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630
FXUS61 KPHI 042105
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
505 PM EDT Tue Jun 4 2024

.SYNOPSIS...
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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.
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&&

.NEAR TERM /THROUGH WEDNESDAY/...
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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.
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&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
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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.
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.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
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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.
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&&

.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
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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.

AKL/DeSilva
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.
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&&

.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...
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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 and Delaware River as SE winds are funneled up the bay. As
a result, a Coastal Flood Advisory has been maintained for areas
surrounding the Delaware Bay for this evening`s high tide
cycle. Given latest guidance, did include Burlington/Bucks
upriver in an advisory, but held
Philadelphia/Camden/Gloucester/Delaware out for now.

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.
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&&

.PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Air Quality Alert until 11 PM EDT this evening for PAZ060>062.
     Coastal Flood Advisory from midnight tonight to 4 AM EDT
     Wednesday for PAZ106.
NJ...Coastal Flood Advisory until 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.
     Coastal Flood Advisory from midnight tonight to 4 AM EDT
     Wednesday for NJZ019.
DE...Coastal Flood Advisory until midnight EDT tonight for DEZ001.
     Coastal Flood Advisory until 11 PM EDT this evening for
     DEZ002>004.
MD...None.
MARINE...None.
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&&

$$

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