Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 291042

Area Forecast Discussion
National Weather Service Mount Holly NJ
642 AM EDT Thu Sep 29 2016

A frontal boundary will remain stationary to our south today through
Saturday as a couple of low pressure systems pinwheel to our south
and west. The low to our west will eventually lift through the Great
Lakes region and into the northeast over the weekend, before
weakening on Monday. This will pull the frontal boundary across our
area Sunday. High pressure builds to our north for Tuesday into


Model guidance hasn`t been handling overnight extend of the rain
well at all, so there is considerable uncertainty even with the
near term period of this forecast. However, mid and upper level
mean flow is expected to shift from south southwesterly to
southeasterly through the day. As a result, the axis of heavy
rain, and even of widespread light rain should shift east of the
region, at least through the day time hours.

Thanks to extensive cloud cover, do not expect temperatures through
the day to be much higher than what we saw overnight. This will also
limit instability, though isolated thunderstorms are still possible
thanks to meager elevated instability.


Low level flow should shift more easterly, and mid and upper
level flow back to southerly. As a result, another round of rain,
heavy at times will be possible for the southern half of our
region. The persistent surface high just to our north and
associated subsidence may be enough to keep heavy rain out of the
northern half of the region, but with the onshore flow, expect at
least light rain for almost all of the region. Persistent low
level cloud cover will once again limit nocturnal radiational
cooling overnight, meaning our lows should be within 10 degrees of
Thursday`s highs.


Unsettled weather continues to be forecast for much of the extended
period, especially the end of this week into the weekend.

For Friday, an couple of areas of low pressure at the surface
will continue to be located to our south and west, while high
pressure remains to our north. In between, a stationary boundary
will remain in place just to our south. This will keep an onshore
flow across our area. Meanwhile, a closed low aloft will be
spinning to our west as well. This will keep a persistent
southerly flow aloft across the area at the same time. With the
southerly flow aloft, cloudy conditions, and a chance of light
rain and/or drizzle will continue across the area. It will not
likely rain the entire time, but several periods of rain will be
associated with several short waves/vorticity impulses rounding
the closed low aloft to our west.

By Saturday, and especially Sunday, the high to our north begins
to move eastward, and the low to our west will begin lifting back
toward the Great Lakes region. This will eventually pull the
frontal boundary to our south across our area on Sunday. There
will continue to be a chance of showers Saturday through Sunday as
several short wave/vorticity impulses move across the area as the
closed low aloft begins to break down and lift to the northeast.

On Monday, the mid-level trough will be moving across the area,
and the low to our north will weaken as it moves into New England.
As the trough aloft crosses the area, there could be some
scattered showers affecting the area.

By Tuesday and Wednesday, high pressure builds to our north and
noses its way across our area. With the high to our north, an
onshore flow will develop, which may end up leading to more cloud
cover and cooler conditions. There could also end up being some
light rain and/or drizzle if enough moisture moves across the


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Widespread IFR ceilings are spreading over the region now, and
should continue through at least 15Z. There may be several hours
of MVFR conditions through the mid day hours, before ceilings
lower again to IFR near 00Z.

There is a chance for showers through out the TAF period,
bringing temporary visibility restrictions. Isolated thunderstorms
are possible too, but coverage is expected to be too limited to
mention in the TAFs at this time.

Winds will be easterly or northeasterly through the TAF period.
Sustained wind speeds of 10 to 20 kts possible with gusts up to 30
kt possible (highest gusts are expected to be at KACY primarily
this evening.


Friday-Saturday night...A prolonged period of MVFR or IFR conditions
with periods of rain is expected to affect the TAF sites through the
period. East to northeast winds are expected to gust 20-30 knots
for much of the area Friday, with the strongest winds near the

Sunday-Monday...Some improvement, possibly to VFR. Showers remain


The gale warning was extended for the coastal waters as the
latest guidance indicates that gale force gusts are possible
through at least the overnight hours tonight. Waves are expected
to build through the day and could approach 10 ft by this evening.


Friday...Gale Warning continues across the northern half of the
Atlantic coastal waters. Small Craft Advisory level likely to
remain elsewhere.

Friday night-Saturday...Winds expected to drop below Small Craft
Advisory levels overnight Friday into Saturday, however, seas may
remain above advisory levels through the period.

