Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 200123

Area Forecast Discussion
National Weather Service Mount Holly NJ
923 PM EDT Wed Oct 19 2016

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. At the same time, another area of low pressure will move
northward in the Atlantic and merge with the front in New England.
High pressure then builds in from the south as low pressure
deepens to our north over the weekend.


9:30 pm update:

Cloudcover will be slow to increase overnight ahead of a low
pressure moving northeast along a frontal boundary from the Ohio
Valley eastward across our region. This frontal boundary has led
to a sharp divide between a seasonable and a very humid airmass.
This will make a challenging forecast for dewpoints in the
overnight, dewpoints were raised quite a bit along the Jersey
coast based on the latest position of the front. The HRRR and RAP
are both showing enough moisture overruning the boundary to
develop some scattered showers toward daybreak along the Eastern
Shore that move northward during the morning hours on Thursday.
QPF continues to look very light overall. Temperatures also
started off the evening warmer than modeled but the slow increase
of cloudcover may compensate for the warmer start this evening.

Previous still applies:

Cold front through much of PA and into central NJ. With ridging
along the Mid-Atlantic coast, and high pressure anchored over the
Southeast U.S., it will be hard for that front to make much
southward progression tonight, but it should get through much of NJ
before stalling out across the Delmarva, most likely just north of
MD/DE and extreme S NJ.

Tonight, H5 trough with several strong shortwaves will dig into the
central U.S., and this combination will allow weak surface low
pressure currently over the Midwest to intensify as it lifts into
the OH Valley. As that low lifts to the north and east, the
stationary front over the Delmarva will begin to lift back to the
north as a warm front late tonight.

Latest model QPF fields keep much of the CWA dry, with only some
light precip encroaching into western zones late in the period.
Since there is not much support for precip across the region, will
go ahead and forecast dry conditions, with slight chance PoPs moving
into the Lehigh Valley and Pocono Mountains towards daybreak.

Clouds ahead of the low will spread into the region tonight, and
this should inhibit the development of fog.

Lows tonight will range from the low to mid 50s across far northern
zones to the low 60s across southern zones.


Deepening H5 trough will continue to dig into the Midwest and then
into the Great Lakes region throughout the day Thursday. Low
pressure continues to intensify over the OH Valley, and will lift
to the north and east throughout the day, mainly lifting into
western NY/PA. This will also continue to lift that warm front north
through the region.

In terms of precip, the heaviest of the rain will remain well to the
west, around the center of the low. But ahead of that low, and along
the warm front, rain will develop over eastern PA and into northern
NJ. Most precip will be light, and there is the possibility that
DE/MD, and most of NJ will be caught in the dry slot and not see
much, if any, precip. The bulk of the rain across the CWA will be
over the Lehigh Valley, Pocono Mountains, and into northern NJ,
where up to 1/4 inch QPF is possible.

With that warm front lifting to the north, southerly winds will
usher a warm airmass into the region. Northern areas will not be
quite as warm as southern areas, mainly due to rainfall, and highs
will top off in the low to mid 60s there. Temps will generally warm
through the 70s through SE PA and most of NJ, and will be around 80
across DE/MD.


At the start of the extendd pd, a complex wx scenario will be
setting up. A strong cdfnt will be approaching from the w Thu
night and low pres will be movg nwd in the Atlc. Attm, it appears
that the bulk of the precip with the cdfnt will stay to our w, but
the fropa will occur Fri or Fri eve. At the same time, the low
over the Atlc will merge with the front and move nwd and rapidly
intensify over New Eng.

So, it looks like there will be some rain chcs beginning Thu
night, with the best chcs on Fri and then tapering off Fri night,
though its psbl there could be some lingering pops into Sat AM,
especially n.

Then, the next story will be the gusty nw wind Sat into Sat night
before subsiding on Sun. The pgrad between the aforementioned low
and high pres overt the sern states will make for a stiff nw wind
that make it feel even colder than it is and with temps that will
struggle out of the 50s both Sat and Sun it will be a sharp
change, especially with the unseasonably warm wx we have had.

The high pres will then build in for the start of next week and
bring dry wx with temps at or slightly below seasonal values.


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

Cold front continues to slowly work its way south through the
region, and then will return north as a warm front on Thursday as
low pressure passes to the north and west.

VFR forecast for the rest of the afternoon and through tonight.
Not expecting much, if any, rain until after 12Z Thursday. CIGs
gradually lower to MVFR over KABE/KRDG by 12Z, and then MVFR CIGs
will continue to spread east through 18Z Thursday. Rain will
develop first over western terminals, and will spread east
Thursday morning. Possible that KMIV/KACY/KILG will remain dry
through the TAF period, and conditions at those terminals my
remain VFR through 18Z.

NW winds less than 10 KT, veering to the NE 5 KT or less through
this evening. Winds become E-SE 5-10 KT Thursday morning.


Thu night through Fri night...SHRA developing Thu night, becoming
more widespread into Friday, especially n, then tapering off
Friday night. MVFR conditions likely, with the chance for IFR and
lower. Moderate confidence.

Sat through Sun...Some MVFR psbl erly Sat, especially n, then
mainly VFR. NW winds with 25-35 KT gusts psbl. Moderate to high

Mon...VFR.  High Confidence.


Sub-SCA conditions on tap through tonight.

A warm front lifts north across the waters on Thursday. Gusts to 20
KT possible on northern ocean waters in the afternoon, but
conditions should remain below Small Craft Advisory levels.


Thu night through Fri afternoon...Forecast winds and seas below
SCA criteria. Scattered showers Thu thru Fri.

Fri night through Sun...A strong cdfnt passes across the waters
Friday night and strengthening low pressure moves into ern Canada
with high pres building to the sw.  Tight pressure gradient
develops over the weekend with winds gusting to at least 30 KT
with the potential for gale force wind gusts, especially Fri night
thru erly Sat night, then wind subsiding to SCA on Sun.

Sun night and Mon...Winds and seas will drop back below SCA


The following sites tied or set daily record high temperatures
today (Wednesday, 10/19)

New RecordOld Record
Allentown, PA       84          82 (1963)
Trenton, NJ         86          83 (1963)
Philadelphia, PA    86          80 (1947)
Atlantic City, NJ   86          80 (1991)
Wilmington, DE      87          81 (1963)* record tied
Georgetown, DE8681 (1953)

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.

Here are the record high temperatures for Thursday (10/20).

                   THU OCT 20

Mount Pocono, PA   75 in 1963

Reading, PA        80 in 1947/1953/1969

Allentown, PA      78 in 1936

Trenton, NJ        80 in 1969

Philadelphia, PA   80 in 1916/1938

Atlantic City, NJ  85 in 1987

Wilmington, DE     82 in 1969

Georgetown, DE     83 in 1953

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.




Near Term...Gaines/MPS
Short Term...MPS
Long Term...Nierenberg
Tides/Coastal Flooding...
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