Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 182246 AFDCTP Area Forecast Discussion National Weather Service State College PA 646 PM EDT Fri Aug 18 2017 .SYNOPSIS... A cold front will move through late today. An upper trough will move across the area on Saturday. Temperatures will stay above normal but rise even higher each day through Tuesday as a ridge builds aloft. Another cold front should trigger showers around mid-week and the week should end on a cooler note. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Convective line has pushed east of the forecast area this evening, but some cu development noted at 2230Z along trailing cold front over the central mountains. Will maintain the chance of a shower/storm along and east of this boundary through the late evening hours. SPC mesoanalysis still showing CAPEs of around 1500 j/kg ahead of this boundary, but based on radar trends, HRRR output and cooling/stabilizing boundary layer over the next hour or two, have cancelled the remaining portion of the severe thunderstorm watch. Some patchy fog will develop after midnight. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Minor update with new data focusing showers in the afternoon. No other significant changes. Previous: The high pressure moving in finally clears everyone out in the morning. Any low clouds in the NW will dissipate nicely with the sunshine. The trouble there is that the lingering moisture, the passage of the upper trough and enhancement from a potent short wave coming around the base will meet up at peak heating. These factors and the wind field will generate multiple showers in the NW half of the area in the aftn. Some of these will make some good gusts - and some could get severe. A little small hail is also possible with colder air aloft than today. SPC does have that area in a MRGL risk for severe wx. The showers/storms will struggle to get past the Allegheny Front (roughly IPT-UNV- AOO line). Max temps will be right near normals. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... The mid range models are all in good agreement on the timing and strength of the passing shortwave Saturday night. Once that passes, the heights will rise and become quasi-zonal. This will bring fair weather to the region Sunday through Tuesday. Dry westerly flow will also bring warm summertime temperatures with Tuesday continually trending warmer. A new shortwave moving through SRN Canada will an bring an increasing chance for rain, possibly as early as Tuesday afternoon over western sections of the forecast area. There are differences in timing of the rain with the ECMWF suggesting it holds off until Tuesday night. Blended MOS POPs show a small chance of showers moving into western sections Tuesday afternoon, but the highest POPs are reserved for the overnight. Cyclonic flow aloft will then dominate the flow pattern through Thursday. The cool air aloft will help trigger a few mainly diurnal showers Wednesday and Thursday. The showers will tend to favor northern and western higher elevations. Temperatures will be significantly cooler for the second half of the week. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Last of the thunderstorms now pushing east out of Lancaster county. Still some residual showers over the Lower Susquehanna Valley, and northeast of KIPT, but expect these to dissipate/push east over the next few hours. Have removed all mention of TSRA and SHRA from the 21z TAF updates. Fog is expected for most of the area tonight, with MVFR to IFR restrictions. An upper level trough and rather strong forcing passing directly overhead in the cooler air aloft could make scattered SHRA/TSRA across the northern third/half of Pennsylvania on Saturday afternoon. Much drier air will make for a mainly-VFR Sun-Mon with only valley fog in the AM a potential issue. .OUTLOOK... Sat...Mainly VFR, but with sct SHRA/TSRA northern 1/3. Sun-Mon...Mainly VFR, but restrictions in morning fog. Tue-Wed...SHRA/TSRA poss. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Fitzgerald SHORT TERM...Grumm/Dangelo LONG TERM...La Corte/Ceru AVIATION...Jung

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