Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 092121 AFDCTP Area Forecast Discussion National Weather Service State College PA 421 PM EST Fri Dec 9 2016 .SYNOPSIS... A broad and very cold upper level trough over the Great Lakes and southeastern Canada will remain in place for the next few days. This weather feature and a well-aligned westerly low level flow off the lower Great Lakes will bring a prolonged period of lake effect snowfall and significant snow accumulations to northwest PA today through Saturday. High pressure will briefly build across the commonwealth late Saturday and Saturday night causing the Lake Effect snow bands to lift north of the region with a brief period of clearing elsewhere. Then, a weak low pressure system is likely to track east from the Ohio Valley and impact Pennsylvania with another bout of wintry weather Sunday into Monday. Unsettled weather will persist next week with additional storm chances during the mid...and late week periods. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... An anomalously cold cross-lake flow will maintain a long-duration, multi-band lake effect snow event across northwest PA...with bands extending into the Central Mountains and Ridge and Valley regions of central PA through this evening. No big changes from previous thinking going on...as activity persists in moderate northwest flow supporting multiple bands of moderate to heavy snow showers. Shortwave traversing north central PA is maintaining an intense band which is currently crossing Interstate 80 between Beach Creek and Lewisburg producing dangerous travel conditions there. Elsewhere the main impacts are over the northwest mountains where western portions of Warren County have likely exceeded a foot and will add substantially to totals tonight. Will maintain the Lake Effect Snow Warning (Warren County) and Lake Effect Snow Advisory (Mckean County) through 17Z Saturday, before the llvl mean wind gradually backs to about 250 Deg carrying the LES bands north of the PA/NY border Saturday afternoon. Little change to forecast storm total snow amounts as 12-18" with locally 20"+ is expected over the NW third-half of Warren County by Saturday. A light coating to one inch will occur in select areas of the central Ridge and Valley Region of PA today...with some spots receiving additional light accums tonight and Saturday. Skies in this region of the state will stay mostly cloudy to cloudy. Across the Mid and Lower Susquehanna Valley Region, it will be partly to mostly cloudy with generally just some scattered flurries. But will need to watch the southeast extent of current banding crossing I-80 which could bring a rush hour headache to areas that don`t usually see heavier snowshowers/squalls. Mins tonight will be fairly uniform...ranging from the upper teens northwest to the mid 20s southeast. A brisk northwest wind will gust between 20 mph and 30 mph...putting wind chills in the single digits and teens. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Additional significant accumulation will occur across the 2 NW PA counties into Saturday morning...while some areas of light additional accumulation is possible across the west-central mtns and Laurel Highlands. Gradually improving conditions will take place later in the morning and afternoon as lake effect snow bands become more scattered and slowly wind down. Despite decreasing in intensity... WSW fetch off the lakes should continue to produce snow showers until Sat evening across the N Mtns. Skies should be clear across southern PA Saturday thanks to 1032 mb surface high building into the region. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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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, with both GFS and ECMWF better coming together on timing for light precip moving into the area from the west on Sunday. Model consensus low track west of PA should bring in enough warm air to cause snow to change to rain (or a period of more problematic freezing rain) across Southern PA, and esp the Lower Susq Valley, a before precip tapers off Monday afternoon. Potential with this event for advisories to be issued, but being a 4th/5th period event will hold off for now. Another fairly short respite Mon night into Tue night, with some lake effect snow showers over nw mtns. But progressive pattern brings another wave through in the GFS for Wed with chance for rain/snow, before westerly flow keeps mention of snow showers over northern mtns after that. After warm advection Sun night into Mon brings temps above freezing across the SE, temps gradually fall back early next week. Longer range models continue to indicate a significant cold front passage Wed with noticeably below normal temps filtering in starting Wed night and continuing for the rest of next week as 850MB temps fall to -20C.
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&& .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... Cold W-NW flow pattern downwind of the Great Lakes will continue to support a prolonged period of MVFR/IFR conditions over the western 1/3 of the airspace into the weekend, with frequent lake effect/upslope snow showers at KBFD/JST. MVFR cigs and ocnl vsby reductions in -shsn are possible over the central terminals with VFR prevailing across the eastern sites. Expect sfc wind gusts 20-25+kt from 270-300 degrees for most of today before winds subside after 10/00z. Lake effect snow showers should decrease in coverage and intensity by later Saturday as area of high pressure briefly slides over the airspace. Low pressure tracking from the lee of the Rockies to the Ohio Valley will bring a broad area of snow/rain to the area Sunday into early Monday. Outlook... Sat...MVFR/IFR western 1/3 with snow showers decreasing. Sun-Mon...Widespread MVFR/IFR in snow/rain. Becoming breezy Monday night with snow showers over the wrn 1/3. Tue...VFR to MVFR cigs. Snow showers ending. && .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...DeVoir Near Term...DeVoir Short Term...DeVoir Long Term...Lambert/RXR Aviation...DeVoir/Steinbugl

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