Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 071156 AFDCTP Area Forecast Discussion National Weather Service State College PA 656 AM EST Wed Dec 7 2016 .SYNOPSIS... A ridge of high pressure over the Ohio Valley will build into Pennsylvania later today and tonight. A cold front will sweep southeast across the area on Thursday. A weak low pressure system is likely to track west of Pennsylvania through the Great Lakes Sunday and Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Nearly saturated 0-1km layer remains across Central Pa at 09Z, resulting in areas of drizzle and fog over the high terrain. However, occluded front pushing into the Allegheny Plateau at 09Z will sweep across the rest of Central Pa by around 14Z, ushering in a drier westerly flow and causing drizzle to end from west to east between 5-9AM. Can`t find any sub-freezing readings at 09Z in mesonet and expect a brief rise in temps with arrival of front as low level cold air is scoured out, so not anticipating any significant icing issues this morning. Surface high pressure building into the region should supply a dry Wednesday to Central PA. However, low level moisture trapped beneath inversion and upslope flow will likely result in stubborn low clouds across the NW Mtns. A downsloping westerly breeze should result in clearing skies east of the Mtns. Temperatures there should respond by rising into the low-mid 40s, while cloud cover holds readings to the mid 30s across the NW Mtns. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... High pressure ridge will remain over the region tonight, producing generally fair and tranquil conditions. A fast-moving shortwave lifting out of the Mississippi Valley will track across NW Pa around dawn, likely producing no more than an increase in mid level cloudiness. However, colder air working into NW Pa in the wake of this feature will result in developing lake effect snow downwind of Lake Erie on Thursday. All model data currently indicating the boundary layer flow will remain WSW for much of Thursday, keeping the accumulating snow north of the border. However, a gradual veering of the flow will likely bring snow into at least NW Warren County by Thursday evening. Lake effect watch likely begins a bit too early, but will leave start time at 18Z for now. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Main focus at the start of the long term will be the expected lake effect snow event across NW Pa. The subsidence inversion base lifts rapidly up to, then well over 7-10 kft agl Thursday night right through Friday night, as the mean low to mid level flow becomes well-aligned from the West-Northwest. The subsidence inversion base will drop gradually down to below 7 kft agl during the day Saturday as the mean 925-700 mb flow backs to more of a west, then swrly direction by around 12Z Sunday. This scenario of inversion heights near 700mb, combined with anomalously cold air at 850mb and relatively warm lake waters of around 50F, support locally heavy snowfall (mainly NW Warren Co) between Thu night and Saturday. Examination of omega time sections indicates the max lift should be just below the DGZ. This combined with a fairly gusty wind should hold snow/water ratios to no more than 20 to 1. Based on QPF input from WPC and latest higher resolution models first guess is for 36-hour totals of 12+ across the snowbelt of NW Warren by Sat AM. Further south, scattered narrow bands of snow showers will stream SE into the Central Ridge and valley Region occasionally, with a coating to an inch possible in a some locations. Orographic forcing over the Laurels should lead to an inch or two of accum Thu night through Fri night. A generally westerly flow is unfavorable to draw lake moisture that far south. Diminishing LES expected Saturday as inversion heights fall upon approach of high pressure. A bubble of high pressure at the sfc (and a weak ridge aloft) will bring a brief period of tranquility (though very cold overnight min temps) as it slides east across the forecast area late Saturday into early Sunday. Expect partial clearing (and perhaps mostly clear skies across the SE part of the CWA) for the middle third of the weekend. Deep, mean-layer flow backs to the southwest with a slug of low-mid level warm advection sliding up and over the deep/retreating cold airmass. This could create an area of light snow or snow showers across mainly the northwest half of PA Sunday afternoon and Sunday night. The boundary layer could become warm enough by Monday to mix in or changing the scattered light precipitation to rain showers, throughout the Lower Susquehanna Valley. Seasonable temps indicated early next week, but both the 00Z ECENS and NAEFS indicate a significant cold front for mid week with below normal temps likely late next week. && .AVIATION /11Z WEDNESDAY THROUGH SUNDAY/...
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Expect most areas to become VFR by late morning as the storm moves away from the area. Some snow showers will likely work into the north and west late Thursday into early Saturday afternoon, as winds shift more to the west and northwest off the Great Lakes. A weak storm system tracking northeast across the Great Lakes on Sunday may bring a few snow showers to the area late. Outlook... Thu-Fri...Becoming windy with periods of snow showers, mainly late Thursday into Friday. Mainly MVFR/IFR west to MVFR/VFR east. Sat...Decreasing winds. Low cigs/-SHSN psbl NW. VFR east. Sun...Some snow possible. Mainly late across the NW.
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&& .EQUIPMENT... Temp/dewpoint sensor at KIPT appears to be malfunctioning. It continues to read too warm compared to meso obs and surrounding METARs. Techs have been advised and repair is estimated to be done on Wed. && .CTP WATCHES/WARNINGS/ADVISORIES... Lake Effect Snow Watch from Thursday afternoon through Saturday morning for PAZ004-005. && $$ SYNOPSIS...Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Fitzgerald/Lambert AVIATION...Gartner/Martin EQUIPMENT...

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