Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 210052 AFDCTP Area Forecast Discussion National Weather Service State College PA 852 PM EDT Thu Jul 20 2017 .SYNOPSIS... Pennsylvania will be on the northern periphery of a subtropical ridge passing across the southern states through the weekend. A slow moving cold front will push through the area early next week. && .NEAR TERM /THROUGH FRIDAY/...
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The line and the best instability has moved eastward. A final cluster of showers with perhaps of a rumble of thunder continues to move through the Laurels and will slowly moves through south central PA. Expect these showers to diminish by midnight as the atmosphere stabilizes. Hot and very humid weather will continue across the CWA through tomorrow. Across the Lower Susq Valley, combination of heat and humidity will likely push heat indices near 100F for at least a couple of hours late tomorrow afternoon so possible heat advisory tomorrow.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH 6 PM FRIDAY/... Both SPC SSEO and NCAR ensemble suggest a dwindling band of convection will push southeast across the region overnight, as best forcing ahead of shortwave shifts into New England and trailing low level jet sags south across Pa. Large scale subsidence and arrival of much lower PWATs progged for Friday, resulting in a mostly sunny day for most if not all of the forecast area. Have maintained just a slight chance of a lingering shower across Somerset county, which will remain on northern edge of ring of fire. GEFS mean 850 temps still around 17C-18C Friday, which should translate to max temps from the low 80s over the northern mountains, to the low 90s in the Susq Valley. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Upstream developments Friday night and Saturday will largely determine convective impacts across western and central PA on Saturday as large MCS may propagate ESE towards the Ern GLAKS Sat morning. It is possible that this feature continues ESE as a derecho into southwest PA and the panhandles of MD/WV. Latest SPC outlook covers southwest 2/3 of PA in SLGT RISK on Saturday and this appears well placed, but exact location of pcpn will depend on details not well resolved until the very short term time frame. Will keep high chc to likely POPs going for this timeframe given higher than usual confidence in widespread convection to affect the region. Beyond Saturday, today`s medium range models generally agree that continued/gradual weakening and east-southeast shift of the persistent central U.S. upper ridge can be expected with time, as shortwave troughing shifts slowly southeast out of the Canadian Prairie across the northeast quarter of the country by early next week. The associated cold front is progged by med range guidance to push slowing southeast through the forecast area early next week. Above average temperatures (+5-10 degree max T departures) should trend toward mid to late July climo numbers by next Tue- Wed...as WNW upper flow and persistent southeast Canadian and ern GLAKS upper troffing become prevalent by the middle of next week. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... A weakening line of what is now mainly showers is moving southeastward across Central Pennsylvania at 00z this evening. The only cluster of activity that will affect central Pennsylvania airfields is in the southwest. This will bring some rain and maybe a rumble of thunder in the next hour or so to KJST, and a possibility of -SHRA to KAOO. A single isolated shower in northwest Lycoming County may sneak into KIPT as well, but this is showing signs of weakening, so have not included in the TAF at this point. Models continue to insist that visibility restrictions will occur overnight at all airfields, with an accompanying low stratus deck across the west and north by morning. Have maintained this thinking in the TAFs for now, but with most of the airfields avoiding precipitation this afternoon, am a bit skeptical on just how much low level moisture will be around overnight to bring in the stratus. Visibility restrictions in BR/HZ are likely though. Mainly VFR Friday, but isolated to scattered SHRA/TSRA still possible, mainly south. .OUTLOOK... Fri...AM BR/HZ with CIG restrictions possible North and West. Isolated TSRA in the afternoon, mainly south. Sat-Sun...AM valley fog possible. TSRA likely. Mon...AM valley fog possible. Scattered TSRA. Tue...VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT this evening for PAZ035-036-056- 057-059-063>066. && $$ SYNOPSIS...Fitzgerald/Gartner NEAR TERM...Ceru/Gartner SHORT TERM...Fitzgerald/Gartner LONG TERM...DeVoir AVIATION...Jung

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