242
FXUS61 KPBZ 132200
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
600 PM EDT Sun Jul 13 2025

.SYNOPSIS...
Scattered showers and thunderstorms, with a risk of isolated
damaging wind gusts and flooding, are expected this afternoon
and evening. A slow-moving boundary continues rain chances on
Monday, with relatively drier conditions Tuesday. By midweek,
heat, flooding and severe weather concerns return to the region.

&&

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

- Marginal severe risk to the east of Pittsburgh this
  afternoon/evening; isolated flash flooding possible areawide
- Temperatures continue to run above seasonal levels
- Patchy fog development possible Sunday night in areas that see
  rainfall during the day

---------------------------------------------------------------

Longwave troughing remains over the Great Lakes through tonight,
with the axis slowly rotating across Lake Michigan/Lower Michigan
through tonight. This will slowly push a surface boundary eastward,
reaching northern Ohio/Lake Erie by sunrise Monday. As compared to
Saturday, less subsidence and a bit more moisture in southwest flow
will exist, leading to better chances of scattered diurnally-
driven showers and thunderstorms. Showers are already starting
to fire in Ohio, where more agitated cumulus are apparent on
satellite loops. CAMs are suggesting more widespread initiation
after 18Z, peaking in coverage during the late afternoon/early
evening. SPC has maintained the marginal risk of severe
generally east of I-79, in an area with 600-800 J/kg of DCAPE
expected, suggesting a low-end downburst threat still exists.

Also, PWATs of 1.6 to 1.7 inches, deep warm cloud depths, and
up-shear vectors of 10 knots or less also suggest an ongoing
threat of isolated flash flooding. However, the HREF continues
to maintain the higher risk of heavy rainfall off to our east,
where better low-level moisture convergence and higher mean-
layer CAPE values of 1500-2000 J/kg lie. This matches well with
the WPC slight risk of excessive rainfall. This slight risk area
actually intersects our easternmost ridges, which makes sense,
as upslope flow could tie storms to the terrain for at least
brief periods. Still, think any flooding issues will remain
isolated for the most part, with urban/poor draining areas the
most likely impacted. Think that this precludes the need for a
Flood Watch at this time.

Convection will taper after sunset with the loss of daytime
heating, followed by a quieter (but still warm and muggy) Sunday
night period, although a few isolated showers will remain
possible. Patchy fog will be possible in places that see
accumulating rainfall during the day.

&&

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

- Best storm/shower chances Monday afternoon south of Pittsburgh
- A bit warmer Tuesday with lower precipitation chances

----------------------------------------------------------------

A shortwave trough is still slated to cross the region on Monday,
bringing the weak surface boundary with it. The trend in hi-res
models appears to include a slower movement, such that the axis
will be in/near the Pittsburgh area during the early afternoon,
as opposed to previous runs showing quicker movement. This will
result in higher precipitation chances than in previous
forecasts, especially from Pittsburgh on south and east. This
region is also where low- chance severe and flooding risk would
be present, with continued high PWAT, respectable DCAPE, and
slow storm motions. Afternoon high temperatures in the mid 80s
remain seasonable, although sticky dewpoints near or above 70s
will linger.

Activity will diurnally fade Monday night, and balmy overnight lows
can be expected. The weak front may have trouble clearing our region
by Tuesday, perhaps hanging up to the south of Pittsburgh in weak
flow aloft, while 500mb heights build back above 590dm. This may
result in another round of scattered diurnal convection. PoPs are
lower overall but remain highest in the PA/WV ridges, where better
low-level convergence is suggested. Low end severe/flood risk may
remain, if a bit lower than Monday. In contrast, temperatures will
not be lower, but higher, as a result of the building heights. NBM
shows a general 30-50% chance of highs of 90 or higher, with 50-70%
chance in valleys/urban areas. Heat index values may rise into the
mid to upper 90s as a result in these warmer locations. This will be
followed by another night with little relief from the warmth after
convection fades again, with overnight lows/dewpoints mostly 70 or a
bit higher.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
KEY MESSAGES:

- Heat Wednesday and Thursday
- Daily rain chances through the work-week with forecast
  uncertainty increasing into the weekend.

-------------------------------------------------------------------

Wednesday appears to be the hottest day of the week as it
stands with the greatest extent of upper ridging. Because of
this, heat risk generally maximizes in the moderate/major
category; though realization of this threat will require no
afternoon rain/storms in any given area. For areas that do see
rain, there is some severe potential. Though not outlooked,
subsidence in the upper mid-levels undercut by warm, moist
southwest flow during a mid-level shortwave passage south of the
main surface front may allow for a downburst wind threat. This
is highlighted in roughly 30% chance of severe within 70 miles
of a point in CIPS analogs, though CSU machine learning is a bit
less bullish in probabilities. As for flooding, PWATS will be
near the 90th percentile, though sfc to 500mb mean flow of
15kts may hit that realizing a flood threat will rely on
training.

Environmentally, the area will remain quite similar Thursday
and Friday before the main cold frontal passage. This will
support non- zero severe threats, and multiple rounds of diurnal
storms will also increase the flooding risk slightly. WPC has a
marginal risk of excessive rainfall for Wednesday and Thursday
for now, though perhaps more cloud cover and some height falls
may result in a a small "cooling trend", even though
temperatures will remain above average.

Ensembles seem to be in relatively good agreement with quasi-
zonal flow through mid-week. This breaks down late week. There
are some uncertainties in western ridging amplitude. Should the
western ridge exist (or be stronger) this would reinforce
eastern troughing for the weekend with temperatures near normal
and slightly drier behind a Friday cold frontal passage (45% of
clustered ensemble guidance). Should the western ridge not
develop, the same mid-week pattern may persist (55% of clustered
ensemble guidance).

&&

.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
High confidence /greater than 70%/ save for two things:
* how widespread IFR VIS will be between 8-12Z at airports that
  received rainfall today?
* coverage of showers and perhaps a thunderstorm tomorrow
  afternoon?

VFR weather this evening will yield to MVFR and perhaps IFR
conditions at most terminals given rainfall during the daylight
hours. If this happens the most likely time window would be
8Z-11Z. NBM VIS probs are highest from LBE to MGW where values
are around 30%, however elected to keep an expanded area of
airports in IFR given the observation history from the GFS
LAMP.

VFR weather rapidly returns Monday morning and carries through
the balance of the forecast. Continued with PROB30 for all
airports save for I80 ones during the afternoon as an upper
level disturbance moves through and this could lead to a shower
or storm.

Outlook... Scattered diurnal convection now appears likely again
on Tuesday, potentially leading to brief restrictions during
the afternoon/evening hours. Localized morning fog also can`t be
ruled out. Precipitation and restrictions become more
widespread on Wednesday and Thursday as southwest flow and
moisture increase.

&&

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

&&

$$

SYNOPSIS...CL
NEAR TERM...CL
SHORT TERM...CL
LONG TERM...Milcarek
AVIATION...CL/McMullen