Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 170023
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
823 PM EDT Wed Aug 16 2017

.SYNOPSIS...
Weak high pressure will shift offshore tonight and Thursday. A warm
front will lift northward towards the area late Thursday and move
through the area Thursday night. At the same time, a cold front
will approach the mid-atlantic region from the west. This front
will track off the coast Friday night into Saturday. Surface
high pressure will return for Sunday and persist into Tuesday.
The affects of the next cold are expected to arrive late Tuesday
into Wednesday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Showers have stubbornly persisted in portions of Talbot and
Caroline Counties in Maryland and in coastal Ocean County in New
Jersey as the continued small-scale lift provided by associated
sea/bay breezes supports their development. Should see a
downward trend in the next couple of hours, but needed to extend
PoPs a little longer in these areas. Though coverage is quite
isolated, locally heavy downpours may occur, especially in
Maryland.

Main question tonight is fog formation. Conditions are not
nearly as favorable for widespread fog versus last night given
that most of the area was dry today and dew points are several
degrees lower. Nevertheless, with light winds and sufficient
residual near-surface moisture in play, patchy fog is likely,
especially in the favored valley/rural locations (e.g., KPTW,
K22N, KMIV, and KFWN). Will be making some tweaks to the Wx
grids to fine-tune timing/location of expected fog formation.

Lows tonight will be in the upper 50s in the Poconos and in the
mountains of northwest NJ, and otherwise in the low to mid 60s. The
urban heat island effect will keep the Philly metro area in the low
70s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Made some adjustments to cloud cover and wind forecast on
Thursday, as latest short-range model simulations are a little
slower in bringing increased clouds to the region through the
day. Will reevaluate the PoPs/Wx forecast later this evening,
but first impression is that may need to slow the onset of
precipitation (chances) from what is currently in the forecast.

Previous discussion below remains relevant...

Warm front continues to lift north through the region on Thursday,
but may not clear northern zones until late. This results in surface
dewpoints in the low 60s north and west of the Fall Line, and in the
mid to upper 60s across much of southern NJ and the Delaware Valley.
Extreme southern NJ and the Delmarva should have dewpoints in the
low 70s.

Meanwhile, low pressure currently over the Midwest will track to the
north and east, and will move into the upper Great Lakes by Thursday
afternoon. Upper level ridging builds into western and central NY/PA
during the day, and despite several shortwaves spinning out ahead of
the storm system, think most of the precip should hold off until
late in the afternoon. Best chances will be across southwest zones,
where the dewpoints are the highest.

Highs will generally top off in the low to mid 80s, except for the
mid to upper 80s in the Delmarva and in the upper 70s along the
coasts and in the mountains.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Overview...The period starts with a warm front to our north and
cold front across the Ohio Valley. The cold front will cross
the region later Friday night into Saturday. By Sunday morning,
the front is expected to be well offshore with high pressure
building in. The center of the high will move across the region
on Monday and then move offshore on Tuesday. A pre-frontal trof
is likely to set up on Wednesday as a cold front moves through
the eastern Great Lakes.

Temperatures...Normals at KPHL will run in the mid 80s and upper 60s
through the period. Friday will run near normal with clouds and
precipitation present. Saturday will run above normal. Sunday and
Monday will run normal. Tuesday and Wednesday will run above normal.
No major extremes are in the forecast.

Precipitation...PoPs will increase Thursday night into Friday.
Calendar day Friday appears to be the most unsettled during the
period. We`ll run with likely PoPs most everywhere. PoPs will
decrease on Saturday. Small PoPs will be included for Saturday
night as a mid-level feature tracks through the region. Sunday
and Monday look dry. PoPs will be reinserted into the grids
starting Tuesday afternoon.

We are included in general t-storms on the day 3 SPC outlook. PW`s
will be between 2.0 and 2.5 inches Thursday night into Friday. As
such, WPC has our area in a marginal risk for excessive rain.

Winds...Winds are forecast to be mainly 15 mph or less through much
of the period. Southerly winds will increase on Friday ahead of the
cold front. Gusts in the 20 to 25 mph range can`t be ruled out on
Friday...especially as one approaches the coast. Winds could also
gust in and near thunderstorms.

Impacts...Limited through the extended, minus Thursday night through
Friday night. Although the SPC Day 3 Convective Outlook has us in
general, we`re lying just outside of marginal. We`ll need to keep on
eye on the threat for some strong to severe thunderstorms as well as
isolated high-rate rainfall. WPC has us in a marginal risk for
excessive rainfall. Localized flooding is possible.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

For the 00Z TAFs...Main concern is patchy fog tonight. Decided
to add at least a mention of slightly lowered visibilities at
KRDG, KABE, and KILG and maintained sub-VFR VSBYs at KMIV after
midnight. However, not confident that KACY will see prolonged
lower VSBYs based on latest guidance. Fog should quickly
dissipate after 12Z. Winds will become southeast or south 5-10
kts tomorrow, with increasing mid and high clouds through the
day.

OUTLOOK...

Thursday night...Mainly VFR. MVFR conditions possible in showers and
thunderstorms. Fog possible late reducing vsbys.

Friday...Fog possible early morning. Additional MVFR conditions
likely in showers and thunderstorms.

Saturday...Some MVFR conditions expected the first half of the day
in isolated showers and thunderstorms. MVFR conditions improving to
VFR during the afternoon.

Sunday and Monday...VFR conditions expected.

&&

.MARINE...
Seas remain well below 5 feet this evening, with winds generally
light southerly at this time. Expect winds to veer to northerly
late tonight and tomorrow morning before returning to
southeasterly by afternoon. Speeds should generally remain at or
below 10 kts. Seas should hover around 3 feet through the period
(lower in Delaware Bay).

OUTLOOK...

Thursday night through Saturday morning...Sub-SCA conditions
expected, although gusts could approach 25 knots on Friday afternoon
and evening. Showers and thunderstorms becoming likely late Thursday
through Saturday. Locally higher seas and winds in heavier showers
and stronger thunderstorms.

Sunday into Monday...Sub-SCA conditions with no precipitation
expected.

RIP CURRENTS...

Buoy observations indicate that the longer-period swells
generated by Hurricane Gert are beginning to diminish (or at
least becoming less frequent). Observations from the beach (via
patrols and webcams) suggest rip currents were prevalent today,
but conditions are expected to improve tonight and tomorrow. As
such, the risk for dangerous rip currents is downgraded to
moderate for tomorrow. The rip current statement will be allowed
to expire at 9 pm this evening.

Swim only in the presence of lifeguards where safety prevails
and if beaches are closed...respect the decisions of the local
officials. Do we need a reminder? There have been numerous
drowning fatalities this year along the NJ coast, and most of
those at unguarded beaches.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...High Rip Current Risk until 9 PM EDT this evening for NJZ014-
     024>026.
DE...High Rip Current Risk until 9 PM EDT this evening for DEZ004.
MD...None.
MARINE...None.

&&

$$
Synopsis...Kruzdlo
Near Term...CMS/MPS
Short Term...CMS/MPS
Long Term...Kruzdlo
Aviation...CMS/Kruzdlo
Marine...CMS/Kruzdlo/MPS



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