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000
FXUS61 KPHI 260122
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
922 PM EDT Sun Sep 25 2016

.SYNOPSIS...
High pressure centered over western Quebec will move into New
England tonight before moving offshore on Monday. A cold front
moves across the region Monday night into Tuesday morning, and
then stalls off the coast Tuesday afternoon. Several waves of low
pressure will develop over the Mid-Atlantic and will pass either
through or south of the area into next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Few changes needed for the evening update. Temperatures were
lowered in a few areas and a couple dew points were adjusted also.
Sky cover will remain mostly clr with only some thin ci/cs
overhead tonight.

High pressure across the northeast will keep mostly clear, calm
conditions across the area. Temperatures will cool quite
efficiently tonight with the clear skies and light winds. Some
areas across the far north could drop low enough for some patchy
frost to develop, but we do not think it will be widespread enough
for a Frost Advisory. There could also be some patchy light fog in
some areas, but we have left this out of the forecast as well as
we do not expect it to be very thick or widespread.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
High pressure moves off the east coast during the day Monday,
well ahead of an approaching frontal system. Monday will continue
to be dry, although cloud cover will be on the increase through
the day. With the high building offshore, winds will increase
during the day as well as the pressure gradient increases. Winds
could begin to gust around 15-20 mph by the afternoon.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
A prolonged period of unsettled weather shaping up for most of
the upcoming week, possibly into next weekend.

Warm front will lift north through the region Monday evening
ahead of a cold front west of the Appalachians. Not expecting much
in the way of WAA, but temps should mainly hold somewhat steady
for most areas. Surge of humid air expected between the warm front
and the approaching cold front, allowing dewpoints to climb into
the low 60s and max PWATs to increase to 1.75-2". Closed upper low
digs into the Great Lakes behind the cold front, and several
strong H5 shortwaves will rotate around the low and into the local
CWA as the cold front passes through the region Monday night.

Despite a 40 KT LLJ passing through the region Monday night,
there is not much instability with this system, so not
anticipating much in the way of convection. Cannot rule out a few
rumbles of thunder, so will carry slight chance for thunder with
categorical PoPs. With high low level moisture, can expect periods
of moderate to locally heavy rain. Latest QPF forecast has about
1/2 to 3/4 inch rainfall, but if there is convection, then some
areas could get around an inch. Not anticipating any flooding
issues, given how dry it has been, and while this will not be a
drought-buster, any rainfall is welcome.

Cold front pushes through the region Tuesday morning, and becomes
nearly stationary offshore and extending into the Mid-Atlantic
area. Showers taper off over western zones in the morning, but
showers will persist into Tuesday afternoon for southern and
coastal areas.

By Wednesday, closed low digs into the Great Lakes and Ohio
Valley and will meander there through the end of the week. With
shortwaves rotating around the low, and with the aforementioned
stalled frontal boundary hanging over the Mid-Atlantic, several
waves of low pressure will develop south of the local area, and
will lift to the north and east into the end of the week.

What remains to be seen is when this upper low will depart.
Latest ECMWF keeps the low west of the area into Sunday, while the
latest GFS has the low departing on Saturday, and has high
pressure building east on Sunday. The trend among the models has
been a cooler and wetter solution. Will therefore carry slight
chance to chance PoPs for most of the region from Wednesday
through Saturday, and then slight chance PoPs on Sunday. Given the
rainfall deficit, any rainfall will be welcome.

Temps will be near to slightly below normal for the long term
period.

&&

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

VFR conditions are expected to prevail through the TAF period as
high pressure controls the weather tonight, then builds offshore
Monday. Mostly clear skies are expected tonight into Monday
morning, before clouds increase and lower through the afternoon.
Winds become light and variable/calm overnight. The winds will
increase out of the southeast during the day Monday as high
pressure builds offshore, and could gust in the upper teens by the
afternoon.

The first mention of showers was added to the 00z 30-Hr. TAF for
PHL. A tempo group for showers and a MVFR cig for the last 3 hours
of the fcst.

OUTLOOK...

Monday night...Showers and isolated thunderstorms spread into the
region from west to east. Conditions lowering to MVFR, but IFR and
lower conditions possible in heavier showers. 40 KT LLJ will move
overhead, but not anticipating LLWS in the TAFs.

Tuesday...MVFR/IFR conditions early, and then improvement at
western terminals (ABE/RDG) in the morning. Eastern terminals
(MIV/ACY) may not improve to VFR until late afternoon. Winds shift
from SW to W Tuesday morning.

Tuesday night...Mainly VFR.

Wednesday through Friday...Sub-VFR conditions in showers
possible. Best chances are Thursday and Friday. Low confidence in
forecast for the late week period.

&&

.MARINE...
The Small Craft Advisory has been cancelled for the Atlantic
Ocean waters as seas have dropped below 5 feet. Winds and seas
will remain below Advisory levels for the remainder of tonight
into Monday. However, as high pressure builds offshore Monday,
winds are expected to increase through the day and could begin
gusting around 20 knots later in the day.

OUTLOOK...

Monday night and Tuesday morning...SCA possible. Southerly winds
ahead of a cold front increase to around 20 kt with gusts near 25
kt. Seas build to 4-5 ft in our coastal waters.

Tuesday afternoon through Wednesday...Winds and seas below SCA
threshold.

Thursday through Friday...Seas may build to SCA levels. Low
confidence in forecast for late week period.

RIP CURRENTS...

A moderate risk of rip currents will continue for the remainder
of today.

The risk for rip currents on Monday may likely remain moderate
due to long period swells reaching the shore.

&&

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

&&

$$
Synopsis...MPS
Near Term...Robertson/Po
Short Term...Robertson
Long Term...MPS
Aviation...Robertson/MPS/Po
Marine...Robertson/MPS