Duncan, Pennsylvania Weather Forecast Discussion

974
FXUS61 KCTP 231119
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
719 AM EDT Tue Sep 23 2025
.SYNOPSIS...
* Above average temperatures for the last week of September to
  begin astronomical Fall
* Periods of much needed rainfall expected at times through
  Thursday
* Trending drier again for the beginning of October.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Radar starting to get quieter, but another shortwave trough is
moving in from the SW. That should reprise SHRA and TSRA for the
daytime. The bulk of the rain will be over the NW half of the
CWA during the late morning and afternoon. The instability there
is not strong and may not be rooted in the boundary layer. But,
we`ll continue to mention thunder for all the area. SPC MRGL
risk for the SE is well-placed since that is the location which
should receive the most sun and best heating to realize CAPEs
over 1000J should the NAM be trustworthy. Storm motion looks
SW-NE without much of a turn in the lowest layers. So, the main
threat is for a marginal SVR gust or two and perhaps small hail.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
The storms over the SE should lift into the Poconos and out of
the CWA in the evening hours. A weak sfc trough will linger over
ern PA tonight and will help slow down the exit of the moisture,
esp over the NE/Poconos. Any clearing (most-possible S and W)
will lead to fog. Any SHRA lingering after midnight will be
light, more likely DZ.
Layered clouds on Wed will thicken up from SW to NE as a wave
approaches from the SW. But, the morning will be generally dry.
High PoPs return to the grids in the late aftn. However, the
timing of the rain is in question. It could be right around
peak heating or later in the evening. We`ve held off on likely
PoPs until after 00Z with only high chc (40-50pct) numbers for
the aftn in the W.
Temps will be mild-warm for this time of year (5-10F > normals)
and dewpoints/humidity continued higher than we`ve become
accustomed to over the past month or so.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
4 AM Update holds little change in big picture with SHRA/TSRA
Wed night and Thurs and decent, widespread rainfall as a
frontal system moves through. However, we go back to a rather
dry pattern after that.
Prev...
The long-term period will start out unsettled and then trend
quieter by the end of the weekend. On Wednesday, an upper low
centered over the Great Lakes will be accompanied by a very
positively tilted trough bringing warm/moist southwest flow into
the Commonwealth. That broad trough will rotate through
Pennsylvania through the end of the week, with multiple
shortwaves and associated enhanced rounds of convection along
it.
Periods of showers and storms are likely Wednesday afternoon
through Thursday evening as an approaching surface low moves
across the region. Widespread beneficial soaking rainfall of at
inch or more seems increasingly probable thanks to the multiple
rounds of rainfall expected. After a cold front moves through
later this week, wrap-around moisture in northwest flow could
lead to continued scattered showers.
By the weekend, a potent and quasi-zonal jet core across
southern Canada will sag south as a closed upper low across the
southern US drifts east. If the low stays south as the most
recent model guidance depicts, Pennsylvania will likely remain
rain-free for much of the weekend (perhaps dealing with some
clouds across southern PA). If the jet core across Canada (and
any associated fronts) trends farther south, or if the upper low
ends up drifting farther north, unsettled weather could persist
through the weekend.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Early this Tuesday morning, flying conditions ranged from mainly
VFR over the southern and eastern portion of Central PA, to
predominantly MVFR with patches of IFR conditions across NW Mtns
of PA. The lower flight conditions across the northwest should
improve just slightly today.
A well-defined upper level trough (currently over the KY, VA,
WVA borders) embedded in the southwest flow aloft will move
northeast today, enhancing large scale lift and impacting much
of the region with a few more rounds of rain/showers and
scattered thunderstorms. The greatest potential for brief strong
wind gusts from the storms will be over the Lower Susq Valley
and Western Poconos this afternoon, where the prob of SFC Based
CAPE exceeding 1000 and 2000 J/KG is the greatest.
Lowest CIGs and vsbys across the Lower Susq Valley will come in
the 22Z Tue - 03Z Wed period as a cold front pushes through and
will likely be accompanied by numerous showers and some
embedded, moderately tall showers.
Later tonight and Wednesday morning, a few breaks in the cloud
cover will enhance radiational cooling and cause locally dense
fog to form after 04Z Wed.
Not much change with the pattern, weak systems will bring some
showers and storms to central PA through Thursday and even some
chance on Friday. Conditions trend drier by the weekend.
Outlook...
Tue-Sat...Multiple rounds of SHRA and PM TSRA (best chances Tue
and Thu) with sub-VFR conditions expected.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Dangelo
NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...Dangelo/Banghoff
AVIATION...Lambert/Martin

NWS CTP Office Area Forecast Discussion