Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 190921

Area Forecast Discussion
National Weather Service Mount Holly NJ
521 AM EDT Wed Oct 19 2016

High pressure will remain over the Southeast coast before moving
into the western Atlantic waters by the end of the week. Meanwhile,
a weak cold front will move southward through the region today and
tonight, before returning to the north as a warm front on
Thursday. Low pressure developing over the Ohio Valley will pass
to the north on Friday, dragging a strong cold front through the
region. High pressure then builds in from the south as low
pressure deepens to our north over the weekend.


3 AM surface analysis shows a 984 mb low east of James Bay. The
attendant cold front extended southward from low into New England
and then southwestward through north-central PA and the Ohio Valley
while a warm front was located over northern New England. Looking
downstream, a ridge axis associated with high pressure that was
centered east of the Canadian Maritime stretched southwestward
across the Southeast U.S.

The cold front is forecast to arrive in the Poconos by mid morning
and progress southward across eastern PA and NJ through this
afternoon. During this time, the forward motion of the front will
decelerate in response to the downstream ridge blocking and as the
boundary becomes increasingly oriented parallel to the zonal
steering flow aloft.

An organized band of showers once accompanied the cold front early
last night when it was well north and west of us but mosaic radar
loop over the past several hours shows this activity has steadily
dissipated as it advances downstream toward the area. Just about all
of the models depicted this downward trend in shower coverage. This
means a dry fropa across our area today.

Similar to yesterday, daily record high temperatures will likely be
tied or broken at many of our climate sites today. However, the
presence of a frontal boundary will provide some complexities to the
temperature forecast for today (especially compared to a relatively
straightforward forecast yesterday). Therefore, there is some
forecast uncertainty inherent with high temperatures. The arrival of
colder and drier air will lag behind the surface front, so thermal
advection will not be much of a factor except across the far north
this afternoon (north of I-80). Therefore, cloud cover appears to be
the one obstacle that could potentially preclude record-breaking
warmth in some spots.


The west-east oriented cold front will drift southward through the
Delaware Bay and lower Delmarva regions this evening. The surface
boundary may then stall or even start to return back northward late
tonight. Meanwhile, a wave of low pressure is forecast to organize
over Mid South and Ohio River Valley tonight. Isentropic lift in the
H9-H7 layer will ensue as the flow to the east of this developing
wave backs out of the south. There is still some discrepancies
between models regarding how quickly overrunning precipitation
develops in the vicinity of the front. We anticipate at a band of
light rain to develop by early Thursday morning somewhere between
ILG and ABE but PoPs were kept low due to  forecast uncertainty.

Forecast low temperatures range from the lower 50s in northeastern
PA-northwestern NJ (since cloud cover will arrive late in the
period) to the mid 60s from about the Philly metro southward (where
clouds will arrive much earlier in the night).

Surface winds will veer from north to northeast tonight as high
pressure builds southward from New England. Wind speeds will be 10
mph or less.


A cold front and low pressure across the Ohio Valley and a storm
offshore will eventually merge and become a strong system north of
our area this weekend. Clouds and shower chcs will increase from
Thu thru friday night. A strong cold front will cross the area Fri
night with showers likely. Above normal temperatures will continue
Thu and (to a lesser extent) Fri. Once the cold front crosses the
area, readings will turn sharply colder.

Showery weather with cool temperatures is expected Sat with
decreasing chc for showers Sat night and Sunday. The models are at
odds with how much moisture circulates across our region. The
ECMWF has more showers Sat across our area than its previous runs
while the GFS is notably drier. We will continue with mostly chc
or slgt chc for showers attm. Highs Sat and Sun will be in the
upper 50s north and low 60s elsewhere. These temperatures will be
several degrees below normal.

Mon and Tue will feature dry weather with cooler than normal temperatures
as high pressure builds across the area. Highs will again be mostly
in the 50s up north and low/mid 60s over srn NJ and Delmarva.


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

Fog development has been hindered by mid-level clouds that are
overspreading the area early this morning. Therefore, expect mainly
VFR this morning but there may be a brief opportunity for patchy fog
to develop at the fog-prone terminals toward daybreak. Have included
a two-hour MVFR TEMPO group at these sites. Winds will be 6 kt or
less from the SW thru 12Z.

