Flash Flood Warning 111, NWS Pittsburgh, PA

Area Forecast Discussion
National Weather Service Pittsburgh PA
235 PM EDT Wed Jul 16 2025

.SYNOPSIS...
Warm, moist airmass in place will keep chances for showers and
thunderstorms in the forecast through much of the weekend. The
risk for localized flooding continues particularly with daily
rounds of heavy rain possible over the same area.

&&

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

- Slight Risk outlook for excessive rainfall today, but
  confidence is low on a widespread flooding event
- Marginal Risk outlook for damaging wet microbursts during the
  afternoon to early evening
---------------------------------------------------------------

Showers and thunderstorms will continue to increase in coverage
as a mid-upper level shortwave approaches the region. While
there is a marginal severe threat (that will be mentioned below)
the bigger concern will be heavy rainfall through this evening
as PWAT values are projected to increase to near 2", which is
above the climatological max. Warm cloud depths are also
exceeding 11kft, further supporting efficient rainfall. The
latest Hi res guidance does suggest rates reaching 1-2 inches
per hour with some instances exceeding 3 inches/hr as noted in
the previous discussion. The atmospheric parameters support the
slight risk of excessive rainfall as noted by WPC. The one
factor in consideration for flash flood threat is residence time
with storms expected to be moving in the mean 20kt flow. That
being said, if cells move over the same area, the flash flood
threat will increase particularly in urban locations where
flash flood guidance is lower. At this time, with instances of
flash flooding considered to be widely scattered with
probabilities of exceeding 1hr/3hr FFG generally under 30% in a
25mi radius have opted to hold off on a Flash Flood Watch.

As noted above, there is a marginal risk for strong/severe storms
with gusty wind being the primary threat. This is due to the
presence of some shear but with a mostly moist column will be the
result of water loading from the heavy rain.

Areal coverage of thunderstorms will lower with the loss of diurnal
heating but the continued passage of the shortwave will allow for
heavy rain showers and isolated thunderstorms to continue (mainly
across western PA and northern WV) through about 06z (2am).

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
KEY MESSAGES:

- Flash flood potential continues with showers and thunderstorms
  favoring the southern half of forecast area.
- Some uncertainty in boundary placement which will impact
  coverage of thunderstorms.

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

The shortwave train continues with a second wave, currently back
in IA moving over the lower Great Lakes overnight. This should
help push a boundary south over the region for the day on
Thursday but there remains some slight differences in it's
location which could have influence on convective initiation for
the afternoon. Some model members push the boundary further
south toward the southern PA/WV border while others keep it
further north. Still others initiate some convection of the lake
breeze so opted to not make too many wholesale changes in the
NBM PoPs based on these scenarios.

Conditions tomorrow will be much like they are today, with
PWATs expected to remain high for the time of the year. Wind
field will be slightly more zonal/unidirectional which could
support training/backbuilding storms. With some uncertainty in
coverage, the risk for excessive rainfall was kept at a marginal
risk, but still supports the isolated threat for flash flooding,
particularly in any location that receives heavy rain today.

With more dry air aloft tomorrow, there remains the potential
for some storms to produce strong/severe storms as well.

Storm coverage and threat potential Friday is likely to be
dependent on the positioning of the stalled boundary as another
shortwave within quasi-zonal flow traverses the region.
Ensembles favor areas along and south of I-70 for another round
of afternoon to evening showers/thunderstorms. The environment
will remain moist (75-90th percentile PWATs) and marginally
unstable (1000 J/kg SBCAPE) that supports higher rainfall rates
and localized flash flooding. An influx of convective modeling
in the next day may further push this axis south and limit
precipitation potential in the area. The post-frontal
environmental for areas north of the boundary is expected to be
more seasonable with near average temperature and lower daytime
humidities.

&&

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

- Ensembles trending toward continuing the active weather
  pattern Saturday into next week.
- Flood and severe potential remain highly uncertain and is
  likely largely predicated on prior days outcomes.
-------------------------------------------------------------------

The initially advertised reprieve Saturday is seemingly
vanishing as ensemble models continue to trend toward
maintaining the active weather pattern for the Upper Ohio River
Valley. Saturday into Sunday weather will be driven by shortwave
movement within increasingly northwest flow as ridging attempts
to build over the southern Great Plains. This could lift the
previously stalled boundary slightly northward to help foster
convection while it aligns parallel to the upper flow; combined
with PWATs trending back toward/above the 90th percentile, flash
flooding will be a potential concern pending finer resolution of
mesoscale features closer to the event.

Early next week appears to feature additional shortwave movement
over the ridge top as it slides toward the lower Ohio River
Valley, putting the forecast area in the NE ridge quadrant.
Again, pending finer details, this pattern will be conducive to
shortwave driven thunderstorms within an environment that may
support severe and flooding hazards.

This long range forecast is bound to fluctuate more from current
depictions as convective evolutions from one day to the next is
also likely to shape storm potential/coverage/timing and more.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Expect numerous showers and thunderstorms to continue to cross
the area through early evening, as a shortwave trough and
surface warm front crosses the region. Maintained MVFR
restrictions for now, though with high precipitable water
efficient rain producing storms could result in localized IFR
conditions. Will include this potential as storm location
becomes more certain.

Showers and thunderstorms should wane this evening as the
shortwave begins to exit, and diurnal instability diminishes.
MVFR to IFR stratus is expected to develop overnight with low
level moisture in place. Additional showers and thunderstorms
are expected Thursday afternoon as the surface boundary drifts
back south across the region.

Outlook...
Daily shower and thunderstorm chances are expected to
continue through the weekend, especially in the
afternoons/evenings, as a front becomes quasi-stationary and
drifts across the region. Fog and stratus is also possible each
morning, especially where rain fell the previous day.

&&

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

&&

SYNOPSIS...34
NEAR TERM...34
SHORT TERM...34
LONG TERM...Frazier
AVIATION...WM

Hazardous Weather Outlook
National Weather Service Pittsburgh PA
152 AM EDT Wed Jul 16 2025

OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>022-029-
031-073>078-WVZ001>004-012-021-509>514-170600-
Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH-
Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango-Forest-
Lawrence-Butler-Clarion-Jefferson PA-Beaver-Allegheny-Armstrong-
Washington-Greene-Westmoreland-Higher Elevations of Westmoreland-
Fayette-Higher Elevations of Fayette-Indiana-
Higher Elevations of Indiana-Hancock-Brooke-Ohio-Marshall-Wetzel-
Marion-Monongalia-
Ridges of Eastern Monongalia and Northwestern Preston-Preston-
Eastern Preston-Western Tucker-Eastern Tucker-
152 AM EDT Wed Jul 16 2025

This Hazardous Weather Outlook is for east central Ohio, western
Pennsylvania, and northern West Virginia.

.DAY ONE...Today and tonight.

Widespread showers and thunderstorms through tonight can produce
heavy rain that may result in flash flooding. If confidence increases
in an area more likely to see flooding, a Flood Watch may be needed.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Multiple rounds of showers and thunderstorms are possible through
early next week may pose varying risk levels of flooding. Continue to
monitor the latest outlooks as impact potential could change based on
previous days outcomes.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

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