FXUS61 KPHI 121657
Area Forecast Discussion
National Weather Service Mount Holly NJ
1157 AM EST Wed Dec 12 2018
High pressure will build into the area for today and tonight. A low
pressure system will move through the region on Thursday. An area of
low pressure will track through the deep south on Friday and into
the Mid Atlantic by this weekend. High pressure will then return
early next week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Clouds continue to spread SE across SE PA and Nrn NJ. we have
added some to the sky grids for the afternoon. Temps and winds,
overall, well behaved. Highs will be a few degrees short of
normal, generally topping off in the lower 30s in the Poconos to
the upper 30s north and west of the Fall Line, and in the lower
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
High pressure off the Mid-Atlantic coast continues to drift
offshore this evening. Meanwhile, weak surface low pressure with
a mid-level closed low and several strong shortwaves passing
through the Great Lakes will move into western NY/PA after
midnight tonight, then this low passes north of the region
during the day Thursday. Some light snow will move into western
portions of the forecast area prior to daybreak Thursday, and
then snow moves into most of the region Thursday morning.
Going through Thursday afternoon, winds become east-southeast.
Onshore flow will allow for warmer air to filter into the
region, and snow mixes with and changes to rain from south to
north during the afternoon. Temps should remain cold enough in
the southern Poconos to keep precip all snow.
For the most part, less than an inch of snow will fall along
and north of the I-95 corridor, but with colder temperatures in
the Poconos, up to an inch or so of snow accumulation is
Highs on Thursday warm into the low to mid 40s in SE NJ and
Delmarva, and in the upper 30s to low 40s in most of northern NJ
and southeast PA. Highs in the southern Poconos and far
northern NJ will top off in the upper 20s to low 30s.
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Thursday night...An upper low/open trough will exit to the east of
the region Thursday night. Model soundings show moist low levels
(dry upper levels so no ice in the snow growth zone), especially
across the southern Poconos and portions of the Lehigh Valley and
northwestern New Jersey. Could see some patchy drizzle occur through
the evening and into early Friday and have added it to the forecast.
With temperatures dropping, some areas may see some patchy freezing
Friday through Sunday...The next system of the extended starts to
develop in the deep south. This system starts to track up into the
southeastern United States by Friday night. As the low makes its way
to the northeast, a secondary low forms along the Carolina coast.
The GFS, Canadian, and the ECMWF show this low developing out ahead
of the stronger low to its west. But that is where the similarities
start to end. The ECMWF takes the coastal low and makes it more
dominant, weakening the inland low. This solution would have more
rain impact us from Friday night through Saturday and leave Sunday
mostly dry as the inland low tracks to the east and offshore (with
the center of the low remaining to our south). The Canadian keeps
the inland low suppressed to the south as the associated upper low
cuts off. The coastal low it moves quickly to the northeast, drying
us out by later Saturday, leaving Sunday dry. The GFS is by far the
wettest of these three models. It takes the coastal low up into our
area Friday night and Saturday and then takes the inland low on a
more northerly track into our area by later Saturday into Sunday.
With such diverse output from the this model run, confidence remains
fairly low. We continue to keep the highest chances for rain from
Friday night through Saturday and then only leave a slight chance
for some rain on Sunday. One good thing is all the guidance is
showing a warming trend so confidence is growing that we will see
mostly, if not all, rain with this event.
Monday through Tuesday...this period looks to be fairly quiet. The
GFS shows a cold front dropping down from the northwest later on
Monday while the ECMWF keeps any boundaries to the north of our
area. The GFS also shows a much deeper and stronger closed upper low
crossing the area while the ECMWF doesn't show much more than decent
trough rotating through. A few light showers may occur later Monday
but confidence is low as the models have widely differing opinions
on what to expect. For now, we will keep Monday dry and see if
things clear up a bit over the next few days. However, even if a
boundary moves through and is mostly dry, one thing the models are
consistent with this far out is that colder air will be arriving for
Tuesday. High pressure builds into the area on Tuesday and will
persist through the middle of the week.
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
This afternoon...VFR. SCT-BKN 4000 feet NE areas (including
KABE and KTTN). NW winds 10 kt or less, becoming LGT/VRB late
Tonight...VFR initially. CIGs lowering to around 5000 feet by
daybreak Thursday. Some light snow possible at KRDG/KABE after
09Z with MVFR or lower conditions. LGT/VRB winds.
Thursday...MVFR/IFR conditions in light snow in the morning,
then snow mixes with and changes to rain from south to north
during the day. Precip may stay as snow in KRDG/KABE for most of
the day. Light east-southeast winds.
Thursday night...Mainly VFR conditions expected. Light east
winds. Patchy drizzle/freezing drizzle possible at KABE/KRDG.
Friday...Mainly VFR early with conditions deteriorating towards
midday. Rain will develop by late morning and overspread the
terminals through the afternoon. East to southeast winds less
than 10 knots.
Friday night and Saturday...MVFR/IFR conditions expected.
Periods of moderate to heavy rain. East to northeast winds
around 5 to 10 knots, becoming more northerly later Saturday.
Sunday...Mainly VFR conditions expected. Northeast winds around
SCA flag taken down around noontime with winds and seas
continuing to diminish. Sub-SCA conditions on tap tonight
Thursday night and Friday...Sub-Small Craft Advisory conditions
expected. Southeast winds will increase through Friday and may
approach advisory levels late.
Friday night and Sunday...Small Craft Conditions likely. Seas will
build reaching 5 feet on the southern waters by late Friday night.
Winds will increase and exceed 25 knots with gale force gusts
possible late Saturday.
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