026
FXUS61 KPBZ 172340 AAA
AFDPBZ

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
740 PM EDT Tue Jun 17 2025

.SYNOPSIS...
Showers and thunderstorms, along with the threat for flash
flooding, continue through this evening, as a stalled front
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 /UNTIL 6 AM WEDNESDAY MORNING/...
KEY MESSAGES:

- Moderate Risk of flash flooding for much of the region this
  evening
- Flood Watch in effect until 10pm
---------------------------------------------------------------

...Mesoscale Update...

Convection continues across the region as a surface warm front
lifts slowly north across the area. The front was analyzed from
NE OH through northwest/west central PA. Several outflow
boundaries from earlier showers and thunderstorms have been the
focus for additional shower and thunderstorm development, with
continued vorticity advection providing ascent aloft. PWATs of
1.8 to 2.0 have resulted in heavy rainfall rates, with several
Flash Flood Warnings continuing. Overall, expect a gradual
diminishing trend later this evening with the loss of diurnal
instability. Flash Flood Watch continues through 10 pm.

A few showers/isolated thunderstorms will then remain possible
overnight, especially toward morning, as a mid level trough
approaches.

Previous discussion...
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 /6 AM WEDNESDAY MORNING 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 TUESDAY/...
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 /00Z WEDNESDAY THROUGH SUNDAY/...
Numerous showers and thunderstorms and associated restrictions
will continue this evening as a warm front lifts north across
the region. Outflow boundaries will also be the focus for
additional showers/storms this evening. The convection should
gradually diminish with the loss of daytime heating and diurnal
instability, though expect more showers/isolated thunderstorms
to affect the region overnight especially toward morning, as a
mid level trough approaches. Low level moisture in place should
also result in MVFR, and eventual IFR, conditions developing
late tonight, lasting through Wednesday morning.

The showers/isolated thunderstorms will continue into early
Wednesday afternoon as the trough completes its passage. Capping
warmth aloft should then help to limit thunderstorm chances for
the rest of the afternoon. Thunderstorm chances will increase
again late Wednesday evening as a line of thunderstorms
approaches from the west, though the eastern extent of its
progress remains in question at this time. Did add a prob30
mention for storms at PIT toward midnight Wednesday eve.

Outlook...
Restrictions are possible in showers/storms Wednesday night
ahead of an approaching cold front. This potential continues
Thursday as the front crosses the region. General VFR is then
expected through the weekend under a building ridge of high
pressure.

&&

.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...WM/MLB
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Frazier