FXUS61 KPHI 090036

Area Forecast Discussion
National Weather Service Mount Holly NJ
836 PM EDT Wed Jul 8 2020

Weak high pressure will continue to influence our weather into
Thursday. Weak low pressure centered along the Carolina coast
this afternoon is forecast to progress to the north. The low is
expected to pass through or near our region on Friday and Friday
night. A frontal boundary is anticipated to approach from the
northwest on Saturday. The front is expected to move slowly
through our region on Sunday and Monday before drifting away to
our southeast during the middle of the new week.


815 pm update: Have included mention of fog for most of the
region overnight. Latest guidance is quite aggressive in
developing fog over much of the region, with two areas
particularly emphasized: (1) The Lehigh Valley and adjacent
areas, where widespread precipitation occurred today. (2) The
Pine Barrens and vicinity, with close proximity to the ocean and
onshore flow beneficial factors. The main question is if fog or
low stratus will dominate, especially in New Jersey. Guidance is
not particularly convincing either way, and given the lack of
precipitation in New Jersey today, was inclined to leave mention
of dense fog out of the forecast for now. Would not be surprised
if dense fog develops in the more susceptible/sheltered
locations, especially in the Lehigh Valley and vicinity, however.

600 pm update: Major changes to the forecast early this evening.
Have canceled the flash flood watch, as storms across the watch
area have diminished/moved south and have effectively used the
available potential energy in the atmosphere today. Have also
modified PoPs considerably this evening to accommodate recent
radar trends. Generally, this involved lowering PoPs in the
Poconos and maintaining higher PoPs between Reading and Trenton
and locations just south through mid evening.

Perhaps the biggest change was to temperatures, which have been
lowered substantially thanks to the convection in the Lehigh
Valley and northern New Jersey this afternoon. Used the
available NAM guidance in particular, as this was verifying much
better than other available output. This dropped temperatures
about 10-15 degrees for much of this region through the evening

May add some fog mention to portions of the Lehigh Valley based
on latest guidance and given the heavier precipitation today.
Will make that determination in the next couple of hours.

Previous discussion...

Convection will wane into the overnight with sunset. Low clouds
and patchy fog will once again be possible with increased
moisture and light winds (similar to last night). Trying to
pinpoint where exactly this occurs remains tricky business. Lows
will drop into the low 70s across the region.


A very similar day tomorrow before the coastal storm begins to
work into the region. Patchy fog is possible in the morning,
with low clouds and stratus persisting into the early morning
once again. Think the overall risk for showers and thunderstorms
will be lower given the more robust forecast trends for the
coastal storm system. Weak ridging pushes ahead of this system
over our region through the early afternoon, with high
temperatures forecast to reach into the upper 80s to near 90 in
the urban corridor. Current forecast trends begin to push this
system near our region up the Delmarva Peninsula with initial
rain showers possible by late afternoon to evening starting
across Delaware and Maryland late Thursday evening and working
northward into the overnight. More to come on this system as it
rapidly evolves and we continue to provide the latest forecast
information as it becomes available.


We continue to keep a very close eye on the low that will be
approaching our region from the south on Thursday night. The
guidance has been trending westward with the track, so the
feature may pass over or very near our region from Friday into
Friday night.

The low is not forecast to be particularly strong by the time
it reaches our area, so the wind is not much of a concern.
However, it will have a good deal of moisture associated with
it. There is the potential for widespread heavy rain in
northeastern Maryland, Delaware, New Jersey and eastern
Pennsylvania. The recent heavy rainfall in parts of our region
has increased our susceptibility to flooding. We will work to
refine the threat area as we get closer to the event. It appears
as though most of the heavy rain will lift to our north on
Friday night.

A frontal boundary is forecast to approach from the northwest
on Saturday and it is expected to move slowly through our region
on Sunday and Monday. There will likely be enough moisture and
instability during the afternoon and early evening each day to
result in scattered showers and thunderstorms.

The front is anticipated to move away to our southeast on
Tuesday and Wednesday. As a result, there is a decreasing chance
of precipitation at that time.

