PBZ issues Area Forecast Discussion (AFD) at Aug 4, 8:11 PM EDT667
FXUS61 KPBZ 050011
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
811 PM EDT Tue Aug 4 2026
.WHAT HAS CHANGED...
Messaging and storm outlooks for the latter half of the week
remain unchanged, but discussion attempts a deeper scenario
dive. The aviation discussion has also been updated for the 18z
TAF issuance.
&&
.KEY MESSAGES...
1) A moist airmass develops Wednesday and results in daily
thunderstorm chances into the weekend, with varying degrees of
hazard risks.
&&
.DISCUSSION...
KEY MESSAGE 1...
----- Overview -----
The upper Ohio River Valley is set to be positioned between
an Atlantic high and western Great Lakes trough Wednesday
through the weekend, resulting in moist airmass that allows
for daily thunderstorm chances and varying degrees of hazard
risks. Weak flow and forcing combined with convective evolution
uncertainties leave lots of unknowns in timing/coverage/hazards
during this period.
For Wednesday/Thursday/Friday:
Ensemble models favor the area remaining east of the upper
trough axis within moist, southwest flow while having the
potential for embedded weak shortwaves to cross at varying
times. Moisture currently pooled in the Carolinas will be drawn
northward and push PWAT values toward the 90th percentile,
staying there due to little to no airmass changes (i.e. frontal
boundaries), while enough heating creates sbCAPE values around
1200 J/kg each day.
Thunderstorms are likely to be diurnally driven with total
coverage dependent on the presence of a mid- level shortwave
(which could materialize based on upstream convection evolution)
and degree of surface heating with any lingering cloud cover.
Hazardous weather threats, in the form of isolated flash
flooding and downburst winds, thus hinge on higher lift - larger
buoyancy scenarios (not likely as evidence by limited outlooks
from SPC/WPC) that remain difficult to discern now. Greater
understanding of the environmental risks may not be fully
realized until the morning of.
For Saturday/Sunday:
Latest guidance favors a more concentrated eastward progression
of the upper trough axis this weekend, aiding greater lift to
the moist/unstable airmass still in place. The resultant shear
increase combined with similar sbCAPE and slightly higher dCAPE
values seen in model mean outputs suggest a slightly higher
severe risk (damaging wind) when this axis crosses. This assumes
an afternoon/evening passage that also sees enough surface
heating to reach idealized buoyancy levels.
There is even a larger caveat to forecast outlooks during this
period than the late-week section due to even larger spreads in
shortwave timing and its progression after passage. This
includes ranging from quick passage Saturday with dry conditions
developing Sunday to slow passage Saturday and residual weak NW
flow that maintains storms chances into next week. It is best
for users to monitor forecast trends as the weekend approaches
and know understanding of timing and risks may remain clouded
until the morning of.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Patchy fog will be possible mainly south of I-70 during pre-
dawn hours Wednesday morning as the surface high shifts east of
the are and moisture begins to return from south to north. A
greater coverage in diurnal cu (sct-bkn) is expected Wednesday
afternoon with the increasing moisture, but cigs should remain
VFR.
Scattered showers and storms (and associated restrictions)
return Wednesday afternoon/evening with an approaching
trough. Due to the disorganized nature of the storms, there is
low confidence in where/when they will develop. PROB30s where
added to each terminal to show the general period of time when
storms are possible.
Outlook...
This trough will persist across the region through the remainder
of the week and possibly into the weekend, supporting daily
shower and storm chances especially during afternoon/evening.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
DISCUSSION...Frazier
AVIATION...Cermak/Lupo
Source:
PBZ issues Area Forecast Discussion (AFD) at Aug 4, 8:11 PM EDT---------------
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