-- Discussion containing changed information from previous version are highlighted. --
636
FXUS61 KPBZ 202333
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
733 PM EDT Fri Jun 20 2025

.SYNOPSIS...
A dangerous heat wave is expected to impact the region beginning
Sunday through mid-week. Near record breaking high temperatures
could occur Monday and Tuesday. Low predictability chance for
showers and thunderstorms returns Wednesday.

&&

.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --
KEY MESSAGES:

- Some isolated showers/storms north of Pittsburgh and in the ridges.
- Otherwise dry with seasonable temperatures.
---------------------------------------------------------------

Precipitation coverage has been fairly widespread around and
north of Pittsburgh with the mid-level shortwave moving down.
While one storm attempted to break the cap at roughly 15kft (as
evidenced by the 21Z ACARS sounding), storms seem to be
inevitably capped my a mid levels inversion and dry air at
roughly 650mb. Sub-severe storm/shower coverage is expected to
pass areas north of and including Pittsburgh before dissolving
after midnight with both shortwave ridging and a loss of diurnal
heating. The most widespread coverage will generally be north of
I-76, though an isolated shower or two may be south of that area
into western PA or eastern Ohio.

.. Previous Discussion..

A dry day for a good chunk of the region is expected today as
surface high pressure builds off to our south and extends ridging to
the north. While mid-level heights will be on the rise as well, a
shortwave will dive through the Great Lakes in northwest flow aloft
this afternoon and may spark off a few showers and storms, perhaps
aided by the lake breeze. SBCAPE values are forecast to sit around
1000 J/kg this afternoon with around 25-30 knots of deep layer
shear, but layers of subsidence within the column may cap updrafts
before they`re able to achieve much height. Some CAM solutions favor
little to no convective initiation, or at most just some showers.
Will have to monitor trends through the afternoon, but thinking that
if any storms can maintain, it would be north of Pittsburgh or in
the ridges where stronger forcing may be able to punch through
caps/wet-bulb the profile enough. HREF probability of measurable
precip at anytime between 2pm-8pm peaks around 80% in our northwest
PA/eastern Ohio counties with another local maximum along the
PA ridges likely owing to orographic assist. Could see some
gusty wind and/or small hail with the strongest storms, but
expect that that threat will be very limited at best.

Coverage is expected to be scattered and not everyone will see
precipitation. Elsewhere, diurnally driven cu will dot the sky
through sunset giving way to some mid-level clouds overnight. A
dry overnight period expected with lows a bit above normal owing
to the degree of cloud cover and light southerly flow.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Dry weather with increasing heat.
- Excessive Heat Watch in effect beginning on Sunday.
----------------------------------------------------------------

The heat starts to build on Saturday as warm advection ramps up
pulling 850 mb temperatures to 17-19C with some scattered clouds.
This will translate to highs in the upper 80s with some urban area
and valley readings possibly touching 90. Overnight lows will remain
mild in the upper 60s. A few rogue showers/storms are possible
again north of I-80, but the best support should remain off to
our north into Canada riding atop the ridge.

Further warming occurs on Sunday with 12 hour height rises of 2-4
dam and highs likely to top 90 degrees across most of the area.
Plenty of subsidence will keep the area dry. An Excessive Heat
Watch has been hoisted for the entire CWA beginning Sunday
through Thursday.

&&

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

- Excessive heat threat ramping and peaking Monday and Tuesday.
- Potential record high and low temperatures.
- Excessive Heat Watch in effect through Wednesday.
- Low predictability showers and storms possible Wednesday and
  Thursday.
-------------------------------------------------------------------

The story of the long term is a prolonged period of dangerous,
excessive heat.

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. Ensemble mean 850 mb temperatures soar to 21-23C.
NBM probability for highs >90F is remarkably high at 80+% Sunday
through Thursday, but of note is that NBM probabilities and
statistical distribution in a high-predictability period of heat can
often be artificially inflated/widened when post-processing is
applied to a small spread in the distribution like we have in this
case for MaxTs. What this means is that the most likely high
temperature falls a degree or two below the NBM post-processed mean
(more likely 90-95F) and true probabilities for >95F aren`t quite as
high as suggested. Dew points are progged to be in the mid 70s, and
last year`s period of extreme heat showed that the NBM handled the
dew points pretty well while overdoing the MaxTs, so it`s most
likely that we find a middle ground with low to mid 90s temps and
upper 60s/low 70s dew points. Either way, heat indices are very
likely to reach the 100-105F range for several consecutive days.
Compounding the effects of excessive daytime heat will be little
relief at night; probability for lows >70F is 80-90+% Sunday-
Wednesday nights. The Excessive Heat Watch remains in effect, and
further decision on warning vs. advisory will likely come within the
next 24 hours. Record lows and highs may be in jeopardy as well...
see the climate section for more. In preparation a few days out, it
is a good idea to find out more about your local cooling shelters
and consider altering outdoor plans to at least outside of the
afternoon peak heating window.

One thing to keep in mind is that at times we can get affected by
diurnally driven clouds and precipitation in these patterns with
such warm temperatures and plenty of near-surface moisture. This
looks most likely on Wednesday and Thursday as some subtleties in
the flow/regression of the ridge allow for convective potential atop
it. Some of this convection could be on the strong to severe. NCAR`s
medium-range machine guidance highlights the Ohio River Valley has
an area for hazardous weather (15-30% chance) for Wednesday into
Thursday. With light winds and dry air aloft, downbursts are
expected to be the primary threat followed by localized flooding.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
A few scattered showers and isolated thunderstorms have
developed this evening in northwest flow. Dry air aloft and
subsidence capping have limited development, and activity is
expected to wane after sunset.

Otherwise, VFR is expected through the TAF period with high
pressure and light southwesterly surface flow.

Outlook...
The outlook favors a prolonged period of VFR through at
least early next week under the influence of high pressure and large
ridging overhead. A heat wave looks likely to settle in Sunday
through at least Tuesday, with ensembles suggesting high
probabilities for temperatures above 90 degrees each afternoon.
-- End Changed Discussion --

&&

.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...Extreme Heat Watch from Sunday morning through Wednesday
     evening for PAZ007>009-013>016-020>022-029-031-073>078.
OH...Extreme Heat Watch from Sunday morning through Wednesday
     evening for OHZ039>041-048>050-057>059-068-069.
WV...Extreme Heat Watch from Sunday morning through Wednesday
     evening for WVZ001>004-012-021-509>514.

&&

$$

SYNOPSIS...Hefferan/MLB
NEAR TERM...MLB/Milcarek
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Rackley
CLIMATE...