VFR today with mid-level clouds passing thru. Winds 5-10 kt will
veer out of the W mid to late morning and then NW during the
afternoon as a cold front progress southward thru the region.

Lower clouds are expected  to develop over the southern terminals
(ILG-MIV-ACY) this evening and expand northward overnight. CIGs will
most likely be between 3500-5000 ft AGL. However, cannot rule out
MVFR restrictions early Thursday morning if CIGs lower a bit more
than forecast, especially if rain develops.


Thursday through Friday night...Showers developing on Thursday,
becoming more widespread into Friday, tapering off Friday night.
MVFR conditions likely, with the chance for IFR and lower.

Saturday through Sunday...Mainly VFR. NW winds with 25-35 KT
gusts possible.


SCA remains in effect for the northern coastal waters through 7 AM.
S-SW winds continue to diminish early this morning but seas are
hovering near 5 ft still. We may need to extend the SCA for a few
more hours this morning so we will continue to monitor the latest
trends in buoy observations.

A cold front will move southward through the waters tonight. SW
winds ahead of the front will become NW and then NE with speeds
under 20 kt.


Wednesday through Friday afternoon...Forecast winds and seas
below SCA criteria. Scattered showers Thu thru Friday.

Friday night through Sunday...A strong cold front passes across
the waters Friday night. Tight pressure gradient develops over the
weekend with winds gusting to at least 30 KT with the potential
for gale force wind gusts.

Sunday night...Winds and seas will drop back below SCA criteria.


Observed tidal anomalies are around two-thirds of foot above
astronomical normal early this morning. The ETSS guidance predicts
Cape May to reach minor tidal flooding threshold of 6.7 ft with
the upcoming morning high tide. Although this is below our
threshold to issue a Coastal Flood Advisory, spotty minor tidal
flooding may occur later this morning.

The same ETSS guidance indicates the potential for several of the
forecast sites along the oceanfront and lower Delaware Bay to
come within a tenth of a foot of minor Thursday morning.


The following sites tied or set daily record high temperatures
yesterday (Tuesday, 10/18)

New RecordOld Record
Allentown, PA8581 (1963)
Reading, PA8585 (1908) *record tied
Georgetown, DE8481 (1996)
Wilmington, DE8381 (1938)
Trenton, NJ8382 (1908)

Warmth of this magnitude seen yesterday (and potentially again
today) was/is a rare occurrence for this late in the year:

For Allentown, the only other year that recorded a high
temperature of at least 85 degrees this late in the calendar year
was 1947. In 1947, the high was 85 degrees on the 21st and 23rd of
October. Climate records at Allentown go back to 1922.

For Philadelphia, yesterday (10/18) marked the latest occurrence
in a calendar year with a high of 84 degrees or warmer since 1950
(it was 84 degrees on November 11, 1950).

Here are the record high temperatures for today (10/19)...and
across southern portions of the area on Thursday (10/20).

                   WED OCT 19     THU OCT 20

Mount Pocono, PA   80 in 1963     75 in 1963

Reading, PA        84 in 1963     80 in 1947/1953/1969

Allentown, PA      82 in 1963     78 in 1936

Trenton, NJ        83 in 1963     80 in 1969

Philadelphia, PA   80 in 1947     80 in 1916/1938

Atlantic City, NJ  80 in 1991     85 in 1987

Wilmington, DE     81 in 1963     82 in 1969

Georgetown, DE     81 in 1953     83 in 1953

Thursday is dependent on sunshine. For now, no daily record highs
are forecast but this could change in future forecasts. We`ve
left the records in this section since it could be with a few
degrees of the record at a few locations, especially south of

Monthly average temperatures are projecting 3 degrees or so above
normal, which would rank in the top 15 warmest Octobers at
Philadelphia and Allentown. This is stated with the usual mid
month uncertainty. What we do know is that the warmth of this week
will virtually lock in an above normal month, especially since the
pattern for the last week of October does not indicate any lengthy
period of below normal temperatures.


MARINE...Small Craft Advisory until 7 AM EDT this morning for


Near Term...Klein
Short Term...Klein
Long Term...O`Hara
Tides/Coastal Flooding...Klein
Climate...Klein is the U.S. government's official web portal to all federal, state and local government web resources and services.