370
FXUS61 KPBZ 112349
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
749 PM EDT Fri Jul 11 2025

.SYNOPSIS...
Seasonally warm temperatures with isolated shower storm coverage
are expected Friday and Saturday, before storm chances increase
Sunday with severe weather and flash flooding risks. A
relatively drier period is forecast next week with cumulative
heat concerns.

&&

.NEAR TERM /THROUGH SATURDAY/...
KEY MESSAGES:

- Warm overnight with additional valley fog chances.
---------------------------------------------------------------

Evening Update...The daytime heating has certainly waned with
the lessening cu across the area and the dissipation of the
remaining showers and thunderstorms. A few more remain over
Indiana and Westmoreland but these cells are weakening. Have
updated the forecast to keep these cells in the area for another
hour or so. The activity should cease by the 01Z or 02Z time
period. Overnight, expect another night with a fog potential,
especially those locations that received precip.

Previous Discussion...Save a quick bout of morning convection
riding the I-70 corridor, and the ridges in orographic lift,
most of the region will experience mostly clear skies with
mixing allowing for some fair weather cumulus. As the 12Z
sounding and storms have already shown this morning, instability
in low level moisture will continue to allow for
afternoon/evening shower/storm chances. Meso-analysis tends to
suggest up to 1000 to 2000 J/kg MLCAPE into this afternoon with
radiative heating, which will allow for mostly popcorn
convection. Two things that will locally lower severe potential
today will be effective shear of only around 20kts on the high
end with evidence of a couple capping inversions at 500mb and
600mb with plentiful dry air in the upper levels. Realizing any
low-probability severe threats will be reliant on the breaking
of these caps and ingestion of bountiful dry air for downburst
winds (900 J/kg environmental DCAPE). While not impossible, this
remains quite low probability with no definitive forcing
mechanism. Because of shallow convective development, warm rain
processes will dominate in 1.5" PWATS, so flooding could not be
written off , but only around 5% of ensemble guidance shows
amounts exceeding FFGs somewhere, depending on training or up-
shear growth (mean corfidi vectors of 8kts).

In areas where it does not rain, there will be moderate heat
risk into this afternoon, with chances of heat indices roughly
>50% in the valley/urban locations. Much of the ensemble spread
encompasses highs between the upper 80s and low 90s.

Into tonight, convection chances drop off to less than 10% with
a loss of mixing and unstable, surface-based profiles. Just a
few high clouds should not limit radiative cooling as
temperatures drop to near their respective dews in the lower 70s
and upper 60s. This will lend on to another night of fog
potential most likely for the river valleys. There is a >50%
chance of lows >70F in eastern OH, the lowlands of northern WV,
and far southwest PA which will provide little heat relief
overnight.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Heat risk increases to major for most of the area Saturday.
- Slightly higher severe wind threats and flash flooding
  threats Sunday.
----------------------------------------------------------------

The environment will be similar Saturday with perhaps a bit more
ridging in the flow pattern and upper subsidence, keeping
convective initiation a bit lower probability, but the
conditional probability of severe wind slightly higher. HREF
soundings show 1000 to 1500 J/kg MLCAPE with DCAPE up to 1000 to
1100 J/kg, but with the low probability of deep convection in a
stout dry layer with no definitive forcing, this may be
difficult to tap into. The highest chances of realizing the
threat are in east- central Ohio with a low- to-medium
probability of a pre-frontal trough passage. Once again,
flooding threats remain relatively lower with perhaps a bit
shallower low-moisture profile and very isolated shower/storm
coverage. On the contrary, with PWATS again near the 75th to
90th percentile, warm rain processes, and up-shear vectors of
>5kts, it could not be ruled out completely.

HREF shows a chance of heat indices pushing 95F to 100F during
peak heating Saturday in areas that do not experience rain
under the upper ridging, with brings heat risk into the major
category but with values slightly below advisory criteria.
Nonetheless, heat impacts will again be the most prevalent in
urban and valley areas. Little relief is expected overnight yet
again with NBM showing a >50% chance of lows >70F in eastern OH,
the lowlands of northern WV, and far southwest PA.

