Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 271537
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1037 AM EST Fri Jan 27 2023

.SYNOPSIS...
High pressure centered to our south will dominate our weather
through Saturday. This high will retreat to the east by later
Sunday with a cold front moving through Sunday night into
Monday and then stalling near or just south of the region. A
series of disturbances are forecast to track north and east
along this frontal boundary next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
930 AM...Some shortwave energy influence remains over the
region. Very light snow/flurries were noted earlier over the
northwestern most counties of NJ and have since dissipated. Some
very light snow showers/flurries in the next few hours may move
into the southwestern most counties of NJ, New Castle County in
DE, and southeastern most counties in PA. These light showers
should weaken with time with no accumulation besides maybe a
trace to be expected. Otherwise, high pressure will build in to
our south over the southeastern states through the day today
resulting in generally tranquil weather. There will still be a
fair amount of strato- cu around near and north of the urban
corridor where skies will be partly to mostly cloudy with more
in the way of sunshine farther south towards the coast. The good
news is winds will be lighter compared to Thursday as the
pressure gradient continues to relax. Generally expect west
winds around 10 mph. Highs will be mainly in the upper 30s to
low 40s.

For tonight, high pressure remains centered to our south near
the Carolinas while a low pressure system moves by well to our
north as it passes eastward from northern Ontario into Quebec.
This will result in a warm advection pattern developing aloft
along with some mid and high cloudiness moving through. However
diminishing winds at the surface should help with modest
radiational cooling balancing out the warm advection so expect
lows mainly in the 20s to low 30s (similar to this morning`s
lows).

For Saturday, the high pressure system to our south moves eastward
off the east coast helping create a continuing warm air advection
pattern due to W/SW winds around 10 mph. This will result in a
moderating trend in temperatures with highs mainly in the upper 40s
to low 50s...so about 10 degrees warmer compared to today. The
day should begin mainly sunny followed by some increasing mid
and high clouds moving in by afternoon.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
High pressure remains in control Saturday night, keeping the
forecast quiet across the region. Offshore high will provide
weak warm air advection into the region overnight, in addition
to some mid to high clouds, helping keep temps fairly mild
overnight. Lows will generally be in the low to mid 30s.

For Sunday, ahead of a positively tilted upper- level trough,
surface low pressure is forecast to track to our west and north.
The energy overall looks to split with one low going to our
north and northeast and another one trailing to the southwest.
This should result in the more organized precipitation shield to
our west breaking up or splitting as it moves through our
region along with an associated cold front. We continue to
include slight chance to chance PoPs as the intensity of the
system moving looks to be on the weak side. Increasing southerly
winds ahead of the cold front will drive increasing warm air
advection. Despite clouds increasing during the day Sunday,
temperatures should get into the low to mid 50s across the
coastal plain (cooler along the coast however) and low to mid
40s north and west of the fall line. Temperatures Sunday night
will be milder for areas mainly south of the I-80 corridor with
lows in the 30s to near 40.

Come Monday, the departing weak low will pull a cold front
across our area. Additionally, the trailing low pressure system
across the Southeast will become more invigorated as the
positively tilted polar trough begins to dig. As a result, there
could be still enough lift to provide mainly some rain/showers
across especially the southern areas to start Monday. There may
end up being a lot of cloud cover lingering for much of the
region as well, and as a narrow but weak zone of high pressure
slides across our region that could be enough to break up the
cloud cover.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Summary...Active weather pattern will linger across the eastern
US through the end of the week. Colder air will be lurking to
the north/west and this may settle south depending on a storm
track centered Tuesday through Thursday.

Synoptic Overview...As more energy is shifted into western Canada
from the Pacific, more of a trough is across central to eastern
Canada with this dipping into the U.S. This setup tends to favor the
baroclinic zone shifting farther south and east and therefore
between the Ohio Valley and the Southeast U.S. The ensemble guidance
continues to show this overall pattern setting up, however there
remains differences in the handling of the Canadian trough and also
the southern energy. The northern trough however looks to drive low
pressure along a front and this may slide right across the Mid-
Atlantic region in the Tuesday through Wednesday time frame. One of
the questions is how much cold air can press southward and meet up
with moisture as this system slides on by. Given the trough that is
forecast, the surface low reflection should be a quick moving
system. The timing also varies at least some among the guidance.
Plenty of time to hammer out any details, however the pattern is
looking more favorable for energy sliding near or just to our south
with moisture potentially teaming up with colder air arriving from
the northwest.

Through Thursday...High uncertainty remains in the long-term
forecast period. The evolving pattern in the model guidance,
including ensembles, is pointing toward a farther south and east
storm track from what we have been dealing with. This is
courtesy of the storm track off the Pacific more into western
Canada, which drives more of a trough from central/eastern
Canada down into the eastern U.S. This tends to favor the
baroclinic zone setting up between the Ohio Valley and the
Southeast U.S. This shifting pattern, while is evident in the
guidance, carries differences regarding the timing and also
magnitude of southern energy sliding along a baroclinic zone.
There looks to be at least two waves that traverse the thermal
gradient corridor during this time frame, although the details
are much more less certain. What may occur is a series of weak
and strung out surface features tracking along the boundary,
however decent lift can accompany these especially along the
front and into the colder air to its north. With time however,
the baroclinic zone may be shoved farther south and east as the
upper-level trough shifts east and potentially strong/cold high
pressure builds in from the west.

The air mass to our north and west is forecast to becoming
increasingly colder with time. As a result, and depending on the
timing and track of the southern waves of energy, we may trend
colder into the second part of next week. Given the uncertainty, we
continued to stick very close to the National Blend of Models (NBM)
guidance.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Cloud cover will vary but generally will be most
widespread near and north of the I-95 TAF sites where once
again there will likely be a broken deck around 5 kft
developing. West wind around 10 knots. High confidence.

Tonight through Saturday...VFR with west winds to southwest
winds around 5 to 10 knots.

Outlook...

Sunday and Monday...Mainly VFR, however there is the chance for some
showers later Sunday into Monday. Southwest winds 10-15 knots Sunday
becoming west to northwest at night and diminishing, then north-
northeast winds around 10 knots Monday. Low confidence.

Tuesday...Sub-VFR conditions may develop along with a chance for
some rain/snow. Northwest winds around 10 knots. Low confidence.

&&

.MARINE...
Another period of Small Craft Advisory level conditions will be
possible for the ocean zones for the overnight period tonight into
Saturday morning as southwest winds increase to around 20
gusting up to 25 knots.

Outlook...

Sunday...Southerly winds may gust close to 25 knots for a time,
mainly on the Atlantic coastal waters.

Monday and Tuesday...The conditions should be below Small Craft
Advisory.

&&

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

&&

$$
SYNOPSIS...Fitzsimmons/Gorse
NEAR TERM...Fitzsimmons/Wunderlin
SHORT TERM...Gorse/MJL
LONG TERM...Gorse/MJL
AVIATION...Fitzsimmons/MJL
MARINE...Fitzsimmons/MJL/Wunderlin


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