985
FXUS61 KPBZ 161146
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
746 AM EDT Wed Jul 16 2025

.SYNOPSIS...
Increased risks for localized flooding are expected through
Friday as rounds of showers and thunderstorms cross the region.
Additional waves of convection are likely starting Saturday
evening through the middle of next week.

&&

.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
---------------------------------------------------------------

A 700mb shortwave currently located over the lower Ohio River
Valley will lift northward today and cross the region through
tonight before advancing through New England. This wave will
lift the stalled surface boundary northward that, combined with
modest mid-level jet ascent, will promote fairly widespread
shower and thunderstorm coverage for much of the daylight hours
(but favoring noon to 10pm).

The main focus for hazard potential today is tethered to flash
flooding as the shortwave provides an influx of column moisture
that will shoot PWATs to near 2", which is near the daily
climatological record. Add in modest heating through varied
cloud decks that creates 1500-2000 J/kg CAPE and warm-rain
processes, showers and thunderstorms will be capable of
producing rainfall rates that average 1-2"/hr but could briefly
be on the order of 3-4"/hr. A few factors playing in the role in
the lack of a Flood Watch issuance: 1) hi-res modeling is
bearish on strong convergence/forcing that would allow for
focused training of storms (meaning all areas have relatively
equal chances to experience flash flooding but it will more
likely be very localized); 2) increased mid- level wind should
push storm motion closer to 15-20kts that may not allow for long
enough storm residence time to exceed flash flood guidance; and
3) a relative "dry" preceding period is keeping flash flood
guidance higher at most locations than the likely storm
accumulation. Additional evaluation of latest guidance and storm
trends may better clarify a location of higher flood potential
that would lead to a more short-fused Flood Watch.

A more limited but non-zero threat will be damaging wet
microbursts as the aforementioned SBCAPE could allow for
precip- loading of cells that falter with updraft decay given
the lack of shear.

Areal coverage of thunderstorms is likely to lower after sunset
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 heavy rain showers and
  thunderstorms favoring the southern half of forecast area.
- High variability on storm coverage Thursday creating large
  uncertainty.

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

Subsidence in the wake of Wednesday`s shortwave prior to the
arrival of another shortwave/surface cold front should result in
a dry morning Thursday. Approach of that shortwave/front will
again spawn convection along/ahead of the boundary during the
late morning to evening hours within an environment that is only
slightly less moist/unstable (90th percentile PWATs and
1000-1500 J/KG SBCAPE) than Wednesday. Given similar
characteristics, a Marginal Excessive Rain Outlook highlights
the region for potential flash flooding as areas hit hardest the
prior day will be more susceptible to flooding. Storms will
gradually taper off Thursday night as the shortwave exits, but
the surface front will stall south of Pittsburgh.

There remains large uncertainty, however, in the location of
the surface cold front and the result axis of storm initiation.
Global ensembles have maintained some development along the line
in northeast OH into northwest PA late morning Thursday that
advances southeast; latest hi-res convective models drop that
line closer the the I-70 corridor before storm initiation and
thus leaving areas north relatively dry. Given the moist and
unstable airmass and potential slight aid in convective
initiation from a lake breeze off Erie, have maintained ensemble
mean PoP for Thursday. If this does deviate, look for
drier/cooler conditions north of Pittsburgh and the axis of
greater storm coverage along/south of I-70.

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 TUESDAY/...
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 /12Z WEDNESDAY THROUGH SUNDAY/...
VFR is expected this morning as mid and high clouds increase
ahead of a surface warm front, and a shortwave trough. The CU
rule and model soundings indicate a broken cumulus layer will
develop by mid morning as convective temperatures are reached.
The shortwave trough should spark a few showers/isolated
thunderstorms later this morning as it begins to approach from
the west.

Expect numerous showers and thunderstorms to develop by early
afternoon, and continuing through early evening, as the
shortwave trough 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.
IFR stratus is expected to develop overnight with low level
moisture in place.

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