Flash Flood Warning 73, NWS Pittsburgh, PA

Area Forecast Discussion
National Weather Service Pittsburgh PA
154 PM EDT Wed Jun 18 2025

.SYNOPSIS...
Showers and possible thunderstorms expected Wednesday afternoon
and evening, some of which could be severe late Wednesday night.
Thunderstorm chances will remain on Thursday with the approach
and passage of a cold front. Dry weather returns Friday with
excessive heat probability increasing through the middle of
next week under high pressure.

&&

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

- Scattered showers/thunderstorms capable of heavy rainfall.
- Another push of thunderstorms with severe threat possible
  tonight.
---------------------------------------------------------------

With Tuesday's surface boundary now displaced to our east, we're
left within a transitional zone ahead of low pressure tracking
through the Great Lakes and a cold front sweeping through Indiana
and Ohio. Quasi-zonal mid-level flow with still a southwest
component has maintained the moist, stagnant airmass today. Observed
PWAT value off our 12z sounding was 1.85" which is above the daily
max. Recent PIT ACARS soundings also show a similar environment to
Tuesday with tall, skinny CAPE and the widest CAPE profile below
-10C, warm cloud depths to 14-15kft, and weak deep layer flow
supporting slow moving showers and lower probability
thunderstorms. Rates thus far through the morning have been
slightly less than Tuesday but still falling in the 1-2
inch/hour range and couldn't rule out up to locally 3"/hour
given the similar environment and what has been observed
recently. Thus, localized flash flooding remains a threat today,
especially in areas that see training and those who got hit the
hardest yesterday.

CAMs still want to diminish the coverage into the afternoon hours as
a sinking subsidence inversion sets in. Not completely sold that
we'll see a dry afternoon given the environment in place and
lingering boundaries around, but it's plausible that the flooding
threat should lessen given the lack of coverage to result in
repeated rounds of heavy rainfall.

Uncertainty then creeps in late tonight as what is likely to be an
ongoing line of thunderstorms progresses across Indiana and Ohio
along a pre-frontal trough. As typical, CAMs want to weaken it
considerably after sunset and before it reaches our eastern Ohio
counties as it outruns the best instability, but this could be a
more pessimistic solution than reality, especially across eastern
Ohio. Low and mid level flow is forecast to increase with the
approach of an associated upper trough allowing effective shear to
reach 25-30 knots with notable veering atop backed southerly flow.
Forecast soundings from the CAMs still support 1000-1500 J/kg of
MUCAPE atop a stabilizing surface over that way. This
environment would support maintenance of convection into the
early overnight hours into eastern Ohio and with lesser
confidence western Pennsylvania. If it can maintain, primary
threat would be damaging wind punching through a weak surface
inversion. Couldn't entirely rule out a tornado threat either
with the veering wind profile and >150 m2/s2 of 0-1 SRH, but
that threat will be highly dependent on how strong the surface
inversion is and if the storms root at the surface. Most likely
timing would be after 10pm into eastern Ohio and after midnight
if it reaches into western PA. Accordingly, a Slight Risk (2/5)
has been expanded to our eastern Ohio and WV panhandle counties
while a a Marginal Risk (1/5) remains across to the east, again
with the highest (but still lower) confidence in eastern Ohio.

&&

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

- Additional showers and thunderstorms with severe possibility
  on Thursday.
- Drying out on Friday with above-normal temperatures.
----------------------------------------------------------------

The cold front itself is progged to punch through on Thursday
coincident with the most notable height falls and upper support as
surface low pressure crosses to our north. Most likely timing is the
mid to late afternoon hours, after 3pm or so, but a few models do
suggest a slightly later passage. The biggest question will be how
much instability we're able to regenerate before its passage despite
the passage itself being at a favorable time. The optimistic cloud
coverage solution from the HREF still maintains areas of clouds with
only pockets of clearing while the most likely solution keeps mostly
cloudy skies across the area through the afternoon hours. Thus,
probability for >1000 J/kg SBCAPE peaks around 60-70% south of
Pittsburgh and <50% to the north. Deep layer shear will be in place
with ensemble mean of 30-40 knots of 0-6 km. Some development is
possible by early afternoon along a pre-frontal trough/as convective
temperatures are met which could muddy the picture further. Given
the environment, think that the highest severe probability likely
lies from Pittsburgh and south coincident with the best overlap of
CAPE and shear. The primary threat will be damaging wind in any
congealed line segments with straight hodographs. Machine learning
suggests this area for a lower end threat as well, and SPC has
maintained the Marginal Risk (1/5) across our area.

Friday should finally see a drier day in the wake of the boundary,
though a change in airmass doesn't appear too likely with a brief
bout of northwest flow quickly flipping west to southwest again
as high pressure builds in across West Virginia. NBM MaxT
spread is pretty small with highs likely in the low to mid 80s
and the start of a significant warm up headed into the weekend
and next week.

&&

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

- Turning drier with excessive heat threat ramping up into next week.
-------------------------------------------------------------------

The story of the long term period is going to turn from rain and
flooding to a prolonged period of dangerous, excessive heat.
Saturday will be dry with highs ramping up into the mid to upper 80s
and dew points in the upper 60s.

