Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 210826 CCA
AFDPHI

Area Forecast Discussion...CORRECTED
National Weather Service Mount Holly NJ
326 AM EST Sun Jan 21 2018

.SYNOPSIS...
High pressure remains offshore of the southeast coast through
tonight. A back door cold front will approach the area from the
north through Monday, but likely not make into our area.
Meanwhile, a warm front will be moving into the area later
tonight and linger near the area through Monday night as an area
of low pressure moves through the Great Lakes. This low will
pull a cold front across the area early Tuesday as it moves into
southeastern Canada. High pressure will build across the area
for the end of next week.

&&

.NEAR TERM /THROUGH TODAY/...
High pressure over the Southeast U.S. will drift offshore as
low pressure over the northern Great Lakes will track to the
east and pass well north of the region today. Meanwhile, closed
H5 low over the Southwest U.S. will move into the Central and
Southern Plains, and surface low pressure intensifies over the
Oklahoma Panhandle and begins to lift to the north and east
later today.

Weak surface trough passes through the region this morning, and
weak CAA will allow for a cooler airmass to overspread the
region. However, late in the day, return flow sets up behind the
departing high, and WAA begins ahead of the developing low, as
heights and thicknesses rise. High temperatures today will be
cooler than Saturday, generally topping off in the low 40s in
the Poconos and northern NJ, and otherwise in the mid to upper
40s. Southeast NJ and the Delmarva will get into the low to mid
50s.

Morning cirrus will thicken throughout the day, and skies will
start out partly cloudy, and will become mostly cloudy through
the afternoon.

&&

.SHORT TERM /TONIGHT/...
Low pressure continues to develop and strengthen over the
Central Plains as it lifts to the north. Abundant moisture in
the 1000-700mb layer overspreads the region, and thicknesses
continue to slowly rise. Latest BUFKIT soundings keep surface
temperatures above freezing throughout, even in the Poconos and
northern NJ, so no major ptype issues, as precip will remain all
rain. With limited surface moisture and not much in the way of
upper level support, PoPs will be low, and not expecting much
beyond light rain and drizzle with the increasing moisture.

Lows tonight will range from the low to mid 30s north and west
of the Fall Line, and otherwise in the mid to upper 30s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
On Monday, low pressure will be moving through the mid-
Mississippi Valley. As this happens, the warm front across the
area will try to lift northward, but will likely not make much
progress as it remains dammed up across the area. Along and
north of where the frontal boundary stalls out, some light
rain/drizzle and patchy fog could remain through the day Monday.
It looks like temperatures will remain above freezing, so the
threat for freezing rain/drizzle has decreased. South of the
front, dry conditions will likely move back in and some clearing
may take place.

Overnight Monday into Tuesday morning, as low pressure moves
through the Great Lakes, the warm front will continue to slowly
move northward, before a cold front is expected to sweep across
the area. Again, north of the warm front, some light
rain/drizzle and patchy fog could remain into the evening. Then
as the cold front approaches and moves through the area, we
expect a period of moderate to heavy rainfall. Guidance is
showing the potential for some weak instability within the warm
sector across southern New Jersey and Delaware and Maryland.
So we have introduced isolated thunderstorms across these areas
during the morning hours Tuesday as the rainfall associated with
the frontal passage move through. Dry air will move in behind the
cold front during the afternoon. Winds will become gusty 20 to 25
mph behind the front as well.

For Tuesday night into Wednesday, the low pressure system moves
across eastern Canada, while a secondary cold front moves
across the area. We expect dry conditions across the area as any
precipitation is forecast to remain to our north. Gusty
conditions are expected on Wednesday as winds will be gusting at
least 25 to 30 mph.

High pressure returns for Thursday and Friday, but builds
offshore Saturday, leading to dry conditions through Saturday.
Winds will be less gusty than Wednesday, around 15 to 20 mph.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Cirrus clouds this morning will lower and thicken
throughout the day. Skies become OVC050 in the afternoon. Low
confidence that MVFR CIGs will develop in the afternoon, but
SCT025 possible. VRB winds 5 KT or less become SW less than 10
KT. High confidence.

Tonight...MVFR CIGs develop in the evening, becoming
BKN010-015. Light rain/drizzle possible, especially towards
daybreak Monday. S winds less than 5 KT. Moderate confidence.

OUTLOOK...

Monday...Sub-VFR conditions expected during the first half of
the day. Conditions likely improve during the day, especially
across southeast PA, southern NJ, and Delmarva. West winds may
gust 15-20 knots, especially PHL southward. Moderate confidence.

Monday night-Tuesday..Conditions lower to MVFR then IFR
everywhere with periods of rain associated with a frontal
passage. Conditions improve back to VFR behind the frontal
passage. Southeast winds become westerly behind the front and
begin gusting 25-30 knots. Moderate confidence. Low-level wind
shear is possible to develop Monday night into Tuesday morning.

Tuesday night-Thursday...VFR expected. Northwest winds with
occasional gusts Tuesday night, becoming more gusty 25-30 knots
Wednesday-Wednesday night. Less gusty around 20 knots Thursday.
High confidence.

&&

.MARINE...
Today...Sub-Small Craft Advisory conditions on tap for today.
High pressure over the Southeast U.S. continues to drift
offshore today. Meanwhile, a weak trough will pass through the
waters this morning. NW winds 10 KT or less will back to the SW
this afternoon.

Tonight...Conditions remain below SCA levels. SW winds less
than 10 KT, becoming 10-15 KT with gusts to 20 KT over DE ocean
waters by daybreak Monday.

OUTLOOK...

Monday...Conditions expected to remain below advisory levels,
but winds may periodically gust around 20 knots.

Monday night...Conditions expected to return to Small Craft
Advisory levels.

Tuesday-Wednesday...Small Craft Advisory level wind continue,
but may reach gale force.

Wednesday night-Thursday...Conditions likely to remain at Small
Craft Advisory levels.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Robertson
Near Term...MPS
Short Term...MPS
Long Term...Robertson
Aviation...Robertson/MPS
Marine...Robertson/MPS


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