Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 091817 AFDCTP Area Forecast Discussion National Weather Service State College PA 117 PM EST Sat Dec 9 2017 .SYNOPSIS... Low pressure, located just east of Cape Hatteras early this morning, will track northward today, paralleling the coastline. A deep upper level trough will remain over the eastern conus through next week with clippers potentially affecting Pennsylvania Monday night and Thursday. && .NEAR TERM /THROUGH TONIGHT/..Chilly westerly flow behind the aforementioned vigorous is likely to generate a bit of lake effect snow late tonight into Sunday across the Allegheny Plateau. Ensemble qpf supports accums generally less than an inch across the Allegheny Plateau tonight/Sunday. However, favored snowbelt of northwest Warren could be near 3 inches. Later shifts may want to consider an advisory for Warren, with the benefit of later HREFV2 data.. Regional radar mosaic and webcams continue to show accumulating snowfall over my far southeastern counties with local 2" amounts having occurred over southern York/Lancaster County as of early afternoon. Another few hours of steady snowfall expected with back edge already racing into the D.C. metro area at this hour will keep amounts very close to what we already have indicated, so no changes to amounts at this time. Steady snow will have pushed east of the area by this evening as surface low takes deeper moisture with it towards coastal New England. Later tonight, vigorous shortwave currently dropping through the midwest early this afternoon will sweep across the region tonight, as coastal low tracks into the Canadian Maritimes. Low PWATs in advance of this feature will limit precip to mainly scattered flurries late this evening. However, chilly westerly flow behind this feature is likely to generate lake effect snowfall late tonight into Sunday across the Allegheny Plateau. Fetch is most favorable for accums over Northwest Warren County where more than 3 inches is expected, so will be going with Winter Weather Advisory there from late tonight through Sunday afternoon. && .SHORT TERM /SUNDAY/... Aside from aforementioned lake effect snow into Sunday afternoon, downsloping subsidence should result in partly sunny, dry weather east of the mountains Sunday. Mixing down model 850mb temps of -10C to -12C translate to below normal max temps Sunday, ranging from the upper 20s over the Alleghenies, to the mid 30s in the Susq Valley. A gusty west wind will add an additional bite to the air. Bukfkit soundings support frequent gusts of around 20kts.Chilly westerly flow behind the aforementioned vigorous is likely to generate a bit of lake effect snow late tonight into Sunday across the Allegheny Plateau. Ensemble qpf supports accums generally less than an inch across the Allegheny Plateau tonight/Sunday. However, favored snowbelt of northwest Warren could be near 3 inches. Later shifts may want to consider an advisory for Warren, with the benefit of later HREFV2 data. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... All model guidance showing deep upper trough remaining over the eastern conus next week, ensuring below normal temps and a couple opportunities for light snow from passing clippers. Boundary layer trajectories back to the west-southwest Sunday night into early Monday, focusing lake effect snow showers north of the border. Med range guidance consolidating on track of Alberta Clipper north of Pa Monday night, which should keep the most substantial snow north of Pa. However, blend of latest guidance still supports a likely period of light snow across central Pa, with accums generally in the 1-3 inch range. The coldest air of the season is forecast to arrive behind this system with a shot of arctic air and more lake effect snow lasting through midweek. Both ECENS and GEFS indicate another clipper is likely to affect the area next Thursday with another potential light snowfall. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... VFR conditions north...transitioning to MVFR to IFR southeast as snow impacts especially York and Lancaster Counties. Best window for reductions in the Lower Susq will be through 24z, while remainder of CWA remains primarily VFR. Then focus will shift to a trough moving in from the NW tonight, bringing restrictions and widespread snow showers to the northern/western mountains along with brisk NW flow and the potential for scattered heavier squalls that will linger into the first half of Sunday. Scattered snow showers will bring intermittent MVFR incursions into the central mountains, while downslope flow will keep the SE VFR. Outlook... Sun...AM snow showers/reductions likely Allegheny Plateau, becoming confined to the NW mtns in the afternoon. Scattered squalls also poss. Mon...Cig reductions likely western portions. PM light snow developing, mainly northwest Pa. Mon night and Tuesday...Periods of light snow. Widespread MVFR likely, with periods of IFR and brief LIFR cigs and vsbys. Wed...Reductions poss west in sct snow showers. Otherwise VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 1 AM to 3 PM EST Sunday for PAZ004. Winter Weather Advisory until 8 PM EST this evening for PAZ065- 066. && $$ SYNOPSIS...DeVoir NEAR TERM...DeVoir SHORT TERM...DeVoir/Fitzgerald LONG TERM...Fitzgerald/Gartner AVIATION...DeVoir/RXR

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