Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 142050
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
350 PM EST Tue Nov 14 2017

.SYNOPSIS...
High pressure will continue to influence our weather tonight
and Wednesday before moving off the coast. A cold front
approaching from the northwest is forecast to arrive on Thursday
followed by high pressure for Friday. Another cold front is
expected to pass through our region on Saturday night with high
pressure anticipated in its wake for Sunday and the early part
of the new week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Surface ridge will be draped across the region tonight, with a
vort max moving east through New England. The tail end of this
vort max will progress through the coastal waters and may
contribute enough lift for some showers off the coast, but for
now, I am not expecting these to make it ashore tonight.
However, the lower clouds will slowly make their way onto the
coast (having already made it to Long Beach Island and vicinity
this afternoon). Sprinkles or drizzle here cannot be ruled out,
and obs will be monitored closely this evening to determine if
some of these elements may need to be included in the forecast.

Meanwhile, a stubborn cloud deck over southeast Pennsylvania is
only very slowly eroding westward this afternoon, with more
scattered clouds in New Jersey. Latest guidance may still be too
generous with the cloud erosion this evening, though they seem
to have a better handle on the trends this afternoon.
Nevertheless, with unfavorably oriented surface flow and fairly
homogenous surface dew points, I am rather uncertain if the
amount of clearing expected overnight (west of the NJ beaches)
will pan out. Presumably some dry air advection will be
sufficient to erode the residual moisture sufficiently as the
surface high to our north progresses a little eastward
overnight, so generally maintained continuity with the forecast
for now.

Should the skies become clearer overnight, potential for patchy
fog exists. However, wind speeds may stay a little elevated
(particularly in New Jersey), and dry air advection (albeit
subtle) may be enough to preclude much formation. I did include
some mention in favorable valley locations northwest of the Fall
Line, but I am not expecting more widespread issues.

Low-temperature forecast is a little uncertain given the
questions regarding the evolution of cloud cover overnight.
There is a fairly sizable range of lows from the statistical
guidance overnight. Felt a consensus approach was appropriate,
but I did use a healthy amount of weighting of the high-
resolution 2-m temperature guidance from the latest simulations
of the HRRR as a means of modulating the evening/overnight
temperature trends. Near or subfreezing temperatures are
expected northwest of the urban corridor and in the Pine Barrens
of NJ, with middle to upper 30s in the urban corridor and at
the beaches.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
There is some increased consensus that a few sprinkles or even
light showers may reach the southern New Jersey coast and
portions of Delaware during the day Wednesday as residual lift
from a midlevel vorticity lobe and a westward-migrating surface
low off the southern Mid-Atlantic coast remains in these areas.
Meanwhile, the migrating surface high to our north should
continue eastward near/off the New England coast. Onshore flow
should become well-established during the day, with cloud cover
likely to increase across the area by or during the afternoon.

This makes the max temperature forecast tricky, as the timing
of the developing clouds will be critical in determining the
contributions of diurnal heating and warm-air advection versus
the cooling effects from increasing clouds and a more direct
onshore flow. The typically aggressive (with clouds) MET MOS is
coolest and has remained fairly consistent run-to-run. MAV MOS
has generally been on a decreasing trend during the past 24
hours, whereas Euro MOS has been on an increasing trend (though
both are in the same ball park with max temps).

My suspicion is that the developing clouds may be underdone,
especially given the recent simulations of higher-resolution
guidance. As such, I went slightly below a MAV/MET/ECM MOS
consensus tomorrow, with a nod toward the higher-resolution
output and forecast continuity.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
High pressure centered over Canada`s Maritime Provinces on
Wednesday evening will move to the east and it should lose its
influence over our weather on Wednesday night. Meanwhile, a mid
level short wave trough and its associated cold front will
approach from the northwest. Both will pass over and through our
region on Thursday. Light rain showers are expected on
Wednesday night in advance of the boundary. Showers may linger
into Thursday morning, especially in the northern and eastern
parts of our forecast area.

High pressure is forecast to build across our region from west
to east on Thursday night and Friday, bringing dry weather
conditions.

A strong cold front is forecast to approach from the west on
Friday night and Saturday. There is an increasing chance of
showers beginning late on Friday night. It appears as though
temperatures should increase slowly as the cloud cover lowers
and thickens. As a result, we are not anticipating any freezing
or frozen precipitation at the onset.

The cold front is forecast to push through our region on
Saturday night. Another blast of cold air is expected to follow
for Sunday and Monday. We continue to use the low end of
guidance for temperatures. Cold advection stratocumulus is
anticipated, especially on Sunday. Also, scattered snow showers
and flurries are possible in our northern counties, mainly in
the elevated terrain.

Temperatures may warm a bit on Tuesday as the center of the
high moves out to sea.

&&

.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Cloud deck around 4000-5000 feet is slowly eroding
from east to west this afternoon, but timing the improvement at
the Philly terminals is quite difficult. In general, expect CIGs
to scatter out near/northwest of PHL between 22Z and 03Z from
southeast to northwest. Patchy fog may develop as the skies
scatter/clear, especially at KRDG/KABE. Meanwhile, low clouds
(around 2000-3000 feet) will gradually spread westward
toward/past KACY during the night and may even reach KMIV. Winds
will be light northeasterly. Confidence in CIG forecast is
below average, but for winds is above average.

Wednesday...Low clouds may be slow to erode, or may not at all,
at KACY/KMIV, with potential for fairly prolonged sub-VFR
conditions. Meanwhile, clouds are expected to increase during
the day elsewhere, with a sub-VFR deck possible across the
region by late morning or afternoon. Winds should veer to
easterly during the day, remaining near or below 10 kts.
Confidence in CIG forecast is well below average, and for winds
is above average.

OUTLOOK...
Wednesday night and Thursday morning...Mainly VFR. However,
rain showers may reduce conditions to MVFR at times.

Thursday afternoon through Friday evening...Mainly VFR.

Friday night...VFR lowering to MVFR in spots. A chance of
showers after midnight.

Saturday and Saturday night...Mainly MVFR and VFR with showers
likely. Snow showers are possible around KRDG and KABE late on
Saturday night.

Sunday...Mainly VFR.

&&

.MARINE...
Small craft advisory was extended for the Atlantic waters from
Cape May to Fenwick Island through 6 pm Wednesday, as seas will
likely build again this evening and stay elevated through
Wednesday afternoon. Models are also showing seas building
northward to much of the New Jersey coastal waters late tonight
and tomorrow morning, so have extended the small craft advisory
northward to this region as well, though this begins at midnight
and ends at 1 pm Wednesday. Winds may briefly gust to 25 kts,
especially off the Delaware coast, but the main threat will be
high seas.

There is a change of sprinkles or a light shower through much
of the period, generally from the southern New Jersey coast
southward.

OUTLOOK...
Wednesday night through Thursday morning...No marine headlines
are anticipated.

Thursday afternoon through Friday morning...Northwest wind
gusts of 25 to 30 knots are expected. A few hours of gale force
gusts are possible on Thursday evening.

Friday afternoon and Friday night...No marine headlines are
anticipated.

Saturday and Saturday evening...Gale force gusts from the
southwest are possible.

Late Saturday night and Sunday...Gale force gusts from the west
and northwest are possible.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 11 PM this evening to 1 PM EST
     Wednesday for ANZ451>453.
     Small Craft Advisory until 6 PM EST Wednesday for ANZ454-455.

&&

$$

Synopsis...Iovino
Near Term...CMS
Short Term...CMS
Long Term...Iovino
Aviation...CMS/Iovino
Marine...CMS/Iovino



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