Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 180753
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
353 AM EDT Sat Aug 18 2018

.SYNOPSIS...
A cold front will move into the region today and this evening,
stalling just south of our area Sunday. Several waves of low
pressure will move along the stalled boundary through the
weekend and into early next week. The stalled front will lift
northward as a warm front on Tuesday, followed by a cold front
on Wednesday. High pressure will build in from the west from
Thursday through the end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Another day of potential heavy rainfall and flooding as several
rounds of showers and thunderstorms will move across the area.

A surface trough remains in place across the area early this
morning, and will remain nearly stationary through the day. A
couple of short waves/vorticity impulses will continue to move
across the area, enhancing lift near the surface trough. There
remains a fair amount of instability across the area, so
scattered showers and thunderstorms will continue through the
morning hours.

The main threat for heavy rainfall will begin this afternoon
into this evening as a cold front approaches the area from the
northwest. Showers and thunderstorms are expected to become more
widespread as the front approaches and moves across the area.
With PW values remaining around 2 inches, heavy rainfall will
likely occur. Those areas that received heavy rainfall on
Friday, as well as the more urbanized I-95 corridor will be
particularly susceptible to flash flooding. Therefore we have
issued a Flash Flood Watch for eastern Pennsylvania, much of New
Jersey, and northern Delaware and Maryland; basically along and
north of the I-95 corridor.

There will be plenty on instability for thunderstorms to
develop across the area through today. However, there is limited
shear and the flow aloft is fairly weak. So while there could
be a few strong thunderstorms, mainly due to the instability, we
do not expect much in the way of severe weather this afternoon.

Before the cold front and showers/thunderstorms approach later
this afternoon, temperatures will warm well into the mid-upper
80s, and low 90s for some areas. However, heat index values are
not expected to reach advisory levels at this time across the
area.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Heavy showers and thunderstorms will be ongoing across the area
this evening as a cold front moves across the area. However, as
the cold front continues to move southward through the evening
and overnight, shower and thunderstorm activity is expected to
wane some. Therefore the Flash Flood Watch will remain in effect
through midnight. While the shower activity wanes overnight, it
showers may not completely drop off as there will continue to
be a couple of more short wave/vorticity impulses overnight. So
we will keep a chance of showers and thunderstorms through the
night, although the threat for flooding diminishes overnight.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Sunday through Monday...The cold fronts forward progress starts
to slow down by Sunday and the front will stall over or just
south of our area. For now, the guidance keeps the front just
south of the region but there is potential for it to wobble a
bit as it remains nearby through Monday.

Several waves of low pressure will travel along the stalled boundary
on Sunday and Monday. This will keep us in a now very familiar and
unsettled pattern to end the weekend and start the week. A chance
for showers and thunderstorms will exist through Monday, with the
potential for heavy rainfall to occur as PWATs remain around 2
inches on Sunday. Expect PWATs to decrease some for Monday, down to
around 1.25-1.50 inches as some drier air pushes down from the north
in response to high pressure building across New England. Conditions
across the region remain fairly wet as we have not had very many
days where significant drying can occur. So this will once again
mean that there will be the potential for flooding across our
already saturated region.

An upper trough will dig down and move through the region late
Sunday through Monday. Some cooler air will be brought southward and
that should help to keep Sunday cooler than it has been of late.
However, it is short lived as the airmass will start to modify and
warm for Monday. Highs in the upper 70s to low 80s on Sunday, some
mid 80s possible in southern Delaware due to the proximity to the
stalled boundary. Generally expect highs in the lower 80s for
Monday.

Tuesday through Wednesday...An area of low pressure will start to
organize over the Midwestern states and track towards the Great
Lakes region early in the week. As this low makes its move towards
upstate New York/eastern Canada, it will start to push the stalled
boundary to the north as a warm front.

There is not a lot of instability on Tuesday as the front moves
through. However, PWATs remain high and the lift from the front may
be just enough to allow for some convection to develop. Will
continue to mention a slight chance for thunder through Tuesday.

