594
FXUS61 KPHI 041916
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
316 PM 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 WEDNESDAY/...
A relatively nice Tuesday is ongoing as high pressure centered near
Nantucket is in control. A backdoor front is currently positioned
near the Chesapeake Bay, which has resulted in some showers/isolated
thunderstorms developing. Similar to yesterday, these updrafts
should go up and come right back down, primarily due to a lack of
shear. A brief heavy downpour is possible over the Eastern Shore
through about sunset. Elsewhere, it will be dry with some scattered
cumulus and thin high clouds passing through.

For tonight, low clouds and fog are expected to develop over the
ocean and push ashore. Thinking the fog will mainly be confined to
Delmarva and the NJ coastal plain, with just low stratus
elsewhere. Temperatures will drop into the low to mid 60s.

Tomorrow begins a stretch of unsettled weather that will last into
the weekend as an upper level low moves into the Great Lakes region
where it will meander through about Saturday or so. A warm front
will be positioned just to our south and west, lifting north on
Wednesday afternoon/evening. A subtle shortwave will move through
tomorrow afternoon, with showers/thunderstorms moving in. With PWATs
pushing 2 inches by late tomorrow, some heavy downpours are
possible. Best chance to see thunderstorms/heavy rain will be over
the Delmarva peninsula and southeastern PA. These locations will
also have the most instability present, with the HREF ensemble mean
showing around 1000-1250 J/kg of SBCAPE available. Cannot rule
out some possibility of severe weather with that much CAPE and
effective shear around 25-30 kt. But, given that parameters are
not overly impressive, the threat should not be widespread.
While heavy rain is likely tomorrow for some locations, the
flash flooding threat is low as storm motion should be steady
and training/backbuilding is not expected. The threat increases
Wednesday Night/Thursday though (see the next section for more
detailed information). Temperatures will get into the upper
70s/low 80s tomorrow.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
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 NIGHT THROUGH TUESDAY/...
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 /19Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. East to Southeast winds 5 to 10 knots. High
confidence.

Tonight... VFR to start, then low clouds and fog arrive with a
marine layer pushing inland. Thinking it will be mainly stratus
across the I-95 and Lehigh Valley terminals, but ceilings will
be in the IFR range. Closer to the coast, some patchy fog is
expected which will reduce visibility down to IFR levels with
IFR/LIFR CIGs at KACY/KMIV. Winds out of the southeast around 5
kt or less. High confidence in restrictions occurring, moderate
confidence in timing, low confidence in extent of restrictions.


Wednesday...Conditions should lift to VFR by midday. Any VFR
conditions could be relatively short-lived with showers/isolated
thunderstorms moving through. Winds remain out of the southeast
around 5-10 kt. Low confidence.

Outlook...

Wednesday Night 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...
Sub-SCA conditions expected on the waters through Wednesday.
Seas will be around 2 feet with winds out of the east/southeast
around 10-15 kt. Some fog is expected to develop along the
waters tonight, which will reduce visibility. Fog could be
locally dense and a Marine Dense Fog Advisory may be needed.
Would put the probability of widespread dense (visibility 1 mile
or less) at around 40-50%.


Outlook...

Wednesday Night 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...
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.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Air Quality Alert until 11 PM EDT this evening for PAZ060>062.
NJ...Coastal Flood Advisory from 8 PM this evening to midnight EDT
     tonight for NJZ016.
     Coastal Flood Advisory until 11 PM EDT this evening for NJZ021-
     023-024.
     Air Quality Alert until 11 PM EDT this evening for NJZ001-
     007>010-012-015.
DE...Coastal Flood Advisory from 8 PM this evening to midnight EDT
     tonight for DEZ001.
     Coastal Flood Advisory until 11 PM EDT this evening for
     DEZ002>004.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...MPS
NEAR TERM...Hoeflich
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...Hoeflich/MPS
MARINE...Hoeflich/MPS
TIDES/COASTAL FLOODING...AKL/DeSilva