Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 240119

Area Forecast Discussion
National Weather Service Mount Holly NJ
919 PM EDT Sun Jul 23 2017

A frontal boundary will remain over our area overnight. Low
pressure will ride eastward along the front and it should pass
through our area on Monday. A second low will follow on Monday
night and Tuesday as the boundary sinks slowly to the south.
High pressure is forecast to build down from the northwest for
the middle part of the week. A cold front from the northwest is
anticipated to arrive on Friday. The front is expected to move
slowly to our southeast over the weekend as areas of low
pressure travel along it.


**A Flash Flood Watch is in effect for the I-95 corridor and
areas to the north and west for tonight through early Monday

919 PM Update...The focus for convection this evening has been
north of a stationary boundary. The boundary at the present has
become ill-defined due to cooling from convection but based on
Theta-E analysis from the LAPS which shows a packing of contours
just north of the boundary was still floating around across
southern DE to the central parts of the Maryland Eastern Shore.
Overall the intensity of the convection in the last hour has
trended down and radar has the look of a stratiform type
precipitation more than convective overall.

Models are not doing to well this evening with respect to the
placement of QPF, so I made adjustments to the grids for the
next few hours largely based on radar interpolation. My thought
is in the next 2-3 hours that most of the focus will remain
along and northwest of I-95 towards the Fall Line. The slow
movement to the northeast will keep the flood threat going.
Rainfall rates will generally be under an inch per hour except
in heavier pockets of rain. My thought on the far northwest part
of our area is the flash flood threat here is not as great, but
the watch will stay up for now and can be adjusted as the night

The next area to watch will be over central/southern Virginia
which is potentially where convection may work into our area
from later on tonight. Any additional rounds of heavy rain where
we saw issues earlier (far northeast Maryland - mainly Cecil
County, Berks County and points west of Philadelphia) will need
a close eye if any more heavy rain falls as it will not take
much to cause more flooding.

Temps were adjusted as well based on the latest hourly temps and
I also did a broad 1-2 degree bump in lows down as many spots
were already at forecasted lows for tonight.

Please follow any short fused products for more details on
specific storms and area hazards.

The boundary may move slightly north tonight but will remain
nearly stationary into Monday. A low pressure system will
develop along the boundary and move into our area late tonight.
Heavy rain and thunderstorms will accompany the system. This
second batch of rain is more problematic than the convection we
will see this afternoon and evening. A good swatch of 1-2 inches
of rain fell last night. We have not had ample time to dry out
so the ground will be unable to absorb nearly as much
precipitation as it otherwise would. Models have trended wetter
with the latest runs and put a bullseye, or more of a heavy
swath, of rain across our area. The focus looks to be more along
the I-95 corridor but some of the models show a slight shift to
the north and west of I-95. With PWATS still running around
1.5-2.0 inches across the region, we will have plenty of
moisture to feed into showers and thunderstorms and torrential
rainfall will occur. While the models are outputting pretty
high, and what look like unreasonable, amounts it seems likely
that a good 2-4 inch rainfall will occur within our CWA. A lack
of strong flow at the surface and aloft shows that storms may
not move very quickly (or at all), enhancing the flash flood

With higher confidence that flash flooding will occur somewhere
in the CWA, we have issued a Flash Flood Watch for the I-95
corridor and areas to the north and west through Monday morning.

Temperatures have certainly been cooler today than of late but
expect a decent amount of cloud cover to remain over the region
through tonight. This will keep the temperatures more moderate
overnight tonight. Expect lows to range from the upper 60s
across the southern Poconos to the low to mid 70s across the


The boundary remains in the area with the low pressure system
moving through the region on Monday. A cold front will drop down
from the the north on Monday, taking its time as it makes its
way through our area. A continued chance for showers exists
through much of the day with a chance for some thunderstorms as
well. Heavy rain will remain a threat in some of the stronger
showers and in thunderstorms.

Some clearing may occur during the afternoon, mainly southern
areas, with more clearing expected towards evening.

