Area Forecast Discussion
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000 FXUS61 KPBZ 210108 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 908 PM EDT Sun Aug 20 2017 .SYNOPSIS... Departing high pressure will continue to hold sway across the region through morning with mostly dry conditions prevailing. A progressive flow pattern will support rapidly changing weather into midweek. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... High pressure has moved east of the area this evening, and warm advection has commenced in its wake. A short wave trough is beginning to advance eastward into this environment from its current position around the southern shores of Lake Michigan. Despite the 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 dewpoints. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... 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. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Broad surface high pressure under high-amplitude Eastern CONUS troughing is progged to support dry weather and sub average temperature into the weekend. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... 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. .Outlook... Widespread restriction potential returns with a late Tue/early Wed cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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