-- Discussion containing changed information from previous version are highlighted. --
417
FXUS61 KPHI 040840
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
440 AM EDT Tue Jun 4 2024

.SYNOPSIS...
Surface high pressure remains in control through tonight. An area of
low pressure approaches from the northwest on Wednesday with a warm
front passing through Wednesday night. A cold front will follow
crossing through the region on Thursday into Thursday night.
Unsettled weather looks to persist into the weekend and early next
week as several shortwaves pivot around the upper low over southern
Canada.

&&

.NEAR TERM /THROUGH TONIGHT/...
Upper heights build back across the Middle Atlantic today and
tonight while a surface high remains offshore of New England. The
resulting onshore flow across our region will keep temperatures in
check while humidity slowly builds. Overall, a dry day is expected
with subsidence over the area. One exception will be across the
eastern shore of MD areas where more humidity and less capping may
result in a few showers or perhaps a tstm this afternoon, we`ll keep
the pops there in the low chance range with some surrounding slight
chc pops for Delaware and up into Chester County PA. Sluggish winds
aloft may result in downpours with any tstm.

Highs today will be above normal, like Monday, with readings topping
out on the low/mid 80s for most areas. Cooler temps will prevail
across the NW most areas like the Southern Poconos and close to the
shores of NJ/DE. East to Southeast winds 5 to 10 mph much of the
time.

For tonight, fair weather continues into the evening with only a few
diminishing showers possible for Delmarva. Overnight, the marine
layer and partly cloudy skies will allow for fog formation and
possibly stratus from the ocean moving over the area. We`ll continue
with the previous fcst for now keeping much of the fog across
Delaware and NJ with patchy fog for ern PA. Light east/Southeast
winds tonight. Lows will be in the low/mid 60s most spots with some
upper 50s for the north.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
The upper level ridge will remain over the area on Wednesday before
flattening out by Wednesday night. At the same time, a deep upper
trough will be accompanied by a nearly vertically stacked low
pressure system which will be meandering around southern Canada and
the northern Great Lakes during the period. A subtle shortwave
ejects east out ahead of the parent trough on Wednesday night into
Thursday, which will result in a warm front lifting north across the
area Wednesday night and a cold front passing through by Thursday
night.

All this will result in at least a couple rounds of showers and
thunderstorms during the Wednesday and Thursday period. The first
round is on track to occur late Wednesday afternoon into Wednesday
night as the warm front lifts north. As the front does so, dew
points will rise well into the 60s to near 70 degrees as PWATs will
be up around 2.0 inches. With plentiful moisture around Wednesday
night and Thursday any showers or thunderstorm will be capable of
resulting in heavy rainfall. Currently, WPC has the western half of
our forecast area within a Marginal Risk (Level 1/4) of excessive
rainfall for Wednesday into Wednesday night.

The second round is a bit more uncertain and comes down to the
timing of the cold front. Timing has sped up amongst forecast
guidance, so for now the next round looks to occur earlier in the
day on Thursday with clearing skies during the afternoon. CSU-MLP
guidance indicates there is a 5-14% chance of severe weather on
Thursday, so will be monitoring this window going forward, although
we are not currently outlooked by the Storm Prediction Center. There
may potentially be a third round late in the afternoon into the
early evening with some spotty showers or thunderstorms around, but
by this time the bulk of precipitation will be well offshore.
Showers and thunderstorms will cease on Thursday night as the cold
front moves offshore. In total, QPF values are forecast to generally
be in the 0.5-1.0 inch range, but will be locally higher in any
downpours or thunderstorms.

Highs will be in upper 70s/low 80s on Wednesday with more in the way
of low/mid 80s expected on Thursday dependent on the amount of
clearing. Wednesday night lows will be quite uncomfortable in the
upper 60s to near 70 degrees. Thursday night lows will be cooler in
the upper 50s to mid 60s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
The long term period is forecast to be generally unsettled through
early next week. The aforementioned upper trough and low will
meander across southern Canada and the northern Great Lakes through
the weekend. As it does so, multiple shortwaves will round through
the upper trough resulting in several rounds of showers and
occasional thunderstorms through the weekend into next week. While
no singular day appears to be a washout, there will be quite a bit
of showers around, more likely north and west with drier conditions
south and east. The highest probability of precipitation will be
during the afternoon hours as diurnal heating allows instability to
be maximized.

