856
FXUS61 KPBZ 130706
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
306 AM EDT Sun Sep 13 2026

.WHAT HAS CHANGED...
A portion of the Flood Watch was extended to 5 AM. Showers will
last a little longer through the predawn hours. Uncertainty
regarding the severe threat during the afternoon/evening
continues.

&&

.KEY MESSAGES...
1) Showers will decrease in coverage through the predawn hours,
with lingering low clouds and fog

2) Severe thunderstorms still possible Sunday afternoon and evening
with a cold front, but the level of the threat is uncertain

3) A brief bout of dry weather returns early next week

&&

.DISCUSSION...
KEY MESSAGE 1...
Showers have continued to generate into the predawn hours thanks
to upper divergence associated with a crossing shortwave trough,
plus precipitable water values lingering in the 1.8 to 2.0 inch
range. As a result, the Flood Watch was extended for a portion
of southwest Pennsylvania through 09Z. These factors will start
to tail off after that time as the shortwave departs, with
decreasing support for lift as well as slowly dropping moisture
levels. Thus, only scattered showers should be left by that
point, with perhaps only a few ridge showers remaining by 12Z.
Low clouds and fog will be prevalent through the morning.

KEY MESSAGE 2...
After ceilings lift/mix out by early afternoon, we will be
monitoring the next severe threat, although there continues to
be uncertainty regarding the risk level. As a shortwave trough
digs into the Great Lakes, a surface cold front will drop across
the Upper Ohio Valley during the late afternoon/evening hours.
Deep shear will be increasing into the 35 to 45 knot range ahead
of the front, with even higher values behind it. There remains
some spread in the guidance regarding SBCAPE values ahead of the
front, although 25th/75th percentile values are higher than in
previous runs, with 25th percentile values from 900-1300 J/kg
and 75th percentile levels at 1500-2000 J/kg. HREF member
soundings continue to suggest a warm layer at 800mb of various
strengths. The eventual instability levels will have
implications for convective coverage, updraft strength, and of
course level of severe threat. For now, think that the Marginal
Risk level sent by SPC is the way to go. However, if higher-end
instability levels seem more likely later on, a higher threat
level may be warranted, especially as supercells may become more
likely. Damaging wind gusts and large hail remain the main
impacts. Any risk will end by around midnight as the front
exits, although a few scattered showers may remain in its wake.

KEY MESSAGE 3...
Minor timing issues remain, but ensembles have clustered into some
better agreement that the trough axis crosses the region early
Monday and maintains showers through the early morning hours before
mid-level ridging provides a dry interlude by midday. This
break may last until Tuesday night or Wednesday, depending on
the progress of the next front.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Most shower activity is east of PIT, and will continue to slowly
wane as overall moisture and support for lift decrease. By 12Z,
any showers should be confined to the ridges. However, IFR/LIFR
ceilings/visibility in fog and low stratus will remain present
past sunrise. This should gradually improve to MVFR by mid
morning on Sunday with mixing, and eventually VFR by afternoon.
A broken cumulus/stratocumulus layer is then expected for the
remainder of the day. A cold front will approach and cross the
region from late afternoon into the evening, with scattered
showers and thunderstorms expected. Continued to use PROB30
groups with the most likely timing. However, thunderstorm
chances may increase if higher-end instability scenarios play
out. VFR conditions are expected to develop behind the boundary
as wind shifts to northwest.

Outlook... Outside of morning valley fog, VFR returns Monday
and Tuesday under high pressure. Shower and thunderstorm chances
increase from N-S late Wednesday into Thursday with the
approach and passage of a cold front.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch until 5 AM EDT early this morning for PAZ008-009-
     014>016-021-022-029-073-074-077-078.
OH...None.
WV...None.

&&

$$

DISCUSSION...CL
AVIATION...CL