226
FXUS61 KPBZ 191801
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
201 PM EDT Sat Sep 19 2026

.WHAT HAS CHANGED...
Increased chance for showers and storms Saturday afternoon and
evening.

&&

.KEY MESSAGES...
1) Rain chances return Sunday and continue into early next week.
Longer duration rainfall totals could be high and lead to localized
flooding and/or river rises

2) Much cooler temperatures arrive by mid-week

&&

.DISCUSSION...
KEY MESSAGE 1...
A more active pattern is on the horizon beginning later
Saturday evening and continuing through next week. A breakdown
of the southeastern CONUS ridging will open the door for rounds
of waves embedded within quasi-zonal flow and associated rain.

Round one arrives late Saturday and continues into Sunday as an
initial mid-level wave rides along a baroclinic zone through the
Ohio Valley. Ongoing convection Saturday morning poses an
interesting evolution into the evening hours as CAMs attempt to
handle the previously poorly modeled extent. Warm starts are now
capturing it better and suggest that outflow extends as far south as
south-central Illinois, sparking additional development there. This
is progged to track east through the afternoon and arrive into our
eastern Ohio counties just around dark. This should point toward
weakening, and the 12z suite of CAMs suggests that, though maybe not
quite to the extent that they think as point soundings ahead of it
still show some elevated instability. The severe threat should be
low provided the timing is correct, but lingering showers and
rumbles of thunder are certainly in the cards, especially for the
southwestern part of our area where the storms should be diving
toward the best instability axis during the day. Farther north,
ongoing warm advection and low-level jet driven showers likely
continue as the broad ascent spreads east. While light as drier
lower levels on our 12z balloon need saturated, the expectation is
scattered light showers within mostly cloudy and cooler air.

Another push of precip, this one likely a bit more widespread and
moderate to heavy at times, arrives Sunday morning as another wave
rides atop the surface boundary. This time, a more prolonged
period of southerly flow on the warm side is able to bring HREF
mean PWAT values up to 1.6-1.9" and near the 99th percentile of
climatology. A deep, saturated column with fumes of 100-300 J/kg
of MUCAPE within the warm cloud layer should be supportive of
efficient rainfall rates. That said, it likely will take
repeated rounds of heavy rain over the same area to raise flash
flood concerns as mean cloud bearing layer wind is around 30
knots, and HREF prob of 1" in an hour in any given hour tomorrow
doesn`t reach much above 20-30% thus supporting the lower
probability of intense rainfall rates but rather longer duration
totals to monitor. There are higher pockets of 50-60%
probability for >1" in 24 hours. The deep column moisture should
offset a severe threat with limited instability.

Following a brief lowering of rain chances early Monday, it`ll
remain active into the middle part of the week. While the setup
doesn`t appear to favor heightened flash flooding concerns any given
day, long duration accumulation has the potential to be more
notable. Latest NBM 48 hour QPF from Monday morning - Wednesday
morning has the highest values south of Pittsburgh where a slow
moving/stalled boundary is progged to be. Location of that will be
paramount for who gets the bulk of the rain, and right now, most
ensembles place it south of Pittsburgh. Mean values are around 1.25-
1.5" there, and 90th percentile values up to 2-3.5". Farther north,
the mean is much less at 0.5-0.75" with the high end around 1.5-2".
There are even some solutions (mostly a southward displaced
boundary) in which the northern part of the area sees very
little rain. While this all told wouldn`t pose as much a threat
for flash flooding, areal flooding and river flooding chances
may increase especially if the high-end potential is realized.
The primary way to realize that high end potential would be to
be positioned immediately north of the stationary boundary with
overrunning, and/or on the northwest side of a developing
coastal low. Should the stationary boundary be too far south or
the coastal low to far east, these threats would not be
realized. The area with highest potential for impacts will be
south of Pittsburgh and will need continued monitoring into
early week.

KEY MESSAGE 2...
The other story of the week is going to be the much cooler air
in place with several days where the highs may not get out of
the 50s for some. Surface high pressure across New England will
induce stout, prolonged east-northeast flow locally. NBM probs
for daytime highs exceeding 65F is basically a 50/50 shot from
the ridges to Pittsburgh, then a bit higher farther west, all
that with a summertime-biased NBM and likely a bit too high even
at that; AI guidance and some deterministic models are running
a handful of degrees cooler. Normal highs are in the low 70s and
lows in the low 50s throughout next week, so while lows should
be right around normal, we could be looking at highs some 10
degrees below.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
VFR prevails through at least this evening as a mix of mid and
high clouds overspread the region along with some light rain
showers from pockets of elevated convection. A cu field has
developed, owing to the onset of daytime heating with cigs
hovering at borderline MVFR/VFR levels. However, that cloud deck
should remain mostly scattered in coverage so not much impact is
expected from it.

Rain chances increase overnight into Sunday as the next weather
system approaches, with a greater coverage of showers and
thunderstorms spreading across the area after 00z and especially
after 06z. Expect cig/vsby reductions to accompany the
increasing shower and thunderstorm activity. Winds remain light
and generally out of the south or southeast through the TAF
period.

Outlook... Restrictions are likely to return by Sunday morning
with an increased chance for showers and thunderstorms
associated with an approaching disturbance.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

$$

DISCUSSION...MLB
AVIATION...Cermak