Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 190242
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
942 PM EST Sat Nov 18 2017

.SYNOPSIS...
Low pressure over the Ohio Valley will lift to the north and
east and into southeast Canada tonight, and then a strong cold
front will move across the region Sunday morning. High pressure
then builds in from the west and moves off the Mid-Atlantic on
Tuesday. A cold front moves through the region Wednesday night.
Low pressure develops along that front and may impact the region
on Thursday. High pressure returns on Friday, followed by low
pressure passing north of the area on Saturday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Update: A few more adjustments to hourly temps across the area
with readings running warmer than fcst near Wilmington and
Philadelphia. Pops also adjusted according to recent radar
trends. Showers from central PA moving east and  will arrive
over the area in a few hours ahead of the approaching cold
front. Winds are slow to increase this evening, so far.

An area of low pressure will move across the eastern Great
Lakes region and toward the northeast tonight. A strong cold
front associated with this low will approach the area overnight
tonight and toward Sunday morning. Southwest flow aloft will
continue across the area, with several short wave/vorticity
impulses moving across the area. A couple rounds of showers are
expected tonight across the are. One short wave will approach
the area around/after midnight, leading to a round of showers.
Finally, as the cold front approaches, the final round of showers
will move into the area toward daybreak Sunday. There is not
much instability, although the front and short wave/vorticity
impulse are fairly potent. So it would not be surprising to see
an isolated lightning strike or rumble of thunder, but the
chances are pretty small so we did not include them in the
forecast. PW values continue to be forecast to reach 1.00-1.25
inches, so there could be some moderate, to occasionally heavy
rainfall at times.

Another concern overnight is the increasing winds. Winds will
be increasing through the night and wind gusts of 25-35 mph are
possible through the night. It will likely not be gusty
everywhere overnight as mixing will not be very deep everywhere
during the night time period. However, as any showers move
through, and as the cold front approaches, gusts have a better
chance of mixing down. Winds have the potential to gust to
around 50 mph as the front moves through around daybreak, so we
have issued a Wind Advisory across the area.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
The cold front pushes through the area around and shortly after
daybreak Sunday, and the rain showers will be ending as the
front moves through. The main concern for the daylight hours
Sunday will be the winds. Right as the front moves through, a
surge of wind is possible to occur, then the winds could
continue to gust 45-50 mph through the morning and into the
early afternoon hours. Therefore the Wind Advisory will continue
into the afternoon hours Sunday across the entire area.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Strong NW flow continues night as low pressure lifts into
eastern Canada and high pressure builds into the TN valley and
Gulf Coast states. Winds will gust to 25-30 mph in the evening,
and will gradually diminish after midnight Sunday night. Though
precip will be over for the vast majority of the forecast area,
some Lake Effect Snow streamers may make it into the Pocono
Mountains, and could result in some spots picking up 1/4" snow.
Cold night in store with lows dropping into the 20s for the
Poconos and NW NJ, otherwise in the low 30s for the Lehigh
Valley, southern NJ, and the Delmarva. Wind chills will range
from the teens up north to around 30.

High pressure just north of the Gulf Coast will build east on
Monday, and will gradually move off the Mid-Atlantic coast on
Tuesday. Chilly conditions on Monday with highs in the 30s up
north and in the 40s elsewhere will moderate back into the 50s
to near 60 on Tuesday as return flow sets up.

From there, low pressure develops off the Southeast U.S. coast
and lifts to the north along the coast as a cold front
approaches from the west. That front passes through the region
Tuesday night or Wednesday. Confidence is low for this
timeframe, as there is uncertainty with how far west that low
will track and how much precip will fall. For now, will follow a
blend of guidance and carry chance PoPs Tuesday night-
Wednesday.

High pressure builds in from the west on Thursday, but models
are indicating another coastal low passing south and east of the
area during this time, and depending on how close it tracks,
more precip is possible for the area. Will carry slight chance
PoPs for southeast portions of the forecast area, but it will
take a couple of days or so before the details are ironed out
with this potential low.

Dry conditions on tap for Friday.

Low pressure passes north of the area Saturday and drags a cold
front through the region. Some snow is possible up north Friday
night, and then precip changes to rain on Saturday.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR conditions across the area this evening will
diminish  over the next few hours with MVFR conditions possible
as showers move across the area thru the overnight. A cold
front moves across the area around daybreak Sunday.

Winds will increase through the night, and could gust 15-25
knots for much the night, then increase after midnight, and
especially through daybreak as the cold front moves through to
around 25-35 knots.

Sunday...MVFR conditions are expected right around daybreak as
the showers move through the area, then a return to VFR is
expected through the morning hours into the afternoon. Winds are
expected to be gusting 30-40 knots through much of the day.

Outlook...

Sunday night...VFR. Some flurries possible at KRDG/KABE. NW
winds 15- 20 KT with gusts up to 30 KT, diminishing to 10-15 KT
late. High confidence.

Monday through Tuesday...VFR. West winds 10-15 KT on Monday
become S 5-10 KT Monday night, and then 10-15 KT with gusts up
to 20 KT on Tuesday. High confidence.

Tuesday night through Thursday...Potential for rain Tuesday
night/Wednesday, then again on Thursday with sub-VFR conditions.
Low confidence forecast.

&&

.MARINE...
We raised the Gale for Delaware Bay early with the winds nearby
at KDOV already at Gale gusts. A Gale Warning is also in effect
for for the ocean waters through Sunday night. Showers
increasing overnight as the cold front approaches.

OUTLOOK...

Sunday night...NW Gales continue Sunday night, but may end just
after midnight on DE Bay.

Monday through Monday night...NW winds gusting to 25 KT on the
ocean waters, along with 4-6 ft seas.

Tuesday through Tuesday night...SW winds 15-20 KT with 25-30 KT
gusts on the ocean; SW winds gusting to 25 KT on DE Bay. Winds
diminish after midnight Tuesday night.

Wednesday...Winds and seas subside to sub-SCA conditions.

Thursday...Low confidence forecast with the potential for SCA
conditions on the ocean.

&&

.TIDES/COASTAL FLOODING...
There is a potential for blow out tides on Sunday, especially
in the Delaware Bay and the tidal portion of the Delaware River,
where strong W-NW winds will effectively drain water out of the
bay. The low tide Sunday afternoon/evening seems to be the most
susceptible for low water concerns that could impact navigation
in the area.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Wind Advisory from 5 AM to 4 PM EST Sunday for PAZ054-055-
     060>062-070-071-101>106.
NJ...Wind Advisory from 5 AM to 4 PM EST Sunday for NJZ001-007>010-
     012>027.
DE...Wind Advisory from 5 AM to 4 PM EST Sunday for DEZ001>004.
MD...Wind Advisory from 5 AM to 4 PM EST Sunday for MDZ008-012-015-
     019-020.
MARINE...Gale Warning until 5 AM EST Monday for ANZ430-431-450>455.

&&

$$
Synopsis...MPS
Near Term...Robertson/PO
Short Term...Robertson
Long Term...MPS
Aviation...Robertson/MPS/PO
Marine...Robertson/MPS/PO
Tides/Coastal Flooding...


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