Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 272130 AFDCTP Area Forecast Discussion National Weather Service State College PA 530 PM EDT Thu Apr 27 2017 .SYNOPSIS... A strong subtropical ridge over the western Atlantic will dominate our weather through Monday. A front will moves into Pennsylvania this evening, triggering showers and thunderstorms. Then the ridge will build westward over the weekend. We will be on the warm, moist western side of the ridge most of the weekend. A classic dirty warm up with warm moist air and potential diurnal thunderstorms. Alas, a strong trough should bring cooler drier weather to the region for the second part of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... GOES-16 finally shows low clouds breaking up and mixing out under the strong late April sun. The winds at the surface to 925 mb were still running from the south to southeast leading to continue marine influenced flow into central PA this afternoon. This was limiting the temperatures even in areas where there was sunshine with the clouds breaking up. The low clouds will continue to break up more as the afternoon progresses into the evening. Water vapor channel from the mid to upper levels shows a short wave moving east across the Ohio Valley. This feature was a wave that was rotating around the closed low just north of Minnesota. As this wave moves east it is projected to continue to support convection as it moves into PA and NY. Even with the marine layer in place dewpoints have climbed into the upper 50s and lower 60s in PA. NAM is projected mixed layer CAPEs of between about 400 J/kg and almost 1000 J/kg. SPC mesoanalysis is showing mixed layer CAPEs of a few hundreds J/Kg as this point with significant CIN as per the low-level inversion. As this wave moves east, it is projected to lift this inversion out and lead to the continuation of the convection moving east from the Ohio Valley. Almost all of the CTP forecast area was in a marginal risk for severe weather into this evening given the strong 0-6 km shear of 40-50 knots which is advecting eastward. 0-1 km helicity is projected to be around 250 m2/s2 at AOO and MDT, and 212 m2/s2 at UNV. This is not surprising given the low-level southeast flow east of the mountains which was not that strong. The 850 mb winds are projected to southwest up to 40 knots. 0-1 km shear values are projected to be between 20 and 30 knots. So the bottom line is the pojected CAPEs are the limiting factor. But if CAPES can get high enough there could be supercells. So will continue mention of potential severe storms with in the HWO and expand the area farther east. SPC has mentioned that they might upgrade to a slight risk with the 3 pm update. Used the HRRR timing for the convection in the POP grids. After this wave passes, the convection will die down and drop pops off. Friday looks fair with weak high pressure over the region. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... For Friday night and Saturday boundary sets up over PA with a few waves rippling along the boundary. There is some uncertainy on how much instability is left over and exactly where this boundary sets up so went with superblend POPs and blended with neighbors. Upper level ridge tries to builds in for Saturday night to Sunday but continued southerly flow and instability will lead to additional chances for showers and storms. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Used superblend for this time period. Main feature will be a massive cyclone that tracks through the Western Great Lakes from Sunday night through Monday night. This will push a strong cold front through PA and lead to another round of showers and thunderstorms. Once this feature passes by much chillier air will advect into PA with unsettled weather mainly for the northern part of the state right into Wednesday. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/...
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Warmest temperatures to the west of the mountains. For the 21Z TAF package, did keep some thunder in, but cut back on it some, given the more stable air east of western PA. Earlier discussion below. Lingering MVFR conditions continue at UNV, IPT and AOO rest of TAFs have become VFR. We expect these sites to finally go to VFR by around 19-20z. Then we expect at least a broken line of thunderstorms to work east and reach the terminals from west to east between 22z and 03z. We bring conditions to MVFR with any thunderstorms. After some lingering showers we expect mostly MVFR ceiling and/or visibility to develop after midnight. Then conditions will improve to VFR Friday after 13z. Some IFR conditions are expected at LNS in BR between 09z and 14z and at JST in BR/FG and ceiling between 9z and 15z. Confidence at JST is medium with confidence for IFR at LNS low. Winds will be south to southeast 5 to 12 knots overnight with some gustiness late this afternoon/early evening. Winds will shift to west to southwest under 10 knots after midnight. Outlook... Fri...No significant weather. Sat-Sun...A few showers possible. Mainly dry with VFR conditions for much of the time. Mon...Breezy with showers and thunderstorms likely with FROPA. Tue...Mainly VFR, possible MVFR in shra in BFD
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Grumm NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...DeVoir/Fitzgerald AVIATION...Grumm/Martin/Steinbugl

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