Areal Flood Advisory 185, NWS Philadelphia/Mount Holly

Area Forecast Discussion
National Weather Service Mount Holly NJ
359 PM EDT Thu Aug 3 2017

.SYNOPSIS...
A warm front will lift northward toward the area Friday, while
a cold front approaches from the west. The cold front will move
across the area Friday night into early Saturday. High pressure
moves across the area Saturday night into Sunday. A low pressure
system is expected to pass near the area Monday into Monday
night, pulling a warm front, then a cold front across the area.
The frontal boundary will likely stall to our south through the
end of the week. High pressure then builds back across the area
for Tuesday night then moves offshore Wednesday into Thursday as
the front to our south begins to lift back northward.

&&

.NEAR TERM /THROUGH TONIGHT/...
A 1009 mb surface low as analyzed over the Upper Midwest this
afternoon. A stationary front extended to the east-northeast
across the eastern Great Lakes and into St. Lawrence Valley. The
low will continue to deepen gradually over the Upper Midwest
but overall not much change in the pattern is expected tonight.

At 330 PM, the bulk of the convective activity so far this
afternoon has been focused near a lee trough to our west across
central PA and the Shenandoah Valley. The only storms in our CWA
thus far have been along the sea breeze in southern Delaware.
The environment will be more conducive for pulse-severe wet
microbursts across Delmarva, extreme southeastern PA and
southern NJ where greater instability (MLCAPE around 2000 J/kg
per 19Z SPC mesoanalysis) and low-level moisture (dewpoints in
the mid 70s) reside. We saw this structure with an earlier storm
in the Georgetown, DE area that had a Severe Thunderstorm
Warning. Expect additional showers and storms to develop farther
north into eastern PA and NJ (away from the immediate
coastline) late this afternoon and early evening. Still
expecting mainly scattered coverage of storms and with a weak
wind field aloft, cells should remain disorganized and slow
moving. This could result in locally heavy rainfall (isolated
2-3" amounts). Accordingly, poor drainage flooding and perhaps
even isolated occurrences of flash flooding are a possibility
through this evening.

Expect convection to wane after sunset with the loss of heating
though leftover showers may linger late this evening and
overnight across eastern PA and NJ (particularly northern areas
with a general northerly storm motion).

Breaks in the cloud cover is expected tonight, leading to fog
development overnight. Locations that see rain this afternoon/
evening as well as the sheltered valleys in E PA will be most
susceptible to fog. Cannot rule out patchy dense fog but do not
anticipate it to be quite as extensive as last night.

Low temperatures range from the mid 60s in NE PA and NW NJ to
low 70s in the cities and along the coast.

&&

.SHORT TERM /FRIDAY/...
Surface low pressure will continue to gradually strengthen to
sub- 1000 mb MSLP by afternoon as it drifts northeastward
through the northern Great Lakes region. The flow over the
eastern seaboard will back more from the south as the upstream
trough amplifies over the Midwest.

Models depict the coastal Mid Atlantic positioned in an region
of favored subsidence on the western periphery of an offshore
low pressure system and downstream of a pre-frontal surface
trough that sharpens on the lee side of the Appalachians during
the afternoon. A subsidence inversion noted in the NAM/GFS
forecast soundings looks to strengthen with eastward extent and
also with time as dry air aloft mixes down to the surface during
the afternoon. Accordingly, this atmospheric lid is likely to
inhibit deeper convection, particularly east of the Fall Line.
Went with isolated coverage of showers and storms during the
afternoon just west of the Fall Line, increasing to scattered
farther inland toward Reading, the Lehigh Valley, southern
Poconos and far northwestern NJ. The primary lifting mechanism
for convection will be terrain circulations as the more
organized lift near the surface trough will likely stay to our
west during the daytime hours.

Temperatures should on par with the past few days, though the
current thinking is more locations may reach 90F owing to the
stronger subsidence overhead. Forecast highs are at or slightly
above MAV/MET blend.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
By Friday evening, a warm front lifts toward the area, as a
cold front approaches from the west. The warm front may not make
it much into our area before the cold front moves through late
Friday night into Saturday morning. There will remain
instability ahead of the frontal boundary, although it will
weaken some overnight. Enhanced moisture and lift will move
north of the warm front and ahead of the cold front, so there
will continue to be a chance of showers and thunderstorms
overnight Friday into Saturday morning. PW values increase ahead
of the front, so there could be some heavy rainfall overnight
Friday into Saturday morning.

The frontal boundary is expected to move offshore during the
daytime morning hours Saturday. Behind it, drier and cooler
conditions are expected for the remainder of Saturday, through
Sunday as high pressure moves in from the west.

For Monday into Tuesday, an area of low pressure is expected to
lift near the area, pulling a warm front, then a cold front
through. The warm front is forecast to lift into the area early
Monday, then the cold front is expected to move through
overnight Monday into Tuesday morning. PW values could approach
or exceed 2 inches during this time, which could lead to periods
of heavy rainfall. The front is expected to move to our south
and temporarily stall.

Behind the cold front, drier conditions are expected to build
across the region as high pressure begins to build in from the
west Tuesday night through early Wednesday. Later Wednesday into
Thursday, high pressure shifts offshore and return flow
develops. The stalled boundary to our south may begin lifting
back northward, but may not fully reach our area through
Thursday. However, moisture and lift could move across our area
and lead some scattered showers and thunderstorms.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Showers and storms have thus far been isolated in coverage thru
1930Z, but are expected to increase slightly through about 00Z.
A TEMPO group for TSRA has been added with the 18Z TAF. Will
closely follow radar trends and make amendments accordingly. The
storms will bring a risk for brief IFR restrictions.