Sunday begins the period of excessive heat. Longer range ensembles
exhibit quite a bit of certainty on a strong upper ridge building
across the eastern CONUS with a 90+% chance of 500 mb heights >590
dam. NBM probability for highs >95F peak at 70-80% in the urban
areas and valleys Monday and Tuesday. Combined with dew points into
the 70s, heat indices are likely to top the 100-105F range for
multiple days. Climatological tools point toward heights 2-3+ SD
above normal for late June. While we can get plagued by
diurnally driven clouds and precipitation in these patterns with
localized effects, a significant warm up to well-above normal
temperatures is likely, and the threat may be long lived over
the course of several days with little relief at night.
Probability for lows >70F is 80- 90+% Monday-Wednesday nights.
The takeaway message at this point is that several days
excessive, dangerous heat is increasing probability across the
entire area and compounding effects could be significant. If
trends hold, heat headlines will be likely. Record lows and
highs may be in jeopardy as well... see the climate section for
more.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Shower activity wanes towards evening as weak subsidence
overspreads the area from the west, with the exception being
FKL/DUJ as hi-res models continue to suggest ongoing convection
along the Lake Erie shoreline eventually pushes southeastward
into northwest PA.

Gradual improvement in ceilings has occurred over the course of
the afternoon, with most terminals now at high-end MVFR or VFR.
Widespread improvement to VFR should continue to occur through
the rest of the afternoon.

A potentially decaying MCS will approach the region from the
west after 02z with uncertainty on its ability to maintain
lighting/heavy rain/gusty wind potential. Probabilities of such
impact are highest at ZZV but notably drop off toward western
PA. Moisture convergence ahead of the main surface boundary and
the upper trough favors MVFR to localized IFR cig development
just prior to 12z lasting into mid Thursday morning. West-
southwest winds increase Thursday mid to late morning as the
local pressure gradient tightens ahead of an approaching front.
Scattered development of showers and storms is also likely
during that time with the onset of daytime heating/mixing.

Outlook...
The passage of a surface front and upper trough axis will
generate scattered to numerous showers with isolated
thunderstorms Thursday afternoon; probabilities favor MGW/LBE
as most likely to experience highest gusts/rainfall rates and
lightning impact.

Outside of lingering moisture fueling isolated to scattered
showers Friday, the outlook favors a prolonged period of VFR
Friday afternoon into next week under the influence of high
pressure and large ridging overhead.

&&

.CLIMATE...
Daily record high maximum (left) and daily record high minimum (right)
temperatures will be in jeopardy starting this coming Sunday:

Sunday June 22nd
Pittsburgh, PA:         98F (1988)              75F (1988)
Zanesville, OH:         99F (1988)              71F (1997)
Morgantown, WV:         96F (1923, 1988)        73F (1988)
Dubois, PA:             92F (2024)              69F (2024)
Wheeling, WV:           95F (1923, 2024)        72F (2011)
New Philadelphia, OH:   97F (1988)              71F (1997)

Monday June 23rd
Pittsburgh, PA:         95F (1894)              76F (1888)
Zanesville, OH:         96F (1899)              70F (1975)
Morgantown, WV:         95F (1899)              71F (1957)
Dubois, PA:             88F (1966)              66F (2017)
Wheeling, WV:           94F (1948)              69F (2013)
New Philadelphia, OH:   97F (1988)              72F (1948)

Tuesday June 24th
Pittsburgh, PA:         96F (1882)              72F (1884)
Zanesville, OH:         98F (1930)              73F (1937)
Morgantown, WV:         94F (1921, 1949)        76F (1924)
Dubois, PA:             88F (1966)              67F (2013)
Wheeling, WV:           98F (1933, 1943)        73F (1908)
New Philadelphia, OH:   94F (1964)              70F (1975)

Wednesday June 25th
Pittsburgh, PA:         98F (1988)              75F (1952)
Zanesville, OH:         101F (1988)             72F (1952)
Morgantown, WV:         94F (1921, 1952, 1988)  74F (1952)
Dubois, PA:             91F (1966)              67F (2000)
Wheeling, WV:           97F (1943)              75F (1952)
New Philadelphia, OH:   92F (1966, 2002, 2005)  68F (2013)

Thursday June 26th
Pittsburgh, PA:         95F (1966)              75F (1952)
Zanesville, OH:         97F (1952)              73F (1952)
Morgantown, WV:         96F (1952)              74F (1952)
Dubois, PA:             91F (1966)              66F (2000)
Wheeling, WV:           96F (1943, 1952)        73F (1952)
New Philadelphia, OH:   99F (1988)              71F (2022)

&&

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

&&

SYNOPSIS...MLB
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Cermak/Frazier
CLIMATE...MLB

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Special Weather Statement
National Weather Service Pittsburgh PA
350 PM EDT Wed Jun 18 2025

PAZ007>009-013>016-022-077-078-182300-
Mercer-Venango-Forest-Lawrence-Butler-Clarion-Jefferson PA-
Armstrong-Indiana-Higher Elevations of Indiana-
Including the cities of Sharon, Hermitage, Grove City, Oil City,
Franklin, Tionesta, New Castle, Ellwood City, Butler, Clarion,
Punxsutawney, Brookville, Kittanning, Ford City, Indiana,
and Armagh
350 PM EDT Wed Jun 18 2025

...THUNDERSTORMS WITH GUSTY WIND THIS AFTERNOON...

A line of thunderstorms will move across the region through late
afternoon. Wind gusts from 40 to 50 mph will be possible in the
strongest storms, along with brief heavy rain. With saturated
soil, this could result in a few downed trees, and ponding of
water on roads. Small tree limbs could also be blown down. Use
caution when encountering these storms.

WM

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