893
FXUS61 KPBZ 311143
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
743 AM EDT Fri May 31 2024

.SYNOPSIS...
The next window for rain will arrive late Saturday into Sunday
with passing low pressure. Above normal temperature and low
probability showers and thunderstorms are favored thereafter
until the next system arrives mid to late week.

&&

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

- Temperature rebounds to near the daily average.
-------------------------------------------------------------------

Update to let the frost advisory expire, otherwise rest in fine
shape.

Waning dry northerly flow as an upper level ridge approaches
from the west will continue to promote dry weather and abundant
sunshine today. Concerns for patchy frost in parts of northwest
PA and far eastern Tucker County (the only local with a Frost
Advisory) will dissipate quickly after sunrise.

The upper level ridge axis will position over the ridge
overnight as surface high pressure begins to slide to the east.
Dry weather and clear skies are thus going to persist and favor
strong radiational cooling that leads to low temperature falling
around 5-10 degrees below the daily average.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Showers and low probability thunderstorms arrive late Saturday
  through Sunday.

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Approach of a shortwave trough within westerly flow will shift
the upper level ridge east through the day Saturday. As flow
aloft becomes more southwesterly, warm/moist advection is
expected to increase cloud cover during the afternoon and
evening hours while boosting area temperature to slightly above
the daily average.

The shortwave will traverse the area late Saturday night into
Sunday morning, producing areas of generally lighter rain
showers. Probability for thunderstorms during this period will
be low as even 75th percentile SBCAPE values don`t exceed 100
J/kg. Chances will continue through the day until the wave
exits, but flooding/severe threats should remain minimal due to
weak instability and weaker deep-layer shear. The timing of the
wave exit is slightly varied amongst deterministic models due
to variations in shortwave depth, but trends suggest
precipitation chances ending by midnight Sunday into Monday.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
KEY MESSAGES:

- Low probability showers and thunderstorms with above normal
  temperature likely to start the next work week.
- More widespread precipitation favored with mid to late week
  low pressure system.
-------------------------------------------------------------------

Ensembles generally favor gradual ridge building across the
Tennessee and Upper Ohio River Valleys Monday into Tuesday with
some shortwave movement to the north as troughing develops over
the northern Rockies. This should promote above normal
temperature and at least dry weather for Monday as subsidence
and weak flow keep diurnally driven convection very isolated.
The deviation for that forecast could come Tuesday if shortwave
movement is more robust/deeper to the north Tuesday, which would
increase convective potential during the day (favored ECMWF
route). Either scenario would still be somewhat dependent on
storm evolution well west of the region and its impact on the
larger scale flow.

The synoptic patter shows greater variation mid-week as not all
model solutions track the northern Rockies trough toward the
Great Lakes. Current model consensus, and this forecast package,
does trend toward the approaching/passing trough scenario which
would promote more widespread showers/thunderstorms during the
mid to late week period. If ridging proves to be more stout
ahead of the troughs approach, that could delay the uptick in
precipitation chances till next weekend while maintaining a
more dry and seasonable warm pattern. Nonetheless, the
variations remain too wide for any discussion of severe or
flooding threats at this time.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
High confidence forecast of VFR weather. High pressure centered
over the region will maintain light wind and limited cloud
coverage through the TAF period.

.Outlook...
The potential for flight restrictions returns early Sunday with
crossing low pressure. Latest guidance shows probabilities of
MVFR and IFR between 50%-70% and 20%-30% respectively on Sunday.

&&

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

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...88/McMullen