071
FXUS61 KPHI 190551
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
151 AM EDT Sun May 19 2024

.SYNOPSIS...
An area of low pressure moves offshore to our south today. High
pressure then builds across our area through Wednesday. A cold
front approaches and swings through the area on Thursday into
Thursday night. High pressure returns for Friday with another
low pressure system approaching by next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
While showers have mostly dissipated, widespread low clouds
continue to shroud the area early this morning. Any breaks may
allow fog to develop until after dawn, so keep patchy fog in the
forecast and will be watching observations closely, but right
now it looks pretty socked in with clouds so widespread dense
fog is not looking likely.

Weak easterly flow to the southwest of high pressure centered
over northern New England will keep the marine influence in
place today, so while strong mid-May insolation should help
clouds lift through the day, it may not get much better than
partly sunny across much of the region by late this afternoon
given the plentiful low-level moisture to work with. Towards the
western flank of the marine layer, could even be a pop-up
shower, most likely out in Berks County. The insolation and
general lack of rain should allow most areas to pop back into
the 70s, except near the shore.

Short-term guidance suggests a new push of marine clouds will
move into the region tonight, so have another mostly cloudy
forecast tonight. If clouds are less widespread, fog may become
an issue, but for now have kept it patchy in the forecast. Lows
mostly in the 50s again.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The short term period will be focused mainly on the mid to
upper level ridge that approaches and builds overhead through
the period. At the surface, broad high pressure over New England
will expand southwest and become elongated into the Appalachian
region Monday. The high will sink south of the region on Monday
night before moving offshore late Tuesday into Tuesday night.
During this period, dry conditions are expected with mostly
sunny skies during the day and mostly clear skies at night.
There may also be some patchy fog at night. For now, best
chances appear to be north and west of the I-95 corridor.

In terms of temperatures, it is looking like we will return
close to normal on Monday with highs in the mid to upper 70s and
lows in the low to mid 50s. For Tuesday, winds become more
southerly as the high shifts offshore resulting in warmer temps
being brought north. Generally looking at the upper 70s to low
80s for Tuesday. However, with rather light surface winds, this
should allow a sea breeze circulation to develop each day, so do
anticipate cooler temps closer to the coast.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Summary: Main focus through the long term is on a cold front
which is expected to cross through the region Thursday into
Thursday night bringing a chance for thunderstorms. High
pressure will return in the wake of the front with another
disturbance that approaches by next weekend.

Details:

Wednesday...Upper ridge axis will shift offshore on Wednesday.
Guidance has overall slowed to progression of the pre-frontal
trough so Wednesday now appears to remain dry. Increasing clouds
late with temperatures above average. Shower chances increase
Wednesday night with a chance of thunder as the pre-frontal
trough approaches.

Thursday...Guidance remains persistent with the timing of the
cold front during the afternoon hours on Thursday. With the
location of the mid and upper level trough over the Great Lakes,
this keeps the better forcing north and west of the area.
However, with enough surface instability aided by diurnal
heating, this should support at least scattered thunderstorm
develop across the area. This is supported quite well by analog-
based guidance. Cold front then moves offshore by Thursday
night. Temps should be above average again, depending on timing
of the cold front.

Friday and Saturday...The forecast for Friday and Saturday is
quite uncertain and depends on how far the front makes it past
our area. At this time, the 12Z/GFS is more aggressive with the
progression of the front, bringing in high pressure into the
area on Friday and most of Saturday. In comparison, the 12Z
ECMWF is much slower with the progression of the front, keeping
the front stalled over our area into next weekend with shower
chances. For this reason, have used NBM guidance which keeps
most of the area within a 20-30% chance of showers/thunderstorms
for Friday and Saturday.

&&

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

Through today...MVFR through the morning with intervals of IFR
likely either due to cigs dropping or patchy fog developing.
Cigs and vsby should rise to VFR this afternoon. Light easterly
winds. Moderate confidence.

Tonight...MVFR cigs/vsby looking likely again with continued
light easterly flow. IFR possible with any patchy fog or lower
clouds. Low confidence.

Outlook...

Monday through Wednesday...VFR with mostly clear skies.

Wednesday night through Thursday...Sub-VFR possible especially on
Thursday with a chance for thunderstorms.

&&

.MARINE...
Conditions over the waters will be sub SCA through tonight with
seas 3 to 4 feet. Northeast may gust to around 20 knots but
stay below SCA levels.

Outlook...

Sunday night through Thursday...No marine headlines are expected.
Fair weather expected through Wednesday with a chance for
thunderstorms on Thursday.

Rip Currents...

A prolonged period of N to NE winds at 10 to 15 mph during the
day and 5 to 10 mph at night will continue on Sunday and Monday.
Along with 3 to 4 ft seas, this will result in a MODERATE risk
for the development of dangerous and life threatening rip
currents Sunday and Monday at New Jersey and Delaware beaches.
The rip current risk may be low for most of the day Monday for
southern New Jersey beaches.

&&

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

&&

$$

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