Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 081602 AFDCTP Area Forecast Discussion National Weather Service State College PA 1102 AM EST Thu Dec 8 2016 .SYNOPSIS... A upper level trough over the Great Lakes will pivot eastward across the region over the next couple of days. High pressure will briefly build into Pennsylvania late Saturday, then a weak low pressure system is likely to track west of Pennsylvania through the Great Lakes Sunday into Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Batch of mid level clouds streaking eastward across the Lower Susq River Valley late this morning. Timing on track to exit my southeastern counties early this afternoon. Colder air deepening downwind of the eastern GLAKS and organized LE band developed shortly after sunrise this morning over the snowbelt of SW New York State. All model data currently indicating the boundary layer flow will remain WSW for much of the day, keeping the bulk of the accumulating snow north of the border. But expect a gradual backing of the flow anticipated by late afternoon, bringing snow into Warren/Mckean counties. A lake effect snow warning/advisory goes into effect at 18Z across Warren/Mckean Co, where a light coating appears likely by early evening. Increasing sunshine will push temps into the low 40s across the Susq Valley. Further west, where lake clouds increase over western and northern PA...highs will top out in the upper 20s and 30s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... A fairly long-duration lake effect snow event will play out across the NW Mtns tonight through Saturday, as anomalously cold WNW flow follows the passage of upper trough axis this evening. Cross lake flow will result in multiband le snow across the northwest Pa, with the heaviest accums in the favored snowbelt of NW Warren Co. Model soundings showing a deep, moist boundary layer with an inversion height around 700MB and although the 850mb temps of around -13C aren`t exceptional, relatively warm lake waters of around 50F will result strong instability/moisture flux. The passage of a shortwave around midday Friday could briefly support lake effect snow extending well downwind of the lakes, with a quick coating likely in the ridge/valley region of Central Pa and possibly even into parts of the Susq Valley. The boundary layer flow is progged to remain close to 270 degrees across Southern Pa, excluding the Laurel Highlands from a direst link to lake moisture. However, persistent upslope flow should yield occasional light snow with accumulations of 1-2 inches between Friday and Sat morning. An examination of model time sections shows the greatest lift occurring just below the DGZ, which in combination with fairly gusty winds should hold snow/water ratios to no better than 20/1. Based on a blend of available high res model and WPC QPF, have come up with 48-hour event snow totals of 12-18 inches over extreme northwest Warren Co, with rapidly decreasing amounts further southeast. Although not an exceptionally cold air mass for this time of the year, this will be the coldest air mass so far this season with temps 5-10F below normal Friday/Saturday. A gusty wind will make it feel even colder. Expect relenting wind and clearing skies across Southern Pa Saturday, as high pressure builds in from the Ohio Valley. However, WSW fetch off the lakes should continue to produce le snow showers until Sat evening across the N Mtns. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... High pressure will bring a brief period of tranquility Sat evening. However, a developing overrunning scenario is expected Sunday into Monday, as weak low pressure lifts into the Eastern Grt Lks and high pressure remains lodged over northern New Eng. Enough cold air is in place to support a light snowfall across much of area by Monday AM. Model consensus low track west of Pa could cause snow to change to rain across Southern Pa before precip tapers off later Monday. Seasonable temps indicated early next week, but both the 00Z ECENS and NAEFS indicate a significant cold front passage late Tue/early Wed with below normal temps likely the rest of next week. && .AVIATION /16Z THURSDAY THROUGH MONDAY/...
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Deepening W-NW flow pattern will support a prolonged period of MVFR/IFR conditions over the western 1/3 airspace into the weekend, with frequent lake effect/upslope snow showers. MVFR cigs and ocnl visby reductions are possible over the central terminals with VFR prevailing across the eastern sites. Expect frequent sfc wind gusts 20-25+kt by this afternoon resulting in low level mechanical turbulence during takeoff and final approach. Lake effect snow showers should decrease in coverage/intensity by later Saturday as area of high pressure briefly slides over the airspace. Outlook... Sun-Mon...MVFR/IFR with mixed rain/snow likely.
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&& .CTP WATCHES/WARNINGS/ADVISORIES...
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Lake Effect Snow Advisory until noon EST Saturday for PAZ005. Lake Effect Snow Warning until noon EST Saturday for PAZ004.
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&& $$ SYNOPSIS...Fitzgerald NEAR TERM...DeVoir/Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Fitzgerald AVIATION...DeVoir/Steinbugl

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