West Manheim, Pennsylvania Weather Forecast Discussion

642
FXUS61 KCTP 241852
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
252 PM EDT Wed Sep 24 2025
.SYNOPSIS...
* Muggy with periods of much needed rain through Thursday
* Drying out and not as humid on Friday
* Above average temperatures forecast through the end of
  September; however rainfall potential remains low/uncertain
&&
.NEAR TERM /THROUGH TONIGHT/...
Another mostly cloudy and muggy period with rain showers
expected to expand from SW to NE across CPA into tonight. The
clouds have kept instability and rain rates in-check so far, but
can`t rule out a couple of heavy downpours this evening or
overnight as above normal PWs creep higher in response to an
increasing SSWly LLJ. Very warm and humid conditions for late
September with low temps +15-20 degrees above climo in the
60-70F range.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A broad upper low over the OH Valley will gradually devolve into a
positive-tilt trough before moving eastward over the Northeast
Thursday. At the surface, a weak low will traverse the St Lawrence
Valley dragging a cold front the OH Valley and Appalachians.
Expanding shower/thunderstorm activity and extensive low cloud
cover is probable Thursday morning ahead of the cold front.
With widespread clouds, minimal surface heating and poor lapse
rates are expected over much of the warm sector. Still, a very
moist air mass for late Sept. with 60s to 70s F dewpoints
should support some weak buoyancy (MLCAPE generally less than
1000 J/kg). Southwesterly flow aloft will favor slightly
cyclonically curved hodographs with around 30-40 kt of deep-
layer shear. This could support some storm organization ahead of
the front into linear clusters with transient updraft rotation.
Isolated damaging gusts are the most likely threat, though a
brief QLCS tornado is also possible near the effective front
where low level flow is more backed. However, given the limited
buoyancy and marginal storm organization, a broader severe risk
appears unlikely. SPC maintained a MRGL severe tstm risk across
the southeast portion of the area with a 2% tornado prob. Hi
pwats around 2" could also support another round of locally
heavy rain focused over the eastern half of the CWA.
The +tilt northern stream trough tracks across NY state early
Friday with the cold front reaching the coast by 12Z. There may
be a couple of lingering showers with the upper trough passage,
but on balance conditions should dry out through Friday night as
weak area of high pressure migrates eastward from the Great
Lakes. A wind shift to the WNW should advect slightly drier/less
humid air into the area to end the week with more
comfortable/seasonable min temps in the 45-60F range Friday
night.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Model and ensemble data show a highly complex pattern evolving
over the Eastern U.S. this weekend into the final days of
September. A southern stream cut-off low over the central
Appalachians will interact with a pair of tropical systems over
the western Atlantic. While the details remain unclear, there
is general agreement with a plume of deep tropical moisture
being transported northward along the coast into the northern
mid Atlantic region. An easterly component to the low level flow
suggests more clouds and increasing odds for rain particularly
over the southern half of CPA this weekend into early next week.
There are signs of drier weather pattern unfolding by the time
the calendar flips to October.
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
VFR to MVFR conditions this afternoon and evening will trend
toward widespread MVFR/IFR tonight. LIFR is probable at several
sites overnight into early Thursday morning. Ongoing showers
over the western and southern airspace will expand to the
northeast through the evening and continue through Thursday.
Cloud cover will limit thunderstorm potential, but can`t rule
out some localized t-storm impacts and periods of moderate to
high intensity rainfall.
Outlook...
Fri: Low cigs early trending VFR by Friday afternoon. Decreasing
odds for rain.
Sat-Mon...Low confidence in sub-VFR cigs/rain across the
southern/eastern portions of the airspace.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Steinbugl
AVIATION...Steinbugl

NWS CTP Office Area Forecast Discussion