Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 201936 AFDCTP Area Forecast Discussion National Weather Service State College PA 336 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 /UNTIL 8 PM THIS EVENING/... Shortwave energy/weak defined cold front moving across the eastern Great lakes is helping to force strong to severe convection east of Lake Ontario. Broken line of weaker showers/storms is trying to develop over northwest PA. Both areas are moving E/SE and will have potential impact on parts of central PA later this afternoon and evening. Severe Thunderstorm Watch #424 included Tioga and Sullivan counties until 8PM. Elsewhere, isolated showers/storms remain possible into this evening, but most places will be rain free today. Hot and very humid weather will continue across the CWA at least today and tomorrow. Across the Lower Susq Valley, combination of heat and humidity will likely push heat indices above 100F for at least a couple of hours later this afternoon. Thus have issued a Heat Advisory til 8PM for of the lower susq counties and as far west as Fulton County. && .SHORT TERM /8 PM THIS EVENING 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/...
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Upstream developments Friday night and Saturday will largely determine convective impacts across western and central PA on Saturday as large MCS may propogate 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.
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&& .AVIATION /20Z THURSDAY THROUGH TUESDAY/... A weak cold front moving across the eastern Great lakes is helping to force strong to severe convection/thunderstorms east of Lake Ontario. Broken line of weaker showers/storms is trying to develop over northwest PA. Both areas are moving E/SE and will have potential impact on parts of the airspace, mainly northern TAF sites, this afternoon and evening. Severe Thunderstorm Watch #424, including Tioga and Sullivan counties, is in effect until 8PM. Elsewhere, isolated showers/storms remain possible into this evening, but confidence remains too low to include at other TAF sites with most air fields will be rain free today. Tonight, scattered convection over central mtns will be diminishing. Areas of valley fog will again become likely, with CIG restrictions poss over the NW. Isolated TSRA poss on Fri, with VFR otherwise. TSRA become likely again for Sat and Sun as humid airmass remains in place. .OUTLOOK... Fri...AM valley fog. Cig restrictions likely NW half. Isolated TSRA. Sat-Sun...AM valley fog poss. TSRA likely. Mon and Tue...AM valley fog poss. Scattered TSRA. && .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...Fitzgerald/Gartner SHORT TERM...Fitzgerald/Gartner LONG TERM...DeVoir AVIATION...DeVoir/Gartner

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