Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 241312
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
912 AM EDT WED AUG 24 2016

.SYNOPSIS...
High pressure will continue to build offshore today and out to sea
Thursday. A cold front will move across the area Friday and stall to
our south over the weekend. High pressure builds to our north over
the weekend, then offshore Monday. An area of low pressure may pass
to our north Monday, bringing a front across the area Monday into
Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Forecast on track. Will update hourly grids based on latest
surface obs, but no significant changes will be made to the
database.

An upper-level ridge, stretched across the southern states, will
have an extension on its northeastern side move across our region
during the course of today. As this occurs, surface high pressure
over the area will become more centered offshore.

The pressure gradient is not all that tight, and therefore, the
flow is on the weaker side. With ample heating of the boundary
layer this afternoon, there should be sea breeze development. This
will back the winds a bit more south-southeast along the coast.

As the ridge expands northeastward some today, there will be some
warming aloft as reflected by an increase in the thicknesses. This
will result in a warmer afternoon for many places from what was
observed yesterday. Overall a warm afternoon, however dew points
while a bit higher are expected to remain below humid thresholds
for much of the region. Despite some ridging into the area today,
convection in the Midwest early this morning will send some high
level debris clouds downstream some of which will move through
parts of our area at times.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
The northeastern extension of the southern states ridge shifts
offshore tonight as a weakening short wave trough slides across the
Great Lakes region. This is accompanied by a surge in low-level warm
air advection up the Ohio Valley. The southwesterly flow will also
start to bring in some increase to the low-level moisture as we go
through tonight, however this does not appear to be real robust. It
looks like the best forcing remains well to our west more in the
Ohio Valley due to the warm air advection with the aforementioned
short wave trough, plus a wind shift is noted around 850 mb. As a
result, we kept the forecast dry with the expectation that any
convection associated with this remains well to our west.

We are anticipating some high level clouds around at times,
otherwise a bit warmer night due to some uptick in the dew points.
This may also result in patchy fog in the valley areas as well as
some rural spots.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
High pressure continues to move out to sea Thursday, which will lead
to return flow around the western side of the high. This will allow
temperatures to warm and moisture to begin increasing. There will be
a chance of showers/thunderstorms Thursday into Thursday evening as
a couple of short wave/vorticity impulses slide across the area.

The return flow will continue into Friday ahead of an approaching
frontal boundary. There will again be a chance for isolated showers
to develop during the day, but overall chances are small at this
time. 925/850 mb temperatures and thicknesses will continue to
increase, making Friday the warmest and most humid day of the week.

The frontal boundary will sag south of the area Friday night, and
stall just to our south over the weekend while high pressure builds
to our north. This high will keep dry weather in place across the
area through the weekend.

The high pressure will build offshore of New England by Monday, and
a cold front will begin approaching the area Monday into Tuesday as
an area of low pressure skirts to our north. There are a couple of
short wave/vorticity impulses forecast early next week, so there
will continue to be a chance for isolated showers or thunderstorms
Monday into Tuesday.

&&

.AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Today...VFR. Light and variable to calm will become southwesterly
at 5-10 knots by midday. A turn to south or southeast at ACY and
ILG should occur by late afternoon as a sea/bay breeze develops.

Tonight...VFR overall. Southerly winds becoming light and variable
at most terminals during the evening. Local MVFR visibility is
possible toward daybreak Thursday due to light fog, mainly at RDG,
ABE and MIV.

OUTLOOK...

Thursday-Friday...Generally VFR conditions expected. A chance of
isolated showers and thunderstorms which may lead to temporary lower
conditions.

Friday night through Sunday...VFR conditions expected.

&&

.MARINE...
High pressure at the surface eases more offshore through today and
tonight. This will allow for the surface flow to turn more southerly
today and continue tonight. While the flow is not forecast to be all
that strong with the departing surface high, the southerly flow will
increase especially by late this afternoon across the northern
coastal waters. There should be some nearshore enhancement
particularly this afternoon and early evening as a sea/bay breeze
circulation occurs, however the speeds (also seas) are expected to
be below Small Craft Advisory criteria through tonight.

OUTLOOK...

Thursday through Friday...Winds may approach Small Craft Advisory
levels Thursday into Thursday night. Winds will begin diminishing
Friday morning.

Friday night through Sunday...Sub-Small Craft Advisory conditions
expected to continue across the waters.

RIP CURRENTS...For today, the risk for the formation of dangerous
rip currents is low. However, conditions may reach moderate this
afternoon and evening especially if the waves in the surf zone
increase to 2-3 feet combined with the south-southeast winds
increasing faster.

This coming Sun-Tue...model ensemble guidance on every successive
cycle continues to send 2-4 ft long period (15 to 17 second) east
southeast swell into our waters from the central Atlantic. If that
occurs, swimming and wading dangers will increase markedly.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Robertson
Near Term...Gorse/MPS
Short Term...Gorse
Long Term...Robertson
Aviation...Gorse/Robertson/MPS
Marine...Gorse/Robertson



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