Temperatures during this period will remain quite seasonable for
early June with a mix of 70s/80s during the day and 50s/60s at
night.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

.Thru dawn... Largely VFR at the terminals but KACY will likely
have some IFR (or perhaps lower) fog with the rains of
yesterday and clearing skies locally. High, except with regards
to fog KACY.

.Tuesday... Once this fog dissipates after 12Z/13Z, all the terminals
will have VFR thru the day and into the evening. East to Southeast
winds 5 to 10 knots, locally higher KILG/KMIV/KACY. High/medium
confid overall.

.Tuesday night... VFR to start, then low clouds and fog arrive
with a well established marine layer remaining across the
region. Timing and CIG/VSBY category rather uncertain attm. 12Z
TAFS will include the latest thinking, but uncertainty will
continue. East/Southeast winds decreasing to around 5 knots
overnight. Low/medium confid overall.

Outlook...

Wednesday through Thursday night...Sub-VFR conditions probable with
showers and thunderstorms. Possible improvement in conditions by
Thursday night.

Friday through Saturday...Primarily VFR expected with sub-VFR
conditions possible. A chance of a shower or thunderstorm each
afternoon.

&&

.MARINE...
A continuation of sub-SCA conditions across the waters today and
tonight. Winds will be mostly East to Southeast around 10 to 15
knots much of the time. Seas will remain around 2 ft. Fair weather
today and tonight with perhaps a few isolated showers possible
across the Delaware waters. Tonight, fog may develop across the
waters and possibly become locally dense. Not the highest confidence
in fog development/location however.

Outlook...

Wednesday through Thursday...No marine headlines expected, however
winds may gust around 20+ kt on Wednesday night into Thursday. Seas
around 3-4 feet. Showers likely with a chance of thunderstorms.

Thursday night through Saturday...No marine headlines expected.
Winds generally around 10-15 kt with seas of 2-4 feet. Slight
chance of a shower or thunderstorm each afternoon.

Rip Currents...

For Wednesday, winds increase to 10-15 mph but winds will be
less directly onshore. Combined with continuing 1 to 2 foot
waves and short to medium period keeps the overall risk for rip
current development at LOW.

For specific beach forecasts, visit weather.gov/beach/phi

Rip currents occur often in the vicinities of jetties and
piers. Utilize any guarded beaches if venturing out into the
water.

&&

.TIDES/COASTAL FLOODING...
-- Changed Discussion --
With sustained onshore flow expected through at least Wednesday and
the approaching New Moon on Thursday, there will likely be some
tidal flooding for much of our coastal region. For today, tidal
flooding looks to be confined to areas around the Delaware Bay
as SE winds are funneled up the bay. As a result, a Coastal
Flood Advisory has been issued for areas surrounding the
Delaware Bay for this evening`s high tide cycle. Have less
confidence further upriver, so have held off on any advisories
for there at the moment.

For Wednesday and Thursday, the threat for widespread minor
flooding looks to increase as winds strengthen then turn and
become shore parallel on Thursday, potentially trapping water
along the coast. Recommend to continue to monitor upcoming high
tides and make adjustments to the forecast accordingly.

Overall, the threat for tidal flooding appears to be lower along
the Chesapeake Bay than elsewhere in the region but by the
early morning high tide Thursday, water levels may also approach
spotty minor.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None.
NJ...Coastal Flood Advisory from 8 PM this evening to midnight EDT
     tonight for NJZ016.
     Coastal Flood Advisory from 5 PM this afternoon to 11 PM EDT
     this evening for NJZ021-023-024.
DE...Coastal Flood Advisory from 8 PM this evening to midnight EDT
     tonight for DEZ001.
     Coastal Flood Advisory from 5 PM this afternoon to 11 PM EDT
     this evening for DEZ002>004.
MD...None.
MARINE...None.
-- End Changed Discussion --

&&

$$

SYNOPSIS...DeSilva
NEAR TERM...OHara
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...DeSilva/OHara
MARINE...DeSilva/OHara
TIDES/COASTAL FLOODING...WFO PHI