Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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
000
FXUS61 KPHI 222343
AFDPHI

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

.SYNOPSIS...
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.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
655 PM Update...Did some tweaks to hourly temps/dewpoints to
lower temps and raise dewpoints where convection has hit in the
last hour or so. Also bumped up PoPs in areas of Central/South
Jersey based on latest radar trends in the last hour. Main
threats continue to be gusty winds and downpours in the next few
hours and short fused products will handle these.

We are concerned about the heavy rain potential for Central and
North Jersey tonight as well as parts of East-Central PA, mainly
from Bucks/Mercer/Monmouth Counties on north. Higher resolution
short term models are showing a heavier rain somewhere in this
area resulting from lift from this afternoon`s sea breeze, the
moisture boundary in place in that area and the approaching
remnant MCV over eastern PA heading east. Larger scale global
models, except the GFS, also show a threat for this but have it
further north across North Jersey toward the New York border. We
will keep an eye on radar trends but Flash Flooding may increase
as a threat in these areas tonight if things all come together.
PWATs are very juicy so the unload factor will be there if
anything can ring it out of the clouds.

538 PM Quick Update...Bumped up PoPs and adjusted timing for
the next 3 hours for southeast PA/west-central NJ based on the
latest radar trends. Activity over Chester County as of writing
should work into much of Philadelphia and the northern and
western suburbs. Gusty winds and downpours causing water to
collect are the main hazards with this line. Follow any short
fused products for more details.

A couple of convective complexes will impact the region through
tonight.

The first complex is a persistent MCS that is moving through
the region this afternoon. The strongest portion is moving
across Delmarva, where the greatest threat for severe presently
exists.

Good shear along with high CAPE values supports the potential
for severe storms. SPC continues the slight/marginal risk across
our forecast area with the greatest threat being damaging
winds. Additionally, PWATs have been creeping up through the day
as low level moisture is on the rise. Dew points into the mid
70s, especially across Delmarva, are present and any convective
development will have some heavy rainfall rates. This combined
with the deep shear and a well mixed boundary layer indicates
that there is the potential for wet microbursts to occur. Poor
drainage and urban flooding looks like the most likely outcome
of the heavy rain but if the flow slows in any way, we could see
some slow movers or training cells and flash flooding may
become more of a threat and needs to be monitored.

More convection is expected to arrive in our area through
tonight as a second complex/boundary arrives. However, there is
some uncertainty as to how much we will see across the region as
atmosphere gets a bit cleansed from the first round of
convection. Confidence is lower as to the coverage of the second
batch of convection and have kept pops low across the region
overnight and into the early morning hours.

The convection will start to move offshore late tonight/early
morning but we won`t feel all that much relief from the humid
conditions.

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.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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
time.

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.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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.

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.

OUTLOOK...
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
VFR.

Tuesday night through Thursday...Mainly VFR.

&&

.MARINE...
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.

OUTLOOK...
Sunday night through Thursday...No marine headlines are
anticipated.

RIP CURRENTS...
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.

&&

.TIDES/COASTAL FLOODING...
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
evening.

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.

&&

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory until midnight EDT tonight for
     NJZ012>014-020>027.
DE...Coastal Flood Advisory until midnight EDT tonight for
     DEZ002>004.
MD...None.
MARINE...None.

&&

$$
Synopsis...Iovino
Near Term...Meola/Stachelski
Short Term...Meola
Long Term...Iovino
Aviation...Iovino/Meola/Stachelski
Marine...Iovino/Meola
Tides/Coastal Flooding...Iovino
Equipment...PHI



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.