PBZ issues Area Forecast Discussion (AFD) at Aug 17, 1:33 AM EDT463
FXUS61 KPBZ 170533
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
133 AM EDT Sun Aug 17 2025
.SYNOPSIS...
Scattered showers and thunderstorms return today as a front
crosses the area and stalls to our south. The stalled front will
then lift north next week, keeping periodic shower and
thunderstorm chances in the forecast for much of the week.
&&
.NEAR TERM /THROUGH TODAY/...
KEY MESSAGES:
- Mostly dry with above average overnight lows expected
- Scattered showers and thunderstorms today
---------------------------------------------------------------
An Upper Plains ridge will slowly shift east across the Great
Lakes now through tonight, bringing a cold front into our area
today. Regional radar shows storms well upstream currently
across Wisconsin into Illinois and Indiana, sliding down the
eastern side of the Plains/Central CONUS ridge. Though a quiet
rest of the overnight period is expected, high uncertainty
remains in regards to the evolution of this upstream convection
and any possible impacts to our forecast area after sunrise.
Latest CAM runs continue to poorly initialize and model these
MCSs and are of little use beyond environmental trends. Our
expectations are that convection dives to the south through the
early morning, staying west of our area and/or weakening as
they near our area. However, cannot rule out the possibility of
a few stronger storms crossing into Northwest PA by mid-morning
with the potential for damaging wind and hail.
Likewise, afternoon diurnal convection is uncertain and will be
contingent on morning evolution. Mid-morning arrival of
convection would likely limit afternoon coverage to areas south
and east of Pittsburgh with little chance for redevelopment
behind the MCS. Later arrival would certainly be more conducive
for strong to severe storms (more favorable environment), but
increased cloud blowoff from dying upstream convection could
limit afternoon development. Regardless of uncertainty, it
appears rain coverage will be somewhat spotty and isolated to
scattered in nature. Would expect some locations to not see much
rain at all. PWATs will range from 1.5 to 2.0", so brief heavy
downpours are possible. The front eventually stalls along the
Mason-Dixon this evening, with any lingering convection
diminishing with the loss of daytime heating.
While above average, afternoon highs will run around five
degrees cooler than Saturday.
&&
.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
KEY MESSAGES:
- Dry weather returns on Monday.
----------------------------------------------------------------
Any lingering convection should diminish this evening, leaving a
dry overnight for most. Overnight lows will cool to near-
average.
We dry out again on Monday as the ridge axis begins to rotate
over the area and local height rises result in subsidence and
drying of deep layer moisture profiles. Temperatures remain
above average both Sunday and Monday with highs in the upper 80s
to low 90s, though heat impacts will be worse on Sunday due to
the increase in moisture/humidity.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
KEY MESSAGES:
- Several rounds of showers/storms possible Tuesday and
Wednesday.
- Low-probability rain chances Thursday and Friday.
-------------------------------------------------------------------
The central CONUS ridge begins to slowly retrograde back over
the southern high plains and southwest US on Tuesday, allowing
the stalled front to our south to lift back northward as a warm
front. This re-introduces shower and thunderstorm chances both
Tuesday and Wednesday as an upstream trough digs into the Great
Lakes. The coverage and intensity of showers and storms on
Tuesday/Wednesday will depend on the interaction between
this Great Lakes trough and Hurricane Erin in the western
Atlantic. As previously mentioned, troughs upstream from
recurving tropical systems tend to overperform (verify deeper
than modeled). Following this logic, would favor solutions that
have a stronger trough moving into Great Lakes and thus a bit
more vigorous rainfall event. This is reflected by the WPC
Excessive Rainfall outlook for Tuesday. Will continue to monitor
guidance trends. NBM PQPF remains at 10-30% chance of 1"+ for
the period, with the highest probabilities occurring northeast
of Pittsburgh.
Guidance shows ridging extending eastward from a dominant and
persistent Four Corners upper-level high, stretching across
central Plains and into the Ohio Valley Thursday and Friday.
This would support drier weather, however diurnal isolated
showers/storms will remain possible each afternoon, especially
across the higher terrain. Another trough is expected to dive
southeast into the Great Lakes and southern Ontario Saturday
into Sunday, which may renew local precipitation chances.
Typical timing errors and uncertainty associated with a Day 7
forecast render this as relatively low in confidence.
Temperatures start the period above average on Tuesday before
eventually settling around climo normals mid to late week.
&&
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Aside from some isolated shower/storm development through or an
hour or two after sunset tonight, the trend will be for
diurnally driven cumulus to dissipate and give way to increasing
cirrus overnight downstream of a convective complex across
Michigan and Wisconsin. Light wind prevails overnight.
The challenging and lowest confidence part of the forecast for
the TAF period comes Sunday morning as the remnants, or
lackthereof, of the convective complex dives toward the area.
CAMs have struggled, and continue to struggle, to resolve the
complex in its present state, let alone how it's going to
progress overnight. They notoriously have issues resolving these
features, and given all of these uncertainties, forecast
confidence is low. The current TAF suite reflects PROB30s
covering the case that the storms do make it here in which
associated restrictions in TSRA return. There is also an
alternative scenario in which it weakens/dissipates before
sunrise and we're mainly left with mid-level debris clouds and
VFR. Lower level moisture is progged to be a bit more pronounced
farther north, and probs for prevailing MVFR cigs are elevated
at FKL in the morning hours.
Into the afternoon hours, some additional showers are possible
with weak cold advection and lingering low level moisture,
though confidence is even lower behind whatever happens in the
morning, and further TAF updates will work to resolve this. Wind
will prevail from the southwest in the morning ultimately
veering to the northwest in the afternoon between 5-10 knots.
Outlook...
VFR weather returns Monday and Tuesday. There could be patchy
fog Monday morning depending on where and if it rains Sunday.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Rackley
NEAR TERM...Rackley/MLB
SHORT TERM...Cermak/McMullen
LONG TERM...Cermak
AVIATION...MLB/McMullen
Source:
PBZ issues Area Forecast Discussion (AFD) at Aug 17, 1:33 AM EDT---------------
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