Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 210645 AFDCTP Area Forecast Discussion National Weather Service State College PA 245 AM EDT Fri Jul 21 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 6 AM THIS MORNING/...
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Satellite loop at 06Z showing fairly widespread low clouds and fog have formed where rain fell last evening over northern Pa. Based on 06Z dewpoint depressions, expect valley fog to become more extensive toward dawn. However, little if any fog is anticipated across the Lower Susq Valley, where no rain fell yesterday and 06Z dewpoint depressions remain fairly high. It will be another very warm and muggy night with min temps from the mid 60s over the northern mountains, to the mid 70s across the Lower Susq Valley.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/...
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Model soundings and LAMP guidance indicate early low clouds/fog should mix out by around 14Z, then large scale subsidence and arrival of much lower PWATs should result in a mostly sunny Friday for most if not all of the forecast area. Have maintained just a slight chance of an afternoon thunderstorm near the Mason Dixon Line, which will remain on northern edge of ring of fire. GEFS mean 850 temps still around 18C today, which should translate to max temps from the mid 80s over the northern mountains, to the low 90s in the Susq Valley. The southeast counties fell just short of heat advisory criteria yesterday and expect a similar scenario today with heat indices over that part of the state peaking in the upper 90s.
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&& .LONG TERM /TONIGHT 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 /07Z 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...
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None.
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&& $$ SYNOPSIS...Fitzgerald/Gartner NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald/Gartner LONG TERM...DeVoir AVIATION...Jung

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