Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
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FXUS61 KPHI 070229
Area Forecast Discussion
National Weather Service Mount Holly NJ
929 PM EST Tue Dec 6 2016
High pressure over the northeast will give way to developing low
pressure off the Carolinas into tonight. Meanwhile, low pressure
nearing James Bay sends a cold front thru our area on Wednesday,
sweeping the Carolinas low well offshore. The low pressure over
James Bay will move to Atlantic Canada into Friday, while high
pressure over the central United States moves into the middle
Atlantic this weekend. A warm front may approach our region by
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
9:30 pm: Conditions are largely unchanged from an hour ago.
However, the back edge of the rainfall is entering the region now
and precipitation will be ending in the next couple of hours and
likely end as drizzle or freezing drizzle where temperatures are
below freezing. A slow warming trend is still expected over the
next few hours. Top snow amounts were raised to around 5 inches
8:30 pm update: Low level cold air with temperatures near
freezing on many mesonet obs is still ongoing from Northampton
countyeastward toward Morris county. SPC mesoanalysis shows both
the 925 MB 0C line and the 850 MB 0C line have already advected
north of these locations. SO the precipitation will likely be
freezing rain for the next few hours before temperatures slowly
overnight. The winter weather advisory has expanded into portions
of the Lehigh Valley and Northern New Jersey through 1am.
6:30 pm update: Brightbanding on radar coupled with numerous
ground reports show sleet to be falling across many locations in
the Lehigh valley, NW suburbs of philly and northern New Jersey. A
minor accumulation of sleet was added to the forecast with this
update for those locations. A spotter in Sussex county indicated
that the elevation cutoff is about 900 feet for the snow/no snow
cutoff in the areas that are expecting elevation dependent
accumulating snows. Top amounts look to be slightly higher with a
little more QPF in the forecast now, around 4 inches at Mount
Pocono. An updated snow map was sent to our website.
3:30 main forecast:
A double-barrel low pressure system is
expected to combine energy off the Carolina coast this evening,
then intensify before the system moves slowly northeast out over
the Atlantic on Wednesday. Precipitation associated with this
system has already overspread the CWA this afternoon, with a brief
period of sleet reported on the leading edge. The atmospheric
profile still looks conducive for snow in the far north
(Carbon/Monroe/Sussex counties), especially in the higher
elevations, and since current QPF guidance is similar to previous
runs, 2 possibly up to 4 inches mainly above 1000 feet still looks
plausible, with several hours of moderate snowfall possible in
those areas this evening. The current Winter Weather Advisory will
therefore continue through the overnight hours. Easterly winds
this afternoon generally under 10 mph are expected to veer to the
northeast during the overnight hours as the speed increases to
around 15 to 20 MPH with higher gusts near the coast. Areas that
see mainly rain (generally south of I-80) can expect around one-
half inch of precipitation from this event, with light rain or
drizzle after midnight.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
As the low continues to move out to sea, precipitation will end
during the morning hours basically from southwest to northeast...and
any remaining wind gusts (especially closer to the coast) will
gradually diminish as the pressure gradient relaxes. Expect cloudy
conditions in the morning...with gradual improvement from west to
east as the day wears on. Northwest winds are expected around 10
MPH...perhaps slightly stronger along near the coast.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Temperatures will continue to be mild on Thursday, ahead of an
approaching cold front. Models are in better agreement backing
off on precip for Thursday however will hold on to a slight chance
of rain due to increasing moisture. The long wave trough and
attendant cold front continues east, pushing the cold front across
the the region late Thursday into Thursday night.
High temperatures on Friday will be mainly in the 30s to lower
40s. A few snow showers occuring beneath the cold mid level
trough and downstream from the Great Lakes may make it into the
far northwest corner of the forecast area on Friday, mainly
northwest of I-95-276-76 where the BTV Snow Squall Parameter
values are the highest. Models are also in a little better
agreement bringing precip in Sunday night into Monday. The cooler
temperatures will continue into Saturday.
Models are also in a little better agreement for early next week.
bringing the next storm system across the region late Sunday into
Monday. GFS thermal profiles support wintry precip initially with
a changeover to rain Monday, while the slower ECMWF is much
warmer, suggesting a primarily rain event. Given the antecedent
cold air mass in place, wintry precip is plausible at the onset,
with a changeover to rain.
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
IFR conditions are still expected to become predominant through
the evening hours at many TAF locations as bands of moderate rain
move through. ..but no major problems are expected. Rain is
expected to taper off from SW to NE late tonight, but low clouds
will remain over the area through a good portion of the overnight
hours, with lingering IFR conditions.
NE winds around 10 kt with higher gusts closer to the coast are
expected tonight. Northwest winds in the 5 to 10 KT range are
expected on Wednesday as the low continues to move out to sea. A
slow improvement to MVFR around noontime and VFR by sunset is
Predominantly VFR at all TAF sites through the period.
Northwest winds may gust up to around 25 knots Thu night into
A Gale Warning continues for tonight for the coastal waters of DE
and S NJ as well as the lower DE Bay as easterly winds strengthen to
the north of the coastal low. Obs the last few hours indicate
gusts are getting close to gale force, will continue with the
current warning. A SCA continues for the northern coastal waters
and for the upper DE Bay with gusts 25-30 kt possible tonight. 4-7
ft seas are expected in response to the strengthening wind field
with the higher seas the further south you go. Although northwest
wind gusts are expected to remain below 25 knots on Wednesday,
seas are forecast to remain elevated, at or above 5 FT. Thus, a
Small Craft Advisory for hazardous seas may be needed for the
Gusts over 25 knots from the northwest are likely Thursday night
and Friday with some potential to reach gale force. Winds will
decrease on Saturday below 25 knots from the northwest. Seas are
likely to remain below five feet for the outlook period.
PA...Winter Weather Advisory until 1 AM EST Wednesday for PAZ062.
Winter Weather Advisory until 6 AM EST Wednesday for PAZ054-
NJ...Winter Weather Advisory until 1 AM EST Wednesday for
Winter Weather Advisory until 6 AM EST Wednesday for NJZ001.
MARINE...Gale Warning until 6 AM EST Wednesday for ANZ452>455.
Small Craft Advisory until 6 AM EST Wednesday for ANZ450-451.
Small Craft Advisory until 4 AM EST Wednesday for ANZ430.
Gale Warning until 4 AM EST Wednesday for ANZ431.