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266
FXUS61 KPHI 212358
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
658 PM EST Tue Jan 21 2025

.SYNOPSIS...
Arctic high pressure centered in the Plains extends into our
area, then it settles right over our region Wednesday before
moving offshore into Thursday. A system tracks well to our south
and east later today and tonight, with another one tracking
offshore during Thursday. A cold front moves through later
Friday with high pressure sliding across our area Saturday. The
next cold front may arrive later Sunday with a possible area of
low pressure developing along it Monday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
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7 PM update...tweaked snowfall forecast and POPs a bit further
northwest this evening given model and radar trends. Don`t
expect measurable for most of the region but southern NJ and DE
definitely have a decent shot, with perhaps an inch or so in far
southeast Sussex County as snow ratios look to be 20:1 given the
cold. Made some adjustments to lows given potential for clearing
and radiational cooling towards morning especially north and
west, though the forecast gets more uncertain the further south
and east one gets. No other adjustments at this time.

3 PM discussion...
Near term forecast remains on track. Dangerous cold continues
through Wednesday morning. No changes made to the cold weather
headlines. A Cold Weather Advisory is in place for a large
majority of the region. The exception being the Pocono Plateau,
where an Extreme Cold Warning is in place. All headlines are in
place through noon Wednesday.

Temperatures this afternoon are in the teens for the vast
majority of the area with overcast skies. As we head into the
evening, a wave of low pressure passes by to our southeast. The
precipitation shield should get up into lower Delmarva and South
Jersey, resulting in a brief period of light snow/flurries down
that way. Accumulations up to half an inch are expected, with
localized areas of a half inch to an inch possible, most likely
in the Delaware Beaches/southeast Sussex County.

Otherwise, another bitterly cold night expected. Single digit
lows are expected, with some spots in the northern Lehigh
Valley, Poconos, and northern New Jersey falling below zero.
Wind chills of - 5 to 5 are expected, with values as low as -10
to -20 expected in the Pocono Plateau.

Wednesday will be another dry day as high pressure becomes
centered over the region. Temperatures look to top out in the
upper teens to low 20s underneath mostly clear skies.
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&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
Bitterly cold conditions continuing through Wednesday night,
then not as harsh Thursday afternoon.

Arctic air remains firmly entreched across the region through
Wednesday night. The passage of an upper-level trough axis
early Wednesday morning results in the flow aloft turning more
zonal for a time. This then may back more to the southwest later
Wednesday night into Thursday as an upper-level trough starts
to approach from the west during Thursday. The airmass will
modify some ahead of this trough and therefore temperatures,
after starting out very cold early Thursday morning, climb into
the lower to mid 30s for parts of the coastal plain and 20s
elsewhere. In association with the aforementioned trough axis
exiting to start Wednesday, an offshore system moves farther
away with the western extent of a snow shield also to our south
and east. Surface high pressure then crests over our area
Wednesday before shifting offshore into Thursday.

Ahead of the the next upper-level trough, which looks to have a
positive tilt, approaches Thursday night. A weak cold front
should approach our region from the northwest Thursday night,
however higher pressures linger across our area overall. Some
guidance though hinting at a quick but mainly small system
spinning up off the Mid-Atlantic coast initially focused along
an inverted trough. This feature overall should remain offshore,
however will have to monitor this in the event that some snow
showers brush some of the coastal areas.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Summary...The cold eases with temperatures forecast to get to
about average Sunday and Monday. A few systems should move
through as the air mass continues to transition out of the
bitter cold.

Synoptic Overview...An upper-level trough is forecast to be
sliding eastward across eastern Canada to the Great Lakes Friday
with a stronger shortwave extending this trough across the Gulf
Coast states. These features look to quickly shift off the East
Coast Friday night into Saturday. The next upper-level trough
across central Canada shifts south, 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 initially moves into or crosses our area late
Sunday and Monday.

For Friday and Saturday...An upper-level trough shifting
eastward across eastern Canada Friday 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, at
least some guidance has trended a bit colder and the NBM has
reflected this. Some areas especially across the coastal plain
are forecast to get to or a few degrees above freezing Friday
afternoon, and then this expands slightly more Saturday
afternoon. Low temperatures Friday night drop into the teens to
single digits, then teens to low 20s Saturday night. Latest
guidance now suggests much of the I-95 corridor will now remain
at or below freezing through the day Saturday as well.

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
slides out of the four corners region during the second half of
the weekend. This all results in a system tracking well to our
north with a trailing cold front arriving 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. This feature may then may make a run at our area early
next week, however the track, timing and strength of it remains
uncertain. This is especially the case as the positioning of the
troughs themselves will likely change over the coming days.
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 lower side which is pretty much with the
NBM output suggests.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR. Northwest winds around 5 kt. A few snow showers
possible (25-35%) at KACY-KMIV until around 06z, though
conditions should primarily remain VFR. Moderate confidence.

Wednesday...VFR. Northwest winds 5 kt. High confidence.

Outlook...

Wednesday Night through Saturday...VFR with no significant
weather anticipated.
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&&

.MARINE...
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Through Wednesday, mainly sub-Small Craft Advisory conditions
are expected with west/northwest winds around 10-20 kt and seas
2 to 3 feet. A few gusts around 25 knots are possible late
tonight/early Wednesday.

Buoys have reported ice accretion, so caution is advised when
navigating the waters. The Freezing Spray Advisory has been
extended through 4 PM Wednesday given persistent cold waters and
expected wind gusts.

Some snow showers are possible on the southern ocean waters and
lower Delaware Bay this evening, which could result in some
visibility restrictions.

Outlook...

Thursday through Sunday...The conditions should be below Small
Craft Advisory criteria.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...Gorse/Staarmann
NEAR TERM...AKL/Hoeflich/RCM
SHORT TERM...Gorse/Staarmann
LONG TERM...Gorse/Staarmann
AVIATION...AKL/Gorse/RCM
MARINE...AKL/Gorse/RCM