Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
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FXUS61 KPHI 082010
Area Forecast Discussion
National Weather Service Mount Holly NJ
310 PM EST Thu Dec 8 2016
An area of low pressure will continue to slowly drift across eastern
Canada today through Friday, and end up south of Greenland by
Saturday. With high pressure to our west, a strong west to northwest
flow will remain through the end of the week. High pressure briefly
affects the area Saturday night, then moves offshore Sunday. A warm
front is expected to lift across the area Sunday night, before an
area of low pressure is forecast to move near or just north of the
area around Monday. This system will pull a cold front across the
area Monday, then another quick moving frontal boundary may move
across the area around Tuesday night.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Morning summary: had a smattering-scattering of .01 rainfall this
morning southern 2/3rds De and a ptn of Md E shore.
Remainder of this afternoon...west wind will continue increasing
to 22-28 kt around 21z then should decrease after sunset but PHL
may gust 18-20 kt all night.
Tonight...mostly clear with a light west-northwest breeze except
PHL may gust 18-20 kt all night as well as adjacent all bodies of
water as boundary layer temps show increasing land-sst differential
and resultant enhanced land breeze effect, near the water.
Exception to the mostly clear skies: near the Poconos where lake
effect clouds arrive and then flurries should eventually develop
there sometime tonight.
Fcst was a 50 50 blend of the 12z gfs/nam mos guidance.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Cold air advection and lake effect streamers of moisture, flurries
and snow showers from the Great Lakes combined with the cold
trough aloft increase the snow squall probabilities tomorrow and
so at least sct flurries to near I-95 (not expecting flurries or
sprinkles along the coast) and suspect small accumulation in
parts of poconos Friday afternoon. A snow map will post shortly
followed by snow probs around 5PM for this first little terrain
related accumulation event.
otherwise...mostly sunny skies to start (mo cloudy Poconos) becomes
considerable cloudiness everywhere during the afternoon. Breezy
with west northwest wind gusts 25 to possibly 30 mph.
FCSt basis was a 50 50 blend of the 12z gfs/nam MOS and added a
degree to the max T per the 12z/8 EC 2m temps.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
FB posted and tweeted WPC mid shift Day 4 winter prob 1/4" w.e.
outlook. Briefing package will post on the web tomorrow.
Low pressure continues to drift across eastern Canada Friday, then
moves offshore and ends up south of Greenland by Saturday. Meanwhile
high pressure remains across the central part of the country. This
will keep a steady west to northwest flow across the area. On
Friday, although the strong vorticity impulse is expected to be east
of the area, there will remain steep low-mid level lapse rates
across the area with enhanced moisture as well. With the strong
northwest flow, it is possible that some lake effect streamers could
set up and bring some snow showers/flurries to portions of the area.
The best chances would be across the northern portions of the area,
so we keep scattered/isolated snow showers/flurries there. Elsewhere
we will keep isolated flurries/sprinkles. On Saturday, the steep
lapse rates and moisture combination lifts northward some. We`ll
keep isolated snow showers/flurries for the far northern counties,
but will keep flurries/sprinkles for the middle half of the area as
the northwest flow begins to weaken some, so the flurries may not
have as great of a reach southward as on Friday. While most areas
probably won`t see much snow accumulation Friday and Saturday, if
any snow bands or squalls do develop, it would not be surprising
to see some accumulating snow in some areas.
High pressure briefly affects the area Saturday night, providing dry
conditions. Friday and Saturday will be a cold and windy period,
with Friday being the windiest, and Saturday being the coolest of
The high builds offshore Sunday ahead of the next storm system. As
this happens, it is possible that some showers could develop
during the day across the area as a short wave passes just to our
north and spreads an area of moisture across the area. However,
the best chance of precipitation looks to be Sunday night into
Monday. A warm front is forecast to lift across the area late on
Sunday night into Monday as an area of low pressure is forecast to
move near or just north of the area. Conditions should be cold
enough overnight Sunday into Monday for a period of snow to affect
a good portion of the area, before much of the area warms up and
precipitation turns to rain during the day Monday. There is the
potential for an accumulating snow for much of the area, with the
northern half having the greatest potential. As the low continues
to lift northward, a cold front is expected to move across the
area late in the day Monday and overnight. Precipitation chances
should diminish behind the cold front.
On Tuesday and Tuesday night, the GFS is indicating another cold
front moving across the area as low pressure passes to our north.
It in turn brings a period of rain and snow to the area late Tuesday
into early Wednesday. The ECMWF does not have as strong of a cold
frontal passage, so it does not bring any precipitation to the area.
For now, we`ll introduce a small chance into the forecast.
.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Remainder of this afternoon...VFR sct clouds aoa 4000 ft. West wind
with gusts increasing 22 to 28 kt by 21z. Already 25 kt PHL.
Tonight...VFR mostly clear. wnw wind with scattered gusts 15-20
kt, mainly PHL area.
Friday...Generally VFR sct-bkn aoa 4000 ft, although CIGS may
briefly lower to MVFR in scattered snow showers e PA nigher
terrain. An afternoon flurry or sprinkle is possible to ILG-PHL-
TTN. Gusty west to northwest winds 22-30 knots.
Friday night - Saturday...Generally VFR, although CIGS may
occasionally lower to MVFR. Scattered showers or
flurries/sprinkles are possible during the daytime of each day
which may temporarily lower conditions. Gusty west to northwest
winds 15-25 knots, strongest winds Friday which may approach 30
knots at times.
Sunday...VFR early, possibly lowering to MVFR by the afternoon. Rain
or snow possible late in the day.
Sunday night-Monday...Conditions continue to lower to MVFR and then
IFR. Rain or snow becoming likely. Accumulating snow possible for
eastern Pennsylvania, much of New Jersey, and the northern portions
of the Delmarva.
Gale warning posting momentarily for lower De Bay and adjacent
DE, Cape May waters. and a gale watch is posted for Fri-Fri eve
per collab with OKX.
Many reports 29kt upstream.
The wind orientation down De Bay, steep lapse rates possibly
manufactures several more kts of wind than modeled in the caa
pattern. NAM sounding indicates mid 30s gales possible.
May need a marginal mid 30s gale for the remainder NJ waters 10z
Friday - 06z Saturday and issuing a watch for that area shortly.
Friday night-Saturday...Small Craft Advisory in effect through
Friday night, which may need to be extended into Saturday. Winds
may approach gale force at times on Friday.
Saturday night...Winds expected to drop below Small Craft Advisory
levels, but pick up again late Sunday.
Sunday-Sunday night...Winds may increase and approach Small Craft
Advisory levels at late in the day into the overnight.
Monday...Small Craft Advisory conditions possible.
MARINE...Small Craft Advisory until 6 AM EST Saturday for ANZ430-
Gale Warning from 6 PM this evening to 6 AM EST Friday for