472
FXUS61 KPHI 181255
AFDPHI

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TONIGHT/...
855 AM...Skies have clouded over again with showers starting to
move into the area from the west as we head into the mid
morning hours. These showers are associated with an approaching
system from the west as a lead shortwave runs out ahead of the
main upper level trough. Overall the trend has been and should
continue to be for these showers to weaken as they move into the
area of weak ridging situated along the east coast. That all
said, still expect them to produce at least some rain today over
Delmarva into SE PA (including Philly) and adjacent portions of
southern NJ where we have POPs in the 60 to 70 percent range.
Heading not too far to the east from here to places like
Burlington County NJ north towards Trenton and then on into NW
NJ expect showers to be a bit more scattered in nature with POPs
here generally 40 to 50 percent. Overall, best chances for
precip look to be from around midday to roughly 5 PM or so. Also
worth mentioning is that no thunder is expected as we just
don`t have or won`t have the instability. 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/...
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.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
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.

&&

.AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Today...Generally VFR early this morning with patchy MVFR in
mist. 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.

&&

.MARINE...
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.

&&

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

&&

$$

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