760
FXUS61 KPBZ 210552
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
152 AM EDT Fri Aug 21 2026

.WHAT HAS CHANGED...
A dense fog advisory was issued covering portions of the region
through 9am this morning. The rest of the forecast messaging is
unchanged.

&&

.KEY MESSAGES...
1) Areas of fog this morning with potential for locally dense
fog that impacts the early morning commute.

2) Dependent on onset timing, damaging wind threat may develop
with thunderstorms Saturday afternoon and evening.

&&

.DISCUSSION...
KEY MESSAGE 1...
The combination of daytime rainfall and clear skies is the main
drivers for fog development for portions of the region early
this morning. However, subtle easterly winds and potentially
some dry advection within the boundary layer seems to be
disrupting that process enough to keep most fog within select
river valleys and more patchy than widespread. While there may
be variations in coverage and intensity, the conditions are
ideal enough that a Dense Fog Advisory was issued through 9am
for portions of eastern OH through western PA.

Area fog will dissipate shortly after sunrise as diurnal
heating/mixing commence.


KEY MESSAGE 2...
Hi-res modeling has continued the trend of suppressing most
convection this afternoon/evening thanks to strong subsidence
from high pressure to the north; any precipitation that develops
may be along the eastward facing slopes of the Laurel
Highlands/WV higher terrain where upslope flow may induce enough
lift for isolated initiation.

The main focus remains on a shortwave that acts to deepen upper
troughing over the region Saturday into Sunday morning while
driving a cold front west to east through the region. Confidence
is fairly high on the potential storm environment to feature around
1500 J/kg CAPE, around 850 J/kg DCAPE, and weak shear that would
be conducive to a localized downburst wind threat. SPC
convective outlooks are likely to remain Marginal, though, as
this threat is conditional on storms (and to an extent, the
front) arriving early enough to tap into this environment before
the boundary layer stabilizes; i.e. the threat is more likely to
materialize if the scenario of storms starting between 4pm-8pm
comes to fruition. Hi-res modeling remains fairly evenly split
in whether that is the likely outcome versus storm/front arrival
being more 7pm-11pm which sees a stabilizing airmass. In either
case, the general outlook favors scattered to locally numerous
thunderstorms ahead of the cold front that slowly exits east by
early Sunday morning.

Cold core processes underneath the deeper trough will keep lake
enhanced shower and low probability thunderstorm chances in the
forecast through Sunday evening. Thereafter, building high
pressure underneath height rises fosters dry weather while also
lifting seasonably cooler temperature Sunday/Monday back toward
daily averages Tuesday.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Patchy fog that is or could be locally dense will continue to
meander near area terminals through 13z, favoring those that
received plenty of daytime rainfall and/or are near river
valleys. The presence of some few/sct cloud decks as well as
battles between strong radiational cooling and weak dry
advection favors wild bouncing of visibilities/restriction that
TAFs won`t attempt to capture.

VFR develops by 14z as diurnal heating/mixing commences with
only a few to locally scattered CU likely to develop through the
day. Any rain chance favors the eastern-facing slopes of the
Laurel Highlands and WV higher terrain this afternoon where
enough moisture/upslope flow could result in an isolated storm.

Outlook...
Localized fog, favoring river valleys, may develop again
Saturday morning. Otherwise, an approaching cold front and upper
trough passage fosters scattered to locally numerous showers and
thunderstorms that cross Saturday afternoon into early Sunday
morning. Additional rain/restriction chances linger through
Sunday evening thanks to cooler NW flow and lake moisture
enhancement.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Dense Fog Advisory until 9 AM EDT this morning for PAZ009-
     014>016-020>022-029-031-073>078.
OH...Dense Fog Advisory until 9 AM EDT this morning for OHZ049-050-
     058-059-069.
WV...Dense Fog Advisory until 9 AM EDT this morning for WVZ001>004-
     012-021-509.

&&

$$

DISCUSSION...Frazier
AVIATION...Frazier