The low continues to pull northward into eastern Canada and as it
moves along, it will drag a cold front towards and then through our
region on Wednesday. A secondary front may push through the region
later on Wednesday. The bulk of the moisture looks to be tied to the
primary cold front so not expecting much precipitation to occur with
the second frontal passage.

Thursday and Friday...High pressure will start to push eastward and
into our area on Thursday. Expect conditions to dry out for the end
of the week. However, the only fly in the ointment is the location
of the front that moved through the area on Wednesday. Guidance
shows the boundary stalling offshore which could keep the chance for
some showers mainly across our southern and coastal areas.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
Today...Scattered showers will continue at times this morning,
with an isolated thunderstorm possible, which may temporarily
lead to sub VFR conditions. However, VFR conditions are
expected this morning outside of showers and thunderstorms.

Showers and thunderstorms are more likely this afternoon into
this evening as a cold front approaches. VFR conditions will
continue outside of the showers and thunderstorms. However, sub
VFR conditions will occur as the showers and thunderstorms move
across the TAF sites. The heaviest thunderstorms activity is
expected after 19z-20z.

Winds today will generally be south to southwest 5-10 knots
early, shifting to more westerly later today.

Tonight...Showers and thunderstorms will move across the area
through the evening hours. Generally VFR conditions are expected
outside of the showers and thunderstorms. However, sub VFR
conditions remain possible as the showers and thunderstorms
move across the TAF sites. Shower and thunderstorm activity is
expected to wane during the overnight hours.

Ceilings are expected to lower later in the overnight period,
and may lower to MVFR or even IFR for some areas. Winds will
become northwest behind the cold front, before shifting to
northeast overnight with speeds around 5 knots.

Outlook...
Sunday through Monday...Chance for showers and thunderstorms
with MVFR/IFR conditions possible. Light winds through the
overnight periods with northeast around 5 to 10 knots through
Sunday and Monday. Gusts up to 20 knots possible on Sunday.

Tuesday...Chance for showers and isolated thunderstorms with
MVFR/IFR conditions possible. East to southeast winds around 5 to 10
knots.

Wednesday...Chance for showers and thunderstorms with MVFR/IFR
conditions possible. West to southwest winds around 5 to 10 knots
with gusts up to 20 knots possible.

&&

.MARINE...
Conditions expected to remain below advisory levels today and
tonight across the area. Multiple rounds of showers and
thunderstorms will occur through today and tonight which will
lead to locally higher winds and waves.

A cold front will move across the area this evening and tonight
which will shift winds to the northwest then northeast
overnight with gusts around 20 knots possible.

Outlook...

Sunday...Seas and winds will increase as a boundary remains
stalled south of the area waters. Winds may gust near 25 knots
Sunday afternoon. Seas will rise to near 5 feet by mid morning
on Sunday. A Small Craft Advisory may be needed. Additionally, a
chance for showers and thunderstorms will produce locally
higher winds and waves.

Monday...Seas are expected to subside early and remain below 5 feet
through Monday. Winds will remain below Small Craft Advisory
criteria.

Tuesday through Wednesday...Conditions expected to remain below
Small Craft Advisory Criteria. Winds may gust around 20 knots
through the afternoons on each day.

Rip Currents...

A low risk for the formation of dangerous rip currents is expected
to continue today. However, lightning will be a concern through
the day as well.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flash Flood Watch from 2 PM EDT this afternoon through this
     evening for PAZ054-055-060>062-070-071-101>106.
NJ...Flash Flood Watch from 2 PM EDT this afternoon through this
     evening for NJZ001-007>010-012>020-026-027.
DE...Flash Flood Watch from 2 PM EDT this afternoon through this
     evening for DEZ001.
MD...Flash Flood Watch from 2 PM EDT this afternoon through this
     evening for MDZ008.
MARINE...None.

&&

$$
Synopsis...Meola
Near Term...Robertson
Short Term...Robertson
Long Term...Meola
Aviation...Robertson/Meola
Marine...Robertson/Meola


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