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604
FXUS61 KPHI 160148
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
948 PM EDT Tue Aug 15 2017

.SYNOPSIS...
Weak low pressure moves off the Mid-Atlantic coast this
evening, and then a cold front works its way through the East
Coast late tonight. High pressure returns on Wednesday before
moving offshore on Thursday. A warm front lifts north across the
region Thursday night through Friday morning, followed by a
cold front Friday night through Saturday morning. Weak low
pressure may affect the area Sunday, then high pressure builds
back for the new week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
The main area of showers continued to move farther off the
coast this evening. However, a frontal boundary was dropping
down from the north and into the Poconos and far northern New
Jersey around 9:30 PM. There were additional showers with the
front but they were in the process of dissipating with the loss
of daytime heating.

The frontal boundary is forecast to progress southward through
our forecast area during the night. There does not appear to be
a strong push of drying with the front. The wind is expected to
remain light and variable in our region. The abundance of low
level moisture will likely result in areas of fog and low
clouds. It seems possible that widespread dense fog will develop
in parts of our region, especially the south, and a Dense Fog
Advisory may become necessary for some areas.

Minimum temperatures are anticipated to favor the 60s.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
West-northwesterly midlevel flow will become established
Wednesday with weak subsidence in the wake of the passing
shortwave trough today. Northwest surface winds will become
established, which (in combination with morning insolation)
should aid in the rapid dissipation of fog.

Wednesday looks to be a mostly dry day for the region with the
lack of any synoptic-scale lift to speak of. However, the 12Z
NAM Nest does develop an isolated storm or two in the northern
CWA during peak heating - so a dry forecast is not exactly a
slam dunk. On the other hand, coverage would be sparse enough,
and confidence is certainly low enough, to preclude mention of
any PoPs at the moment.

With some subtle downsloping and ample surface heating
expected, temperatures look to warm to just above seasonal
averages. Forecast highs are near 80 in the Poconos, near 90 in
the urban corridor, in the lower 80s at the beaches, and mid to
upper 80s elsewhere. Used a combination of MAV (warm) and MET
(cool) guidance, with some subtle extra weighting for the MAV
given the cool bias of MOS this summer in such patterns.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
High pressure over the area Wednesday night will gradually
slide offshore, and will then anchor itself over the western
Atlantic on Thursday. Meanwhile, H5 trough digs into the
Northern Plains and western Great Lakes, and surface low
pressure organizes and develops. That low will slowly track east
on Thursday, and a warm front extending out ahead of that low
will lift north into the Mid-Atlantic and Northeast late
Thursday and Thursday night. Several shortwaves will slide
across the region as well, and this will touch off scattered
showers and thunderstorms across the region Thursday afternoon
and Thursday night.

With the warm front north of the region on Friday, strong
southerly flow will usher a very warm and humid airmass into the
region. Although highs on Friday will generally top off in the
mid to upper 80s, with the warmest temps (near 90) along and
south of I-95 from Trenton to Philadelphia to Wilmington,
surface dewpoints will be well into the lower 70s. This results
in a heat index around 95 from Philadelphia to Wilmington, and
possibly near 100 for northeast Maryland and Delaware.

Cold front then approaches Friday afternoon and evening as low
pressure over the Great Lakes lifts northeast into eastern
Canada. Showers and thunderstorms are likely Friday with the
passage of this front, but conditions only marginally cool off
and dewpoints only marginally fall back into the upper 60s/low
70s on Saturday. A secondary cold front will pass through the
region on Saturday afternoon, and then dewpoints drop back into
the low/mid 60s on Sunday. Weak low pressure may have an impact
on the region Sunday, hence slight chance PoPs, but confidence
is low.

High pressure then returns for the start of the new week.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Some improvement took place this evening as the main area of
rain showers moved off the coast. However, abundant lingering
low level moisture will likely result in the development of fog
and low clouds overnight with deteriorating conditions
anticipated.

The low clouds and fog should linger until the 1200Z to 1400Z
time frame then improvement to VFR and scattered cloud cover is
forecast for the balance of Wednesday.

A light and variable wind overnight is expected to settle into
the northwest and west at 4 to 8 knots on Wednesday. A sea
breeze front may push inland past KACY early in the afternoon.

OUTLOOK:
Wednesday night...Sub-VFR conditions possible in fog/stratus.

Thursday through Friday...Sub-VFR conditions in mainly
afternoon and evening showers and thunderstorms. Late night and
early morning fog/stratus possible as well.

Saturday...Scattered showers and thunderstorms possible.

Sunday...VFR.

&&

.MARINE...
Seas have risen to 4-5 feet at the buoys off the NJ/DE coast as
Hurricane Gert churns well offshore. Longer-period swell is
reaching the buoys (generally 12-14 seconds) and will continue
into Wednesday. Seas are expected to build to 4-7 feet tonight
and Wednesday, and have continued the small craft advisory to
account for this.

Meanwhile, east to southeast winds around 5 kts will veer to
the north and northwest late tonight before veering to a
southeast direction again by Wednesday afternoon. Some fog may
develop near the coast and near Delaware Bay late tonight, with
some visibility restrictions possible. However, this fog should
dissipate rapidly during the morning, with a nice/dry day
expected, save for the aforementioned higher seas.

OUTLOOK...
Wednesday thru Sunday...Sub-SCA conditions expected through
this week and into the early part of the weekend. Scattered
thunderstorms may bring locally higher winds and seas. Southerly
wind gusts 20-25 KT possible Friday afternoon as a cold front
works its way east.

RIP CURRENTS...
We have upgraded to a high risk for the development of
dangerous rip currents for the balance of today and for
Wednesday. Long period swells from Hurricane Gert will continue
to impact the coasts of Delaware and New Jersey.

Swim only in the presence of lifeguards where safety prevails.
Otherwise, you`re on your own with any rescue potentially
critically delayed. There have been numerous drowning fatalities
this year along the NJ coast.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...High Rip Current Risk through Wednesday evening for NJZ014-
     024>026.
DE...High Rip Current Risk through Wednesday evening for DEZ004.
MD...None.
MARINE...Small Craft Advisory for hazardous seas until 2 PM EDT
     Wednesday for ANZ451>455.
     Small Craft Advisory for hazardous seas until 2 PM EDT
     Wednesday for ANZ450.

&&

$$

Synopsis...MPS
Near Term...Iovino
Short Term...CMS
Long Term...MPS
Aviation...Iovino/MPS
Marine...CMS/MPS