Area Forecast Discussion
Issued by NWS State College, PA

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390 FXUS61 KCTP 100304 AFDCTP Area Forecast Discussion National Weather Service State College PA 1004 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 7 AM SATURDAY MORNING/...
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Another update for all elements. Most areas will remain cloudy to mostly cloudy. Radar shows snow bands over central areas weakening. Band that came through our office gave us a dusting. Most of the accumulating snow will be in the northwest. The HRRR keeps snow in Warren County overnight with the potential in the extreme northwestern part of the county for another 4-8 inches of snow before all is said and done. Grids were nudged with HRRR QPF to get numbers close to this. The blends were much lower than the HRRR. Overall a cold night. Snow showers mainly in northwestern areas and some lighter snow in central and southwestern mountains. Most accumulating snows in northwestern areas closer to the lake. Overnight lows mainly teens and 20s.
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&& .SHORT TERM /7 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
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The HRRR was used to show the snow lingering into the day and the total snow is likely 4-8 as stated above. Most of this should fall before 7 AM Saturday morning. Perhaps 1-3 will fall in this period as things wind down. To the south and east a quieter and sunnier day. Still quite cold. Most areas will be several degrees warmer than Friday was and there will be less wind. Always a plus when the wind is light.
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&& .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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We modified the Sunday into Sunday night forecast with the new guidance. This produced faster onset of the warm advection induced snow. Some models are very fast with light snow in western areas before sunrise Sunday. We blended the superblend and some slower guidance to compromise. But snow will spread west to east Sunday. It gets really complicated as nearly all forecast systems show some accumulating snow potential but, all show the surge of the 850 hPa 0C line into southwestern PA Sunday afternoon/evening and into north-central areas overnight Sunday around midnight or so. It is possible northwestern areas will never get that warm. Thus had to show mixing snow to ice pellets in southwest and then southeast. Could be some freezing rain. It is too early to get to specific as there is considerable uncertainty. But at this time it is sufficient to acknowledge the potential of snow likely changing to a wintry mix and probably all rain in the southeast early Monday. The cold air comes in during the day Monday into Monday evening to change lingering rain and wintry mix to snow as it winds down. Temperatures behind the front Monday into Tuesday are close to seasonal. A bit cooler than normal temps indicated early next week, but longer range models indicate a significant cold front passage Wed with noticeably below normal temps filtering in for the rest of next week. Ahead of the arctic surge expected later in the week there could be another QPF event. Potentially mostly snow in central and western areas. But the GEFS shows some -18 to -20C air at 850 hPa with the cold front. About 3-5C colder than the airmass we had come through today.
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&& .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... Bands of lake effect snow showers will continue overnight into Saturday morning. Conditions will improve during the afternoon, as warming aloft occurs and winds shift more to the west and southwest. As of 6 PM, still an band of heavier snow showers from near BFD to just southwest of IPT. Expect a wide range of conditions overnight at BFD and JST. UNV and AOO should be VFR for much of the period. VFR conditions expected at IPT, MDT, and LNS. Earlier discussion below. 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... Sun-Mon...Widespread MVFR/IFR in snow/rain. Becoming breezy Monday night with snow showers over the wrn 1/3. Tue...Mainly VFR. Wed...More snow showers possible. && .CTP WATCHES/WARNINGS/ADVISORIES... Lake Effect Snow Advisory until noon EST Saturday for PAZ005. Lake Effect Snow Warning until noon EST Saturday for PAZ004. && $$ SYNOPSIS...DeVoir NEAR TERM...Grumm SHORT TERM...Grumm LONG TERM...Grumm/RXR AVIATION...Martin

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