Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS61 KPHI 230124

Area Forecast Discussion
National Weather Service Mount Holly NJ
924 PM EDT Sat Jul 22 2017

A frontal boundary extended from the southern Great Lakes to
our region this afternoon. Low pressure will ride eastward along
the front and it should pass through our area tonight. Another
low is expected to follow on Monday. The second low is forecast
to pull the boundary southward and away from our region allowing
high pressure to build down from the northwest for the middle
part of the new week. A cold front from the northwest is
anticipated to arrive on Thursday night.


It was an active late afternoon and early evening across much of
the area, mainly from Central NJ and Berks County on south to
the Delmarva where several areas of thunderstorms moved on
through. Activity initially developed in Central NJ along the
sea breeze while activity elsewhere developed from what was left
of any MCSs (Mesoscale Convective Systems) that moved east from
Central Pennsylvania and Central Maryland as well as Northern
Virginia. This activity has either moved offshore or weakened
altogether. Radar mainly shows light showers with embedded
moderate to heavier showers as of 9 PM across Central NJ and
Bucks County heading east. We cannot rule out any thunder here
given how unstable things are, but lightning detection has shown
a downward trend in activity across our area. The heavier
activity near Ocean City, Maryland and Chincoteague, Virginia
was heading offshore and should not bother southern Delaware
with just some light showers there.

The grids were revamped overnight based on the latest radar
trends initially for the first 3 hours. Afterwards, we leaned
towards the NAM 3 km, which seems to best have a handle of QPF
based on the look of satellite. All eyes now turn to the
convective complex that has impacted southwest PA and West
Virginia this evening. Most of the models, including the global
models at higher resolutions, and some of the higher resolution
short term models like the HRRR and RAP, take energy from this
complex and move it across Central PA toward Central and North
Jersey overnight. Given the 500 mb flow is west-northwest and
the 1000-500 mb thickness contours are also west to east
(basically zonal), I am not sold on this activity heading
further north. MCSs like to track parallel to the 1000-500 mb
thickness contours and thus I think the NAM 3 km is more likely
which would take it towards DC/central Maryland and then toward
the Delmarva and far South Jersey (Cape May/Atlantic/Cumberland
and maybe far southern Ocean Counties) overnight. As a result,
we updated the grids to reflect this thinking.

The heavy rain threat is greatest south of a line from
Wilmington to Atlantic City but may get as far north as
Philadelphia overnight if convection sneaks up that far. So we
kept in enhanced wording for heavy rains and gusty winds given
the complex now as we see things. Further north, it looks to
stable overnight for much thunder and north of Trenton and
Freehold/Asbury Park we yanked it.

Temperatures overnight will be mild as cloud cover increases
across the region. Fog may start to develop in some areas
towards late tonight/early morning, especially where heavy rain
has fallen. Lows will drop down into the low to mid 70s across
the region, with some mid to upper 60s across parts of the
southern Poconos and northwest New Jersey.


Another slightly muggy day on tap for the region but
temperatures will not be quite as high as they have been
recently. Sky conditions will be pretty cloudy which should help
to keep the temps a bit lower. With a boundary across the
region it may be the tale of two cities (or parts of the
forecast area). Areas to the north of the boundary should remain
slightly cooler than those areas to the south of the boundary.
For now, anticipate that the boundary will remain just south of
or along the Mason-Dixon line. Areas to the north will remain in
the 80s, while areas to the south look likely to reach into the
lower 90s.

Low pressure is slated to travel along the boundary and another
round of showers and thunderstorms is expected, mainly during
the afternoon and evening hours. Once again the abundance of
moisture across the region will bring the threat for heavy rain
and we will need to monitor it closely, especially for those
areas that see heavy rain today. SPC continues the
slight/marginal risks across our forecast area for Sunday with
damaging winds being the greatest threat.


Unsettled conditions are forecast to continue from Sunday night
into Monday night. The frontal boundary is expected to remain
in our region on Sunday night with another low expected to pass
through our area on Monday.

We are anticipating the likelihood of showers and thunderstorms
associated with another convective complex on Sunday night.
Precipitable water values should be in excess of 2 inches across
the central and southern parts of our forecast area. As a
result, we will mention the potential for heavy rain at that

The chance of showers and thunderstorms will continue into
Monday and Monday night with the passage of the low. The low is
expected to begin pulling the front to our southeast and south
on Monday night.

