Lebanon, Pennsylvania Weather Forecast Discussion

487
FXUS61 KCTP 211748
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
148 PM EDT Sun Sep 21 2025
.SYNOPSIS...
* Above average temperatures for the last week of September to
  being astronomical Fall
* Periods of much needed rainfall expected this week across
  central PA
&&
.NEAR TERM /THROUGH TONIGHT/...
Low clouds showing very little signs of breaking up over the
central mtns into the Susquehanna Valley this afternoon. The
western edge of the stratus has mixed to bkn stratocu along the
Allegheny Front with mostly sunny skies over Warren County.
Bulk of hires data keeps rain showers out of the NW mtns
through 06Z with an increasing chance through early Monday
morning. Otherwise, mostly cloudy tonight with lows in the 50s.
&&
.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
The greatest chances for rain/showers during the short term
period will be 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.
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 /TUESDAY THROUGH SUNDAY/...
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 /18Z SUNDAY THROUGH FRIDAY/...
MVFR to low VFR cigs expected into the evening. With upslope
southeasterly flow (low level wind from the east- southeast)
continuing into tonight, expect more sub-VFR cigs into Monday
morning. LLWS is close to key thresholds over the western and
central TAF sites. Breaks in the clouds expected by Monday
afternoon with flight cats trending MVFR to VFR. Added PROB30
for showers at KBFD after 22/15Z which correspond to an uptick
in precip/thunder probs by 18-24Z Monday.
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/Steinbugl
NEAR TERM...Lambert/Steinbugl
SHORT TERM...Lambert/Steinbugl/Bowen
LONG TERM...Lambert/Steinbugl
AVIATION...Steinbugl/Colbert
CLIMATE...Steinbugl

NWS CTP Office Area Forecast Discussion