Area Forecast Discussion
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FXUS61 KPHI 081445
Area Forecast Discussion
National Weather Service Mount Holly NJ
945 AM 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 /THROUGH TONIGHT/...
930 AM ESTF: little change to the 735 AM update. 12z version of
the NAM/HRRR and reality observed data continue to advertise a
period of light showers for the Delmarva into midday asstd with
trough aloft and 100m+ 500 mb hfc heading east from OHIO Valley w
PA this morning and the asstd sfc wind convergence.
Gusty west wind to 25 MPh developing mid afternoon.
Highs were raised a deg or 2 for mid afternoon highs subsequent
to the abrupt west to east clearing expected Noon-2PM.
Tonight...from the mid shift and will update at 2 PM. colder air
will continue to settle in over the region thanks to the continued
northwesterly flow (and associated cold air advection). The
pressure gradient across the region will continue to increase as
the trough moves further east, so winds are not expected drop off
much overnight. This will mean we won`t have efficient radiational
cooling conditions, but given the cold air advection, lows tonight
will as much as 10 degrees lower than what we will see this
.SHORT TERM /FRIDAY/...
Cold air advection and streamers from the Great Lakes as well as
cold trough aloft increase the snow squall probabilities tomorrow
and so at least sct flurries. W ill update the details at 2 PM.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
FB posted and tweeted WPC mid shift Day 4 winter prob 1/4" w.e.
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 /15Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Today...VFR cigs aoa 4000 ft this morning becoming sct clouds this
afternoon. scattered brief shower for an hour or two near and south
of KMIV later this morning. west wind with gusts increasing 22 to
28 kt during mid afternoon.
Tonight...VFR mostly clear. wnw wind with scattered gusts 15 kt
Friday...Generally VFR sct-bkn aoa 4000 ft, although CIGS may
briefly lower to MVFR in scattered snow showers e PA nigher
terrain. 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.
Winds will increase around midday today for what will be a prolonged
small craft advisory event.
Considered a gale warning for lower De Bay and adjacent 453, 54,
55 for the prd 21z today - 11z Friday. Am pretty sure we`ll see
mid 30 kt gale gusts some time this evening but no issuance at
this 930 am issuance, at least not until can categorically be
sure. 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 but no decision until late today.
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 ANZ430-431-
Near Term...Drag/Johnson 945A
Short Term...Drag 945A
Long Term...Robertson/Drag 945A