Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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899
FXUS61 KPHI 160701
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
201 AM EST Thu Nov 16 2017

.SYNOPSIS...
A cold front moves across our area this morning, then high
pressure builds during Friday. A warm front lifts to our north
Saturday, followed by a cold front Saturday night. High pressure
then builds to our south Monday into Tuesday.

&&

.NEAR TERM /THROUGH TODAY/...
1230 AM ESTF. New 330 am forecast issued. Please see below.

Prior to 7 AM...Bands of showers preceding the cold front will
probably intensify as they exit NJ around 6 am. Patchy fog may
develop around 6 or 7 am as the drying aloft arrives e PA and e
MD with the light south wind trending west at that time in e PA
and e MD. Mild.

Today...any remaining showers and sprinkles exiting e Nj at 12z
is followed by clearing and with the mild start...temps will
rise into the upper 50s/lower 60s I95 corridor eastward...not
quite as mild to the west of I95. A 150m 12 hr HFC will pass
through ne PA or se NYS around 18-20z and both the HRRR and
HRRRX have a band of showers developing ne PA around 17z exiting
NNJ around 20z. This band is in the grids-fcst (WINDEX like
with steep somewhat moist low lvl lapse rates - Tsection pf both
NAM and GFS show this nicely--tops below 15000 ft) and
thereafter, pretty strong cold advection ensues with gusty west
northwest winds to 30-35 MPH mid and late afternoon just about
everywhere.

Forecast basis was the 00z/16 50 50 blended GFS/NAM MOS. I had
to raise the wind gust tool manually by about 5 kts during mid
and late afternoon per the NAM transfer signal.

(I do realize the wrong decision ydy at 3 am on skycover - NAM
was biased high in the morning resulting temps 1-2F warmer than
fcst and the NAM 2m temps were poor ydy).



&&

.SHORT TERM /TONIGHT/...
Mostly clear and breezy with rising heights at aloft (500mb)
and not much radiational cooling. West-northwest wind gusts
20-30 mph most of the night... well up in the 30s over the
Poconos and terrain above 1500 feet far nw NJ. There could be
some sprinkles and flurries in the Poconos during the evening.

The basis of this part of the forecast was a 50 50 blend of
00z/16 GFS/NAM MOS tending to just use the 3hourlies to fcst the
low temp. This forecast may be a degree or two on the cold side.
Tsection shows this nicely with any echo tops probably below
12000 ft.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Summary...Strong cold front moves through Saturday night with
milder air ahead of it, followed by colder air and gusty winds.

Synoptic Overview...A strong upper-level trough lifts out on
Friday. Some weak ridging then arrives, but another upper-level
trough quickly arrives Saturday night into Sunday. As more
pronounced ridging moves across west-central Canada, a
downstream trough is forecast to begin amplifying across the
Great Lakes and Northeast Tuesday. The flow aloft overall looks
progressive for awhile, however there are signals that next week
may feature more amplification with a trough settling into the
East.

For Thursday night, the winds will diminish some, however given
the continuation of cold air advection in the lower levels and
the pressure gradient remaining tight this process may be
slowed.

For Friday and Saturday...The strong upper-level trough moves
away during Friday with the flow becoming more zonal. High
pressure at the surface builds across our region Friday which
will result in less wind through the day. It is noted that the
stat guidance especially is warmer for Friday, however the
modeled 2 meter temperatures are colder. The latter is rather
close to our going forecast, and therefore we opted to make
little in the way of changes. Clouds increase Friday night ahead
of the next incoming upper-level trough. There is fairly strong
warm air advection in advance of this, allowing a warm front to
become better defined as it lifts northeastward. This should
produce a zone of showers or rain along and to its north,
however this appears to be slower in the guidance overall as we
go through Saturday. As a result, we slowed down the PoP
increase from west to east Saturday. Low pressure is forecast to
strengthen as it lifts across the eastern Great Lakes region
Saturday morning and then into Canada. The associated cold front
sweeps through our area Saturday night. Increasing southerly
flow ahead of the cold front Saturday will drive milder air into
the region, then be replaced by west to northwest winds behind
the frontal passage. We continue to bring in likely to
categorical PoPs through Saturday night. Given the timing, held
off in adding thunder.

