Duncan, Pennsylvania Weather Forecast Discussion

289
FXUS61 KCTP 211118
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
718 AM EDT Sun Sep 21 2025
.SYNOPSIS...
* Above average temperatures to close out astronomical summer
  2025
* Rain chances will increase across the region Monday and
  Tuesday
* At this early vantage point, there is uncertainty as to
  whether showery, unsettled conditions last into next weekend,
  or improvement takes place by then
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Recent high resolution model guidance over the past few days
accurately depicted the formation/advection and extent of a
large area of stratus/stratocu across the Commonwealth early
this morning under an extended period of low level serly flow.
We`re seeing a transition to a definitive, deepening south to
swrly flow that will feature several opportunities for showers
and perhaps a few rumbles of thunder with the passage of a few
weak boundaries. More on that below.
For today, SE to southerly flow respectively, in the sfc-4 kft
agl layer should help to greatly delay or prevent the break up
of the stratus/stratocu decks, leading to noticeably cooler late
morning/afternoon temps than Saturday.
Max temps this afternoon will range from the upper 60s across
the highest terrain (including the NW Mtns and Laurel
Highlands and the north-central mtns.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
The greatest chances for rain/showers during the period will be
late tonight into early Monday and again late Monday afternoon
and evening (across the NW zones along a NEWD lifting warm
frontal zone, SE edge of a band of 1.5+ PWATS and swrly LLJ
axis. That portion of the state resides at the SE edge of the
DY2 SPC MRGL threat for SVR TSRA.
High pressure and slightly lower PWATs to the east will keep
any rain showers to a minimum east of I-99 and south of I-80.
Lows tonight will be mainly in the mid to upper 50s with the
Western Poconos seeing some readings right around 50 deg F.
High temps Monday will range from the mid 70s over the higher
terrain of the north and west, to the upper 70s and around 80F
elsewhere.
&&
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Strong sfc high shifts to the Northeastern Seaboard early in the
upcoming week. This will allow a +tilt upper level trough and
llvl frontal boundary to move southeast from the Great Lakes
bringing the best odds for rain particularly on Tuesday focused
across the northwest 1/2 of central PA.
Uncertainty with regard to the timing, northward extent and
amount of rain still permeates the last few days of the long
term period with the results whittled down to the
outcome/location of two key features.
First will be the development of a slow moving closed low
during the middle of the week acrs the Central Plains and Mid
Miss valley as a significant jet max/potent short wave dives SE
across the Central and Northern Rockies. The timing of this
feature`s trip across the Ohio Valley, Central Appalachians and
Mid Atlantic Region should be mainly in the Wed through Fri
night period. The second feature of concern is the timing and
amplification of a northern stream upper shortwave within the
potent and quasi-zonal jet core across southern Canada.
Yesterday`s model runs phased the timing of the northern and
southern stream troughs better and caused the southern
trough/closed low to be a few hundred NM further south. After a
12Z Sat - 00Z Sun pair of runs that became more unphased with
this feature and allowed it to drift north into flat ridge over
southern Ontario and SW Quebec, the timing of the northern
stream trough appears to be more a kicker and once again
suppresses the southern low a bit more south with faster
movement across the Eastern U.S.
Based on this, the greatest probability for rain will reside in
the late Wed through Friday evening period. Lingering, scattered
showers appear to be the outcome for later Friday night and
Saturday.
&&
.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Low stratus is expanding across central PA as of 1030 UTC
Sunday, now reaching  as far north as BFD. MDT and LNS are just
outside the area of low clouds, but there is a 60 pct chance
that MVFR cigs will expand east and include these sites as
well. In the Laurel Highlands, the cigs are as low as 300 ft at
JST.
Restrictions will continue this morning, followed by slow
improvement this afternoon. Improvement to VFR will likely take
place first at LNS and BFD around 15-16z, then MDT and IPT, and
eventually reach AOO, UNV, and JST around 18-19z.
E-SE surface winds of 5-10 kt are expected through the day. Wind
gusts near 20 kts are possible especially in the Laurel
Highlands and northwest mountains.
With upslope southeasterly flow continuing into tonight, most
guidance has another round of MVFR or lower cigs developing
between 05z and 12z Monday. A warm front will trigger some
showers and thunderstorms across the west later in the day.
Outlook...
Tue-Thu...Multiple rounds of SHRA and PM TSRA with sub-VFR
conditions possible.
&&
.CLIMATE...
Astronomical fall officially begins with the autumnal equinox
on Monday, September 22, 2025 @ 2:19 p.m. EDT. The Autumn 2025
season will last 89 days, 20 hours, and 43 minutes. Daylight
saving time will end just after Halloween with clocks falling
back at 2 a.m. Sunday, November 2, 2025.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Lambert
NEAR TERM...Lambert/Bowen
SHORT TERM...Lambert/Bowen
LONG TERM...Lambert/Steinbugl
AVIATION...Jurewicz/Colbert
CLIMATE...Steinbugl

NWS CTP Office Area Forecast Discussion