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521
FXUS61 KCTP 180300
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1100 PM EDT Tue Sep 17 2024

.SYNOPSIS...
A cut off upper low, located over the western Carolinas this
evening, will drift slowly northeast into Virginia by late Wednesday
before tracking off the coast Thursday. An upper level ridge
over the Great Lakes is likely to build into Pennsylvania by
next weekend.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
-- Changed Discussion --
Regional radar late this evening shows light rain has pushed
into Southern PA associated with an upper low and weak surface
low over the Carolinas. The combination of this system to the
south and high pressure east of New England is resulting in an
anomalous easterly flow off of the Atlantic. This low level jet
is currently trained on Virginia. However, all near term model
guidance indicates it should shift slightly northward overnight,
spreading rain into the southern part of the forecast area.
Latest ensemble mean qpf by dawn Wednesday is <0.1 inches over
the southern tier counties, with no rain expected over the
northern half of the forecast area.

Mostly cloudy skies and an active easterly breeze should result
in a milder night than we have seen since the beginning of the
month with daybreak readings ranging from the low and mid 50s
over the northern tier, to the low and mid 60s in the Lower Susq
Valley.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
The weak surface low off of the NC coast is progged to drift
northeast and out to sea Wednesday, resulting in low level flow
backing to the northeast and advecting drier air into the state.
Therefore, expect morning light rain/showers over Southern PA to
diminish during the afternoon. Across Northern PA, all guidance
continues to keep the entire day dry.

Most likely additional rainfall Wed based on ensemble qpf
ranges from nothing north of I-80, to between 0.1 and 0.25
inches over the southern tier counties. Locally higher amounts
are possible along the southern tier, where some models indicate
a bit of elevated instability and the potential of heavier
showers in the 12-18Z time frame.

Thick cloud cover, an upsloping easterly flow and showers should
result in below normal temps Wednesday across the Laurel
Highlands/SC Mtns, where highs in the 60s are expected.
Elsewhere, see no reason to deviate from NBM max temps in the
low to mid 70s.

An increasingly northerly flow should dry things out Thursday
into Friday. However, the remnant upper low/trough is progged
to linger over the eastern part of PA, so will maintain a slight
chance of showers there. Model RH profiles support an increasing
amounts of sunshine Thursday into Friday with GEFS 850mb and
surface temps indicating a return to above average afternoon
readings.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Higher confidence in dry wx/no rainfall particularly early in
the period (through the upcoming weekend) thanks to deep layer
ridge pattern at the sfc and aloft. While model variability
remains elevated into next week, the ensemble means generally
favor weak upper troughing centered around the Great Lakes which
will support a marginal increase in rainfall/shower potential
along/ahead of an approaching front by next Monday or Tuesday.
Forecast max temps 75-80F peak +5-10F above mid/late September
climo to start the weekend and trend modestly cooler to 65-75F
(near the historical average) into early next week.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
MVFR to low VFR ceilings will trend lower tonight across the
southern portion of the airspace. We have above average
confidence >70% in MVFR to IFR conditions developing late
tonight into Wednesday morning over this area.

Partly clear skies in the far northern tier may allow for fog
formation overnight with reduced confidence <=50% in local
visibility restrictions. A band of showers over southern PA is
bringing increased mid-level clouds to the north, and this could
hinder any potential fog development.

The highest probability of rain will be over the southern
terminals late tonight and into Wednesday. At this time -SHRA
has been mentioned where confidence is increasing with this TAF
cycle at KJST/KAOO/KMDT/KLNS. A few PROB30 lines were also added
as there remains a high degree of uncertainty with regards to
the spatial extend of these showers.


Outlook...

Thu...MVFR cigs possible in the southern and eastern portions of
the airspace.

Fri-Sun...Valley fog in the morning; otherwise VFR/no sig wx.

&&

.CLIMATE...
The first day of Autumn 2024 (Fall Equinox) begins at 8:44 am
EDT on September 22nd.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Lambert/DeVoir/Dangelo
NEAR TERM...Fitzgerald
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Fitzgerald/Steinbugl
AVIATION...Steinbugl/Bowen
CLIMATE...NPB