Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 110510

Area Forecast Discussion
National Weather Service Mount Holly NJ
1210 AM EST Wed Jan 11 2017

A warm front will continue to lift through our region overnight
tonight. A secondary warm front is expected tomorrow night. A large
high pressure system will build off the coast of the southeastern
United States before a cold front moves through Thursday night. High
pressure will then build across to the north of our area through the
weekend. A low pressure system will develop across the Ohio River
Valley and move through the Mid Atlantic late Saturday into Sunday.
High pressure returns for early next week.


The Winter Weather Advisory was extended for the counties along
the Berks to Sussex County, NJ line through 3 am. While many areas
are above freezing, with dew point temperatures below freezing and as
precipitation falls, temperatures could fall below freezing as
well. So there could remain some pockets of freezing rain for a
few more hours. There will also be pockets of sleet as well, so
this was added into the forecast. The  is expected to clear the
area between 2/3 am out west, and 5/6 am along the coast.


The warm front will have passed N/E of the area Wed morning. The
precipitation will end across the ern-most areas early then a slow
improvement is expected through the day as drier air arrives from
the S/W. The MOS guidance is quite a bit different with what happens
Wed with the NAM showing low clouds and fog much of the day and the
GFS offering mid-day fair weather across the Del Valley. With
limited confidence in any solution, I decided to bring the
improvement to the area, but a few hours later than the GFS is
indicating. Skies should become partly sunny by afternoon. Tomorrows
temperatures will depend on how fast things clear out, readings
rising to the upper 40s/low 50s are possible, so we have cautiously
sided with the GFS attm. Winds will be southwest to west at around
10 mph.


Wednesday night and Thursday...A secondary warm front lifts through
the region. As a result, Thursday will be quite warm - Forecast
highs are generally 20 to 25 degrees above normal and near records
at most of our climate sites (see the climate section for details).

Thursday night and Friday...models continued the trend with bringing
the cold front through Thursday night (a bit more progressive than
what we saw yesterday). As noted by the previous shift, frontolysis
is expected to be occuring as the front moves into our region. That,
combined with the fact that the associated low will stay well north
of our region, means that we probably won`t see a widespread precip
event for our region. None the less, there will still be some
significant cold air advection with the front as by Friday highs
will be about 10 degrees lower.

Saturday through Sunday...The cold front is still expected to stall
through this period, though exactly where it will stall is quite
uncertain as there remain large differences between the models on
the location of the stalled front. A pair of surface lows along the
front will  result in precip chances in the vicinity of the front,
but precip type is highly dependent on the location of the front, so
highly uncertain at this time.

Monday...By late Monday or Monday night, a surface low is expected
to lift out of the Midwest towards the Great Lakes Region, lifting
another warm front through our region.


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

Winds through tonight will be mostly South 10 to 15 knots but with
occasional higher gusts. Increasing and lowering CIGS with
precipitation arriving 04-05Z at ABE/RDG and a couple hours later
in the Delaware Valley. Most areas will just have rain but a
mix with freeing rain is possible at KRDG/KABE early. We went
along with the guidance which steadily lowers conditions to IFR

Wednesday, the speed at which things change from IFR/LIFR is the
biggest challenge for todays tafs. The NAM MOS has low conditions at
PHL for the entire day, while GFS MOS has a return to VFR by 15z.
Not a fcst with any great degree of confid after 12Z Wed, but
generally brought better conditions after 15Z-17Z across the area.


Wednesday night...Conditions falling to MVFR and IFR in rain.

Thursday...Conditions slowly improving to VFR. Small chance for MVFR
at KABE and KRDG with rain.

Thursday night...Low clouds, fog, and rain may bring conditions back
down to MVFR and IFR primarily for KRDG, KABE, and KTTN.

Friday...Mostly VFR conditions expected.

Saturday and Saturday night...Conditions expected to deteriorate as
precipitation moves back into the area. A wintry mix of
precipitation possible.

Sunday...small chance that precip may continue through the day.
Otherwise, conditions should gradually improve to VFR.


Approaching low pressure and a warm front will cross the waters
overnight. A warming flow associated with the low level jet will
become established across the cold waters tonight. The degree of
mixing is problematic and even a few well mixed gusts are enough for
gale flag criteria overnight. We have thus decided to upgrade the
Gale Watch for the northern NJ coastal waters to a Gale Warning and
also keep the SCA flag for the southern waters. The SCA flag was
extended into lower Del Bay also. Overall confid in fcst is moderate
at best. Winds will be mostly srly tonight and then shift to
southwest late and remain Southwest Wednesday. Gales will likely be
scaled back to SCA after the low level jet passes, and SCA
conditions will probably remain on the waters Wed morning. Rain and
fog expected overnight.


Wednesday night...Once winds and seas drop below SCA criteria by mid
day, no more marine headlines are anticipated through this period.

Thursday through Friday morning...South to southwest flow over the
ocean waters will start to build seas to 5 to 7 feet. Winds may gust
above 25 knots at times especially on Thursday, diminishing towards
Friday morning. A SCA will likely be needed.

Friday afternoon through Sunday...Winds and seas should stay below
SCA criteria.


Thursday should be quite mild with current forecast near record
highs for many of our climate sites. Here are the records for
January 12:

GED, MPO, TTN were updated at 515P.

Location/     Record/Year
Atlantic City/63/1913
Wilmington   /63/1913
Allentown    /60/1932
Reading      /61/1913
Georgetown   /70/1975
Mount Pocono /56/1975
Trenton      /68/1890

At this time, we are forecasting that Philadelphia
will stay well below its record of 72 set in 1890.

Also for todays 441PM CLI: we assumed .01 for the MPO 2 hrs of
snow with vsby variable down to around 2mi. At 9PM we received a
report fm Mount Pocono of 0.2 snowfall this afternoon, and also
saw a twitter report of a dusting in the Heidelberg/lehigh area.

The .29 at ABE was an obvious error.


PA...Winter Weather Advisory until 3 AM EST early this morning for
     Winter Weather Advisory until 5 AM EST early this morning for
NJ...Winter Weather Advisory until 3 AM EST early this morning for
MARINE...Small Craft Advisory until 1 PM EST this afternoon for ANZ431-
     Gale Warning until 7 AM EST this morning for ANZ450-451.


Near Term...AMC/CMS/Robertson/O`Hara
Short Term...CMS/O`Hara
Long Term...Johnson
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