Spring Grove, Pennsylvania Weather Forecast Discussion

068
FXUS61 KCTP 211044
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
644 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 next
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.
Confidence is increasing for a more southern track to the slow
moving cutoff low late next week and weekend, with an increasing
probability of dry/pleasant cool conditions Friday through
Sunday. The ICON and EC and its ensembles have been the most
consistent with their handling of this system and keeping it`s
impacts minimal if any here in Central PA.
GFS`s jet core is across James Bay Canada for the Fri-Sun
9/26-9/28 period, but the northern stream flow veers and becomes
more nwrly with the passage of a significant and fast moving
short wave in that northern branch of the jet. 00Z EC is much
more northwesterly and 300-400 NM further to the south with its
main upper level jet, which places much of PA in the sweet spot
for confluent flow aloft and deep dry air with low daytime
humidity.
Latest...06Z Sat run of the NBM v4.3 6 via WSUP viewer shows
6-hourly POPS AOA 15 percent for much of the CWA SAT 9/27, after
some potentially minor WAA ahead of the upper trough at POPS of
20-25 percent Friday 9/26.
&&
.AVIATION /10Z 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