889
FXUS61 KPBZ 141925
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
325 PM EDT Sat Jun 14 2025

.SYNOPSIS...
A flash flood watch is in effect portions of Pennsylvania
through the evening. Near- normal temperatures continue early
week with occasional daily flash flood and precipitation
chances. Temperatures warm up towards the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
KEY MESSAGES:

- Convection has started to bubble on an axis across the middle
  of the forecast area, which will carry the brunt of flooding
  threats into tonight.
---------------------------------------------------------------

PWATS will be slightly higher this afternoon (on the order of
1.7" to 1.8" (1.78" on the 12Z sounding) or >90th percentile of
climatology. Satellite into the afternoon shows evidence of
clearing in all areas save northwest PA, that will allow a
favorable environment for instability generation and
convection. 2pm trends show the development of towering cu and
cb reflecting this, as an uptick in rainfall rates is expected
over the next couple of hours. With better surface heating in
this environment, one might expect flash flooding potential. The
highest threat will be along the east-west outflow dropping
south from Butler across the center of the forecast area near
Pittsburgh, particularly areas where the flow and boundary
orientation are parallel in an east-west direction with
training. This is mostly in the southern half of the flood
watch, where a convergence zone is evident.

In other areas, particularly south of the boundary, flash
flooding is also possible but the ability to generate training
convection will be harder with no established boundary.
Nonetheless, discrete cells over an area for long enough will be
able to generate flood threats with a deep warm rain layer and
near record PWATs in weak flow.

After collaboration with WPC, this will justify a slight risk
for excessive rainfall over portions of western PA in the
afternoon and evening hours. While coverage and intensity may
decrease after sunset, flash flooding could not be ruled out in
training yet again.

All in all, cloud cover, rain chances, and deep saturation
should keep daytime highs slightly cooler than Friday, and lows
around 5 to 10 degrees above average yet again.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
KEY MESSAGES:

- Continued storm chances with flash flooding potential continue
  Sunday over much of the area.
- Similar flash flood chances Monday, in a smaller area
  southeast of Pittsburgh.
----------------------------------------------------------------

By Sunday, the mid-level disturbance and corresponding surface
low will approach the upper Ohio Valley, along for a continued
saturated environment (with PWATS near the 90th percentile ~1.7"),
warm rain processes, and mostly-diurnal storm chances in weak
flow. With the profile so saturated in heating, there is some
uncertainty as to the extent of cloud cover which will affect
the extent of instability generation, though most ensembles have
between 250 and 750 J/kg skinny SBCAPE. With a mere 10kts of
sfc to 3km shear and lcl-to-el (cloud layer) mean wind at or
below 5kts. This has all the favorable signs for slow moving
storms with very efficient warm rain processes and heavy rain
rates. All in all, these factors come together to maximize a
flash flooding threat tomorrow afternoon/evening between noon
and 8pm. Looking and the maximum reasonable rainfall from 12pm
to 8pm using HREF max QPF, a reasonable localized high end total
of 4" to 6" is entirely possible, but confidence in exactly
where that will be will remain low confidence until just before
it occurs. Elsewhere, totals will be quite spotty, with
convection expected to be erratic and random with no definitive
forcing system besides synoptics combined with fairly
homogeneous instability. After collaboration with WPC, a slight
risk of excessive rainfall has been extended across much of the
area, with even contours of 25% chance of flash flood within 25
miles into much or northern WV and southwest PA. This is
particularly concerning for the region, especially areas that
received heavy rain in the days prior. Rainfall rates are
expected to subside some after sunset with the loss of diurnal
heating as a lifting mechanism.

Monday will bring additional chances of flooding, however, they
are expected to be on the northwest periphery of the low with
perhaps slightly lower PWATS ~1.5". The main forcing region is
expected to be much smaller and largely southeast of Pittsburgh,
but impacts may linger nonetheless. Timing, again, seems to
highlight the noon to 8pm timeframe when heating and forcing
combine. While HREF statistics do not go out that far yet, it is
possible to see hourly rates in the 1-2" range which may exceed
FFG.

&&

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

- A mid-week warmup will be followed by increasing late-week
  severe potential.
-------------------------------------------------------------------

By Tuesday and Wednesday, there is some indication of a return
to quasi-zonal flow to even weak ridging, with nearly 100%
membership in clustering suggesting heights between 583dm and
586dm and NBM highs back into the mid to upper 80s, there is
increased confidence similar heat lingers into at least Thursday
at this point with most ensemble spread encompassed in the 80s.

Beyond that, into Friday and beyond, there is some indication
of troughing with both timing and intensity uncertainty. Though,
in the last 24 hours this has trended farther east and weaker,
keeping much of the late week temperature spread in the low to
mid 80s, providing some, but not dramatic relief. We will also
be keeping an eye on severe potential in the transition from
heat to weak troughing, with CIPS and CSU machine learning
showing increasing probabilities into Thursday and Friday. Into
days 7 and beyond, the strength and progressiveness of this
trough will determine just how long it takes to warm back up
into what could potentially be another ridging pattern with
heat returning.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Light to moderate rain showers and IFR/LIFR restrictions are
ongoing for areas north of I-70 this morning, while farther
south there is no rain and a mix of MVFR/VFR to start the TAF
period. This trend continues through at least mid morning, after
which ceilings should see some minor improvement to MVFR across
much of the area except FKL/DUJ where IFR will linger awhile
longer as a steady band of rain drifting generally west to east
takes its time exiting the area.

Breaks of sun (especially around and south of PIT) during late
morning and afternoon will facilitate deeper mixing. Given the
lack of a thermal capping inversion, even modest heating should
be sufficient to invigorate more robust updrafts by early
afternoon, with tstms possible for a few hours south of I-80.
Although prevailing conditions will favor MVFR during this time,
drastic drops in vsby are possible (30-40% probability) within
the very heavy rain of afternoon storms, as are occasional
breaks to VFR in between bursts of rain/storms.

Deep convection tapers towards sunset with the loss of daytime
heating, though scattered light showers linger through tonight
as cigs/vsbys drop back down to IFR or worse after 03-06z.

Outlook...
Restriction potential with rain will continue into early next
week with little change in pattern as a series of disturbances
crosses the area.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch until 11 PM EDT this evening for PAZ014-021-022-
     073-074-077-078.
OH...None.
WV...None.

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...Cermak