACY. South to
southwest winds 5-10 knots.

Sunday...Generally VFR. Showers and thunderstorms may develop
late in the day ahead of an approaching cold front. Southwest
winds 5-10 knots, with gusts 15-20 knots.

Sunday night...MVFR conditions may develop ahead of the passing
cold front, especially with any showers or thunderstorms. MVFR
conditions could continue for several hours overnight once the
showers and thunderstorms end. Southwest winds 5-10 knots ahead
of the front, before shifting to north 10-15 knots behind the
front, with occasional gusts 15-20 knots.

Monday... Mainly VFR but some localized restrictions possible.
Northwest wind 5 to 10 kt gradually shifting to northeast
overnight. Moderate confidence.

Tuesday... Mainly VFR. Northeast to east wind 5 to 10 kt, a
little breezier at the coast. Moderate confidence.

Wednesday... Mainly VFR. East to southeast wind 5 to 10 kt, a
little breezier at the coast. Moderate confidence.

&&

.MARINE...
A southeast to south wind 10 to 20 knots is forecast to become
southwest 10 to 15 knots late tonight. Waves on our ocean waters
will likely stay in the 2 to 3 foot range, with waves on
Delaware Bay remaining at 2 feet or less.

A fog deck over our coastal waters is expected to remain there
for much of the night. We have a Dense Fog Advisory in effect
until 10:00 PM this evening. We will keep an eye on the trends
this evening and we may need to extend the advisory at least
overnight.

The shower and thunderstorm activity into this evening is
expected to remain mostly north of Barnegat Inlet, New Jersey.

Outlook...

Saturday-Sunday night...Winds and waves mostly remain below
advisory levels through the period. However, winds could
approach advisory levels for a brief period Saturday
afternoon/evening, and again Sunday afternoon/evening. Wind will
be south to southwest Saturday through Sunday, shifting to
north behind the cold front.

Monday-Wednesday... No marine headlines are currently
anticipated. Offshore winds early on Monday, becoming onshore
later Monday into Tuesday and through midweek. Seas of 2 to 4
feet generally expected.

&&

.CLIMATE...
A hot and humid air mass is forecast to overspread the region
this weekend. The hottest day will be Saturday. Here is a list
of the high temperature records for Saturday and the record high
temperatures for the month of May.

Locations                    5/21 Record High Temps    May Record High Temps
---------                    ----------------------    ---------------------

Philadelphia, PA                  95 in 1934                97 in 1991
Reading, PA                       96 in 1996                96 in 1996/ 1962
Allentown, PA                     92 in 1934                97 in 1962
Mount Pocono, PA                  87 in 1911                94 in 1911
Trenton, NJ                       94 in 1934                99 in 1986/ 1911
Atlantic City (airport), NJ       93 in 1996                99 in 1969
Atlantic City (marina), NJ        85 in 1934                95 in 1925/ 1895
Wilmington, DE                    95 in 1996                98 in 1895
Georgetown, DE                    94 in 1996                98 in 1991

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 11 AM to 10 PM EDT Saturday for PAZ070-071-
     101>106.
NJ...Heat Advisory from 11 AM to 10 PM EDT Saturday for NJZ008>010-
     012-013-015-017>020-027.
DE...Heat Advisory from 11 AM to 10 PM EDT Saturday for DEZ001.
MD...None.
MARINE...Dense Fog Advisory until 10 PM EDT this evening for ANZ431-
     450>455.

&&

Synopsis...O'Brien
Near Term...Iovino
Short Term...Robertson
Long Term...AKL
Aviation...AKL/Kruzdlo/Robertson
Marine...AKL/Iovino/Robertson
Climate...WFO PHI

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