Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 131714
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
114 PM EDT Fri Oct 13 2017

.SYNOPSIS...
High pressure, initially centered near northern New England
however it extends into the Mid-Atlantic region, shifts to near
and south of the Canadian Maritimes through Saturday. Meanwhile,
a weak system from the south moves over our area later tonight
and Saturday. A strong cold front moves across our region Sunday
night, followed by a weak cold front late Tuesday. High
pressure builds in Monday night and Tuesday and remains right
over our area during Wednesday into Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1100 am update: Only change needed to the grids this morning
was a slight decrease in both hourly temperatures/dew points.
Otherwise, forecast is in good shape.

High pressure was centered over Canada`s Maritime Provinces
early this morning. The high will drift southeastward today.
Meanwhile, an inverted surface trough is forecast to develop off
the Middle Atlantic coast.

The surface pattern will maintain an onshore flow in our region
for today. The wind should be from the east and northeast
around 10 to 15 MPH near the coast and 5 to 10 MPH inland.

A deck of stratus covered northeastern Maryland, Delaware,
southeastern Pennsylvania, and southern and central New Jersey
around 6:00 AM. A return flow of increasingly moist air is
expected to cause the clouds to continue spreading to the north
and northwest. Spotty light rain is anticipated in our region
today, mainly in southern New Jersey and southeastern
Pennsylvania, and on the upper Delmarva.

Maximum temperatures are forecast to be in the 60s. Readings
should not get above the middle and upper 50s in the elevated
terrain.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
The center of the high is expected to continue drifting out to
sea tonight as the inverted trough remains along the Middle
Atlantic coast. Moist air will remain in place in our region. As
a result, we are anticipating a mostly cloudy sky along with a
low or slight chance of light rain. Patchy fog and drizzle may
develop as the surface flow remains off the ocean.

A light easterly wind is expected. Low temperatures are
forecast to range from the middle 50s to the lower 60s.

&&

.LONG TERM /SATURDAY THROUGH FRIDAY/...
Summary...Potentially unsettled at times Saturday; much warmer
Sunday; strong cold front moves through Sunday night;
significant cooling early next week as high pressure arrives,
followed by some warming mid to late next week.

Synoptic Overview...A ridge centered across the southern states
to start the weekend gets pushed south and east Sunday as an
upper- level trough tracks from the Northern Plains to the Great
Lakes and eventually into the Northeast. This trough settles in
the Northeast and Mid-Atlantic early next week before gradually
lifting out during mid to late next week. At the surface, a
strong cold front moves through Sunday night which looks to be
followed by a weak/dry cold front late Tuesday. Overall, high
pressure looks to dominate much of next week with cool
temperatures (actually closer to where we should be for this
time of the year) before some moderation takes place during the
mid to late week timeframe. We used a model/continuity blend for
Saturday through Sunday night, then blended in mostly the 00z
WPC Guidance.

For Saturday and Sunday...A split weekend looks to occur with
the second half turning brighter and much warmer. As an upper-
level ridge centered across the southern states Saturday gets
pushed south and east through Sunday, high pressure becomes more
established offshore allowing for a strengthening return flow.
The guidance overall continues to bring a weak disturbance
northward across our area Saturday, although there are some
differences regarding the amount of rain/showers that occurs. We
will still have an onshore flow along with some increase in the
surface dew points. Given the majority of the moisture is
locked in within the lowest levels of the atmosphere, Saturday
may start out with areas of either light rain or drizzle with
some fog. Some improvement should take place in the afternoon
from south to north but some showers are still possible for much
of the area. There should be some breaks of sunshine in the
afternoon to help boost the temperatures. We leaned closer to
the warmer GFS as the NAM may be locking the stratus in to long.


A more pronounced south to southwest flow develops Sunday as an
expansive warm sector takes hold. Therefore after some possible
low clouds and/or fog with light rain/drizzle to start Sunday,
afternoon temperatures should surge into the upper 70s and lower
80s. This occurs ahead of a sharpening upper-level trough in
the Midwest and Plains, which drives surface low pressure up
across the Great Lakes Sunday with a trailing cold front. The
cold front should arrive into our western areas early in the
evening then progress eastward Sunday night. A band or broken
band of showers (perhaps embedded thunder) may weaken with an
eastern extent Sunday night as the main forcing lifts to our
north. The overall instability is less certain at this time,
thus lower confidence in thunder this far east. As a result,
kept PoPs no higher than the chance range and did not add in
thunder. A wind shift to the northwest occurs with the passage
of the cold front and the surface dew points will start to lower
later Sunday night from west to east as drier air advects in.

