Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 052030
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
330 PM EST Thu Dec 5 2019

.SYNOPSIS...
High pressure builds across our region tonight, then it slides
offshore early Friday. Weak low pressure quickly tracks just to our
north on Friday which pulls a cold front across our area. Strong
high pressure builds in Saturday before shifting offshore Sunday as
a warm front lifts to our north. Low pressure tracks from the
southern Plains to across the lower Great Lakes Monday through
Tuesday, with a strong cold front sweeping across our area later
Tuesday. A secondary cold front may move through Wednesday, then
high pressure builds in for Thursday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Building H5 heights and sfc high pressure nosing in from the South
will bring fair weather to the Middle Atlantic tonight. Clouds will
decrease this evening with mostly clr skies expected early tonight.
After midnight, some increase in clouds N/W is possible as the next
system will begin to make its presence known. No precipitation is
expected. Lows tonight will be cooler than previous nights with
widespread 20s, except for the more urban areas where lows around
freezing are expected. Winds will be mostly West at 5 to 10 mph this
evening then less than 5 knots later on.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
While an area of high pressure remains south of the area early, a
clipper low will be moving north of the area, across NY state.
Clouds and perhaps some light snows may brush across the southern
Poconos and north NJ associated with this system. We will keep some
small chc pops for these areas attm, but do not expect much to
occur. A cold front attached to the low will cross the area late in
the afternoon. The SW winds ahead of the front will switch to W
behind it and become gusty. Highs Friday will be a little warmer
than Thursday with upper 40s/low 50s for the southern areas and mid
30s to mid 40s for the southern Poconos/north NJ and the Lehigh
Valley.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Summary...Much colder air arrives to start the weekend, then turning
much warmer early next week in advance of showers and a strong cold
front. Much colder air then returns for Wednesday and Thursday.

Synoptic Overview...A short wave trough slides across the Northeast
and then off the New England coast Saturday morning. The digging
trough energy is then forecast to be focused initially across the
West and into the Plains over the weekend which then shifts eastward
early next week. This allows for significant warming to overtake our
region early next week. This warm up however is forecast to come to
an end as an amplifying trough drives low pressure to our northwest
Tuesday, with a strong cold front sweeping across our area later
Tuesday. High pressure then builds in Wednesday night and Thursday.

For Friday night through Sunday...An upper-level trough is forecast
to sharpen some as it moves across New England Friday night and then
offshore early Saturday. This will take a clipper system off to our
northeast with an associated cold front (mostly dry) shifting to our
east Friday evening. There could be some sprinkles/flurries early
Friday evening. Much drier low-level air and also strengthening cold
air advection follows this front through Saturday. High pressure
then builds over our area during Saturday before shifting offshore
into Sunday. After a cold Saturday into Sunday morning, a developing
return flow on the west side of the departing high will increase the
warm air advection some. In addition, a warm front lifts to our
north during Sunday and therefore Sunday afternoon will be milder
compared to Saturday. The leading edge of a surge in precipitable
water of around an inch arrives from the south toward daybreak
Monday with showers possible arriving then.

For Monday and Tuesday...An upper-level trough is forecast to
strengthen across the mid-Mississippi Valley Monday then track
northeastward across the eastern Great Lakes Tuesday. Meanwhile,
strong surface high pressure will be centered in the western
Atlantic. These two combined will assist to enhance the warm air
advection across the East ahead of a strong cold front. This is
anticipated to result in much warmer air surging across the area
until a strong cold front arrives later Tuesday. While this will
boost temperatures well into the 50`s, with even some lower 60`s
across portions of the coastal plain, increasing shower activity may
hinder the overall warming to some extent. A surge in showers/rain
still looks to occur during Monday within the warm sector regime and
a lead short wave, and this may arrive in our southern areas early
Monday morning as a surge in the precipitable water to around an
inch arrives. A second round of showers/rain then on Tuesday as the
strong cold front arrives, and even a rumble of thunder cannot be
ruled out. Some of the rain could be heavier given precipitable
water values in the 1.00 to 1.50 range. Showers should rapidly end
behind the front, then much colder air starts to surge into the area
Tuesday night as strong cold air advection sets up.

For Wednesday and Thursday...A strong eastern Canada upper-level
trough also slides across the Northeast. This will result in strong
cold air advection in the wake of the Tuesday cold front. This may
be reinforced by a secondary cold front on Wednesday before high
pressure builds in on Thursday. This translates to a return of
colder temperatures along with a gusty northwesterly breeze, with
the winds diminishing Wednesday night and especially Thursday. There
should be some lake effect snow off the Great Lakes, however at this
point in time given the forecast trajectory it should remain north
and west of our region.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR expected. Some cloudiness across the northern areas
early then mostly clear through the early overnight. Winds mostly W
or NW at 5 to 10 knots. Some increasing high/mid clouds late N/W.

Friday...VFR expected. Clouds across the north/central TAF sites,
but no precipitation is expected at the terminals. Winds become SW
during the morning and then shift back to W or NW by evening. Winds
speeds mostly around 10 knots but becoming gusty again by late
afternoon (for the 30 hr. PHL TAF).

OUTLOOK...
Friday night...VFR with clouds dissipating. Northwest winds 10 knots
or less. High confidence.

Saturday and Sunday...VFR. Northwest winds 5-10 knots becoming light
and variable Saturday night, then southerly 5-10 knots Sunday.

Monday and Tuesday...Sub-VFR conditions probable as showers/periods
of rain move across the region. South-southwest winds 10-15 knots
with gusts to 20 knots, becoming west and northwest later Tuesday.
Low confidence on timing and extent of sub-VFR conditions.

&&

.MARINE...
Tonight...We`ll keep the SCA flags in place with high-end SCA gusts
occurring on the ocean and SCA also across Delaware Bay. Winds will
decrease through the evening as a ridge of high pressure builds over
the waters. Seas will be mostly 3 to 5 ft early then 2 to 3 ft
overnight. Fair weather.

Friday...sub-SCA early, then increasing winds and seas late
afternoon following a cold front. More SCA gusts/seas possible then
but upcoming shifts can get a better handle on the timing and issue
any flags after the present ones come down. Fair weather
expected.

OUTLOOK...
Friday night and Saturday...Northwesterly wind gusts to around 25
knots are expected to diminish during Friday night and especially
Saturday as high pressure builds in.

Sunday...The conditions are anticipated to be below Small Craft
Advisory criteria, however a wind shift to more southerly will take
place.

Monday and Tuesday...Southwesterly winds should gust to Small Craft
Advisory criteria before shifting to the west and northwest later
Tuesday as a strong cold front sweeps through. The magnitude of the
wind is less certain given a warm air advection regime, and the
amount of wind increase will also affect the wave heights.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until midnight EST tonight for ANZ450>455.
     Small Craft Advisory until 7 PM EST this evening for ANZ430-
     431.

&&

$$
Synopsis...Gorse
Near Term...O`Hara
Short Term...O`Hara
Long Term...Gorse
Aviation...Gorse/O`Hara
Marine...Gorse/O`Hara


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