Expect showers and storms to decrease in coverage/intensity
after sunset but isolated convection may linger through about
midnight. Patchy fog could develop between 06-12Z Friday,
especially at TAF sites that see rain this afternoon/evening.
IFR restrictions possible.

Potential for IFR or MVFR CIGs in stratus during the mid
morning, particularly for NW terminals (RDG-ABE-TTN). Otherwise,
VFR on Friday.

OUTLOOK...

Friday night-Saturday...CIGS lowering overnight Friday into
Saturday morning, improving during the day. Chance of scattered
showers and thunderstorms which may temporarily lead to lower
conditions Friday night into Saturday morning. South-southeast
winds Friday night, becoming west-southwest late, then northwest
on Saturday. Winds will gust around 15-20 knots, especially
during the afternoon behind a cold front.

Saturday night-Sunday night...Generally VFR. North-northeast
winds 10-15 knots with gusts possible around 20 knots through
the evening, diminishing overnight Saturday into Sunday morning.
Northwest winds Saturday night becoming westerly during Sunday.

Monday-Tuesday...Lowering conditions with rainfall spreading
across the area.

&&

.MARINE...
Winds and seas below SCA threshold. SMWs with strong storms
late this afternoon mainly for the DE Bay.

RIP CURRENTS...

There is a low risk of rip currents through this evening.

We are anticipating a low risk for the development of dangerous
rip currents on Friday. However, the risk may approach moderate
late in the day along the New Jersey shore from about Barnegat
Inlet northward as the southerly wind there increases a bit.

OUTLOOK...

Friday night-Sunday night...Overall sub Small Craft Advisory
conditions expected. Winds may gust around 20 knots at times,
and could briefly approach Small Craft Advisory levels
Saturday. A cold front is expected early Saturday with showers
and thunderstorms possible.

Monday-Monday...Conditions may approach Small Craft Advisory
levels by the end of the day Monday into Monday night.

Tuesday...Conditions expected to be below advisory levels.

&&

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

&&

Synopsis...Robertson
Near Term...Klein
Short Term...Klein
Long Term...Robertson
Aviation...Klein/Robertson
Marine...Klein/Robertson

Hazardous Weather Outlook
National Weather Service Mount Holly NJ
357 PM EDT Thu Aug 3 2017

DEZ001>003-MDZ008-012-015-019-020-NJZ001-007>010-012-013-015>023-027-
PAZ054-055-060>062-070-071-101>106-042000-
New Castle-Kent-Inland Sussex-Cecil-Kent MD-Queen Annes-Talbot-
Caroline-Sussex-Warren-Morris-Hunterdon-Somerset-Middlesex-
Western Monmouth-Mercer-Salem-Gloucester-Camden-
Northwestern Burlington-Ocean-Cumberland-Atlantic-Cape May-
Southeastern Burlington-Carbon-Monroe-Berks-Lehigh-Northampton-
Delaware-Philadelphia-Western Chester-Eastern Chester-
Western Montgomery-Eastern Montgomery-Upper Bucks-Lower Bucks-
357 PM EDT Thu Aug 3 2017

This Hazardous Weather Outlook is for central Delaware, northern
Delaware, southern Delaware, northeast Maryland, central New
Jersey, northern New Jersey, northwest New Jersey, southern New
Jersey, east central Pennsylvania, northeast Pennsylvania and
southeast Pennsylvania.

.DAY ONE...This Afternoon and Tonight.

Scattered thunderstorms will continue through this afternoon and
evening. A few of these storms could produce locally damaging winds.
These storms will also be moving slowly, resulting in locally heavy
rainfall and the potential for flooding, especially in urban and poor
drainage areas.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

DEZ004-NJZ014-024>026-042000-
Delaware Beaches-Eastern Monmouth-Atlantic Coastal Cape May-
Coastal Atlantic-Coastal Ocean-
357 PM EDT Thu Aug 3 2017

This Hazardous Weather Outlook is for southern Delaware, central
New Jersey and southern New Jersey.

.DAY ONE...This Afternoon and Tonight.

Scattered thunderstorms will continue through this afternoon and
evening. A few of these storms could produce locally damaging winds.
These storms will also be moving slowly, resulting in locally heavy
rainfall and the potential for flooding, especially in urban and poor
drainage areas.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

ANZ430-431-450>455-042000-
Delaware Bay waters north of East Point NJ to Slaughter Beach DE-
Delaware Bay waters south of East Point NJ to Slaughter Beach DE-
Coastal waters from Sandy Hook to Manasquan Inlet NJ out 20 nm-
Coastal waters from Manasquan Inlet to Little Egg Inlet NJ out 20 nm-
Coastal waters from Little Egg Inlet to Great Egg Inlet NJ out 20 nm-
Coastal waters from Great Egg Inlet to Cape May NJ out 20 nm-
Coastal waters from Cape May NJ to Cape Henlopen DE out 20 nm-
Coastal waters from Cape Henlopen to Fenwick Island DE out 20 nm-
357 PM EDT Thu Aug 3 2017

This Hazardous Weather Outlook is for Atlantic coastal waters and
Delaware Bay Waters.

.DAY ONE...This Afternoon and Tonight.

Thunderstorms this afternoon and evening can produce locally strong gusty
winds.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

The probability for widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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