-- Discussion containing changed information from previous version are highlighted. --
227
FXUS61 KPHI 221121
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
621 AM EST Wed Jan 22 2025

.SYNOPSIS...
Arctic high pressure centered in the Ohio Valley this morning will
build over our area later today and tonight before moving offshore
into Thursday. A weak system is expected to remain offshore
Thursday, then a weak cold front moves through later Friday. High
pressure crests across our area Saturday before shifting to our
south, then a cold front arrives later Sunday. The front may stall
in our vicinity as an area of low pressure develops along it Monday
into Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
The bitter cold snap continues. Skies gradually clear out as a
strong upper level jet pushes east, taking the high clouds with it.
OKX`s 00z sounding sampled 200 kt at 250 mb! The Extreme Cold
Warning in the Poconos and the Cold Weather Advisory remains in
effect through noon today.

For today, high pressure moves in from the west, and will be
directly overhead by this evening. This will result in mostly sunny
skies for today. Cold temperatures will continue though as the
arctic airmass keeps its stranglehold over the eastern US. Highs
today will only be in the upper teens/low 20s with low to mid teens
in the Poconos and higher elevations of northern New Jersey.

For tonight, high pressure slides offshore, which will foster in a
light south/southwest flow. Mid to high level cloud cover will
increase as a weak positively tilted trough moves toward the region.
This will be accompanied by a decaying area of low pressure that
will devolve more into an open wave by the time it gets to the
northeast. Temperatures will drop into the single digits, though
with winds going light/calm, wind chills won`t be much different
than actual temps. Will let the current Cold Weather Advisory run
its course, but an extension may be needed, especially in the higher
elevations, where temperatures have been running much colder than
guidance. A light south/southwest flow along the ridgetops could
also enhance wind chills to values below Cold Weather Advisory
criteria.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
After a bitterly cold start to Thursday, the cold conditions
continue however not quite as harsh as previous days. The need for
additional cold weather related hazards are not anticipated.

An upper-level trough approaches from the west during Thursday, and
this drives weak surface low pressure well to our north. Some
guidance continues to show a quick but mainly small system spinning
up off the Mid-Atlantic coast initially focused along an inverted
trough type feature. Overall this feature looks to get pushed
farther away from the coast during Thursday and therefore the
forecast is dry. After a frigid start to the day Thursday, the
afternoon temperatures are forecast to not be quite as harsh but
still well below average. Several places mostly across the coastal
plain are forecast to reach or just crack the freezing mark Thursday
afternoon. Another very cold night Thursday night as temperatures
drop back into the teens and single digits. Surface high pressure is
forecast to be offshore, however if the sky is clear and the winds
go calm then areas where snow cover remains could get colder than
currently forecast given the dryness of the air mass in place.

As we go through Friday, an upper-level trough shifting eastward
across eastern Canada may remain somewhat separated from a strong
tailend trough across the Ohio and Tennessee valley`s to the Gulf
Coast. A surface cold front may arrive into our area later Friday
associated with the northern part of this larger trough, however
this front looks to be on the weak side with limited moisture. The
upper-level trough looks to be progressive and as a surface low
develops off the Southeast U.S. coast, it should tend to track out
to sea. While temperatures will not be as harsh as earlier in the
week, it will still be cold/below average. Overall though we will
gradually climb out of the deep freeze from earlier in the week. One
more very cold night though with low temperatures Friday night
dropping into the teens to single digits.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Summary...The bitter cold eases with temperatures forecast to get to
about average Sunday through Tuesday, and a couple of systems move
through or close to our area.

Synoptic Overview...An upper-level trough is forecast to quickly
shift off the East Coast into Saturday. The next upper-level trough
across central Canada shifts east, however it may amplify southward
some from the Midwest and central Plains over the weekend. This
trough then moves eastward into early next week, however its
positive tilt would suggest stronger energy hangs back longer and
this may develop a wave of low pressure along a cold front that
is around our area Sunday night and Monday.

