-- Discussion containing changed information from previous version are highlighted. --
746
FXUS61 KPBZ 222027
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
427 PM EDT Sat Jun 22 2024

.SYNOPSIS...
Dangerous heat continues today with severe weather possible
tomorrow afternoon; the primary threat remains wind, although
hail and tornadoes are possible. A brief "cool down" is
expected through Monday before temperatures increase yet again.

&&

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

- Excessive Heat Warning and Heat Advisory remain in effect
  until 8pm.
-------------------------------------------------------------------

Temperatures have already risen into the upper 80s and lower 90s
area-wide as we mix up to roughly 700mb, as indicated by the
morning sounding. Temperature rises through this afternoon will
remain a bit slower to rise as the boundary layer continually
erodes into the 700mb cap.

Cumulus has started to form across the area as we tap into the
LCL, but thus far development seems shallow under the initial
cap. With mixing, it is expected that these cumulus grow in
vertical extent, but development will be challenged past around
12kft with yet another elevated inversion. It will take repeated
updraft failures to cool the environment enough to mix into the
500mb-400mb layer, but even then, storms are expected to
encounter yet another inversion at 25kft. This will make it
difficult for mature updrafts to materialize, especially when
combined with notable dry air above the boundary layer. The
main area to watch, if any, will be the lake-shore. Much like
we have seen this week, we will rely on the lake boundary to
initiate convection which may alter the environment enough to
establish a cold pool and propagate southeast.

Into this evening and tonight, a pressure gradient will increase
a a Great Lakes low moves in. This will usher in light southwest
flow at the surface and finally begin to usher in a different
airmass. With the return of clouds tonight and light winds,
tonight may be the warmest night of the week with lows only
bottoming out in the low to mid 70s. This will keep conditions
uncomfortable for one final night. Some nocturnal
showers/storms may develop, primarily across northwest PA, with
increases in 700mb moisture and fumes of CAPE, although a
shallow inversion and little vertical development should keep
any concerns low.

&&

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


- A 2 out of 5 risk for severe weather is forecast on Sunday
  afternoon and evening.
- Damaging wind is the primary threat, though large hail and
  tornadoes remain possible.
-------------------------------------------------------------------

Tomorrow will start with dew point at or around 70 with
temperatures in the middle to upper 70s around around 8am. By
around 10am, ahead of a pre-frontal trough, some local
acceleration of flow will allow shear to creep up, with about a
10% to 25% chance of 0-6km shear being above 30kts. As surface-
based instability creeps up with daytime heating, there is
roughly a 50% confidence of at least 500 J/kg of SBCAPE. This
does not suggest severe criteria by this point, but the
environment will continually become favorable through the
morning.

By around the noon to 4pm timeframe, a pre-frontal trough will
push through and provide weak lift for storms. Additional
heating will push SBCAPE up to >1000 J/kg with 60% to 100%
confidence, while 0-6km shear lingers around a 25% to 60% chance
of >30kts. Low confidence in shear >30kts might typically
suggest sub- severe storms are favored, but much of the shear is
forecast to be in the 0-3km layer with veered profiles. This
gives cause to suggest low- level organization is possible not
long after initial cumulus development. This might favor
tornadogenesis, should LCLs remain below 1000m (which seems
generally unlikely with the initial wave). On the other hand,
the environment will still be primed with antecedent 1000-1200
J/kg of DCAPE, which is a detriment to tornadogenesis and may
suggest higher wind threats. Dry air may also limit convection
altogether as it is entrained into updrafts. Needless to say,
confidence remains lower with initial convection, but may be
binned into 3 scenarios. 1) Convection does not occur with
forcing to weak to overcome the dry air aloft. 2) Convection
does occur and remains cold-pool balanced; this would result in
a higher tornado and hail risk. 3) Convection does occur but the
cold-pool is dominant, allowing wind threats to be maximized in
downbursts.

