376
FXUS61 KCTP 250602
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
202 AM EDT Wed Sep 25 2024

.SYNOPSIS...
An amplifying upper level trough and slow moving frontal
system will bring showery conditions to Central Pennsylvania
through at least Wednesday, along with a few rumbles of thunder.
As such, it will be cloudy and cool through midweek. The latter
part of the week looks milder with at least partial sunshine
expected into the weekend.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Shortwave trough has exited to the northeast leaving a
corresponding lull in shra activity across central PA late this
evening. It will remain overcast and drizzly with pockets of
light rain for much over the overnight hours, and then we
expect another uptick in shower activity across the southern
tier as as deep layer moisture increases and additional large
scale lift arrives. Temps won`t move much (down maybe only 5-8F
thru the entire night, again) and need little editing in the
grids.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
Upper level pattern continues to amplify on Wednesday with the
offshore upper ridge sharpening as split upper trough arrives
into the western GLAKS to the mid Mississippi River Valley, with
a southern cutoff low moving into southeast MO through Wednesday
evening. Deep moist southwest flow will prevail above 925mb with
a llvl easterly component adding to the dreariness over central
and eastern PA, and continuing a showery and cool stretch here
in late September. Basin average QPF is less than half of an
inch over all of the area, and many places will have less than
a quarter of an inch across the short term period (Wed-Wed
night). Very small diurnal ranges will occur given the
persistently cloudy and damp conditions. Sky cover too remains
essentially solid for most of the time on the deep SE flow.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Lingering showers across mainly E PA will continue into
Thursday before a brief reprieve in rainfall. Shower chances
will increase Thursday afternoon into the morning hours of
Friday with the surface cold front lingering across southern
Pennsylvania. The highest chances will mainly be confined south
of the Turnpike; however, can`t rule out showers making it as
far north as the northern tier Friday evening into Saturday
morning with Chc PoPs across the Laurels throughout the day on
Friday and into Saturday morning.

There is still some uncertainty in regards to how Helene will
impact central Pennsylvania, mainly dependent on interactions
with an upper-level low stationed across the eastern Tennessee
Valley. Deterministic model guidance has outlined that the bulk
of rainfall will stay west of the area while a rather
narrow, negatively tilted upper-level ridge holds strong from
the Great Lakes through the Upper Ohio River Valley. Given the
uncertainty with regards to upper-low interactions, did not
deviate much from continuity and NBM guidance this cycle.

The upper-level low and remnants of the tropical system will
likely drift east across the Commonwealth early next week,
bringing increased chances of shower activity into the beginning
of next week, with highest chances generally across the western
highlands.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
06Z TAFS sent.

Main change was to edge off on the low visibility fcst and
drizzle some, based on obs, and also that the airmass is still
working in from the New England area, where dewpoints a bit
lower. Also what showers that were on the radar to the
southeast are almost gone now.

Earlier information/discussion below.

The combination of a moist southeast flow off of the Atlantic
Ocean and a stalled warm front near the PA/OH border will
result in persistent stratus and occasional rain/drizzle across
Central PA through Wednesday.

Upsloping flow should yield the lowest cigs along the spine of
the Appalachians overnight, where LIFR/IFR cigs are very likely
based on current conditions and model output. Further east,
MVFR cigs are currently noted across the Susq Valley, but latest
model soundings and SREF prob charts indicate IFR cigs will
become likely by late tonight. A core of stronger winds aloft
could result in marginal LLWS criteria this evening over the NW
Mtns (KBFD).

Very little change is expected Wednesday, with widespread IFR
cigs and occasional rain/drizzle expected. However, there is
some chance (<50pct) of late day improvement along the spine of
the Alleghenies (KBFD and KJST), as the warm front nudges
eastward.

Outlook...

Thu...AM low cigs/chc showers, mainly early.

Fri...Patchy AM valley fog possible N Mtns. Chance of showers/low
cigs across the south.

Sat-Sun...Chance of low cigs/showers, mainly across the south.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Lambert/DeVoir/Dangelo
NEAR TERM...DeVoir/Dangelo
SHORT TERM...DeVoir/Dangelo
LONG TERM...DeVoir/Martin/NPB
AVIATION...Fitzgerald