Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 190828
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
328 AM EST Thu Jan 19 2017

.SYNOPSIS...
High pressure will build into the region today and move offshore
early Friday. Meanwhile, weak low pressure will impact the region
Friday afternoon into Friday evening. High pressure will return
for Saturday.  Then a stronger and more complex area of low
pressure will impact the Mid-Atlantic beginning Sunday and
continuing through Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Broad surface high pressure was centered over the Ohio Valley and
Mid-Atlantic region overnight. The high will remain over the area
today.

A weakness in the NW flow was noted over the area as H9-H8 the axis
of a shortwave ridge is overhead. Extensive low clouds are noted
over the forecast area overnight as a lull in the NW winds and dry
air advection has allowed moisture to remain trapped beneath the mid-
level subsidence inversion. These low clouds are expected to erode
from west to east during the early to mid morning as the primary
ridge centered over the Gulf Coast states builds downstream toward
our area. Expect additional stratocu development during peak heating
this afternoon but overall, the majority of the locations should
turn out mostly sunny from the late morning onward.

Forecast temperatures today weighted more toward the warmer MAV stat
guidance in anticipation of the sunshine returning. Adiabatic
compression from building large-scale subsidence and even light
downsloping W-NW winds will provide a secondary contribution to the
warming. The end result is highs in the low to mid 50s this
afternoon across most of the area (except 40s across the higher
terrain in NE PA/NW NJ).

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
High pressure at the surface and shortwave ridging aloft will result
in a quiet weather pattern for tonight. Expect temperatures to drop
rather quickly after sunset this evening under mainly clear skies
and light winds. Forecast low temperatures range from the mid to
upper 20s in the rural areas N of I-78 and the NJ Pine Barrens to
the mid 30s in the cities, at the coast and in the Delmarva region.
The arrival of mid to high clouds from our SW overnight is the
primary motive for keep low temps slightly higher in E MD and DE.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Fri mrng starts off dry, but a wk low will bring rain to the area
by aftn and continue into the eve. Overall, this shud be a quick
hitter and most areas will see light qpf. This precip moves out
durg Fri night and high pres builds in, bringing a dry day Sat
into erly Sun.

Then, an area of low pres over the srn plains will move newd and
begin to impact the region durg the day Sun. Mdls differ on the
timing of onset with the ECMWF being faster than the GFS. The
NAM/WRF and CMC are supportive of the slower timing so have
trended the fcst in that direction.

Nevertheless, rain will develop durg the day from s to n and
continue into Sun night. As the low approaches, ely flow will
increase and wind will pick up and precip will get steadier and
heavier Sun night into Mon. The guid is still differing on where
the axis of heaviest precip will be as well as the timing, but it
appears that there will be one wave of precip Sun night into early
Mon, then potentially a break and another shot later Mon into Mon
eve. Precip will then end from s to n Monday night into Tue.

Certainly by the time this is over we could be looking at 1 to 2
inches of rain, and possibly more depending on the track and
strength of the low.

Additionally, due to the persistent ely flow there could be
several tidal cycles of coastal flooding, but this will also be
dependent on the track of the low and will become more evident as
we approach Sun night and Mon.

Once the low passes by, wk high pres will build back in making for
an improving Tue and dry Wed.

ATTM, temps genly look to bee way too warm for any precip type
other than rain. However, there is at least a small potential for
some freezing rain Fri night before the precip ends in the
Poconos. If temps end up being colder than currently fcst than
that potential cud increase.

With that said, temps are expected to be aoa nrml thru the pd, in
some cases by 10 to 15 degrees. Monday will likely be the coolest
day, with an abundance of clouds and rain. Many areas will be aoa
50 degrees thru the pd.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

MVFR CIGs between 2-3 kft AGL have expanded eastward over the I-95
terminals overnight. Expect these MVFR CIGs to move downstream to
ACY shortly. However, improvement was already noted back to the west
with RDG, ABE and ILG CIGs rising to just above 3 kft AGL. CIGs are
expected to increase just enough for Phila and S NJ terminals to
become VFR between 09-12Z.

Skies will clear later in the morning with mainly VFR conditions
expected today. However, with stratocu developing this afternoon ,
there is a possibility that we see localized MVFR CIGs develop
sometime between about 18-22Z. Forecast soundings hint at this
happening at ABE-RDG but overall confidence in MVFR CIGs this
afternoon is low.

Under mainly clear skies and light winds tonight, there is a
potential for radiational fog overnight at the typical fog-prone
rural TAF sites. IFR conditions would be a possibility where fog
forms.

OUTLOOK...
Fri through Fri night...Sub-VFR conditions possible in -RA.
Moderate confidence. Fog possible Fri night.

Sat/Sat night...Improving conditions Saturday morning, otherwise
VFR.  High confidence

Sun...E winds 10-15 KT. Conds deteriorating from s to n durg the
day. Moderate confidence.

Sun night thru Monday...IFR and lower conds possible in RA. E
winds 15-20 KT with 20-30 KT gusts. LLWS possible with 60-65 KT
LLJ Mon aftn. Moderate confidence.

&&

.MARINE...
A Small Craft Advisory for Hazardous Seas is in effect for the
coastal waters of central NJ (ANZ450/451). Observed wave heights
overnight continue to be in the 5-6 ft range at buoys 44091, 44065
and 44025. Seas are modeled to slowly diminish today before dropping
below 5 ft sometime during the mid to late afternoon. Elsewhere,
winds and seas will be below SCA criteria.

No marine headlines expected tonight. W winds 5-10 kt early this eve
will veer out of the N late this eve and overnight, then NE before
daybreak Friday

OUTLOOK...
Fri through Sun morning...No marine headlines anticipated durg
this time. Seas will genly be around 2 ft with wind 10 kts or
less.

Sun aftn thru Mon...Ely flow increases to 15-20 KT with 25-30 KT
gusts starting Sun aftn, and then gale force gusts of 35-40 KT
likely Monday and Monday night. Moderate to heavy rain with low
VSBY expected. Storm conds can not be ruled out for a time,
especially n on Mon. Conditions improve late Monday night, and
winds decrease to sub-SCA levels. However, seas on the ocean
should remain above SCA criteria.

Mon night thru Wed...wind decreases below headline criteria, but
ocean seas will remain above SCA criteria. It is psbl that some
areas, especially s may drop below SCA seas on Wed.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory for hazardous seas until 6 PM EST this
     evening for ANZ450-451.

&&

$$
Synopsis...Nierenberg
Near Term...Klein
Short Term...Klein
Long Term...Nierenberg
Aviation...Klein/Nierenberg
Marine...Klein/Nierenberg


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