Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 202115 AFDCTP Area Forecast Discussion National Weather Service State College PA 515 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/... 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. && .AVIATION /21Z THURSDAY THROUGH TUESDAY/...
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A scattered line of showers and a few thunderstorms is moving southeastward across Central Pennsylvania at 21z this afternoon. Coverage is scattered enough to just include the mention of VCTS in western and central TAFs for a several hour window with the passage of the front. Convection is not expected to maintain itself into the southeastern portions of the Commonwealth, so no mention of thunderstorms in KMDT and KLNS at this point. Scattered convection over central mountains will continue to diminish overnight. Areas of valley fog will again become likely, with CIG restrictions poss over the northwest. Isolated TSRA possible on Friday, with VFR otherwise. TSRA become likely again for Saturday and Sunday as humid airmass remains in place. .OUTLOOK... Fri...AM valley fog. Cig restrictions likely NW half. Isolated TSRA in the afternoon. Sat-Sun...AM valley fog possible. TSRA likely. Mon and Tue...AM valley fog possible. Scattered TSRA.
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&& .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...Jung/DeVoir/Gartner

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