Highs will rebound slightly and dewpoints should start to drop,
although that may be a slower process. It will still feel
humid, especially across Delmarva and extreme southern New
Jersey. Expect highs to be in the lower 90s from
I-95/Philadelphia and points to the south and in the mid to
upper 80s through central New Jersey. Lehigh Valley, Pocono and
northern New Jersey will remain cooler with highs in the 70s to
around 80.


A chance of showers and thunderstorms will linger into Monday
night. Based on the latest model guidance, drying may be delayed
a bit. It now appears as though the mid level short wave trough
from the northwest will not arrive until late Tuesday. As a
result, we will keep some clouds and a slight chance of showers
for Tuesday.

Dry air is anticipated to follow the mid level trough for
Tuesday night through Wednesday night.

A cold front is expected to approach from the northwest on
Thursday and it should pass through our region on Friday. We
will indicate an increasing chance for showers and thunderstorms
at that time.

The forward progress of the front is expected to slow over the
weekend as waves of low pressure travel along the boundary. We
will continue to carry a mainly dry forecast for Saturday and
Sunday, but that could change if the front starts to trend
toward being even less progressive.

Temperatures are expected to be seasonable during the period
from Monday night through Sunday.


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

Scattered convection across the region through tonight with
showers continuing through the overnight hours. Periods of heavy
rain with IFR conditions possible, especially from KILG/KPHL
and terminals to the north and west. There remains the
potential for strong to severe storms today with gusty to
damaging downburst winds and torrential rainfall.

VFR/MVFR conditions have prevailed through much of the day and
we should see mainly VFR conditions at the terminals outside of
showers and convection. Conditions will deteriorate as storms
arrive and ceilings and visibilities will remain MVFR, possibly
IFR, through much of the night and into Monday morning.
Conditions will be slow to improve on Monday but are expected to
return to VFR by late morning/early afternoon.

Winds...Easterly winds at the terminals today have remained
light, around 10 knots or less across the region. Winds will
become light and variable overnight and then become mainly west
to northwest for KPHL/KILG/KMIV/KACY/KRDG and more north to
northeast for KTTN and KABE for Monday. Winds speeds are
expected to remain around 10 knots or less.

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

Tuesday...MVFR and IFR conditions possible in the early
morning, then VFR.

Tuesday night through Wednesday night...Mainly VFR.

Thursday...Mainly VFR. A chance of afternoon showers and

Thursday night and Friday...MVFR and IFR conditions are
possible in showers and thunderstorms.


Sub-advisory conditions are expected to continue on the area
waters through Monday. Seas are 2 to 4 feet on the ocean and
around 2 to 3 feet on the Delaware Bay. While seas are expected
to remain below 5 feet, they may near 5 feet late tonight/early
Monday, mainly our northernmost waters. Additionally, winds will
pick up some overnight our of the east in response to a surface
low moving over the area and a tightening pressure gradient.
The gradient doesn`t look to fully wrap up until the surface low
is to the east of our area. Winds may gusty briefly near 25
knots but confidence is low that a small craft advisory will be

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

Monday night through Friday...No marine headlines are

A low risk remains is expected for Monday for rip currents with
a possible moderate risk along the Monmouth and northern Ocean
County beaches.


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

An onshore flow along the coast from Sandy Hook down to around
Atlantic City almost guarantees minor flooding for the New
Jersey coast. Conditions may be a bit marginal for Delaware.

The astronomical tides will remain high for Monday evening`s
high tide and another Coastal Flood Advisory may be needed at
that time.


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

Hamburg NJ transmitter is off the air. No known rts.


PA...Flash Flood Watch until 6 AM EDT Monday for PAZ054-055-060>062-
NJ...Flash Flood Watch until 6 AM EDT Monday for NJZ001-007>010-012-
     Coastal Flood Advisory until 1 AM EDT Monday for NJZ012>014-
DE...Flash Flood Watch until 6 AM EDT Monday for DEZ001.
     Coastal Flood Advisory until 1 AM EDT Monday for DEZ002>004.
MD...Flash Flood Watch until 6 AM EDT Monday for MDZ008.


Near Term...Meola/99
Short Term...Meola
Long Term...Iovino
Tides/Coastal Flooding...
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