More organized severe and flooding threats materialize Sunday
with the approach and passage of a weak front. The major
difference as this front approaches will be the increase in
moisture, and the erosion of the mid level dry air. This might
make the chance of storms themselves higher, but the conditional
probability of a storm being severe slightly lower. Unlike the
two days prior, this forcing will be a mode for initiation in an
environment that is preconditioned with 1000 to 1500 J/kg
MLCAPE and ensemble mean 700 J/kg DCAPE. This may be marginally
enough to allow for a downburst wind threat. SPC has issued a
day three marginal risk.

As for flooding, the moisture push will likely take PWATS back
towards or higher than the 90th percentile with corfidi up-
shear/down- shear vectors of near or less than 5kts. Again, with
a deep warm later, and proportionately higher coverage of
precipitation, it seems at this time that flooding may be the
main threat to focus on as this wave passes, though we will
continue to analyze and message forecast chances.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:

- Lingering shower/storm chances Monday
- Potentially drier Tuesday/Wednesday ahead of another low
  pressure system passage by late week
- Temperatures remain above average, with a peak in
  heat/humidity possible on Wednesday
-------------------------------------------------------------------

A mid-level shortwave is still timed for passage at some point on
Monday, but there remains some relatively modest differences on
timing - with some ensemble members pushing the axis through during
the morning, and others lagging it into the afternoon. This would
suggest that a west-to-east PoP gradient is called for, which the
NBM does suggest, with highest (50-60%) values along the northern WV
ridges. Some timing adjustments are possible depending on whether
the more progressive solutions become more likely.
Severe/flooding risks may remain on an isolated basis with any
storms, although areal coverage of the threat should be lower as
compared to Sunday. Temperatures remain above normal with a
very modest air mass change behind the Sunday front.

A drier pattern still appears likely Tuesday and Wednesday under
surface high pressure and rising 500mb heights, although diurnal
showers/storms may be possible Wednesday on an isolated basis.
Increasing southwest flow will help to bring the heat and humidity
back up for both days as 850mb temperatures run back up to 19C to
20C. Probabilities of 90F or greater max temperatures increase to
50%-70% on Tuesday and 70%-90% on Wednesday away from the ridges,
again highest in the urban and valley areas. NWS experimental Heat
Risk values again reach the "major" range by Wednesday.

The next chance of more widespread rain may arrive by Thursday, with
northern Great Lakes/eastern Canada low pressure dragging a frontal
boundary to and across the Upper Ohio Valley possibly by Friday.
Strength and timing issues remain in the ensembles, although overall
precipitation chances are heightened compared to earlier in the
week. Temperatures remain above normal, but the increased cloud and
rain coverage may ameliorate the heat index values as compared to
Wednesday.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Loss of diurnal heating will erode lingering isolated convection
across western PA as well as aide in the cessation of area
cumulus.

A persistence forecast is warranted with fog overnight as the
airmass at large is unchanged and conditions will again feature
light wind with mostly clear skies. Slight adjustments were made
in degree of fog formation to account for the occurrence (or
lack there of) of precipitation this afternoon; as such, high
confidence is present at MGW/LBE/DUJ versus other terminals.

Hi-res modeling favors too isolated of afternoon convection for
terminals most of the day Saturday; diurnal scattered CU (that
is occasionally broken at MVFR levels at they rise) is the main
feature. An approaching shortwave may better foster thunderstorm
development aft 20z near ZZV.

Outlook...
Lingering showers/storms may pass over the region late Saturday
into Sunday morning in conjunction with an upper wave and
presence of the warm, moist airmass (but probabilities are
currently less than 20-30% on this occurrence).

Approach of a surface cold front and residual upper level
shortwave movement is likely to foster more widespread
convection Sunday that favors western PA and the higher terrain.
Ensemble models favor high pressure that drastically limits
convective potential Monday/Tuesday (but localized morning fog
can`t be ruled out).

&&

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

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...Milcarek/Shallenberger
SHORT TERM...Milcarek
LONG TERM...CL
AVIATION...Frazier