282
FXUS61 KCTP 151850
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
250 PM EDT Sat Aug 15 2026

.WHAT HAS CHANGED...
* Flood Watch issues for portions of southwestern Pennsylvania
  on Sunday.
* Added details pertaining to strong-to-severe thunderstorm
  threat across portions of southern Pennsylvania Sunday
  afternoon and evening.

&&

.KEY MESSAGES...
1) Rain from thunderstorms could be very heavy over the Laurels
and south-central mountains Sunday morning and again later in
the day. There is still potential for some heavy rain to fall
over the Lower Susquehanna Valley and Ridge-and-Valley region.

2) High pressure yields a short dry window before more storms
arrive in mid-week.

&&

.DISCUSSION...
KEY MESSAGE 1: Rain from thunderstorms could be very heavy over
the Laurels and south-central mountains Sunday morning and
again later in the day. There is still potential for some heavy
rain to fall over the Lower Susquehanna Valley and Ridge-and-
Valley region.

Very light showers over eastern OH at 3PM (Sun) are running
over the slightly drier/more stable air in place over PA. The
rain shouldn`t reach into Central PA until after midnight, and
even then, little/no risk of heavy rain will exist for us until
around 4-5 AM. Upstream convection will continue into the Laurel
Highlands per the preponderance of the newest numerical
guidance. A 30-35KT westerly LLJet will bring in along and above
a warm front inching north and east in the morning. PWATs get
above 2" as the morning convection dives into MD. The first
forecast issue is just how far north the heaviest precip will
track. Some recent guidance does indicate a swath of heavy rain
being possible north of the first (southern) tier of counties in
the morning. FFG over much of Somerset and Cambria Counties is
close to 1"/hr. While a little more drying is expected before
the rain arrives there, the FFG will likely still be close to
being that low when it starts raining. The initial slug of
thunderstorms will cross the southern tier by 10 or 11 AM. While
this first slug may not be enough straw to break the camel`s
back, the piece that may do it and make flash flooding may
arrive in the afternoon. WPC ERO SLGT risk is well into the CWA,
even up almost to Route 6 across the nrn tier.

As alluded to...there will _probably_ be a second surge of
instability and lift during the late afternoon and evening. The
certainty of this second round of storms is dependent on the
erosion of a stable layer which will likely form after the first
batch of rain moves through in the morning. If we do break out
and get the necessary sun/heating, we should see more tall and
wet storms. However, the NAM and GFS paint a layer of sfc/llvl
stability/CIN until very late in the day at KUNV as an example
and over much of the CWA. The FFG is also a bit higher, and
ground able to handle a little more rain, on the whole, over the
eastern counties. Thus, in collaboration with our neighboring
offices, we have posted a Flash Flood Watch for Sunday. However,
we have started a little smaller than what we view as the
potentially-eventually threatened area. It was a tough decision,
with confidence in both the threat area and timing/redevelopment
low. Later shifts will be able to evaluate newer guidance as the
time window closes.

The threat for heavy rain does stop by midnight. So, we have
decided to cover both periods of potentially heavy rain with
one watch. While it does stretch across a span of time in mid-
day and early afternoon when no heavy rain should occur, the
time span is pretty short in length.

Additionally, the potential for strong to severe storms exists
as long as we have unstable conditions. The hodographs in the
morning are actually well-curved in the south/southwest, but
have just a meager LLJet. Shear is stronger in the late
aftn/evening. Wind damage is the most probable severe threat,
but a spinning storm or two is possible.

   ------------------------------------------------------

KEY MESSAGE 2: High pressure yields a short dry window before
more storms arrive in mid-week.

A cold front moves through late Sunday night and Monday.
Dewpoints don`t drop much at all until later in the day Monday.
So, there will still be plenty of time on Monday for instability
to develop and pop showers and perhaps a thunderstorm or two
during the daytime. By sunset, these will be gone as dry air
and loss of heating kill them off. Dewpoints drop into the 50s
for many Tuesday morning. Large scale subsidence should yield a
mostly sunny day, then. Return flow Tuesday night and Wed will
bring the humidity up and a cold front will approach on
Wednesday. Storms are expected mainly in the Wed-Wed night
timeframe, but speed of the CFROPA will determine if all/part
of Thursday will be dry. If showers linger, they would be over
the south.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Widespread VFR conditions and generally expected through 06Z
Sunday with high (~70-80%) confidence. In the near-term, main
concern will be low-end VFR to high-end MVFR CIGs; however,
coverage will likely remain scattered in the lowest levels due
to some remaining low-level dry air in place across the region.

After 06Z Sunday, a lower-level deck ~5000-10000ft AGL likely
begins to enter the region based on a consensus of HREF/NBM
model guidance with an approaching system. Shower activity
likely remains west of BFD/JST until closer to the ~09Z-10Z
Sunday timeframe, where a rapid deterioration is progged by
virtually all model guidance. SHRA will continue west-to-east,
producing widespread IFR-to-LIFR conditions to all TAF sites
outside of MDT/LNS by 14Z Sunday with fairly high (~60-70%)
confidence at this time. A combination of GLAMP/HREF/RAP model
guidance outlines that BFD/JST could show initial signs of
improvement in the 17-19Z Sunday window; however, confidence
remains too low for inclusion in the 18Z TAF cycle. In terms of
TSRA, there will be some chances for TSRA to be observed at
JST/AOO between 11Z-14Z Sunday; however, confidence remains too
uncertain for even a PROB30 at this juncture due to lack of
instability and time of day considerations.

Further southeast, an interesting TAF cycle with southeasterly
winds prevailing at MDT/LNS for an extended period of time after
sunset this evening. This set-up does raise some signal for
lower ceilings at MDT/LNS closer to sunrise (generally between
08Z and 12Z Sunday). Some hi-res model guidance does indicate
this potential, and recent GLAMP runs have warmed up to the idea
of this occurring, thus have penciled in some MVFR CIGs at LNS
that could trend lower. MDT likely struggles to get sub-VFR
conditions in this timeframe; however, as they historically have
a hard time getting BR/FG in this set-up. The bulk of model
guidance also does indicate that MVFR CIGs/VSBYs are more likely
with SHRA activity, and have trended this way in the most
recent TAF package with slightly lower (~40-50%) confidence.

Outlook...

Mon-Tue...VFR most of the time. Chance of showers/tstm Monday.

Wed-Thu...Afternoon showers or a TSRA with brief restrictions
possible. Otherwise, VFR.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Sunday morning through Sunday evening for
PAZ024>026-033>036.

&&

$$

WHAT HAS CHANGED...Dangelo/Beaty
KEY MESSAGES...Lambert/Dangelo
DISCUSSION...Lambert/Dangelo
AVIATION...Beaty