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371
FXUS61 KPBZ 221445 AAB
AFDPBZ

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
1045 AM EDT Wed May 22 2024

.SYNOPSIS...
Another warm day with the risk for showers and storms increasing
this afternoon and evening. On and off showers and storms may
continue through Thursday. Cooler temperatures on Thursday, but
still above normal.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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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.
  _____________________________________________________________

Overall going forecast is in shape, and made minor adjustments
to timing/magnitude of Sky and PoP grids to reflect greater
gradient in observed values at present time. Ongoing showers in
our ern OH counties may struggle initially, but are expected to
renew as convergence increases within a sfc trough/cold front.
Previous discussion follows...


Minor heights rises this morning will be thwarted by an
approaching, rather energetic, shortwave trough that will cross
Ohio. As the shortwave barrels eastward, it will weaken somewhat
and may outrun the main moisture plume that extends
southwestward toward Texas. Current hires Cams are not showing
much activity developing across Ohio ahead of the trough, rather
firing it mainly over western PA this afternoon. This may be
due to increased instability over PA as there will be more time
to destabilize before the cloud cover spreads across the region.
These same models are also indicating an unorganized/broken
line of storms developing. This looks reasonable as the
atmosphere will be unstable and buoyant, but strong shear will
be lacking. There will be a wind threat with the initial
convection, but localized flooding could also be an issue as
PWATS will range from 1.25 to 1.50". There will be limiting
factors to the convection as well. The aforementioned cloud
cover and also very warm air aloft. Forecast soundings are
showing some capping this afternoon which is raising the LFC.
Additionally, the lack of strong shear will also limit the hail
threat.

The shortwave may weaken rapidly as it moves through the western
half of the forecast area this afternoon. Afternoon convection
should exit into central PA early this evening which would allow
for a break in the activity. The surface cold front, will
remain to the west of the region as sunset approaches, reaching
central Ohio early this evening.

Highs today will be a bit tricky, especially if the clouds get
here earlier as well as the initial round of convection. Still
expect a warm day, but not as warm as Monday and Tuesday.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
KEY MESSAGES:


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

The surface cold front will slowly move through Ohio tonight.
Shortwaves, embedded in the main trough, may split, with one
spinning northward toward the upper Great Lakes region and the
other spiraling southward toward the TN Valley. If this split
happens there will be little upper level support with the cold
front as it moves through the region. With sunset, the
atmosphere will slowly stabilize and cooler air aloft will begin
to spread across the region behind the front. We will also see
an increase in wind shear, but most of this looks to be behind
the boundary. Forecast soundings continue to show some capping
aloft as the near surface atmosphere cools. As what we saw this
afternoon, CAM models are indicating an unorganized and broken
line of activity ahead of the front. With some of these models
showing a split with much of the convection to the north of PIT
closer to a passing 500mb jet and a weak shortwave. Another
quandary for the overnight period will be how fast will the
front move through and how far southeast will it push. The weak
shortwave trough should move east of the area as dawn
approaches, however with southwest flow aloft remaining, it may
be difficult for the boundary to make much of a push southward.
The location of the front will have an impact on Thursdays
weather as well.

As the upper trough lifts NE Thursday morning, the surface
boundary will stall in a WSW-ENE orientation somewhere over the
southern half of the forecast area; the quasi stationary
boundary, combined with a passing wave, should favor additional
shower/storm development along and south of the boundary
through much of the day.

Activity should finally begin to shift southward as the front
exits Thursday night.

Though forward prorogation of storms and lack of stronger
forcing should limit flooding hazards, elevated PWAT values
and potential for some training during the day Thursday (as the
boundary becomes more parallel to the upper flow) could lead to
localized flooding.

Ensembles favor high pressure north of the region establishing
more seasonable and dry weather for at least part of Friday in
the wake of Thursday night`s shortwave passage. However, global
models suggest the potential for a weak shortwave to lift
northeast out of the TN River Valley later Friday which may
promote showers and thunderstorms.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
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.
  ____________________________________________________________

The overall pattern will usher additional rounds of shortwave
crossings through the Upper Ohio River Valley as it remains in
between broad ridging over the SE CONUS and troughing over the
northern Great Plains. Expect periods of showers and
thunderstorms with near to slightly above normal temperature,
with potential for severe hazards depending on evolution of
prior day`s convection.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
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...Kramar/22
SHORT TERM...22/Frazier
LONG TERM...22/Frazier
AVIATION...88