Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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215
FXUS61 KPHI 262224
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
624 PM EDT Mon Sep 26 2016

.SYNOPSIS...
A cold front will move across the area later tonight, then stall off
the Mid Atlantic coast on Tuesday. An upper low will meander over
the eastern United States for the rest of the week, lifting to the
northeast and departing sometime this weekend. Meanwhile, several
waves of low pressure will develop along that stalled boundary and
move up the East Coast.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
630 PM Update...Increased the sky cover faster given the overcast
that has overspread most of the region. Adjusted the temperatures
down some for many places based on the obs and cloud cover, then
blended in the LAMP/LAV guidance. Dry low-level air hanging on,
especially across the north where dew points were lowered some
initially. Slowed the POP increase some from west to east given what
appears to be a somewhat slower eastward progression of the cold
front.

Otherwise, a cold front will push eastward and start to move into
our area later tonight. Showers, associated with the front, will
start to enter the region mainly after midnight and spread eastward.
There may be enough lift and instability present for an isolated
thunderstorm and heavy rain, mainly across our southern areas.

With plenty of cloud cover present, temperatures will not drop
off too much overnight, remaining in the upper 50s to mid 60s
through much of the area.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
The cold front continues its eastward movement but it looks like
it gets hung up as it moves through the I-95 corridor and starts
to slow down considerably. This will keep the precipitation
hanging around longer and areas to the south and east of I-95 may
see rain through much of the day. Although, precipitation should
remain lighter as the best forcing moves away from the region.

Areas to the west of I-95 will start to clear out by mid to late
morning with the sun peeking through and starting to help dry out
the area.

Areas that break out on Tuesday will be warmer than those that
remain stuck under relatively thick cloud cover. Highs into the
low to mid 70s across eastern Pennsylvania and central to northern
New Jersey with southern New Jersey and much of Delaware remaining
in the upper 60s to near 70. If the front moves further east
faster, then temperatures may rise a couple degrees above forecast
due to less cloudiness.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
An extended period of unsettled weather is on tap for the rest of
the week, and possibly into the upcoming weekend.

Nearly vertically stacked closed low, along with several strong
shortwaves, will dive into the Great Lakes and Ohio Valley Tuesday
night. Meanwhile, frontal boundary remains stalled along the Mid-
Atlantic. With these shortwaves rotating around the low and
interacting with the stalled front, several waves of low pressure
will develop over the Southeast U.S., and will lift to the north
along the East Coast.

Where the uncertainty lies is where each low will actually track,
and where the axis of rainfall will develop. First swath of rain
looks to come up the coast sometime Wednesday afternoon, with the
bulk of the rain falling Wednesday night and Thursday. Latest GFS
has a swath of rain across central NJ and into E PA, whereas the
ECMWF has that swath over southern PA, MD, and VA. These details
have yet to be worked out, but with onshore flow ahead of the low,
abundant low level moisture will stream into the region, allowing
for at least some periods of moderate to locally heavy rain.

Another wave of low pressure looks to come up the coast on
Friday, but there is less certainty with that track. The closed
upper low, meanwhile, does not look to even begin to depart until
sometime Saturday night into Sunday morning, and even then, models
are not in good agreement as to the timing and placement of it.
Therefore, will carry chance PoPs into the weekend.

Regardless of where the rain does end up falling, given the
onshore flow that will be in place, can at the very least expect
cloudy and cool weather through the week with temps running a few
degrees below the seasonal averages, with highs ranging from the
low to mid 60s across northern zones to the low to mid 70s across
southern zones.

Latest WPC QPF forecast suggests about 2-5 inches of rain across
the region, but that is over the entire period ending on Monday.
Given how dry the area has been, this should not result in
widespread flooding, and this rain is much needed.

&&

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

Tonight...VFR ceilings to start, however as a cold front approaches
from the west MVFR ceilings along with increasing showers will
occur. Showers are expected to impact KRDG/KABE around 04Z,
KPHL/KILG/KTTN/KPNE around 05Z, and KMIV/KACY around 07Z. The
showers will result in lower visibility at times. Periods of IFR
conditions are possible. There is a chance for isolated thunder with
the front but confidence and coverage is too low to include in the
TAFS at this time.

Tuesday...Behind the front, conditions will start to clear quickly
especially north and west of PHL. Ceilings will start to clear out
from west to east and winds will become more westerly, especially
for areas along I-95 and to the west. Areas to the east of I-95 will
continue to have MVFR/IFR conditions through much of the day as the
front slows down and takes longer to clear those areas.

OUTLOOK...
Tuesday night through Saturday...Sub-VFR conditions likely in
showers and fog. Best chances for more widespread rain appear to
be on Thursday and Friday. Forecast confidence: low.

&&

.MARINE...
A Small Craft Advisory is in effect for all waters from tonight
through Tuesday morning.

Southerly winds around 10 to 15 knots will increase as the
gradient tightens ahead of an approaching cold front. In addition,
seas will start to build and will near 5 feet by late tonight.

The cold front will slow down as it nears the coastline and is
expected to move offshore Tuesday morning. Winds just ahead of the
front will be out of the south to southwest and will quickly turn
to the west-northwest behind the front. highest gusts are expected
to occur during the morning just ahead of and behind the front,
with a quick drop off as the front moves slowly to the east. Seas
will remain elevated through the mid morning, and will then
subside, falling below 5 feet by late morning.

OUTLOOK...
Tuesday night through Wednesday...Winds and seas below SCA
threshold.

Wednesday night through Saturday...E winds 15-20 KT with 25-30 KT
gusts possible across northern ocean waters. A period of gale
force gusts is possible Wednesday night. Seas may build to 6-8 FT.
A SCA will likely be needed for the ocean waters for at least
Wednesday and Thursday. Low confidence in forecast thereafter, but
SCA may continue to be needed into the start of the weekend.

RIP CURRENTS...
A moderate risk for the formation of dangerous rip currents
continues through this evening. This moderate risk may continue into
the first part of Tuesday before diminishing toward afternoon as
winds and seas subside behind a cold front.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 11 AM EDT Tuesday for ANZ430-431-
     450>455.

&&

$$
Synopsis...MPS
Near Term...Gorse/Meola
Short Term...Meola
Long Term...MPS
Aviation...Gorse/Meola/MPS
Marine...Meola/MPS



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