For Sunday and Monday...While some showers may linger early
Sunday as the cold front shifts offshore, drying is expected.
Low pressure tracks near northern New England Sunday, with a
tight pressure gradient in place along with cold air advection.
Sunday is looking like another breezy/windy day as mixing
deepens during the day. The air turns colder and therefore lake
effect snow should develop off the eastern Great Lakes. It is
possible that a streamer attempts to approach the Poconos later
Sunday afternoon and evening. The winds should diminish at least
some Sunday night. High pressure starts to build in during
Monday, however its center is to our south- southwest. Overall,
a cold day is expected Monday.

For Tuesday...Renewed upper-level trough development is
forecast to take place into the Northeast. This drives low
pressure once again near and north of the Great Lakes with a
trailing cold front approaching from the west. As the flow backs
in response to this system, some warming will be draw
northward. The main forcing with this system may end up lifting
to our north, therefore continued with a dry forecast at this
time.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Early this morning prior to 12z...VFR cigs with a light south
wind except brief MVFR conds in showers. Wind turns light
southwest to west near 11z over e PA and e MD and there may be
some patchy MVFR fog. Confidence: Average.

After 12z today...VFR sct-bkn bkn aoa 4000 ft with chc of a
brief MVFR vsby shower in the 118z-20z time frame
KRDG/KABE/KTTN/KPNE as the trough axis aloft passes by, then a
west northwest wind develops with gusts to 25-30 kt by 21z most
TAF sites. Confidence: Above average.

Tonight...VFR clear or sct clouds aoa 5000 ft. a gusty west
northwest around 20-25 kt should subside near 11z/Friday
morning.  Confidence: Above average.



OUTLOOK...
Thursday night...VFR with winds diminishing. Moderate
confidence.

Friday...VFR overall, then clouds increase and lower some at
night. High confidence.

Saturday...A period of MVFR/IFR conditions with showers,
especially in the afternoon and at night. Some improvement in
the conditions should occur late at night as a cold front moves
through. Moderate confidence.

Sunday...VFR overall. Some flurries or snow showers possible in
the afternoon mainly north and west of ABE. Northwesterly winds
15-20 knots with gusts up to 30 knots. Moderate confidence.

&&

.MARINE...
SCA being forsaken for simplicity to a gale warning beginning
around 21z all waters and not ending til 11z Friday. Looks like
steepest lapse rates are in the 00z-03z/17 time frame (this
Thursday evening) with a last gasp burst of gale gusts expected
around 09z/17 (4 AM Friday). greatest confidence for verifying
is lower De Bay and the coastal waters of NJ.

Least confidence is vcnty buoy 44009 (ANZ455). 

We appreciate LWX having issued the warning ydy aftn, in the
interest of customer lead time planning for a probable gale
event of 34-40 kt gusts for at least two hours in a 12 hour
period.

OUTLOOK...
Friday...Gale force gusts within a northwesterly flow may
linger Friday morning, however the winds are expected to be
diminishing.

Saturday and Sunday...Gale force gusts from the southwest are
possible Saturday afternoon and evening, then gale force gusts
from the west and northwest are possible later Saturday night
and Sunday.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 6 AM this morning to 6 PM EST this
     evening for ANZ430-431-450>453.
     Gale Warning from 6 PM this evening to 6 AM EST Friday for
     ANZ430-431-450>455.
     Small Craft Advisory until 6 PM EST this evening for ANZ454-
     455.

&&

$$
Synopsis...
Near Term...Drag  2a
Short Term...Drag 2a
Long Term...99
Aviation...Drag/99 2a
Marine...Drag/99 2a



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