For Saturday...In the wake of an upper-level trough the flow aloft
turns more zonal. Surface high pressure is forecast to crest over
our area before it shifts to our south. The air mass is still cold,
although not as harsh as earlier in the week. Daytime temperatures
should reach or edge just above freezing at least for areas near and
south and east of the I-95 corridor. Low temperatures drop into the
teens to low 20s Saturday night.

For Sunday and Monday...The upper-level flow looks to be split
as northern energy continues to cruise across Canada and into the
northern tier of the U.S. Meanwhile, southern stream energy across
the four corners region gradually shifts eastward. Some guidance has
trended stronger with the Canadian upper-level trough, with more
separation with the energy across the four corners region. A surface
low tracking well to our north pulls a trailing cold front into our
area later Sunday. This front however may tend to stall in our
vicinity as the southern stream energy results in a surface low
developing on the tailend of the front in the vicinity of the
southern Plains to Tennessee Valley. This feature may then quickly
make a run toward the Mid-Atlantic area Monday, however the track,
timing and strength of it still remains uncertain. This feature
however may be sheared as it slides eastward especially if the
northern upper-level trough amplifies a bit more and quickly pulls
it eastward faster. The outcome however will depend on how the main
features aloft track and also their strengths. This changing of the
pattern looks to result in temperatures across our area getting back
to right around average. Regarding the chance for precipitation,
given the uncertainty opted to keep the PoPs on the low side (slight
chance range; 20 percent) on Monday.

For Tuesday...The northern stream upper-level trough may amplify
across the Northeast with the four corners energy slower and
therefore lingering in that vicinity longer. The northern stream
trough may then toss a cold front into our area from the northwest,
although moisture availability looks limited with mostly the eastern
Great Lakes moisture becoming actively involved. If this trough ends
up being stronger like some guidance suggests, then some colder air
may then arrive into our area with the aforementioned cold front. As
of now, temperatures are forecast to be near average.

&&

.AVIATION /11Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR. West/northwest winds around 5-10 kt. High
confidence.

Tonight...VFR. Winds light and variable, likely going calm at times.
A south/southwest direction will generally be favored with any wind.
High confidence.

Wednesday...VFR. Light south/southwesterly flow around 5-8 kt.
High confidence.

Outlook...

Thursday through Sunday...VFR with no significant weather
anticipated.
-- End Changed Discussion --

&&

.MARINE...
A Small Craft Advisory is in effect through 8 AM for ocean zones
north of Little Egg Inlet. South of Little Egg Inlet, the SCA goes
through noon as northwest winds around 15-20 kt with gusts up to 30
kt are expected. Sub-SCA conditions are expected on Delaware Bay.

Following the expiration of the SCA, sub-SCA conditions are expected
with winds quickly becoming light under 10 kt, with 1 to 3 foot
seas.

Buoys have reported ice accretion, so caution is advised when
navigating the waters. The Freezing Spray Advisory is in effect
through 4 PM for all marine zones.

Outlook...

Thursday through Sunday...Some gusts may near 25 knots Friday and
again late Saturday, otherwise the conditions should be below Small
Craft Advisory criteria. Some freezing spray cannot be ruled out
into Friday.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Cold Weather Advisory until noon EST today for PAZ060>062-070-
     071-101>106.
     Extreme Cold Warning until noon EST today for PAZ054-055.
NJ...Cold Weather Advisory until noon EST today for NJZ001-007>010-
     012>027.
DE...Cold Weather Advisory until noon EST today for DEZ001>004.
MD...Cold Weather Advisory until noon EST today for MDZ012-015-019-
     020.
MARINE...Freezing Spray Advisory until 4 PM EST this afternoon for
     ANZ430-431-450>455.
     Small Craft Advisory until 8 AM EST this morning for ANZ450-
     451.
     Small Craft Advisory until noon EST today for ANZ452>455.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...Hoeflich
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...Gorse/Hoeflich
MARINE...Gorse/Hoeflich