Some recovery is expected behind the pre-frontal trough,
followed by the cold front itself with higher chances of
convection altogether with stronger forcing in roughly the 6pm
to 10pm timeframe. Afternoon storms will influence what
convection we see for the rest of the day. If storms do develop,
they will utilize the best environment in detriment to storms
that form along the cold front itself. If storms do not develop,
the environment will remain better primed for evening storms.
Convective ensembles suggest that shear ahead of the cold front
may be a hair less, but the best shear may be more confined to
the 0-1km layer with a smoother veering profile while
instability may be conditionally more. With right moving cells
remaining perpendicular to the front, discrete cells are
possible along the line. In discrete, balanced cells, tornados
remain possible as well as a secondary hail threat.
Additionally, LCLs appear to be a bit lower than initial
convection. If the cold pool is dominant, winds remain the
primary threat in discrete cells and storms may evolve to
become more linear and accelerate as the cold pool races ahead
of them. Needless to say, there are still a lot of questions
about tomorrow, but all threats remain on the table.

Monday brings a welcome reprieve to the heat with mostly dry
conditions favored and temperatures back to near normal.
-- End Changed Discussion --

&&

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

-Above average temperatures return
-Mainly dry to start and end the work week, with shower and
 thunderstorms for mid week
-------------------------------------------------------------------

An upper ridge, ahead of an approaching Midwest trough, will
maintain dry weather on Tuesday. Rising 1000-500mb heights and
warm advection will drive temperatures from 5 to 10 degrees
above average.

The trough, and its associated surface cold front, will approach
and cross the region late Tuesday night through Wednesday
evening, with shower and thunderstorm chances returning. Building
high pressure will return dry weather for Friday, with
temperatures closer to average.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
High probability for VFR to persist through the TAF period under
the influence of high pressure. Warm, dry air aloft should limit
convective initiation and keep probabilities very low of
terminal impact with an afternoon thunderstorm.

Approach of an upper level shortwave and associated cold front
will increase thunderstorm chances at the end to after the TAF
period. Latest analysis suggests to waves of thunderstorms, the
first between 15-20z (11am-4pm EDT) along a pre-frontal trough,
and the second between 21z-03z (5pm-11pm EDT) as the cold front
advances southeast. Storm intensity (and probability of
terminal impact) is likely to be highest with the second wave.

.Outlook...
Lingering showers and low probability thunderstorms are possible
through early Monday morning amid cold advection and crossing of
the upper trough axis.  High pressure and northerly flow aloft
will establish dry and more seasonable conditions for the start
of the next work week.

&&

.CLIMATE...
The area has the potential to break various heat-related
records.

There is low probability that climate sites approach the
highest temperatures recorded in the 21st century:

Pittsburgh, PA:       98F  (7/7/2012)
Wheeling, WV:         98F  (7/7/2012)
Morgantown, WV:       101F (7/7/2012)
New Philadelphia, OH: 101F (7/7/2012)
Zanesville, OH:       101F (7/7/2012)
DuBois, PA:           101F (7/22/2011)

There is a low probability many June all-time temperature
records may be at stake:

PIT: 98F (1988)
HLG: 100F (1933)
MGW: 99F (1893)
PHD: 99F (1988)
ZZV: 101F (1988,1934)
DUJ: 92F (1969)  *RECORD TIED ON 6/18/24*

Daily high maximum (left) and high minimum (right) temperature
records are at stake for:

Saturday, June 22nd
Pittsburgh, PA:       98F  (1988)     75F  (1988)
Wheeling, WV:         95F  (1923)     72F  (2011)
Morgantown, WV:       96F  (1923,1988)73F  (1988)
New Philadelphia, OH: 97F  (1988)     71F  (1997)
Zanesville, OH:       99F  (1988)     71F  (1997)
DuBois, PA:           91F  (2022)     68F  (2022)

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 8 PM EDT this evening for PAZ007>009-013-
     015-016-022-031-074-076>078.
     Excessive Heat Warning until 8 PM EDT this evening for PAZ014-
     020-021-029-073-075.
OH...Heat Advisory until 8 PM EDT this evening for OHZ039>041-
     048>050-057>059-068-069.
WV...Heat Advisory until 8 PM EDT this evening for WVZ001>004-012-
     021-509>511.

&&

$$

SYNOPSIS...Milcarek
NEAR TERM...Milcarek
SHORT TERM...Milcarek
LONG TERM...WM
AVIATION...Frazier
CLIMATE...