Saturday night-Sunday...Winds and seas expected to drop below Small
Craft Advisory levels.

Sunday night-Monday...Conditions expected to remain below Small
Craft Advisory levels.


There is a high risk for the formation of dangerous rip currents
along the NJ shore and the DE beaches today. Wave heights may even
approach 10 ft later today, but have held off on issuing a high
surf advisory as guidance is currently running a little high.


Have expanded the flash flood watch to include all of Delaware,
and extended all of the watch to continue through tonight.
Steering flow has been slower to shift than previously forecast.
As such, the heavy rain in our area has stayed confined to
Delaware through 3 AM, expect this to change through the early
morning hours.

Based on the latest guidance, it looks like there may be a bit of
a lull, especially with heavy rain, through the day time hours,
before picking up again this evening. As mentioned by the previous
shift, widespread 1 to 3 inches are possible, but shouldn`t cause
problems. The concern is with any embedded thunderstorms which
will produce locally higher amounts in a short period of time
(ones earlier tonight were showing rain rates upwards of 4 inches
per hour).


Departures on the low tide were one to two feet. It is unlikely
that departures for the next high tide will drop too much.
Therefore, issued a coastal flood advisory for the lower Delaware
Bay and all of the Delaware and New Jersey coast for both this
morning`s high tide as well as high tide this evening. Widespread
minor tidal flooding is expected with both. Some guidance even
shows moderate tidal flooding possible with this evening`s high
tide, and any heavy rain near high tide could exacerbate coastal
flooding. For now have held off on issuing a coastal flood warning
for the evening high tide as we should have a better idea on the
likelihood of moderate flooding once we see the departures with
the morning high tide.


September will be/is a top 10 warmest month through most of our
forecast area, for the 3rd consecutive month!

Also September will be/is enjoying a second consecutive top 5
warmest month in the period of record for PHL and ABE.

We`ve run the actual numbers through the 28th, then added the
forecast high/low for 29th and 30th.

Philadelphia: Expect a 73.8 degree average or about 5 degrees above
the monthly normal of 69.1. This will be a #4 or #5 warmest
September on record for Philadelphia.

Philadelphia September average temperature rankings

75.4 -1881
74.5 -2015
74.1 -1931 74.1 -1930
73.8 -2005 and 2016 #4

(small chance PHL avg will be 73.7 or #5 ranking)
72.9 -2010 72.9 - 1921

Philly ranked #7 warmest July followed by a warmest ever August in
the POR dating back to 1874.

Atlantic City: Expect a 71.2 degree monthly average temperature, or
4 degrees above the monthly normal of 67.2. This would equate to
an 8th warmest September in the period of record dating back to 1874.
Atlantic City recorded a #7 warmest July and then a warmest ever

73.3 - 1961
72.8 - 1881
72.3 - 1931 and 1930
71.7 - 1921
71.6 - 2015
71.5 - 1933
71.3 - 2005

71.2 - 2016 #8
71.0 - 2010
70.6 - 2011 and 1906

Allentown: Expect a monthly average of 69.4 degrees, or 5.5
degrees above the monthly normal of 63.9 and a 4th warmest
September on record. Allentown ranked 8th warmest July and #2
warmest August in the period of record.

70.8 - 1961
70.3 - 1980
69.7 - 2015
69.4 - 1931 and 2016

(small chance Allentown will rank #5 at 69.3 degrees)

68.7 - 2005

Daily rainfall records for September 29 where there is maybe a small
chance of exceeding:

PHL 1.87 1963
ILG 1.97 1963
GED 1.35 2015
RDG 3.55 1934


NJ...High Rip Current Risk through this evening for NJZ014-024>026.
     Coastal Flood Advisory until 11 PM EDT this evening for
DE...High Rip Current Risk through this evening for DEZ004.
     Coastal Flood Advisory until 11 PM EDT this evening for
     Flash Flood Watch through late tonight for DEZ001>004.
MD...Flash Flood Watch through late tonight for MDZ008-012-015-019-
MARINE...Gale Warning until 6 AM EDT Friday for ANZ452>455.
     Gale Warning until 6 PM EDT Friday for ANZ450-451.
     Gale Warning until 2 AM EDT Friday for ANZ430-431.


Near Term...Johnson
Short Term...Johnson
Long Term...Robertson
Tides/Coastal Flooding...Johnson
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