547
FXUS61 KPHI 050540
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
140 AM EDT Wed Jun 5 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 TODAY/...
As of 130am...Have started to see some low clouds and patchy
fog develop along the coast and should progress inland through
the early morning hours. Thinking the fog will mainly be
confined to Delmarva and the NJ coastal plain, with just low
stratus and patchy mist elsewhere. Temperatures will drop into
the low to mid 60s.

Wednesday 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 later this afternoon/evening. A subtle shortwave
will move through during the afternoon, with showers and
thunderstorms moving in. With PWATs pushing 2 inches by late
in the day, 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 for some locations, the flash flooding threat is
low as storm motion should be steady and training/backbuilding
is not expected. The threat increases tonight/Thursday though
(see the next section for more detailed information).
Temperatures will get into the upper 70s/low 80s today.

&&

.SHORT TERM /TONIGHT 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 night and Thursday period.
The first round will be ongoing Wednesday evening and likely
continues much of 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 night.

The second round is a bit more uncertain and comes down to the
timing of the cold front. Latest guidance shows a distinct
additional round of concentrated showers and storms with the
frontal passage in the afternoon, so after dropping pops to
chance in the morning, have them rise back to categorical in 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. 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 low/mid 80s 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 /06Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through 12Z...VFR to continue through about 08Z before low
clouds and patchy fog arrives as the marine layer moves inland.
Still anticipate that it should primarily be low marine stratus
for most terminals dropping to IFR/MVFR. For KACY/KMIV and
potentially KILG, fog may impact these terminals, resulting in
periods of IFR/LIFR. Southeast winds around 5 kt or less
becoming light and variable at times. Low confidence overall,
especially with regard to timing of lowering CIGs/VSBYs.

Today...LIFR/IFR/MVFR CIGs should lift to VFR at all terminals
by 15-16Z. Another round of lowering CIGs down to MVFR are
expected later in the day as rain showers and isolated
thunderstorms move into the region. South-southeast winds around
5-10 kt. Moderate confidence.

Tonight...All terminals should encounter lowering CIGs and
decreasing VSBYs as heavier rain moves in this evening. Heaviest
of rain should continue through about 06-08Z, before lifting
north and east of the region. Still anticipate lower CIGs/VSBYs
to persist after rain exits. South-southwest winds around 5-10
kt. Low confidence.

Outlook...

Thursday 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 today. 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...

A LOW risk for the development of rip currents is in place for
Wednesday. Winds will be on onshore from the SSE, but only around
10-15 MPH with 1-2 foot waves and a medium period. This results
in the LOW risk.

For Thursday, winds 10-15 mph parallel to the shore for NJ and
offshore for DE beaches. With seas 2-3 feet, a medium period swell,
and a new moon, the risk for rip current development is MODERATE for
NJ and LOW for DE beaches.

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. While much
of the tidal flooding is now subsiding, along the Tidal
Delaware including Philadelphia, high tide is yet a few hours
off, and waters are running high. Thus, expanded Coastal Flood
Advisory to include the entire tidal Delaware River. The next
high tide in the morning/midday is the lower of the two, so do
not plan to extend advisories at this time, and will let
existing ones expire.

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...Coastal Flood Advisory until 3 AM EDT early this morning for
     PAZ070-071.
     Coastal Flood Advisory until 4 AM EDT early this morning for
     PAZ106.
NJ...Coastal Flood Advisory until 3 AM EDT early this morning for
     NJZ017-018.
     Coastal Flood Advisory until 4 AM EDT early this morning for
     NJZ019.
DE...None.
MD...None.
MARINE...None.

&&

$$

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