The clouds and precipitation are expected to keep high
temperatures in the upper 70s to the middle 80s on Friday.
Maximum readings should favor the middle 80s to the lower 90s
from Saturday through Wednesday.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Mainly VFR through late evening, but sub-VFR with
fog/low stratus is probable overnight, especially at RDG/ABE/TTN
(where precipitation occurred earlier; dense fog is not out of
the question) and at MIV/ACY (where increased onshore flow
exists; confidence is lower here, as low stratus may preclude
denser/more widespread fog). Best timing is between 06z and
12z, but confidence is rather low in precise timing of MVFR/IFR.
Winds light and variable (high confidence).

Thursday...Conditions likely improving to VFR by mid-morning,
though some lingering fog and/or low clouds may occur through
14z or so. Winds becoming predominantly east or southeast 5 to
10 kt. Moderate confidence in the morning; high confidence in
the afternoon.

Thursday night...VFR conditions in the evening likely
deteriorating to MVFR from south to north with time. Chances
for showers/storms increase overnight as well, with occasional
IFR likely in their proximity. Winds generally easterly 5 to 10
kt. Moderate confidence.


Friday...MVFR/IFR in showers and thunderstorms. The rain will
be heavy at times. Northeast wind around 10 knots, becoming
variable. Medium confidence.

Friday night...MVFR/IFR in showers and thunderstorms with a
decreasing chance of rain overnight. Variable wind 5 to 10
knots, becoming northwest. Medium confidence.

Saturday...Mainly VFR. A chance of afternoon showers and
thunderstorms. West to southwest wind 5 to 10 knots. Medium

Saturday night...Mainly VFR. A chance of evening showers and
thunderstorms. Late night visibility restrictions are possible.
Variable wind 6 knots or less. Medium confidence.

Sunday...Mainly VFR. A chance of afternoon showers and
thunderstorms. West to southwest wind 5 to 10 knots. Medium

Sunday night...Mainly VFR. A chance of evening showers and
thunderstorms. Late night visibility restrictions are possible.
Variable wind 6 knots or less. Medium confidence.

Monday...Mainly VFR. A chance of afternoon showers and
thunderstorms. West to southwest wind 5 to 10 knots. Medium


Sub-advisory conditions expected through the overnight with
south-southeasterly winds from 5 to 10 knots with gusts from 15
to 20 knots. Waves 3 feet or less.

Thursday...Sub-advisory conditions continue as winds turn
easterly from 10 to 15 knots. Afternoon showers and
thunderstorms possible, especially across the southern Atlantic
Waters late in the day. Seas 3 feet or less.


Thursday night...A Small Craft Advisory is in effect for our
ocean waters from Brigantine and Atlantic City southward and for
Delaware Bay for wind gusts around 25 knots.

Friday...A Small Craft Advisory is in effect for our ocean
waters for wind gusts around 25 knots and wave heights building
to 5 to 7 feet.

Friday night...Wave heights on our ocean waters may remain
around 4 to 6 feet.

Saturday through Monday...No marine headlines are anticipated.

Rip Currents...

There is a moderate risk of rip currents on Thursday, as an
east-to-southeast medium-period swell will begin to increase.
This will occur as a coastal low begins to intensify to the
south of the area. Conditions are expected to deteriorate on
Friday, as a longer-period swell begins to develop with seas
continuing to build as the low begins to move into the region. A
high risk of dangerous rip currents is currently forecast for
Friday, with potential for an elevated rip current risk to
continue through the weekend.


The area of low pressure moving northward near the coast from
Thursday night through Friday night is not expected to be
particularly strong, and it should be somewhat progressive. As
a result, we are not anticipating much in the way of tidal
flooding. Positive departures in excess of 2 feet are needed to
produce minor flooding. It seems as though tidal departures
will remain less than 2 feet at most coastal locations on


The Reading Regional Airport (KRDG) ASOS has returned to service.

The NOAA Weather Radio All Hazards broadcast from Hibernia
Park, PA (WNG704) remains off the air until further notice due
to damage to the antenna during the June 3 derecho.


MARINE...Small Craft Advisory from 10 PM Thursday to 6 PM EDT Friday
for ANZ452>455.
Small Craft Advisory from 4 AM to 6 PM EDT Friday for ANZ450-
Small Craft Advisory from 10 PM Thursday to 10 AM EDT Friday
for ANZ430-431.


Near Term...CMS/Davis
Short Term...Davis
Long Term...Iovino
Tides/Coastal Flooding...Iovino
Equipment...WFO PHI
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