Area Forecast Discussion
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000 FXUS61 KPBZ 182233 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 633 PM EDT Thu May 18 2017 .SYNOPSIS... An approaching front will provide scattered showers and thunderstorms through tonight. The front lingers near the Mason-Dixon line Friday, with slightly cooler air behind it. More rain chances arrive this weekend. && .NEAR TERM /THROUGH FRIDAY/...
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While moderate shear remains over the CWA early this evening, earlier convective activity has already largely worked over the boundary layer across the northwestern two-thirds of the CWA. The result is drastically reduced instability as compared to earlier this afternoon. Consequently, owing to the fact that the surface boundary remains well to northwest of the area generally along I-80 from Indiana into Ohio and toward far southwestern Ontario at this hour, a lack of lifting mechanism and decreased instability are both working again robust convective development. That said, high dewpoints and the return of the early evening sun may allow a few updrafts to muster a few more showers and thunderstorms, but the window for enhance convection seems to have closed. Convective development does seem to secondarily increase along the front to our northwest at this hour, however given its slow southeastward wander through the night, an unfavorable passage time in the diurnal cycle, and the face that the vast majority of large scale forcing will shear off to the northeast well northwest of the area, nothing more than showers or a weak storm seems likely along this front as it crosses overnight toward morning. Chance PoPs have been maintained for this at this time. Fries There is still some question as to if/when the boundary finally clears the southern CWA border on Friday. Minor waves and/or convective clusters could cause the front to waver, and thus have maintained some low PoPs near/south of the Mason-Dixon line through the day. A slightly cooler and drier air mass will push in behind the boundary, although temperatures will remain above normal for the most part.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... Zonal mid-level flow at the start of this period will transition to ridging by Sunday, thanks to a lifting trough over the Plains. After a mostly quiet and cooler Friday night on the edge of high pressure, moisture will once again build from the southwest with time. This will lead to a slow rise in shower and thunderstorm chances through Saturday and Saturday night, although coverage will remain fairly limited as the ridge axis passes. More widespread rain is anticipated by Sunday ahead of an advancing frontal boundary. Temperatures will remain above normal, although rises will be tempered by increasing clouds and precipitation. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Rain continues into Sunday night, with chances decreasing late Sunday night/Monday morning with the passage of the front. This will knock temperatures back to near or even a bit below climatology. Fairly broad troughing sets up thereafter, with a couple of shortwaves providing precipitation chances Tuesday through Thursday. Will keep values in the chance category given model timing variations. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... VFR is expected with gusty winds diminishing by early evening. Isolated storms will be possible east of a line running roughly from ZZV to FKL...but chances are not high enough for inclusion in the TAF. .Outlook... Restrictions are possible again late Sat thru Mon with another front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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