Area Forecast Discussion
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FXUS61 KPBZ 202331

Area Forecast Discussion
National Weather Service Pittsburgh PA
731 PM EDT Sun Aug 20 2017

High pressure will maintain dry and seasonably warm weather into
tonight; however, a progressive flow pattern will support rapidly
changing weather into midweek.


High pressure will complete a slide across the region tonight
with warm, moist advection escalating as a short wave trough
advances eastward through the lower Great Lakes. Despite
nocturnal capped surface layer, the latest NAM, RAP, and high
res soundings indicate varying degrees of elevated instability
with the predawn moisture return. Although, overall lift/forcing
will be weak, there may be enough convergence indicated on top
of the boundary layer to support a slight shower chance in
advance of the aforementioned wave.

Otherwise, overnight lows will fall either side of the averages
with the western zones a few degrees above as per rising


That shortwave is the lead disturbance in a series of impulses
which will escalate rain chances into Tuesday. As for eclipse
viewing on Monday, local conditions are not looking as favorable
as previous as that lead impulse is expected to at least spawn
mid level cloudiness, and possibly some isolated convection with
its morning to early afternoon passage. The good news is that
at moment, weak shortwave ridging is timed to suppress precip
during the peak time of the event.

By Tuesday, strong low pressure is forecast to dig between the
James Bay and Great Lakes and pull a cold front toward the Ohio
Valley. Given model-world agreement, likely precip probabilities
have been maintained with ramped-up severe expectations as per
a strengthened pressure gradient and resultant wind profile. That
potential remains slight at moment as warm mid level temperature
will likely retard overall instability. Nevertheless, prudence
dictates inclusion in the Hazardous Weather Outlook, especially
in light of the projected boundary layer warmth and moisture.

Prefrontal trough passage is timed to end the severe threat by
Tuesday eve, with early Wednesday frontal passage heralding
cooler temperature for the remainder of the week.


Broad surface high pressure under high-amplitude Eastern CONUS
troughing is progged to support dry weather and sub average
temperature into the weekend.


High pressure will provide prevailing VFR conditions through the
period. With a day of drying and lower afternoon dewpoints, fog
will be much less of a threat. Expect it to be confined mainly
to valley south of Pittsburgh, with ZZV/HLG perhaps seeing some
MVFR mist. Some mid-level clouds will also spill in overnight
ahead of a weak shortwave.

On Monday, scattered cumulus are expected in the mean, with
light surface flow. Isolated to scattered showers and storms are
possible, but probabilities are too low for inclusion in TAF at
this time. The clouds have more potential impact on eclipse
viewing rather than aviation.

Widespread restriction potential returns with a late Tue/early
Wed cold front.




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