318
FXUS61 KPBZ 131818
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
218 PM EDT Tue Aug 13 2024

.SYNOPSIS...
Dry weather with slowly rising temperature is expected through
Thursday. Precipitation chances will increase Friday with slow
low pressure passage, leading to mainly diurnally driven
convection Saturday into early next week.

&&

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

- Mainly dry day with temperatures near seasonal averages.

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Weak shortwave movement over surface high pressure across the
Upper Ohio River Valley region will yield scattered to
occasionally broken afternoon cumulus development and seasonal
temperature.

Expect another clear sky and seasonably cool night across the
region, creating low probability fog potential favoring the
river valleys of northwest PA (where surface moisture is
slightly more entrenched).

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
KEY MESSAGES:

- Dry weather with slowly rising temperature expected through
  Thursday.

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There is high confidence in surface high pressure slowly
traversing the region underneath height rises Wednesday into
Thursday. Little variance is likely from forecasted values
during this period as dry weather persists and area temperature
climbs to and slightly above the daily average.

Temperature will peak Thursday afternoon, but degree of heating
may be slightly dulled if thicker high cirrus arrives earlier in
the day ahead of the next low pressure system.

&&

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

- Precipitation chances increase Friday into Saturday with slow
  passage of an upper level trough.
- Ensembles favor Great Lakes troughing into early next week
  that would maintain low probability, diurnally driven
  convection.
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Ensemble synoptic pattern analysis shows relatively minor
differences of the progression of an upper level trough towards
the Great Lake region starting Friday and lingering into early
next week. Broadly speaking, this pattern will promote periodic
shower and thunderstorm chances, low probability severe/flash
flood threats, and near to slightly below average temperature.

The initial wave of showers and thunderstorms are likely to
arrive Friday morning ahead of a rotating shortwave through the
based of the trough positioned over Minnesota. Mesoscale
variability does exist on the influence of the antecedent dry
air mass and location of best lift/forcing; these factors will
drive precipitation coverage and intensity. Early trends favor
some splitting of eastward moving convection lending to higher
probabilities south of I-70 and north of the I-80 corridor.

More robust convective development is likely late Friday through
Saturday as the upper trough positions just west of the area and
both the pre-frontal trough and surface cold front swing
through. Ensemble means hint at some marginal instability with
dry air aloft leading to a low end wind threat Saturday
afternoon, but confidence is still low on conditions all
aligning properly.

Sunday into Monday is likely to feature isolated to scattered
diurnally driven convection with the backside of the trough
remaining overhead.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
VFR largely expected through the TAF period with sct-bkn VFR cu
possible with a crossing weak shortwave. Cu will dissipate this
evening leaving a clear sky and light wind as sfc high pressure
remains across the region. Fog development will be possible
overnight under this setup. 12Z guidance had continuity with
previous runs in hinting at an all or nothing type of setup,
but overall decreased probabilities (30-20% chance of both less
than 5mi and 0.5mi). Forecast soundings do show a favorable
hydrolapse dewpoint depressions should be at or very close to
zero.. Forecast confidence will be high later in the afternoon
after observing dewpoints when the boundary layer is well mixed
and crossover temperatures can be determined.

.Outlook...
VFR is expected through Thursday under high pressure. Periodic
restriction chances return Friday through the weekend with slow
moving low pressure.

&&

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

&&

$$

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