Napierville, Pennsylvania Weather Forecast Discussion

201
FXUS61 KCTP 100755
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
355 AM EDT Wed Sep 10 2025
.SYNOPSIS...
* A mainly dry and seasonable weather pattern is expected to
  continue into next week
&&
.NEAR TERM /THROUGH TONIGHT/...
A low level easterly wind flow around narrow/quasi stationary
Appalachian sfc ridge and northward tracking offshore low will
drive/sustain low cloud cover near and south/east of the I-81
corridor today. The clouds will hold max temps in the upper 60s
to low 70s or 5-10 degrees below the historical average across
the mid and lower Susquehanna Valley. We can`t rule out some
insignificant/spotty light rain on the order of few hundredths
of an inch, but peak odds for measurable precip remain quite low
at 10-20%. Farther to the west, predawn to post sunrise valley
fog will dissipate by 9-10AM and give way to partly/mostly
sunny conditions with warmer highs in the mid to upper 70s.
The mean low level flow will take on more of a northerly
component tonight with increasing subsidence/downward motion.
This should result in gradual clearing from north to south
across the middle and lower Susquehanna Valley. It will be
another relatively cool/chilly night with min temps 40-55F and
radiational fog formation in the valleys into early Thursday
morning.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Despite some troughing in the mid to upper levels, the expansive
1020+mb sfc high pressure dome and associated dry air/sinking
motion will spell a rain-free and seasonably warm end to the
week with low humidity. Max temps on Thu/Fri are projected to
trend higher/above climo in the mid 70s to around 80 degrees.
Nights will remain comfortably cool with AM valley fog and min
temps in the 40s and 50s.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
On the large-scale, our ensemble prediction systems continue to
indicate a fairly blocky upper-level pattern into next week,
with a mean upper ridge axis through the central CONUS and
south-central Canada, with a general weakness in the upper
height fields across the upper Great Lakes and the northeastern
states. Despite the troughy nature of the upper levels over PA,
a very dry air mass overall (thanks to confluent NW flow aloft
promoting surface high pressure development) points to a high
likelihood of continued rain-free conditions for the
Commonwealth.
Looking at the latest cluster analyses in DESI, an earlier
"split scenario" (relatively equal weighting/probabilities of a more
amplified wave and better rain chances for PA vs. an open,
progressive, farther north evolution with less rain chances for
PA) with handling of an upstream short-wave coming into the
Great Lakes region Sunday-Monday is trending towards more
weighting/higher probabilities for the latter/drier scenario.
Thus, NBM POPs have reasonably edged lower for the end of the
weekend into next week.
&&
.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
VFR conds will continue overnight for the central and western
areas.
After 06Z, easterly flow off the Atlantic will usher in a lower
level stratus deck into the Lower Susq Valley overnight. The
HREF model suggests a 70+% probability of LNS and MDT seeing
cigs dip to MVFR.
Farther to the west, where skies remain mainly clear, we could
see valley fog develop in the pre-dawn hours on Wednesday. Have
hinted at this possibility by adding VCFG to the TAFs for BFD,
IPT, UNV and AOO.
Fog should dissipate fairly quickly after sunrise on Wednesday.
However, any low clouds over the Lower Susq Valley may be
slower to budge on Wednesday and MVFR cigs could persist into
the late morning or early afternoon hours.
Outlook...
Thu-Sun...Predominantly VFR. Morning valley fog possible.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Jurewicz/Tyburski
AVIATION...Evanego/Tyburski

NWS CTP Office Area Forecast Discussion