-- Discussion containing changed information from previous version are highlighted. --
760
FXUS61 KPBZ 291159
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
759 AM EDT Wed May 29 2024

.SYNOPSIS...
Crossing disturbances will maintain shower and thunderstorm
chances through Wednesday. Cooler than average temperatures are
expected through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:

- Scattered showers and thunderstorms expected throughout the
  day today.
- High temperature around 5 degrees below the daily average.
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5am update...
A Special Weather Statement was issued covering much of western
PA, northern WV, and portions of eastern OH to highlight areas
of fog that can have localized pockets of dense fog (favoring
river valleys). Impending sunrise and initiation of mixing or
the progression of a line of mostly light rain showers eastward
should reduce fog impacts by 9am. The rest of the forecast
package remains on track.

Rest of the discussion...

An embedded shortwave within the Great Lakes trough will
traverse the Ohio River Valley today, sweeping from Indiana
early this morning to the Mid-Atlantic by tonight. Vort
advection induced lift will create one area of showers with
intermittent periods of thunderstorms (favoring the afternoon)
that is likely to move along and just south of I-70 through the
day. Elsewhere, diurnal heating combined with cold air aloft
will generate 500-1000 J/kg that should translate to scattered
shower/thunderstorm activity areawide from the late morning to
early evening hours. Weak shear should preclude a severe threat
but may foster more prolonged deluges as storm propagation will
be minimal and trough axis passage may foster localized
mesoscale rain bands. Flooding is not anticipated, but there is
a low probability for localized flash flooding given those
preceding factors.

Exiting of the upper level trough axis to the east will see
surface high pressure and subsidence build during the evening
and overnight hours. The expectation is for decaying convective
activity and clearing skies as residual cool advection drops
area temperature around 5 degrees below the daily average.
Pockets of fog, favoring river vally locations, may be possible
as well.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
KEY MESSAGES:

- Dry weather is expected through Saturday.
- Temperature moderates through the period.
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Digging of the upper trough along the eastern seaboard will
promote dry but cool northerly flow over the Upper Ohio River
Valley region through Saturday. Slow height rises as upper
ridging edges east from the Central Plains is expected to
promote gradual temperature moderation; slightly below average
temperature Thursday will become slightly above average by
Saturday. Strong influence from surface high pressure centered
near to over the area will result in bountiful amounts of
sunshine during this period.

&&

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

- Shower and thunderstorm chances increase late Saturday into
  early next week.
- Weakly forced systems mean chances will be tethered to
  convective evolution west of the region.
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Ensembles favor increasing shower and thunderstorm chances late
Saturday night into Sunday with the approach and passage of a
shortwave trough that will shunt narrow ridging to the south.
However, variations in shortwave strength alter the timing,
convective environment, and overall storm coverage during this
period. High pressure to the east will promote warm, moist
advection ahead of this system and help to maintain above normal
high/low temperatures.

Thereafter, the overall pattern trends toward weak westerlies
aloft through early next week. Embedded shortwaves may offer
periodic shower/thunderstorm chances but will be much more
dependent on convective evolution to the west to determine
timing/coverage/probability of occurrence for the forecast area.
There is higher confidence that broad height rises should enable
further warming areawide, making low to mid 80 values more
likely by Tuesday.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
An upper level low approaching the area is supporting a band of
light to moderate showers this morning, though only producing
limited impacts with VFR cigs and MVFR vis. Where showers are
not occurring, calm winds and saturated ground due to
yesterday`s rain have combined to produce patchy dense fog,
concentrated in valleys. This fog should dissipate by mid
morning thanks to rain and boundary layer heating/mixing.
Showers and thunderstorms will become more widespread throughout
the day as the upper low continues to track eastward, with
storm motions changing from southwesterly this morning to
nearly stationary this afternoon as the low passes directly
overhead, and then northwesterly as it departs to the east later
this evening. The slow to nearly-stationary storm motion this
afternoon could pose some issues if any heavier storms set up
over area terminals, producing prolonged restrictions due to
the heavy rain and possibly some minor flooding/ponding.

Convection tapers off after dark due to waning instability and
high pressure beginning to build into the area from the west in
the wake of the low. Aside from lingering low cig potential east
and southeast of PIT (looking primarily at LBE and MGW), VFR
conditions set up overnight and prevail throughout the remainder
of the TAF period.

.Outlook...
High pressure builds into the area Thursday through the end of
the week, resulting in areawide VFR through that time. Some
restriction potential returns Saturday night into Sunday as
showers and thunderstorms return with the next disturbance.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Cermak