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647
FXUS61 KPHI 180700
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
300 AM EDT Sat May 18 2024

.SYNOPSIS...
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An area of low pressure slides to our south over the weekend.
High pressure then builds across our area early next week before
shifting southeast. A cold front then moves through Thursday
into Thursday night.
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&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure to our northeast nosing southwestward combined
with the coastal storm now fairly far off the coast continues to
result in marine influence across our region. Thus, despite
approaching shortwave trough, overall forcing for showers will
be dwindling as the system moves into and then crosses the
region through today into this evening. Shower chances will be
highest to the west and southwest of our region, across interior
eastern PA and down across the Delmarva, closer to the edge of
the marine influence where temps are warmer and more instability
is to be had. That said, not expecting any thunder today as its
just not enough to produce strong convection. All that having
been said, still looks mostly dry this morning, but with plenty
of clouds, and shower chances are highest overall across the
region this afternoon as the best upper forcing moves in aloft.
With all the clouds around, temps won`t be very warm, but not
much different from what much of the region experienced
yesterday... upper 60s with a few 70s. Today, however, best
chance of 70s will be in interior central and northern New
Jersey, where precip likely takes longest to reach (if it does
at all).

As our upper forcing heads east out to sea overnight tonight,
shower chances end, and while we don`t expect much clearing
overnight as the winds just don`t provide any push of drier air
behind the upper trough, any breaks could help some patchy fog
develop, especially where rain falls today. Right now, the best
odds appear to be northwest of I-95 across the Lehigh Valley and
Poconos, though also parts of the Maryland eastern shore. Lows
mostly in the 50s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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By Sunday, the trough will be off shore as mid an upper level short
wave ridge builds closer to our region. Consequently, expect mostly
dry conditions Sunday into Monday with a gradual warming trend. A
few deterministic models are depicting precip through the first half
of the day on Sunday, but that seems unlikely given the large scale
subsidence, so continued to leave out any mention of shower chances.

Depending on few clouds there will be Sunday night, fog is possible,
but low confidence on how widespread it will be at this point.
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&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
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Summary: Main focus through the long term is on the cold front which
is expected to cross through the region Thursday into Thursday
night, bringing a chance for thunderstorms.

Details:

Tuesday and Wednesday...Here`s something we haven`t had too many
opportunities to say lately - temperatures on Tuesday and Wednesday
should be above normal, especially for inland areas. Mid and upper
level ridge, combined with southerly return flow will kick off the
warming trend into Tuesday. The one caveat is that it looks like
this will be a good set up both days for a sea breeze. Depending on
early it develops and how far inland it reaches, portions of the
coastal plains could be near or even slightly below normal for
afternoon highs. In general, expect dry conditions both days, though
if a pre-frontal trough trends faster, may see some initial showers
and storms move into the region region during the later half of the
day on Wednesday.

Thursday and Thursday night...Most deterministic guidance seems to
be favoring timing of the cold front during the later half of the
day or Thursday night. As mentioned by the previous shift, the mid
and upper level trough will generally be west and north of our
region, so better synoptic scale forcing will be outside of our
region. That being said, should have enough instability and low
level convergence (especially with the front) to support at least
scattered thunderstorm development in our region.

Friday...with stronger forcing outside of our region, the front
(though it should clear our region), may still be nearby on Friday.
This will have implications for precip chances (we`ll keep a 20 - 30
percent chance of rain through the day), and temperatures, although
expected to be slightly cooler than Thursday (with highs generally
in the 70s, may not be as dramatic as we would normally see with a
cold front.
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&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Through Today...Generally VFR early this morning. Approaching
showers and continued easterly to northeasterly flow will result
in cigs dropping to MVFR most terminals by midday. Vsby may
briefly drop to MVFR but mostly VFR vsby expected despite
passing showers. Winds fairly light and variable at times but
overall, a weak easterly flow will prevail. Moderate confidence.

Tonight...scattered showers end but MVFR cigs linger. May be
some patchy fog to reduce vsby esp NW of I-95 terminals.
Continued light/variable flow with a general easterly
persuasion. Low confidence.

Outlook...

Sunday...Mostly VFR. Fog (MVFR or IFR conditions) possible Sunday
night.

Monday through Wednesday...VFR conditions expected.
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&&

.MARINE...
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Ocean wave heights may flirt with 5 feet early this morning but
should generally subside thereafter, so no plans for a Small
Craft Advisory at present. Otherwise, northeasterly winds will
prevail through tonight with speeds of 5-10 kts today increasing
slightly to 10-15 kts tonight.

Outlook...

Sunday through Wednesday...Winds and seas are expected to remain
below SCA criteria.

Rip Currents...

A prolonged period of N to NE winds at 5 to 10 mph through the
weekend along with 3 to 4 ft seas will result in a MODERATE risk
for the development of dangerous and life threatening rip
currents on Saturday and Sunday.
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&&

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

&&

$$

SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...Johnson
LONG TERM...Johnson
AVIATION...Johnson/RCM
MARINE...Johnson/RCM