757
FXUS61 KPBZ 200628
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
228 AM EDT Sun Sep 20 2026

.WHAT HAS CHANGED...
The main axis of heavy precipitation has shifted south a bit
adding to the complexity of the setup.

&&

.KEY MESSAGES...
1) Rain chances return today 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...
It seems another period of active and wet weather is upon the
region. The upper pattern features a continued flatten ridge
aloft over the eastern CONUS with another shortwave trough
approaching the region. The patten sets up a storm track across
the Midwest and into the Upper OH Valley. This will keep a
series of shortwave trough approaching the area through the
middle of next next week.

Addressing the Saturday night into Sunday threat, showers and
thunderstorms are tracking across Ohio and mainly sliding just
south of the forecast area. There are some scattered development
tracking just north of I-70 but this rainfall is not expected to
be impactful. The amount of instability is below 500 J/Kg and
mainly a flood threat is expected at this point through dawn.

By the 10Z to 16Z period additional development is expected into
central Ohio with PWATs at 1.8 to 2.0. Plenty of moisture to
work with and the NBM giving a 90th percentile amount through
the day on Sunday looks to be around 0.75 to 1.50 as a swath of
heavy rainfall lines up from just south of PIT and south into
the WV counties in the north. The 90th has potential given the
amount of moisture in the air. The only hindrance in reaching
these values is the amount of instability available. This looks
to be a 24 hour probability and would lead to at least a few
issues through the day. On another note, the CAMs and ensembles
are not handling the amount of rain potential very well,
although the track seems to have slide south increasing
confidence in a southern Flash Flood Watch and one may be needed
for the next round since the soils would be primed.

The severe threat for Sunday seems to focus mainly in the
morning with the initial rainfall as profiles would show deep
saturation and no dry air. If a storm does develop, the main
threat would be damaging winds. The Sunday night period will
feature another round of rain crossing the southern portion of
the forecast area. This third or even fourth round of rain would
begin to cause some concern in flooding across the area south
of Pittsburgh. The Monday period will feature some showers
across the area but will be concerning given the amount of
rainfall since Saturday night. It seems that even Monday will
need to be monitored for the potential of flooding.

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 /06Z SUNDAY THROUGH THURSDAY/...
Mainly VFR conditions are expected through the night with the
exception of a few other locations through the next few hours.
Scattered showers and thunderstorms are expected through the
overnight and through dawn. By the 08Z to 10Z period, heavier
shower and thunderstorm activity is expected. This is expected
to continue through 16Z before a break in the precip.

Any thunderstorm activity will most likely be observed south of
PIT near a frontal boundary, where localized instability
resides.

Between 20Z to 23Z Sunday, expect a front to advance south and
winds will shift from the north. Rain coverage will likely
decrease for FKL, DUJ, and BVI during this time period. PROB30s
have been used to highlight this impact. Elsewhere, expected
passing showers to continue into Monday with continued
restrictions.

Outlook... Restrictions will likely continue into Tuesday with
sufficient boundary layer moisture impacting low-level clouds
and passing rain showers continue.

&&

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

&&

$$

DISCUSSION...Shallenberger
AVIATION...Shallenberger