373
FXUS61 KPBZ 171540
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1140 AM EDT Tue Jun 17 2025

.SYNOPSIS...
Showers and thunderstorms continue today, and the ongoing flood
threat has expanded to include areas farther north above the
I-80 corridor as a stalled front currently to our south lifts
north across the region. The ongoing active pattern should
break Friday, followed by drier conditions and area temperatures
climbing into the 90s by the end of the weekend.

&&

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

- Moderate Risk of flash flooding for much of the region today
- Flood Watch in effect until 10pm
- Isolated instances of a damaging wind threat south of I-70
---------------------------------------------------------------

Morning radar shows showers already developing and pushing through
the area aided by weak synoptic lift. Coverage is expected to
increase over the next couple hours both in tandem with
achievement of convective temperature of 80F as well as support
from localized boundaries and a quasi-stationary front overhead.
With further development, we face another day of a risk for
flash flooding, some potentially significant, with a primed
ground and ripe atmosphere.

Our morning sounding depicts a classic heavy rainfall environment.
Skinny MUCAPE with the bulk of the instability packed below -10C,
PWAT of 1.82" (daily max) and increasing in deep moist southwest
flow, warm cloud depths up to 14kft, and area dew points in the low
70s will be very supportive of dominant warm rain processes
with very efficient rainfall producers. In fact, even lightning
is lower probability today given the depth and width of the CAPE
profile. Will likely see very heavy rainfall with reflectivity
values not topping much higher than 30-40 dbz. While storm
motion vectors are a bit higher than previous days, PWAT values
are at record levels, so all we`ll need is a short period of
backbuilding over the same area, especially those that have
gotten hit hard in the past 48-72 hours, and flash flooding will
be likely. It`s also possible that heavier strips of rainfall
concentrate along the aforementioned boundary that will push
north as a warm front through the day today, but confidence in
placement is still on the lower side given the lack of stronger
surface convergence.

HREF probability for >1"/hour rates are high, highest up to 80% east
of Pittsburgh. Further, bumping up the neighborhood probability to
25 km over a window of 12 hours from 10am-10pm (accounting for
placement discontinuities among the CAMs) shows 10-20% probability
for up to 3"/hour rates. HREF max 24 hour QPF values through
Wednesday morning show strips of as high as 4", so while these types
of values are not expected across most of the area, this can give an
idea of the highest end, worst case scenario.

Given all of these factors in play, a Moderate Risk (3/4) is in
place for excessive rainfall for the WV panhandle and southwest PA
south of a line from Butler to Dubois, though it should be noted
that any location that gets hit repeatedly today will be at risk of
flash flooding... WPC Moderate Risks correlate to numerous flash
flooding events with significant flash flooding possible. Typically,
our area has only been placed in Moderate Risks or higher with
landfalling tropical systems. Never drive through flooded roadways
and remain vigilant for rapidly changing conditions in heavy
rainfall.

One other low end threat to be noted is a damaging wind/weak tornado
possibility. With weak low level shear, the threat should be
limited, but forecast soundings do have 100+ J/kg of 3CAPE with
low LCLs this afternoon. If a favorable interaction with remnant
boundaries or other showers/storms occurs, a quick spin up is a
low but not zero threat.

Coverage of rain will decrease with loss of daytime heating, but 850
mb convergence on the nose of an impinging low level jet is likely
to drive additional showers overnight, especially south of
Pittsburgh. A lower flooding threat will exist, but remnant MUCAPE
>250 J/kg and still high PWAT values will support additional heavy
rainfall producers.

&&

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

- Some scattered showers Wednesday with lower coverage and flooding
  threat.
- Possible showers/storms overnight Wednesday and again Thursday
  with low end severe threat.
----------------------------------------------------------------

Wednesday could bring a relative lull in the action as ensemble 500
mb height changes show modest rises of a few mb in 12 hours. Some
scattered showers look more favored in the mid morning to early
afternoon hours before chances lessen headed into the afternoon as
shortwave support exits. Any of these showers could be brief heavy
rainfall producers, but at this time it looks like storm motion and
scattered nature should preclude significant flooding concerns.
Continued deep southerly flow will drive high temperatures into the
low to mid 80s with some afternoon breaks in the clouds possible.

Uncertainty then comes into play late Wednesday night with what will
likely be a line of storms moving across Indiana and Ohio along a
pre-frontal surface trough. Models notoriously struggle with
maintenance of decaying nocturnal convection, especially when there
is lingering MUCAPE, and ensembles all indicate 1000-1500 J/kg still
in place. Will have to see how this evolves and if the CAMs can shed
any better light over the next 24 hours, but if the line holds
together, we could see a damaging wind and hail threat favoring the
post-sunset hours. SPC has maintained the Marginal Risk (1/5)
covering most of our CWA.

The most notable height falls and upper support come Thursday as
surface low pressure drags a cold front through our area. Timing of
this boundary is still a bit uncertain and will be important for a
severe weather threat locally. Dew point SD spread shows the
boundary as far southeast as the ridges or as far northwest as the
Erie to Cleveland corridor by 18z. A slower progression (currently
less likely) would favor a higher severe threat in our area while a
quicker one would confine the threat farther east. Should the slower
one prove true, we`d again face a wind and hail threat primarily..
Machine learning favors closer to the I-95 corridor and a faster
moving boundary, and the SPC outlook is leaned that way with a
Slight Risk (2/5) over there and a Marginal Risk (1/5) locally. This
may change once timing becomes clearer.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
KEY MESSAGES:

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

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 mid 80s.

The story of the long term period is going to turn from rain and
flooding to 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 60-70% in the urban areas and valleys Monday
and Tuesday. Climatologic tools point toward heights 2-3+ SD above
normal for late June. While we often get plagued by diurnally
driven clouds and precipitation in these patterns, a rapid warm
up to well- above normal temperatures is increasingly likely,
and the threat may be longer-lived over the course of several
days with little relief at night. The takeaway message at this
point is that several days of highs into the 90s across most of
the area is increasing probability and compounding effects could
be significant.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
A wide mix of conditions are ongoing across the area to start
the TAF period as decaying showers and weak overrunning along a
stalled boundary are producing instances of MVFR/IFR at some
terminals while VFR prevails elsewhere. This mix of conditions
continues through the morning until heating and mixing allows
for general improvement to VFR, save for FKL/DUJ where MVFR may
persist into the afternoon. Scattered showers and thunderstorms
develop across the area late morning through the afternoon and
evening as an upper trough approaches from the west. Maintained
TEMPOs to reflect the most likely window for heavier rain,
thunder, and associated restrictions. Outside of convection, low
VFR or potentially high MVFR cigs prevail. Widespread IFR
settles in overnight as shower activity tapers but low-level
moisture lingers. Winds remain light through the period and
generally out of the south or southwest.

Outlook...
Periodic restrictions remain possible through Wednesday as
another upper level wave crosses the region. More widespread
showers/thunderstorms (and associated restrictions) are
expected late Wednesday into Thursday with the approach and
passage of a cold front. Late night/early morning stratus and
fog is also likely. General VFR is expected to return Friday
through the weekend as ridging begins to build in.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch until 10 PM EDT this evening for PAZ007>009-
     013>016-020>022-029-031-073>078.
OH...Flood Watch until 10 PM EDT this evening for OHZ039>041-
     048>050-057>059-068-069.
WV...Flood Watch until 10 PM EDT this evening for WVZ001>004-012-
     021-509>514.

&&

$$

SYNOPSIS...88
NEAR TERM...MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Cermak