Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 192054

Area Forecast Discussion
National Weather Service Mount Holly NJ
354 PM EST Thu Jan 19 2017

High pressure over the Mid-Atlantic will move offshore tonight
through Friday morning. Weakening low pressure will lift
northeast through the region late Friday. Weak high pressure
returns for Saturday. A strong and complex area of low pressure
will impact the Northeast and Mid-Atlantic from Sunday through
Tuesday. A series of frontal boundaries will impact the area
late next week.


Considerable cloudiness developed today below the low-level
inversion. With the loss of daytime heating and a continued
building of the mid-level ridge across the area, expect the
clouds to diminish this evening with mostly clear skies
developing. Then a cirrus shield will begin overspreading the
region, around midnight in Delmarva, and reaching northwest NJ
by sunrise. These clouds will work their way over the
aforementioned ridge, in advance of the next storm system to
impact the region Friday.

In spite of the cloudiness, we should radiate efficiently in
the normally colder spots north of I-78, as well as in the
Pinelands, as high pressure centers over the region, maintaining
light and variable winds. In the aforementioned locations, low
temperatures will be in the mid to upper 20s, with low to mid
30s elsewhere.

We also expect additional patchy fog, mainly north of I-78 and
in the Pinelands, particularly where it occurred Thursday
morning, given a similar air mass.


Low pressure moving through the Ohio Valley on Friday begins to
undergo redevelopment offshore of the NC/VA border during the
afternoon. As the mid-level ridge moves east of the area in the
morning, an overrunning regime will setup across the region,
with modest isentropic ascent along the 300K surface. Prior to
that, with high level cloudiness having overspread the region,
there is a sharp gradient in the remaining column moisture,
suggesting the day will start out with sunshine, followed by
overcast skies across the region by late morning.

There is good model agreement in terms of mass fields and PoPs
for precipitation overspreading the region from west to east
between mid-morning and noon. Initially, we expect 2-meter
temperatures to be cold enough (lower 30s) for a brief period of
light freezing rain across Carbon and Monroe counties, ending
around noontime. The more substantial precip should hold off
until early afternoon across this area, which will limit
freezing rain accumulations. At this time, our ice glaze map
maintains a chance for a Trace to one-hundredth of an inch for
portions of Carbon and Monroe Counties. This is less than
previously forecast, per collaboration with our surrounding
offices and WPC WWD. There is still some potential for
additional freezing rain in the early evening if the column wet-
bulbs more than expected, but that is a low probability, as
even the high resolution models and ensembles have trended
warmer. In terms of rainfall amounts, generally two to three-
tenths of an inch across the region.

High temperatures will still average above normal, generally
mid 30s to upper in the Poconos and northwest NJ, with 40s


Weakening low pressure continues to lift NE through the region
Friday evening. Precip will taper off over SE PA, NE MD, DE, and
S NJ by midnight, and then precip gradually tapers off over N
NJ prior to daybreak.

Latest trend is for temps to remain above freezing, at least
during the precip, so will not have freezing rain in the
forecast, and will keep precip as plain rain. Latest
NAM/GFS/ECMWF have the precip working through the region from
00-06Z, so early in the period will carry likely PoPs for N NJ
and the Poconos, and generally chance PoPs elsewhere.

Weak high pressure builds in from the west after midnight
Friday night and into Saturday morning. With abundant low level
moisture in place, and light to nearly calm winds, can expect
areas of fog to develop, and depending on how much rain falls
through Friday evening, fog could be locally dense.

Dry conditions on Saturday as high pressure builds across the
region and moves offshore late.

Storm develops over the Gulf Coast on Sunday and begins to lift
to the north and east Sunday night. Although models in general
agreement, there are some key differences between the GFS and
the ECMWF that have shown up with the morning model cycle.

High pressure over NE Canada will begin to nose its way
southward towards northern New England. Where this high sets up
will have a profound impact on the forecast. Latest GFS has the
high a bit farther south than the ECMWF, as a result, suppresses
the approaching more than the ECMWF does. The GFS holds off on
the heaviest precip until late Monday/Monday night, whereas the
ECMWF has bands of heavy precip sliding along the coast starting
on Sunday. As of now, feel best way to approach this is by
planning on having periods of moderate to heavy rain from Sunday
night through Monday night. Another aspect to consider: If that
high noses a bit farther south, then much colder temperatures
would filter into the region, and there is the potential for
freezing rain sometime during the period. For now, will have a
few hours of freezing rain in the forecast for Carbon and Monroe
counties Monday morning, as this follows with the diurnal
temperature curve.

With a tight easterly gradient developing between the
approaching low and the aforementioned high, there is the
potential for Wind Advisory level winds for much of eastern NJ
and into DE, generally to the south and east of I-95, with
sustained winds of 25-35 MPH with gusts up to 50 MPH. The rest
of the forecast area can expect east winds 15-25 MPH with gusts
up to 40 MPH.

Once the low lifts through the region Monday night, precip will
come to an end fairly quickly.

Unsettled weather on tap for the mid to late week period as
several weak boundaries impact the region. Colder air looks to
make a return by the end of next week. Until then, temperatures
look to remain at above normal levels.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...Occasional MVFR ceilings early will lift for a time,
then possibly scattered IFR ceilings toward sunrise. There may
also be some patchy fog as well. Northwest winds becoming light
and variable.

Friday...Scattered MVFR ceilings in the morning lowering to IFR
in the afternoon. With rain arriving at the TAF sites from late
morning into the afternoon, we expect some visibility
restrictions below 3SM. Winds will be east at 5 to 10 knots.

Fri night...Sub-VFR conditions possible in -RA. Moderate
confidence. Fog possible Fri night. Light winds.

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

Sun...E winds 10-15 KT. Conditions deteriorating from S to N
during the day with IFR conditions possible by afternoon.
Moderate confidence.

Sun night thru Monday night...IFR and lower conds possible in
RA. E winds 15-20 KT with 20-30 KT gusts at terminals north and
west of I- 95, and 20-30 KT with 30-50 KT south and east of I-95
possible. Moderate confidence.

Tuesday...Mainly VFR, but cannot rule out passing showers. Low


SCA for hazardous seas has been extended through this evening
as ocean seas remain at 5-6 feet due to the long period swell.
Guidance has been well underdone.

Otherwise, we expect sub-SCA criteria for the waters late
tonight into Friday.

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

Sun aftn thru Mon night...Easterly 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 force winds possible,
especially on Monday. Conditions begin to improve late Monday
night, and winds decrease to 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 possible
that some areas, especially across southern waters, may drop
below SCA seas on Wed.


Due to the persistent and increasing easterly flow around a
coastal low Sunday-Monday, 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
Sunday night and Monday. Latest guidance indicates the potential
for widespread minor coastal flooding, but that will come into
better focus this weekend.


MARINE...Small Craft Advisory for hazardous seas until 1 AM EST
Friday for ANZ450>455.


Near Term...Franck
Short Term...Franck
Long Term...MPS
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