Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 150734

Area Forecast Discussion
National Weather Service Mount Holly NJ
334 AM EDT Sat Jul 15 2017

Weak low pressure passes through the Delmarva and southern New
Jersey early this morning, and this will pull a cold front
through the region later this morning. That front will become
nearly stationary over the Mid-Atlantic as high pressure builds
in from the west. The high works its way east through the
weekend, and moves offshore Sunday night. Weak areas of low
pressure will develop along the stalled boundary and pass
through the region Monday and Tuesday. High pressure builds
across the region on Wednesday. Several cold fronts then
approach from the west Thursday and Friday.


An upper-level trough will continue to shift across the
Northeast and northern Mid Atlantic this morning. This will push
a cold front off the coast this morning, however it then should
tend to stall. The model guidance indicates that the trough
axis should clear our area by about Midday although general
cyclonic flow remains. At the surface, high pressure builds
across the Ohio Valley through the day, with it getting closer
to our area toward evening.

The slowness of the cold front this morning is keeping the
drier air to our north and west. Given light winds and plenty of
low- level moisture, areas of low clouds and some fog will
continue early this morning. The water vapor imagery shows
significant mid level dry air encroaching on our area early this
morning. This will gradually spread eastward through the
morning hours. The injection of drier air, first aloft, will
work downward as the cold front shifts east with a wind shift to
the northwest. This will translate to dew points lowering some
through the day. It will still have a humid feel to the air,
especially across the central and southern areas, however by
late in the day the humidity will be much less compared to the
last few days (and early this morning). The dry air will also
result in increasing sunshine through the day, although some
diurnal clouds should develop for a time prior to the lower
level moist layer mixing out. Some showers are ongoing early
this morning ahead of the front within a warm and moist airmass.
We cannot rule out a few more showers later this morning ahead
of the cold front, and also early this afternoon ahead of the
upper-level trough axis mainly in southeastern New Jersey and
Delmarva. For now kept thunder out of the forecast. We will
continue to monitor radar trends and add or adjust the PoPs

High temperatures are mostly an even blend of MOS and
continuity. A warmer day is expected across the northern areas
as the flow turns west-northwest and sunshine returns. The low-
level flow though looks light enough where the surface winds may
turn southerly along the coast this afternoon (especially New


An upper-level trough remains in place across the Northeast and
northern Mid Atlantic, with even some amplification over the
Great Lakes as the next stronger short wave digs east-
southeastward. Meanwhile, surface high pressure gradually
extends more to the east into our area.

While some upstream high-level moisture might translate into
some cirrus into our region through the night, overall we are
anticipating a clear to partly cloudy sky. Given lower dew
points and light winds, temperatures are expected to be
noticeably cooler compared to the last few mornings. Low
temperatures are mainly a blend of MOS and continuity, although
did tweak these down a bit for some local areas.


High pressure builds across the region on Sunday. Plenty of
sunshine on tap with warm and mild conditions. Highs top off in
the mid and upper 80s throughout the region with relatively
comfortable humidity levels as surface dewpoints will be in the
low to mid 60s.

The pattern then changes as high pressure moves offshore Sunday
night. Return flow sets up behind the departing high, and
humidity levels build back up as dewpoints climb into the mid
and upper 60s, and possibly into the lower 70s across NE MD and
DE. During this time, H5 trough with several shortwaves rotating
around the base of the trough will move east, with the trough
digging from the Ohio Valley and Northeast down into the
Southeast. This trough will become nearly stationary along the
East Coast Monday and Tuesday, and several weak areas of low
pressure will develop on the stationary front along the Mid-
Atlantic and pass through the region during the start of the new

Best chances for precip will be over the Lehigh Valley and
Pocono Mountains Monday afternoon as surface low pressure
develops on the boundary over the Mid-Atlantic, and then lifts
to the north throughout the day and moves offshore Monday night.
The upper trough remains along the coast, and another shortwave
dives into the base of the trough on Tuesday. Another surface
low develops Tuesday afternoon and passes through the region
Tuesday night.

Surface high pressure builds in from the west on Wednesday, and
the upper trough will be slow to depart. As a result, this
keeps at least a slight chance/chance for showers/thunderstorms
in the forecast on Wednesday.

High pressure moves offshore Wednesday night/Thursday morning.
From there, several weak cold fronts approach from the west for
Thursday and Friday. Each front could touch off at least
isolated to scattered showers and thunderstorms.

The warmest temps during the week look to occur on Wednesday
and Thursday, when a southwest flow ushers a hot and humid
airmass into the region with highs in the upper 80s to low 90s
and surface dewpoints in the upper 60s to low 70s. Dewpoints may
back off a bit on Friday behind one of the weak cold fronts.


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

Today...Varying conditions from VFR to IFR/LIFR due to low
clouds and/or fog. The low conditions are expected to improve to
VFR by Midday. A few showers around through about Midday,
however given low coverage anticipated these were not included
in the TAFs. Light and variable winds, become northwesterly
mainly in the 5 to 10 knot range.

Tonight...VFR. Northwest winds 5-10 knots early, becoming light
and variable at most terminals.


Sunday through Sunday night...VFR conditions expected. Light
and variable winds, becoming SW 5-10 KT. Light and variable
winds at night.

Monday through Wednesday...Mainly VFR conditions expected.
Afternoon showers and thunderstorms with MVFR or lower
conditions possible. South to southeast winds around 10 knots.

Thursday...VFR conditions expected. SW winds 5-10 KT.


The conditions are expected to remain below Small Craft
Advisory criteria today and tonight. A cold front is forecast to
shift off the coast this morning then stall offshore and to our
south. An easterly surface wind has been continuing across the
northern coastal waters, however all areas will see a wind shift
to the west and northwest this morning behind the front. The
flow looks light enough though where the winds should turn
southerly this afternoon and into this evening especially for
the New Jersey coastal waters.


Sunday through Thursday...Sub-SCA conditions expected on the
waters. Scattered showers and thunderstorms possible, mainly
during the afternoon and early evening hours Monday through
Wednesday. Heavy rain, gusty winds, and lightning can accompany
those thunderstorms.

A low risk for the formation of dangerous rip currents is
anticipated for today into this evening, despite a light enough
wind becoming west to northwest then potentially turning back to
southerly this afternoon.




Near Term...Gorse
Short Term...Gorse
Long Term...MPS
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