412
FXUS61 KCTP 180605
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
205 AM EDT Wed Sep 18 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 THIS MORNING/...
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.

&&

.SHORT TERM /6 AM THIS 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 /06Z WEDNESDAY THROUGH SUNDAY/...
MVFR ceilings across the Laurels (JST/AOO) could show slight
hints of improvement over the next couple of hours through 09Z
with HREF probabilities and GLAMP guidance both suggesting
conditions resolving to low-end VFR near 08Z at AOO. Improvement
will be short-lived; however, as ceilings are expected to tank
towards IFR thresholds closer to sunrise (10-12Z) and continue
through at least 16Z at AOO/18Z at JST. There is some
uncertainty with regards there lower ceilings, so have these in
the 06Z TAF package with moderate (~40-50%) confidence. MVFR
ceilings are also expected to begin making way into MDT/LNS
closer to sunrise, with the most reasonable timing near 10Z,
although could realistically see these restrictions pushed back
closer to the 11/12Z timeframe as guidance continues to slow
low-level clouds (~1500ft AGL) into the LSV. Scattered -SHRA
will also be possible mainly at JST/AOO/UNV, although have
limited mentions as the bulk of shower activity has moved west
of these airfields at this time.

Recent GLAMP guidance and HREF probabilities continue to go
heavy on visibilities ~1/2SM at BFD in the overnight period, and
generally could see these coming to fruition given SKC/00000kt
conditions over multiple hours, thus have offered up ~2hrs of
increased restrictions in the 10-12Z timeframe. If ANY cloud
cover gets into BFD over the next couple of hours, this will
likely limit fog potential in the timeframe and BFD could escape
with an hour/two with MVFR thresholds (10-12Z) or, even more
likely, VFR prevailing throughout the overnight period. If fog
does manage to develop, restrictions will be quick to resolve by
13Z with VFR prevailing throughout the daytime hours.

After sunrise, improvement looks unlikely through 17Z at all
airfields (minus BFD/IPT, who outside of the aforementioned fog
restrictions at BFD will remain VFR overnight). Slow improvement
is progged by the bulk of model guidance, with MDT/LNS first to
resolve in the 16Z-17Z timeframe and JST/AOO resolving closer
to 00Z Thursday as low ceilings slowly scatter out towards VFR.

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...NPB
CLIMATE...NPB