Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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171
FXUS61 KPHI 291607
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1207 PM EDT Thu Sep 29 2016

.SYNOPSIS...
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
Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Noon ESTF: essentially no change to the qpf philosophy. 12z GFS
looks way underdone despite considerable instability aloft late
today with NW-SE PWAT axis through the Delmarva and Del Bay and
increasing to nearly 2 inches. Cold air damming front just off
the coast is going to be primary lift mechanism of the unstable
air in a continuing mdt waa pattern. looks to me like a 6 hr
period of R+ 00z-06z s De and 3 hrs in PHL around 09z-12z Fri.

1045 AM ESTF: Have upgraded to a coastal flooding warning tonight
based on modeled increasing ene flow this evening and increasing
positive surge departures over the last 15 hours. Standard warning
details will be added to the warning text once the advisory
portion this morning has been discontinued.

930 AM ESTF: No change in qpf thinking from the 8am below except
to reduce pops NNJ and far ne PA, also dropping small chance thunder
in a portion of that area. Have lowered temps and dews near and
north of I78. Have increased gusts 5 mph throughout the area.


8 AM ESTF: Thinking that guidance is constantly modeling max rainfall
far too far west. the increasingly ely inflow at the sfc this evening
combined with being closer to the sbli subzero and constant instability
aloft through Friday and increasing 850 inflow to -4SD as well as
growing pwat axis to 2" by morning suggests to me another 2-6" in
much of delmarva between 12z today and 12z Friday. That will
include more tstms.

RER`s already GED and will update this later today.

Dual pol STA looks much better than the legacy STP at DOX and DIX
for the Delmarva (DOX returned to service early yesterday
afternoon, missing the morning heavy rain that occurred MD e
shore). That means adding 70 to 90% to LEGACY output on the
DELMARVA should be helpful/useful reality.

8.5" max so far...isolated...more general 4-5 inchers parts of the
Delmarva.

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.

Tonight...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.

&&

.SHORT TERM /FRIDAY/...
A 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.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Unsettled weather continues to be forecast for much of the extended
period, especially the end of this week into the weekend.

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
area.

&&

.AVIATION /16Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Through tonight...MVFR cigs variable IFR conditions in showery
rains. e-ne winds gust 20-30 kt at times, with the gusts 30 kt
vcnty PHL/ILG and ACY. Iso thunder possible but not in the TAF
attm due to low confidence.

Friday...MVFR CIGS variable IFR conditions in stratus/periods of
rain-drizzle. East to northeast winds are expected to gust 20-30
knots for much of the area Friday, with the strongest winds near
the coast.

OUTLOOK...

Friday night-Saturday night...A prolonged period of MVFR or IFR
conditions with periods of rain is expected to affect the TAF
sites through the period.

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

&&

.MARINE...
GLW continued with verification of gales already most areas. Only
upper DE Bay waters have not yet verified and they may not til
late today.

May extend GLW in the 330 PM fcst through Friday for southern NJ
and extend NNJ into Friday night, in large part dependent on the
afternoon collaboration.

Waves heights 8 to 13 ft throughout through Friday morning slowly
subsiding late Friday.

Outlook...

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.

RIP CURRENTS...

There is a high risk for the formation of dangerous rip currents
along the NJ shore and the DE beaches today. Wave heights along
the coasts 5 to 9 feet.

Friday...Mount Holly`s last day of our daily 530am surf zone
forecast this year...probably high risk due to residual heavy
surf DE and ongoing easterly gale NJ.

&&

.HYDROLOGY...
Thinking that guidance is constantly modeling max rainfall far
too far west. The increasingly ely inflow at the sfc this evening
combined with being closer to the sbli subzero and constant instability
aloft through Friday and increasing 850 inflow to -4SD as well as
growing pwat axis to 2" by Friday morning suggests to me another
2-6" in much of Delmarva between 12z today and 12z Friday. That
will include more tstms. note a possible sfc trough just off the
mid Atlantic coast. That aids the lift near the Delmarva coast.
its usually the first lift area that gets the heaviest convective
associatedrainfall.

RER`s already GED and will update this RER later today.

Dual pol STA looks much better than the legacy STP at DOX and DIX
for the Delmarva (recall DOX came back on line early yesterday
afternoon, missing the Wednesday morning heavy rain that occurred
on parts of MD`s eastern upper shore). that means add 70 to 90%
to LEGACY out put on the DELMARVA should be helpful.

8.5" max (isolated in s DE), mostly 4`s and 5`s, so far.

00z/29 ECMWF max rainfall next 48 hours about 5" Md E shore.

&&

.TIDES/COASTAL FLOODING...
Have upgraded to a coastal flooding warning tonight ocean county
southward, based on modeled increasing ene flow this evening and
increasing positive surge departures over the last 15 hours.
Standard warning details will be added to the warning text once
the advisory portion this morning has been discontinued.

Expect a resurgence of inflow wind with gusts near 40 kt at the
time of this evenings high tide cycle.

Otherwise advisories continue as previously forecast today.

Minor tidal inundation flooding has to be occurring this morning
southern NJ and De coasts. The constant inflow may be making it a
bit worse in the back bays than on the coast.

Last evening ACY was a touch into flood at 712PM (6.35 MLLW with
threshold 6.3). This morning Atlantic City NOS registered 6.6Ft
MLLW or .3 ft over the threshold.

This morning Lewes DE registered 6.6` MLLW (threshold 6.3), Cape
May 7.15 ft (threshold 7 feet MLLW)

Since tonight`s high tide cycle is higher than that of this morning,
and inflow should be stronger, flooding will be worse...probably
half a foot to a foot deeper, and expect reaching MDT threshold s
NJ and De Atlc shores.

The following two high tide cycles Friday will probably endure
minor tidal inundation flooding.

Additionally...waves this morning were at least 7 to 8 feet on
the coast (BTHD1) and may grow to 10 feet tonight. This could add
splashover wave runup problems to the lowlands.

&&

.CLIMATE...
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
August.

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

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Warning from 6 PM this evening to 1 AM EDT
     Friday for NJZ020>027.
     High Rip Current Risk through late tonight for NJZ014-024>026.
     Coastal Flood Advisory until 3 PM EDT this afternoon for
     NJZ020>027.
     Coastal Flood Advisory until 2 AM EDT Friday for NJZ016.
     Coastal Flood Advisory until 4 PM EDT this afternoon for
     NJZ012>014.
DE...Coastal Flood Warning from 6 PM this evening to 1 AM EDT
     Friday for DEZ002>004.
     High Rip Current Risk through late tonight for DEZ004.
     Coastal Flood Advisory until 3 PM EDT this afternoon for
     DEZ002>004.
     Flash Flood Watch through late tonight for DEZ001>004.
     Coastal Flood Advisory until 2 AM EDT Friday for DEZ001.
MD...Flash Flood Watch through late tonight for MDZ008-012-015-019-
     020.
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.

&&

$$
Synopsis...Robertson
Near Term...Drag/Johnson  1207P
Short Term...Drag/Johnson
Long Term...Robertson
Aviation...Drag/Johnson/Robertson
Marine...Drag/Johnson/Robertson
Hydrology...
Tides/Coastal Flooding...
Climate...



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