-- Discussion containing changed information from previous version are highlighted. --
541
FXUS61 KPBZ 222136
AFDPBZ

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

.SYNOPSIS...
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.

&&

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

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

4:45pm Update:

Post-MCV subsidence and the lack of a forcing/lift mechanism is
driving current convective minima across the region. Though some
weak convergence is noted via satellite imagery over portions of
eastern OH, the lack of upward growth further solidifies the
meager lift in the region despite MLCAPE values around 1000-1500
J/kg. If any storm can develop (currently not expected), that
energy combined with 30kts shear and DCAPE values exceeding 1000
J/kg would support a downburst wind threat.

The high probability for convection shifts to a pre- frontal
trough laying farther west and the approach of the surface cold
front in conjunction with the upper trough axis lifting through
the Great Lakes. Convection is expected to fire along this
boundary after 00z (8pm EDT) and move eastward. The question
becomes a timing issue: can convection reach the region before
the environment stabilizes? Latest hi-res models suggest
elevated instability will remain to allow convection to persist,
but the drier air aloft will wane and limit the downburst
threat. This bears monitoring through the rest of the evening in
regard to developing any severe threat.

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.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
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).

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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.

&&

.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
A rapid decrease of showers and storms, even cloud coverage,
has taken hold this evening in the wake of departing convection
as localized subsidence has developed and impinging dry air
aloft has put a cap on things. Expecting that this will continue
to be the trend through the evening, though can`t entirely rule
out a thunderstorm developing, but confidence is low given the
lack of an initiating mechanism. For this reason, have removed
thunder and precip chances at all sites until after 00z when
a cold front will approach the area and is expected to then
initiate more showers and thunderstorms, some of which may still
be capable of gusty wind and hail.

Outside of thunderstorms, there is high confidence that VFR
prevails aside from MGW/LBE which have the highest probability
of MVFR CIG and VIS after 08z with increasing low level moisture
and light rain showers continuing. Low probabilities for MVFR
CIGs creep as far north as PIT, but profiles suggest it`s likely
too dry for restrictions. It`s most likely that MVFR CIGs
continue for MGW/LBE until 15z or so when mixing erodes the
cloud deck and returns VFR. Additional showers and thunderstorms
are expected to develop Thursday afternoon primarily south of
PIT which may return associated chances for restrictions in the
afternoon.

.Outlook...
Periodic thunderstorm chances and restrictions are likely
through the weekend as an active weather pattern continues.
-- End Changed Discussion --

&&

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

&&

$$

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