The axis of a mid level short wave trough approaching from the
northwest is anticipated to pass overhead on Tuesday afternoon
and it will be followed by a shot of dry weather for the mid
week period.

A cold front is expected to approach from the northwest on
Thursday and it should pass through our region from Thursday
night into early Friday. We will mention a chance of showers and
thunderstorms with the front.

Dry weather is forecast to return for next weekend.

Temperatures are expected to be seasonable during the new week
with no excessive heat events in sight.


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

Tonight...Scattered showers will continue to impact mainly KABE
and to a lesser extent KRDG through 06Z, with the possibility of
an isolated TSRA. The other terminals have seen showers and
thunderstorms pass through and should remain quiet through 02Z
Sunday. Additional showers/storms may follow in the wake of
convection but confidence is lower as to timing and coverage.
The greatest threat overnight for SHRA/TSRA will be at ACY late
and possibly MIV and ILG with a lesser risk at PHL if activity
makes it that far northward. TAFs were adjusted to the latest

MVFR/IFR ceilings and visibilities are likely to occur in the
wake of the convection and persist into the morning hours. Best
chances will be at those locations that see heavy rain.

There is potential for strong to severe storms today with gusty
to damaging downburst winds and torrential rainfall.

Patchy fog may form tonight especially in areas where any
heavier rain fell early. Visibility could drop to MVFR or lower
for a few periods.

Sunday...Fog/low clouds early should clear into the afternoon
but skies are expected to remain pretty overcast. VFR conditions
are expected to return late morning/early afternoon but
confidence is low that we see significant clearing through the
day. Another round of showers and thunderstorms is expected,
mainly during the afternoon/evening hours.

Winds...light southerly winds today will become more west to
southwest overnight and then will become more north to northeast
on Sunday morning. Winds speeds are expected to remain around
10 knots or less.

Sunday night...MVFR and IFR conditions in showers and
thunderstorms. The rain may become heavy.

Monday...A chance of showers and thunderstorms with conditions
improving to VFR outside of any areas of rain.

Monday night...Conditions lowering to MVFR and possibly IFR. A
chance of showers and thunderstorms.

Tuesday...MVFR and IFR conditions in the morning improving to

Tuesday night through Thursday...Mainly VFR.


Sub-small craft advisory conditions are expected to continue on
the area waters. Winds will generally be south to southwest
through this evening around 10 knots. Winds will become more
west tonight and then northerly into Sunday. Seas are 2 to 3
feet on the ocean today and will gradually rise to 3 to 4 feet
on Sunday. While seas are expected to remain below 5 feet, they
may near 5 feet on the outer waters late tonight into Sunday.

Showers and thunderstorms will impact the area waters through
tonight, with locally higher seas and gusty winds.

Sunday night through Thursday...No marine headlines are

A moderate risk for risk currents is expected to continue
through this evening. The underlying 10-12 second period
continues to show up on guidance and is impacting the rip
current risk. Additionally, with the new moon is occurring on
Sunday, and a moderate risk looks likely for New Jersey with a
low risk for Delaware for Sunday.


There is Coastal Flood Advisory in effect for this evening`s
high tide along the New Jersey and Delaware coasts and along
Delaware Bay.

The surge at this morning`s high tide was about +0.4 to +0.6
feet. There will be an onshore component to the wind today and
it should bring the surge up around +0.6 to +0.7 feet by

The astronomical tides with the upcoming new moon are quite
high, as was the case with the new moon in both May and June. As
a result, the somewhat unimpressive surge values will likely
result in some minor flooding. If heavy rain occurs coincident
with the high tide, the potential for flooding will increase.

Conditions may be similar for Sunday evening`s high tide. An
onshore flow is anticipated for Sunday, especially in areas from
Atlantic City up to Sandy Hook.


Dew point readings at KDOV continue to measure too high
compared to surrounding locations and should be treated as
unrepresentative of the area.


NJ...Coastal Flood Advisory until midnight EDT tonight for
DE...Coastal Flood Advisory until midnight EDT tonight for


Near Term...Meola/Stachelski
Short Term...Meola
Long Term...Iovino
Tides/Coastal Flooding...Iovino
Equipment...PHI is the U.S. government's official web portal to all federal, state and local government web resources and services.