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756
FXUS61 KPBZ 221916
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
316 PM EDT Wed May 22 2024

.SYNOPSIS...
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Showers and thunderstorms are possible through Thursday as
temperature remains seasonably warm. Periodic thunderstorm
chances are expected through the holiday weekend as a series of
upper level disturbances cross the region.
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&&

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

- Strong to severe thunderstorms possible this afternoon into
  Thursday morning.
- Damaging wind is the primary threat, while tornadic threat
  favors northwest PA.
  _____________________________________________________________

3:00pm Update:

Sub-severe convection that has formed along residual MCV outflow
has pulsed up into storms north of I-80 what will continue
their eastward progression. The convection has failed to remain
organized in around 20kts of effective environmental shear.
Nonetheless, small hail and gusty winds are possible in these
storms and will be monitored for any trends as dry air catches
up to cells.

A weak wave has passed over the area, and the region remains in
backing flow behind the mid wave which has induced a local area
of subsidence that is resulting in lower cumulus coverage and
lower probabilities of convective initiation across most eastern
Ohio and western Pennsylvania this afternoon. With a lack of an
evident source of initiation, development remains questionable
this afternoon, but should it materialize in surface-based
instability, it will develop an an environment with as much as
1000 to 1200 J/kg DCAPE, meaning downburst winds will be the
primary threat with hail as a secondary threat.

The higher probabilities of convection arrive along and just
ahead of the cold front later this evening, along with higher
effective shear of roughly 30kts to 40kts in eastern Ohio,
though the surface-based component to instability will continue
to be lost as after sunset. There may be a narrow window for
severe potential into eastern Ohio and northwest Pennsylvania in
this time frame. The persistence of this wind threat will
depend on how readily the nocturnal inversion establishes and
and amount of elevated instability and corresponding DCAPE.

Flooding remains a threat in any training storms with the
afternoon sounding showing near-record PWATs for this time of
year. Additionally, the front may slow its progression overnight
as it drags across the area, which will warrant continued watching.

130pm Update:

Convection currently remains focused within the NW quadrant of a
notable MCV (seen via 700-400mb vorticity advection mesoanalysis
maps), which will shift NE of the forecast hour over the next
hour or two. Areas of light rain and excessive cloud cover to
the SE of this convection appears to be hindering additional
convective initiation by cooling the surface to create some CIN
values. Despite the presence of an MCV to provide lift amid an
environment with SBCAPE near 2000 J/kg and around 30kts
effective shear, this cloud cover may act to limit coverage and
make storm intensification more difficult. All prior mention
hazards (damaging wind and hail with low probability tornado)
remain on the table but latest analysis suggests a slight lower
probability of developing any of those hazards in a given storm.

Subsidence and less surface heating behind the MCV should create
a dry pocket before storm potential increases again as the upper
level trough axis lifts through the Great Lakes and pushes the
surface cold front closer the region. Severe threats can`t be
ruled out with the likely scattered convection along this line
as high-resolution ensemble modeling suggests a narrow corridor
of around 1000 J/KG SBCAPE with increasing shear values
stretching from eastern OH to northwest PA through midnight.

Flooding potential remains low despite rising PWAT values given
faster forward prorogation and lack of strong synoptic lift
within a training setup.
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&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
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KEY MESSAGES:


- Showers and thunderstorms are likely to continue ahead of a
  cold front Thursday.
  _____________________________________________________________

The surface cold front will stall just north of the I-70
corridor Thursday morning as the upper level trough lifts
farther north of the region and broader SW flow develops aloft.
Diurnal heating combined with weak embedded waves is expected to
foster isolated to scattered thunderstorms south of the boundary
through the day. The lack of strong heating and weak shear
should preclude severe potential while flooding likely will
remain limited due to storm motion (though non-zero as flow will
be nearly parallel to the boundary and could foster some
training).

Confidence is high that dry weather will develop Thursday night
into Friday as shortwave ridging crosses the region with high
pressure at the surface. Minimal airmass change with slightly
higher heights should promote above normal temperature again.
The aspect to keep an eye on is progression of lower Ohio River
Valley convection eastward; there remains potential for a late
Friday into Saturday morning arrival (with limited severe
potential as it would hit a more stable environment).
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&&

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

- Variability remains high on long term forecast and may be
  predicated on prior day`s convective outcomes.
- Overall, periodic showers and thunderstorms with slightly
  above normal temperature is favored through the holiday
  weekend.
  ____________________________________________________________

Ensembles are more confident in one of those waves crossing the
region Saturday to produced a wave of showers and
thunderstorms; timing varies but potential exists for convection
to exit east of the area before evening activities. That
variability leads to an inconclusiveness on severe potential but
note that analogs for the pattern and machine-learning analysis
suggests at least a low probability for hazardous weather that
day.

A more well-organized low pressure system is becoming the
favored pattern development to end the holiday weekend as it
lifts through the Great Lakes. Higher probabilities for showers
and thunderstorms are expected during this time frame but it is
unlikely to be "all day" rain type of events. Early analogs for
this pattern also suggest at least a low probability for
hazardous weather, but much variation in that potential remains.

Long range suggests a shift to a cooler, dry pattern by the
middle of next week as upper troughing develops over the Great
Lakes. Expect temperature to fall below the seasonal average,
with Tuesday potentially being the transition day from shower
activity to dry weather.
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&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Shower and thunderstorm chances increase from the west early in
the afternoon and continue into the overnight hours with the
passage of a low pressure system. Outside of thunderstorms,
there is high confidence that VFR prevails. Thunderstorms will
be capable of producing strong, gusty wind, and possibly hail,
but confidence in timing of impacts is low. MVFR CIG
restrictions then become more likely overnight (40-60%) with
increasing low level moisture.

.Outlook...
Periodic thunderstorm chances and associated restrictions are
likely through the weekend as an active weather pattern
continues.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

$$

SYNOPSIS...22
NEAR TERM...Frazier/Milcarek
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...88