Area Forecast Discussion
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992 FXUS61 KPBZ 201731 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 131 PM EDT Sun Aug 20 2017 .SYNOPSIS...
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High pressure will maintain dry and seasonably warm weather into tonight; however, a progressive flow pattern will support rapidly changing weather into midweek.
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&& .NEAR TERM /THROUGH TONIGHT/...
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High pressure will complete a slide across the region tonight with warm, moist advection escalating with the advance of a shortwave out of the Midwest. Despite a 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, think there is enough convergence indicated on top of the boundary layer to support a slight shower chance on the van of the aforementioned Midwestern shortwave. Otherwise, overnight lows will fall either side of the averages with the western zones a few degrees above as per rising dewpoints.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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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 preveious 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.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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Broad surface high pressure under high-amplitude Eastern CONUS troughing is progged to support dry weather and sub average temperature into the weekend.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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High pressure will ensure VFR conditions through this evening. A low, but non-zero, chance of fog development again in the pre- dawn hours Monday. Any fog development should be confined to main stem river valleys, not nearly as expansive and intense as Sunday morning`s. Flow will remain light and variable through the period. .Outlook... Widespread restriction potential returns with a late Tue/early Wed cold front.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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