483
FXUS61 KPBZ 120817
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
417 AM EDT Sat Jul 12 2025

.SYNOPSIS...
Seasonally warm temperatures with isolated shower storm coverage
are expected 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 TONIGHT/...
KEY MESSAGES:

- Hot; high temperatures climb into the 90s and heat indices
  approach 100 degrees in spots.
- Isolated thunderstorms possible this evening into tonight,
  especially across east-central OH.
- Storms will be capable of producing damaging wind gusts and
  localized flooding issues in heavy downpours.
---------------------------------------------------------------

The environment will be similar today with perhaps a bit more
ridging in the flow pattern and stronger subsidence leading to
drier mid-levels. This will have two consequences: 1) dry air
entrainment will inhibit convective initiation keeping shower
and thunderstorm activity even more isolated than recent days,
and 2) the conditional probability of severe winds increases
(in other words, IF a storm with a strong updraft does form, the
chances that that storm produces damaging winds will be higher
than recent days). This is all supported by the latest ensembles
as well which show high confidence in at least 1000 J/kg MLCAPE
and near 1000 J/kg DCAPE. This would typically support a rather
serious damaging downburst wind threat, but with the abundance
of mid-level dry air there is low confidence in storms being
able to form and capitalize on that environment.

The highest chances of realizing the threat are in east-central
Ohio, where there is a low to medium probability of a pre-
frontal trough passage triggering isolated to widely-scattered
thunderstorm activity during late evening into early overnight
hours. The Storm Prediction Center has introduced a Marginal
Risk (level 1 out of 5) for damaging wind gusts should those
storms initiate. With PWATS again near the 75th to 90th
percentile, warm rain processes, and up-shear vectors of >5kts,
a localized flood threat also could not be ruled out.

One other consequence may be more breaks in the clouds, leading
to more sunshine which will help temperatures climb into the
90s across much of the area and could help head indices get near
or reach 100 degrees, especially in river valleys and urban
metros. Little relief is expected overnight with NBM showing a
greater than 50% chance of lows above 70F in eastern OH, the
lowlands of northern WV, and far southwest PA.

&&

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

- Slightly higher severe wind threats and flash flooding threats
Sunday.
- Lingering shower/storm chances Monday.
- Monday temperatures in the mid to upper 80s.
----------------------------------------------------------------

More organized severe and flooding threats materialize Sunday with
the approach and passage of a front. This might make the chance of
storms themselves higher, but the conditional probability of a storm
being severe slightly lower. This forcing will be a mode for
initiation in an environment that is preconditioned with 1000 J/kg -
1500 J/kg MLCAPE and ensemble mean 600 J/kg - 800 J/kg DCAPE. This
is marginally enough to allow for a potential downburst wind threat.
SPC has issued a day two marginal risk.

As for flooding, the moisture push will likely take PWATS back
towards or higher than the 90th percentile with low-/mid-level flow
remaining around 10-15kts. With a deep warm layer 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.

On Monday, a mid-level shortwave is still forecast to move through
the area. The timing has been uncertain with some ensemble members
pushing the axis through during the morning, and others lagging it
into the afternoon. Currently, it looks as if models are beginning
to agree on passing through during the afternoon. The highest
probability for precipitation is 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.

&&

.LONG TERM /TUESDAY 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 drier pattern still appears likely Tuesday and Wednesday under
surface high pressure. The approach of a mid-level shortwave on
Wednesday, will likely provide the instability to produce diurnal
showers/storms on an isolated basis. The mid-level trough is
expected to remain relatively stationary through Friday.

Increasing southwest flow will help to bring the heat and humidity
back up for Tuesday and Wednesday as 850mb temperatures run back up
to 19C to 20C. Probabilities of 90F or greater max temperatures
increase to 55%-75% on Tuesday and 70%-90% on Wednesday with the
highest probabilities in the urban and valley areas while the ridges
will likely remain below 90F. 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 reduce heat index values as compared to
Wednesday.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
A persistence forecast is warranted with patchy fog possible
through early morning 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 where precipitation did or (more importantly)
didn`t fall Friday afternoon; as such, higher confidence in fog
formation is present at MGW/LBE/DUJ versus other terminals.

Hi-res modeling continues to favor too isolated of afternoon
convection for terminals most of the day Saturday to warrant
mention in the TAFs; diurnal scattered CU (that is occasionally
broken at MVFR levels at they rise) will be the main feature.
An approaching shortwave may better foster thunderstorm
development after 20z near ZZV, but confidence in that occurring
remains low so left mention out in this cycle.

Outlook...
Isolated showers/storms may pass over the region late Saturday
evening into Sunday morning in conjunction with an upper wave
and presence of the warm, moist airmass (but probabilities are
still 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...Cermak/Milcarek/Shallenberger
SHORT TERM...Milcarek/Lupo
LONG TERM...CL/Lupo
AVIATION...Cermak/Frazier