Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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490
FXUS61 KPHI 282046
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
446 PM EDT Wed Sep 28 2016

.SYNOPSIS...
An area of low pressure will move across the Ohio Valley and
combine with another low across the central and southern
Appalachians Thursday into Friday. A cold front will cross the
region around Sunday.  High pressure is then expected to build
to our north into early next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
FFA issued where this mornings unexpected heavy rain expanded an
area where it will take only 3-4 inches of rain in 6 hours to cause
flooding. PWAT up near 2 inches, significant e-se 850 mb inflow
and expected tstms was the reasoning for the FFA. Confidence on 6"
occurring between 6P today and 6P tomorrow is low but it is possible.
otherwise, bands of showers and drizzle tonight, especially late
and especially e PA and the Delmarva. nice waa pattern (aloft)
tonight.

fcst basis: 50 50 blend of the 12z/28 gfs/nam mos guidance.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
showers, drizzle. some of the rain heavy. most of the heavier rain
should be Delmarva/se PA. its possible drying from the northeast could
invade NNJ and prevent little if any rain in the afternoon. cool.
ne wind gust 20-30 mph....possibly gusty 40-45 mph along the
immediate coast of NJ and near Lewes DE.

fcst basis: a 50 50 blend of the 12z nam/gfs mos guidance.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Unsettled weather continues for the first portion of the extended
fcst, with some improvement by the end.

A large area of upr lvl low pres will be located to our s and w at
the start of the extendd pd. This low will spin in place then
gradually retrograde to the Grtlks and sern Canada by the weekend.

At the sfc, an area of low pres will be located over the midwest,
with high pres to the ne over New Eng and sern Canada. The sfc
features will keep a persistent moist nely flow over the area at
the sfc with swly flow aloft. As the sfc low moves by to the nw,
one pd of rain is expected and as several other s/wvs rotate thru
the upr low several other pds will occur.

As is usually the case with upr lows, it will not rain the whole
time. It will be cloudy and dreary with pds of rain. The mdls
differ on which times will be rainy and where those rainy pds will
occur. For example on Friday, the GFS is mainly dry, while the
ECMWF is fairly wet and the NAM somewhere in the middle.

Have tried to make adjustments to pops where there was a decent
signal in the mdls, but these times were limited and overall
confidence on which pds will be rainy are low.

By Sat and Sun, the upr low moves nwd into the Grtlks area and
begins to weaken and fill. Overall precip chcs shud decrease.
However, guid today is wetter than it was yda and once again it
will depend on individual w/wvs. Sat shud be wetter than Sun with
precip chcs decreasing with each passing day. Some guid now even
wants to linger precip chcs into Mon until the upr low finally
passes to our e and high pres builds in behind it.

By Wednesday, all eyes turn to the tropics and any potential
impacts from what is now Tropical Storm Matthew later in the week.
Please see NHC advisories for updates.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Rest of this afternoon...MVFR cigs probably becoming more widespread.
scattered showers briefly limit visibility to 3 to 5 mi. ne wind
gust 15-22 kt.

Tonight and Thursday...MVFR cigs variable down to IFR conds in areas
of showers, drizzle, stratus and fog. Some of the rain may be briefly
heavy and there may also be a tstm, (the thunder mainly PHL south)
but for now the tstm is not in the TAF. ne-e wind gusty 15-20 kt
tonight and 20 to 30 kt Thursday.


OUTLOOK...

Thu night-Fri...A prolonged period of MVFR or IFR conditions with
pds of RA expected to affect the TAF sites through the period.
E to Ne winds are expected to gust 20-25 knots for much of the
area, especially KMIV and KACY. Moderate confidence.

Fri night-Sun...Some improvement, possibly to VFR by Sun. SHRA remain
psbl. Moderate confidence.

&&

.MARINE...
Gale warning issued with at least two surges of potential 35 kt gusts
expected, one early Thursday and the more extensive probably late
Thursday afternoon into Thursday night. The Gale supersedes the
SCA and we keep the product simple by using the higher priority
warning. Seas may build higher than 11 ft at 44091 but this is a
forecast start for now.


OUTLOOK...
Thursday night...Gale warning in effect early, will likely need to
be extended.

Fri...Gale wind may remain across the northern half of the
coastal waters. SCA may be needed elsewhere.

Fri night-Sat...Wind expected to drop below SCA, however, seas
will likely remain above 5 feet thru the pd.

Sat night-Sun...Wind and seas expected to drop below SCA levels
and no marine flags anticipated.

Rip Currents...
There continues a moderate risk for the formation of dangerous
rip currents today as per a recheck of the ene sustained wind
~18kt and dominant 4 second short period swell.

Thursday: The probability for the formation of dangerous rip
currents is at least moderate to perhaps high.

&&

.TIDES/COASTAL FLOODING...
A persistent onshore flow is expected for the rest of the week into
the weekend. The strongest winds are expected Thursday through Friday.
Tides levels are forecast to increase through this period, and we
should reach minor coastal flood levels Thursday evening/night
high tide cycle for many of the coastal locations. This per ETSS,
SIT modeled guidance and local in house program.

For Lewes and Reedy point we ran a 1 ft departure this eve, 1.4
tomorrow morning with ene wind gusts around 30 kt and pres at
44009 of 1022MB (a bit high for a coastal flood event where the
astro tide is not extreme). The result is marginal exceedance of
the threshold for the Thursday evening high tide cycle of roughly
.1 to .8 feet.

All of this will be reevaluated by the subsequent shifts to determine
confidence for a cf advisory issuance. we just are not sure yet
what our storm tide will be the next two high tide cycles and we
still have opportunity to adjust the max wind gusts at high tide
and in the preceding hours. Usually, lower pressure than 1022mb is
more favorable for boosting the surge. However, a notable easterly
gradient could be enough to force the minor coastal flood event.



&&

.CLIMATE...
Will add extensive climate information late this afternoon as
time permits.  its been a busy day here.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...Flash Flood Watch through Thursday afternoon for MDZ008-012-
     015-019-020.
MARINE...Gale Warning from 4 AM Thursday to 2 AM EDT Friday for ANZ430-
     431-452>455.
     Gale Warning from 4 AM Thursday to 6 AM EDT Friday for ANZ450-
     451.

&&

$$
Synopsis...Drag/Nierenberg
Near Term...Drag
Short Term...Drag
Long Term...Nierenberg
Aviation...Drag/Nierenberg
Marine...Drag/Nierenberg
Tides/Coastal Flooding...446P
Climate...



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