Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 140025

Area Forecast Discussion
National Weather Service Mount Holly NJ
825 PM EDT Thu Aug 13 2020

A front over the area will slowly sag southward through
Saturday as high pressure builds in from the north and west.
Several waves of low pressure will develop along this boundary
and pass south and east of New Jersey through the weekend. High
pressure tries to establish itself over the area early in the
new week. The old frontal boundary then lifts north as several
areas of low pressure develop on it and approach from the south
late next week.


Instability continue to diminish with loss of diurnal heating.
Showers and thunderstorms continue to taper off and diminish.
Therefore, with the flooding threat over, the Flash Flood Watch
has been cancelled.

Otherwise, it will remain mild and humid overnight with lows in
the mid 60s far NW and upper 60s to low 70s elsewhere. Winds
will be light and variable. Also, areas of fog will develop
after midnight, especially in areas that had rains today.


High pressure will try to move down from the N while the slow
moving front and weak low pressure are S of the area. We will
hold higher amts of clouds and higher pops for Delmarva and SE
PA for Friday. Chc pops will be found for much of NJ and slight
chc pops for the srn Poconos and Lehigh Valley. Any tstms across
Delmarva may be capable for downpours which may cause more
localized flooding. Overall, the extend and degree of the
activity should be a step-down from todays levels. Temperatures
will reach the low to mid 80s for most areas, with the higher
numbers for nrn/wrn areas where more sun will be found.


A prolonged period of unsettled weather on tap for most of the
long term period.

A frontal boundary remains south of Delmarva, along the Mid-
Atlantic, and several waves of low pressure will develop along
this boundary going through the weekend. The first low will be
east of the Delmarva Peninsula Friday night and drifts out to
sea. Best chances for PoPs will be over the far southern zones,
with most of the northern areas dry.

Going into the weekend, however, there are differences among
the 12Z GFS, the 12Z ECMWF, and the 12Z Canadian. The ECMWF and
the Canadian have high pressure building in a bit closer to the
area from the north, and this keeps the next wave of low
pressure and most of the precip south of the region. The GFS has
the high positioned a bit farther north, and as a result,
brings precip into the region Saturday night and Sunday. QPF is
not minimal, too, as model differences range from almost no QPF
for most of the region to as much as an inch of QPF as far north
as Philly and central New Jersey. Will blend the NBM and the
SuperBlend for PoPs this weekend, and carry slight chance/low
chance Saturday, increasing to low end likely on Sunday. But
this may change drastically depending on how that high sets up.

The low passes south of Delmarva and southern New Jersey Sunday
night, and seems to strengthen offshore on Monday. Although
some wrap around precip is possible, will have to see its
position, as the difference between onshore flow and westerly
flow on Monday will affect temps and sky conditions.

Should then be mostly dry Monday night through Tuesday night,
with just a slight chance for PoPs on Wednesday as some weak
upper level energy passes through.

Thereafter, the old frontal boundary south of the region begins
to lift north, and several more waves of low pressure develop
on it. Could have more wet weather for the end of next week.

High temps through the period will generally at or just below
normal levels, but low temps will be at or just above normal
levels depending on how much moisture there is over the area.


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

Tonight...VFR early then IFR with fog and lower CIGS expected
in most areas. The NW sites KRDG/KABE may have only MVFR VSBYS
in fog but confid in what category is rather low. Light and
variable winds.

Friday...After early morning fog, VFR expected after 12Z/13Z NW
and 15Z/16Z SE. Mostly NE to E winds at 5 to 10 knots expected.


Friday night...Sub-VFR conditions possible in fog/stratus. E-NE
winds less than 10 kt. Low confidence.

Saturday...Mostly VFR. Scattered SHRA/TSRA possible with sub-
VFR conditions. E winds 10-15 kt. Low confidence.

Saturday night through Sunday night...An extended period of
MVFR or IFR conditions possible in SHRA/TSRA. E-NE winds around
10 kt. Low confidence.

Monday...Sub-VFR conditions possible in SHRA/TSRA. W winds less
than 10 kt. Low confidence.

Tuesday...Mostly VFR. W-NW winds less than 10 kt. Afternoon sea
breezes possible. Low confidence.


Sub-SCA conditions with mostly E to SE winds 5 to 10 knots and
1 to 2 ft seas for the most part tonight and Friday. Scattered
showers and tstms into the evening then cloudy with fog
overnight. Locally higher winds and seas near tstms.


Friday night...Sub-SCA conditions.

Saturday-Sunday night...Seas will build to 5-7 feet as a tight
E-NE gradient develops over the waters. Winds will gust 25-30 kt
during this time as well.

Monday...Conditions will gradually lower to sub-SCA during the

Tuesday...Sub-SCA conditions.

Rip currents...

There is a low risk for the development of dangerous rip
currents on Friday. However, the risk could become locally
moderate as a northeast wind of 10 to 15 MPH develops. Breaking
waves should be around 2 feet with a medium period southeast to
south swell.

With increasing onshore flow on Saturday, the risk for the
development of dangerous rip currents increases to moderate by
Saturday afternoon.


Onshore flow will increase some Friday and especially Saturday and
persist through Sunday. Astronomical tides will be increasing into
the weekend as well as the new moon occurring early next week. These
factors will combine to increase the chance for minor coastal
flooding with the Saturday and Sunday afternoon/evening high tides.
Spotty minor coastal flooding is possible with the afternoon and
evening high tide on Saturday. Minor coastal flooding to advisory
levels is then more likely with the Sunday afternoon and evening
high tide, especially from Atlantic City southward including
the Delaware Atlantic coast and up Delaware Bay.




Near Term...MPS/O`Hara
Short Term...O`Hara
Long Term...MPS
Tides/Coastal Flooding...WFO PHI is the U.S. government's official web portal to all federal, state and local government web resources and services.