For Monday and Tuesday...A strong cold front is forecast to be
offshore as we start Monday with any associated showers near the
coast ending early. Based on the timing of the front being
offshore Monday, it will be much cooler with a northwest wind in
its wake. High pressure builds in from the southwest Monday
night and Tuesday with cool temperatures, although more toward
where we should be for this time of the year. A strong upper-
level trough though moving across New England Tuesday will push
a secondary weak cold front through our area. This front looks
to be moisture starved here therefore we are carrying a dry
frontal passage.

For Wednesday and Thursday...As a gradually building ridge
replaces the trough in the Northeast, surface high pressure over
our area Wednesday will start to shift east during Thursday.
This will result in rising heights aloft, translating to some
moderation in the temperature department during this timeframe.

&&

.AVIATION /17Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

MVFR CIGs across the area this afternoon may approach VFR for a
short time near sunset today before conditions deteriorate again
near/after 03Z. IFR CIGs are expected across the area generally
in the 06Z to 13Z time frame with sub-VFR VSBYs in fog/drizzle
possible. CIGs will slowly rise to MVFR during the morning but
may begin to break up and/or rise tomorrow afternoon. East-
northeast winds around 10 kts will tend to diminish somewhat
tonight and Saturday.

OUTLOOK...
Saturday night...Areas of low clouds and/or fog should develop
or expand at night. Northeast to east winds 5 knots or less.

Sunday...Any low clouds and/or fog with drizzle in the morning
give way to mainly VFR conditions. A cold front arriving at
night should result in some showers, however the coverage is
less certain. South to southwest winds increasing to 10-15 knots
with possible gusts to 20 knots, then becoming northwest behind
the front at night and diminishing some.

Monday and Tuesday...VFR. Northwest winds 10-15 knots with
gusts up to 20 knots Monday, then diminishing at night and
Tuesday.

&&

.MARINE...
1100 am update: Extended small craft advisory for Lower
Delaware Bay through 2 pm this afternoon, as winds at Lewes and
Brandywine remain near criteria.

The circulation around high pressure to our northeast and a
developing inverted surface trough to our south will maintain an
east to northeast flow along the coasts of New Jersey and
Delaware for today and tonight. Wind speeds should be 15 to 20
knots today and 10 to 15 knots tonight with some gusts.

There is a Small Craft Advisory in place until 11:00 AM for the
lower part of Delaware Bay. A Small Craft Advisory remains in
effect for today and tonight on our ocean waters, mostly for
seas. However, wind gusts in excess of 25 knots remain possible
this morning.

OUTLOOK...
Saturday...The winds are expected to be below Small Craft
Advisory criteria, however seas on the ocean should remain 4-6
feet for awhile. The seas are anticipated to lower later in the
day and at night, therefore only extended the Small Craft
Advisory through the daytime Saturday.

Sunday...The conditions should be below Small Craft Advisory
criteria overall, however southwesterly winds may gust to around
20 knots for a time which may build the seas to near 5 feet on
the ocean. A wind shift to the northwest occurs at night as a
cold front moves through.

Monday and Tuesday...Northwest winds should gust to 20 knots
Monday, then diminish Tuesday. Seas may start near 5 feet on the
ocean Monday, but should favor lower. A Small Craft Advisory is
not anticipated.

&&

.TIDES/COASTAL FLOODING...
We are monitoring tidal gauges at Tolchester Beach and Cambridge
on the eastern shore of Chesapeake Bay and at Lewes and Cape
May on Lower Delaware Bay. At high tide this morning, Cambridge
reached minor flood stage (but not advisory thresholds) while
Tolchester remained well below minor flood stage. Current
projections suggest gauges will not reach advisory thresholds
for this evening`s high tide, so no advisory will be required.
Meanwhile, our updated forecast for this afternoon has Lewes
just reaching minor flooding (but again below advisory
thresholds) with Cape May just below minor flood stage. Spotty
minor flooding is possible, but should be below impacts
necessary for an advisory at this time. We will continue to
monitor, however.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ450>455.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ431.

&&

$$
Synopsis...Gorse
Near Term...CMS/Iovino
Short Term...Iovino
Long Term...Gorse
Aviation...CMS/Gorse
Marine...CMS/Gorse/Iovino
Tides/Coastal Flooding...CMS



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