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987
FXUS61 KCTP 171927
AFDCTP

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

.SYNOPSIS...
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An area of low pressure over the western Carolinas Tuesday
afternoon will drift slowly north into Virginia through
Wednesday before tracking east and off the coast by Thursday.
An upper level ridge over the Great Lakes is likely to build
into Pennsylvania by next weekend.
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&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Central PA remains nuzzled between drier NNE flow of air from
high pressure centered over the Catskills this afternoon and
deep serly flow on the northeast side of low pressure centered
over the western Carolinas. Deep easterly flow is keeping lower
cigs over southern and southeastern PA, and this llvl Atlantic
inflow in combination with the lift from former PTC-8 remnants
within the large upper level low circulation is bringing light
rain into northern VA and MD this afternoon. This initial
rainfall is very light, but is expected to reach north of the
Mason Dixon line by early to mid evening.

Far northern PA to the north of I-80, and especially along and
north of Rt 6, will keep dry conditions in place for tonight. To
the south of I-80, and especially over the southern quarter to
third of central PA, clouds will lower and thicken with areas of
light rain slowly spreading from south to north, with most areas
struggling to see measurable at any given time. The best chance
of seeing measurable rainfall should come after 10 PM across the
SC Mountains and Lower Susq, where up to a tenth of an inch is
possible overnight.
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&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
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It still looks it will remain primarily dry north of I-80 on
Wednesday, with occasional very light rain or periods of showers
across central and especially south central/southeast portions
of central PA. Again, amounts will be very light, as the system
is fighting dry air entrainment in the llvls from the north
thanks to high pressure over New England. Aforementioned sfc low
pressure will slowly track ENE across North Carolina and
southeast VA through Wednesday night, and remain just off the
Delmarva coast through Friday.

The best chance of showers or a few short periods of steadier
light rain across Central PA continues during the daytime hours
Wednesday, as the remnant low makes its closest pass to PA
before shifting off of the East Coast late Wednesday and
increasingly northerly component dries things out into Thursday.
While a 20-30 pct chance for rain continues into early Thu, the
dry air will eventually win out with increasing amounts of
sunshine as Thursday wears on, and as you move from south to
north across central PA.

Far eastern areas remain susceptible to the wraparound flow from
the aforementioned nearly stationary low off of the Delmarva
coast Thursday night and Friday, and even a few light showers
cannot be ruled out from Sullivan/Columbia Counties southward
through Schuylkill County. The remainder of central PA should be
dry as high pressure is wedged down the spine of the Alleghenies
into this weekend.
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&&

.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 /19Z TUESDAY THROUGH SUNDAY/...
MVFR to low VFR ceilings will hold steady into this evening and
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.

Mainly clear skies in the far northern tier may allow for fog
formation overnight with reduced confidence <=50% in local
visibility restrictions.

The highest probability of rain will be over the southern
terminals on Wednesday and have mentioned VCSH with this TAF
cycle at KJST/KAOO/KMDT/KLNS.

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...DeVoir/Dangelo
SHORT TERM...DeVoir/Dangelo
LONG TERM...Steinbugl
AVIATION...Steinbugl
CLIMATE...NPB