970
FXUS61 KCTP 270320
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1120 PM EDT Thu Sep 26 2024

.SYNOPSIS...
*Mostly cloudy with periods of rain and mild nights through the
 last weekend of September; showers continue to start October
*The heaviest rain over the next 5-7 days is expected over south
 central PA which should be largely beneficial
*A shift toward drier/cooler weather is possible by the end of
 next week/first weekend of October

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Late evening update.

There was a very small band of showers for a brief time
across norther Tioga Co earlier this evening.

Area of showers to the south of the PA line did look like
it was trying to lift north, but not much now. Models show
little if anything overnight in that area or otherwise.

Some fog near the MDT area, but most areas just have clouds.
Dewpoints coming down a little as frontal system from NY
state sags southward, and the main front forms just south of
PA.

Late afternoon update.

Rather strong dewpoint front across the region. Main change
was to lower POPS across the north and adjust POPS across the
south. Nothing to the north now, given lower dewpoints.

Showers across the south now fading, will be a while until
more activity to the south can work into the area.

Earlier discussion below.

Min temps will be +10 to +20 degrees above the historical
average for late September ranging from the upper 50s in the
northern tier to the upper 60s in the lower Susq. Some areas of
fog may also develop early tonight, but could dissipate as an
ENE wind picks up into Friday morning.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Main change for Friday was to edge POPS down a bit early on.
This in line better with others, and that the more humid
airmass is expected to stay south of our area this weekend.

For Saturday, models still support the showers to lift to
the north later in the day. That in line with current grids.

Earlier discussion below.

Increasingly strong and anomalously moist (PW 1.5-2") low level
flow from the south/southeast will overrun the aforementioned
frontal zone on Friday. This will result in plenty of clouds
with shower activity expected to expand from south to north
through Friday night into Saturday morning. A tight pressure
gradient on the northeast side of ET/PT Helene (merging with
an upper low centered near the the Bootheel of MO) will promote
wind gusts up to 40 mph on the Laurel ridges tomorrow.

The phased deep layer cyclone will move very slowly to the
northeast toward the IN/KY/OH border and gradually
unravel/weaken through the last weekend of September. A moist
east to southeast low level flow will maintain periods of
showers with a consensus QPF max between 1 and 2 inches focused
over the favored upslope terrain across south central PA.

The cloudy, moist/humid, and showery weather pattern favored
incorporating (blending) the 25th percentile NBM for daytime
highs and 75th percentile NBM for nighttime lows. This idea of
trending cooler during the day and warmer overnight fits the
pattern playbook quite well.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Complex pattern early next week. Hard to see much widespread
dry weather prior to later Wed.

There has been a lot of spread on the large scale pattern
lately.

More information below.

An upper-level low over the Ohio Valley will drift east across
the Commonwealth into the beginning of next week, keeping rain
chances around through at least Tuesday. Uncertainty begins to
increase towards the middle of the week as a northern stream
shortwave tracks near the region, bringing a cold front along
with it. The timing of this feature is a little unclear with
some ensemble members showing the front tracking through early
Wednesday morning while others show a later frontal passage.
Moisture appears to be limited ahead of the front and the best
forcing looks to remain to our north, so widespread rainfall
does not appear likely at this point.

High pressure building in behind the front will bring drier
weather and cooler temperatures for the end of the week. Highs
will generally be in the 60s with overnight lows in the 40s.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
A slow moving cold front will sag southward across Pennsylvania
this evening, then stall over the southern part of the state
late tonight into Friday. Low level moisture ahead of the front,
combined with nocturnal cooling and an upsloping easterly flow,
should yield developing IFR/LIFR cigs across the southern half
of PA tonight. By late tonight, ensemble prob charts indicate
a 60-80pct chance of IFR cigs across the southern half of the
state, with a 80-90pct along the ridgetops. Across the north,
latest guidance indicates there is the chance of IFR cigs over
the high terrain north of KIPT this evening, then the arrival of
drier air behind the front should result in improving
conditions with cigs in the high MVFR/VFR range.

Weak diurnal heating/mixing should result in modest improvement
in cigs Friday, with most locations in the MVFR category by
afternoon and possibly VFR at the Susq Valley airfields.
Moisture indirectly related to the remnants of Hurricane Helene
will start to overrun the stalled frontal boundary lying across
Southern PA Friday PM, leading to deteriorating conditions in
the form of light rain and falling cigs. Model soundings and
ensemble prob charts indicate IFR/LIFR conditions will become
likely over the Central Mtns by the evening hours. The arrival
of a core of relatively strong winds aloft could also result in
marginal LLWS criteria Friday evening, but confidence remains
below 50pct so will keep out of the forecast for now.

Outlook...

Sat-Sun...Low cigs/drizzle likely, mainly Central Mtns during
the AM.

Mon-Tue...Rain/low cigs likely, especially Central Mtns.

&&

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

&&

$$

SYNOPSIS...Steinbugl/Banghoff/Martin
NEAR TERM...Steinbugl/Banghoff/Martin
SHORT TERM...Steinbugl/Banghoff/Martin
LONG TERM...Dangelo/Martin/Bauco
AVIATION...Fitzgerald