Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 190154
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
954 PM EDT Fri Aug 18 2017

.SYNOPSIS...
As low pressure tracks well to our north, a cold front moves
through late tonight into early Saturday. High pressure then
builds in late Saturday and remains in place into Monday before
shifting offshore. The next cold front is scheduled to arrive
during Wednesday, then Canadian high pressure builds in for
Thursday and Friday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
The cold front was still back across central Pennsylvania and
eastern West Virginia around 9:30 PM. The boundary is forecast
to pass through our region after midnight. Until that time
conditions will remain warm and muggy.

The last of the rain showers were in southern New Jersey and
central and southern Delaware. They will continue to make their
way off the coast and farther out to sea overnight. The
potential for severe weather and flooding continues to decrease.
As a result, all watches have been discontinued. All that
remains in effect are a couple Flood Advisories where the rain
continues to fall.

The wind will be generally less than 10 MPH overnight at
varying directions which may begin to favor the northwest and
west with the arrival of the cold front. Low temperatures are
expected to be mostly in the upper 60s and lower 70s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Cold front should be offshore early Saturday morning, and once
west to northwest winds increase a bit, the drier airmass
spreads east, and any lingering fog will burn off. Skies clear
out in the afternoon. Dewpoints drop about 10-15 degrees,
generally into the mid 60s, but temps will be fairly warm,
topping off in the upper 80s to near 90 across the urban
corridor of I-95 from Trenton to Wilmington, and in the
Delmarva. Upper trough approaches from the west, and this may
bring isolated late day showers and thunderstorms to far western
portions of the forecast area.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Summary...Lowering of the dew points through Sunday although
remaining warm to hot, then moistures increases again with some
convection especially Wednesday with the next cold front. A
noticeably cooler and drier airmass arrives for Thursday and
Friday in the wake of the cold front.

Synoptic Overview...An upper-level trough is forecast to exit
the Northeast Saturday night and Sunday, then the flow aloft
turns more zonal through early next week. Another trough is
forecast to amplify across eastern Canada and the Great Lakes to
the Northeast Tuesday into Thursday, which then remains in the
Northeast on Friday. We used a blend of continuity/guidance for
Saturday night through Sunday night, then blended in the 12z WPC
Guidance.

For Saturday night and Sunday...The axis of an upper-level
trough is forecast to slide across the region Saturday night,
then quickly move across and exit New England Sunday. A short
wave embedded within this trough is forecast to move through
Saturday night, although it may shear out to the east-northeast.
While some drying is expected to move in, enough lingering
moisture and instability combined with lift may allow for some
convection to arrive from the west before weakening. We
therefore carried some slight chance PoPs in Saturday evening
across parts of the western zones. The flow aloft then turns
more zonal on Sunday with surface high pressure building in.
This should be accompanied by more pronounced drying, and with
plenty of heating during the day Sunday the dew points are
anticipated to lower to more comfortable levels. A northwesterly
breeze on Sunday may be light enough to allow for a sea breeze
to develop in the afternoon.

For Monday and Tuesday...The zonal flow aloft continues at
least into Tuesday. This drives high pressure eventually
offshore as it weakens some later Monday. The next upper-level
trough amplifies eastward from the Midwest and Upper Great Lakes
Tuesday. This will start to back the flow more southwesterly,
and there may be a lee- side trough present on Tuesday. As the
moisture begins to increase once again combined with the
possibility for some convergence and enough instability, some
convective development is possible Tuesday afternoon. We will
carry slight chance PoPs as a result for Tuesday. Any isolated
convection especially inland should tend to diminish during the
night. It will turn more humid during this timeframe.

For Wednesday through Friday...The prospects for convection
will depend on the timing of an incoming cold front Wednesday.
This will be due to an upper-level trough arriving from the
west, however a pre-frontal trough may serve as the primary
focus for showers and thunderstorms. We will continue with
chance PoPs with the idea for at least scattered convection
possible Wednesday. As of now, the cold front should be offshore
to start Thursday and Canadian high pressure builds
southeastward, which arrives over our area on Friday. A
noticeably cooler and drier airmass overspreads our region for
Thursday and Friday.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Overnight...VFR and MVFR. Low level moisture remains in place
and some local low clouds and/or fog should develop. The extent
of the low clouds/fog is of lower confidence.

Saturday...Any fog dissipates early, otherwise VFR. Northwest
winds increase to 5-10 knots, then shift to the west or
southwest in the afternoon. Isolated late day shower or
thunderstorm possible near KRDG/KABE.

OUTLOOK...
Saturday night and Sunday...VFR overall. Southwest winds 5
knots or less becoming northwest Saturday night, then northwest
winds near 10 knots Sunday.

Monday and Tuesday...Mainly VFR. Southerly winds around 10
knots.

Wednesday...Sub-VFR at times with some showers and
thunderstorms possible as a cold front arrives. Southwest winds
5-10 knots, becoming west.

&&

.MARINE...
The SCA has been cancelled as wind speeds and wave heights
diminish gradually. The last of the showers and thunderstorms
will move out to sea overnight.

Tranquil conditions develop and will remain in place through
Saturday.

Fog may develop late tonight and into Saturday morning, which
could reduce VSBYs down to 1 NM.

OUTLOOK...
Saturday night through Wednesday...The conditions are
anticipated to be below Small Craft Advisory criteria.

RIP CURRENTS...
The rip current risk for Saturday is currently outlooked as
low.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

Synopsis...Gorse
Near Term...Iovino
Short Term...MPS
Long Term...Gorse
Aviation...Gorse/MPS
Marine...Gorse/MPS


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