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422
FXUS61 KPBZ 291431
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1031 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/...
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KEY MESSAGES:

- Scattered showers and thunderstorms expected throughout the
  day today.
- High temperature around 5 degrees below the daily average.
-------------------------------------------------------------------

An upper low is situated across northern Ohio this morning and
vorticity advection associated with an embedded wave has driven
an area of showers with some rumbles of thunder. Intrusion of
mid-level dry air noted on water vapor satellite will provide a
period of dry weather south and west of Pittsburgh through a
good portion of the morning hours. As the the upper low pivots
and moves further south and east however, the atmosphere will
re-moisten and coverage will increase further south, though it
may have a more convective look to it south of Pittsburgh
resultant of differential heating with thicker cloud cover north
and thinner south. The 12z PIT sounding shows PWAT values just
under an inch which isn`t much out of the ordinary for today
climatologically. That said, cloud bearing layer flow of less
than 20 knots will support slow moving areas of showers. Colder
air under the core of the upper low will allow for
destabilization of 500-800 J/kg of mainly skinny CAPE largely
confined to the -10C layer and below which could enhance warm
rain processes thus heavier rates. While widespread flooding
concerns aren`t expected, the areas to watch will be typical
urban areas but also the Columbiana-Beaver-Lawrence-Mercer
region where morning rain has sat the longest and CAMs indicate
a probable deformation zone maintaining showers here this
afternoon thus confidence is higher for this area to see the
most rain. Widespread totals will be a quarter to three quarters
of an inch, but amounts locally up to 1.75" under the heavier
showers are not off the table. Very weak shear should preclude
a severe threat today.

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.
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&&

.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 /14Z WEDNESDAY THROUGH SUNDAY/...
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.

&&

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

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Frazier/MLB
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Cermak/Shallenberger