362
FXUS61 KPBZ 202312
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
712 PM EDT Thu Aug 20 2026

.WHAT HAS CHANGED...
Rain chances will diminish this evening into the overnight time
period, dense fog is expected to develop tomorrow morning. A
passing trough is expected to return showers and thunderstorms
late Saturday evening.

&&

.KEY MESSAGES...
1) Potential for dense fog late tonight into tomorrow morning.

2) After limited shower/storm activity Friday, new rounds of
rainfall are possible over the weekend. Saturday may present a
localized threat for damaging wind gusts, depending on frontal
timing and cloud cover.

&&

.DISCUSSION...
KEY MESSAGE 1...
The probability of heavy rain has decreased over the last 6
hours as a disturbance exits towards the East Coast and drier
air returns. Flood Warnings will remain in effect late this
evening in eastern Ohio and portions of West Virginia due to
heavy runoff from 2-3 inches of rain earlier today. A few Flood
Warnings may need to be extended into early Friday morning if
creek gauges remain high.

The probability of fog increases late tonight into early
tomorrow with clear sky conditions, light winds, and remnant
boundary layer moisture. A Dense Fog Advisory may issued for
portions of the region.


KEY MESSAGE 2...
Weak surface high pressure still tries to build south on Friday.
Model guidance appears a bit less bullish on shower/storm
development during the afternoon. Moisture depth/subsidence-
induced capping may largely suppress development at least north
of the PA turnpike, and potentially further south than that. Will
keep NBM suggestion of PoPs south of I-70/east of I-77, although
some minor modification may be needed with future model runs.

The next 500mb shortwave trough pivots across the Great Lakes
later Friday night/Saturday morning, and lingers across the
Upper Ohio Valley into Sunday with additional vorticity maxima
maintaining lower heights. An associated frontal boundary looks
to swing through during late afternoon/evening on Saturday,
although the timing still is questionable. There are still
scenarios, given favorable timing/clearing, that show sufficient
CAPE and DCAPE for a downburst wind threat. The 12Z RRFS, for
example, does show up to 1500 J/kg CAPE/800-1000 J/kg DCAPE in
areas east of Pittsburgh during the afternoon that could support
the severe threat. Much of the available machine-learning
guidance does continue to highlight the potential. Still,
changes in frontal timing or cloud cover could reduce the
overall threat, and future CAMs runs will be evaluated to
reassess the risk.

That then serves as a precursor to additional shortwave trough
movement aloft combining with a more defined surface cold front
that passes through sometime Saturday afternoon into Sunday.
Variances in upper trough depth/positioning and timing of the
wave makes it difficult to assess potential storm environments
and potential hazardous weather threats. Ensemble guidance,
driven primarily by Canadian modeling, does show scenarios with
enough CAPE/dCAPE for a damaging wind threat (though weak shear
won`t be a boon) that seems to be captured by a few other
machine-learning convective outlook models. This scenario is
mainly tied to clean heating prior to the front/shortwave and
Saturday afternoon/early evening storm occurrence; earlier/later
arrivals or more cloud cover is just as likely that would
dampen or completely squash that risk. Trends will be monitored
to understand how things may track. Scattered showers/storms
remain possible on Sunday, but convective parameters appear a
little less favorable for a severe threat.

Ensembles continue to lend confidence to a drier forecast for
the first part of next week, as surface high pressure returns
under a weakening troughing pattern.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Only spotty showers near ZZV remain across the area and skies
are beginning to scatter. Low-level clouds will continue to
dissipate past sunset yielding a largely SKC stretch into the
overnight and early morning hours. With recent rainfall, lighter
winds and clear skies, fog formation seems to be a likely.
Models favor areas in the eastern ridges and near I-80 for the
worst impacts but other areas like ZZV that saw ample rainfall
could have IFR/LIFR issues as well through 13-14z.

Once fog lifts, a dry VFR forecast is expected with SCT fair
weather CU between 3-5kft. Winds are expected to remain light
and easterly.


Outlook...
Additional rounds of rain and restrictions are likely this
weekend with another passing disturbance.

&&

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

&&

$$

DISCUSSION...Hefferan/CL
AVIATION...AK