Area Forecast Discussion
Issued by NWS State College, PA

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713 FXUS61 KCTP 151542 AFDCTP Area Forecast Discussion National Weather Service State College PA 1042 AM EST Mon Jan 15 2018 .SYNOPSIS... A weakening Alberta Clipper will track north of Pa tonight. A secondary low will then form south of the region Tuesday and lift northeast off the Mid Atlantic coast Tuesday night. A deep upper level trough will swing through the area Wednesday, then be replaced by a building east coast ridge next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Low clouds banked over eastern third of PA, while mid and high clouds increase across central portions. Most of PA now bkn-ovc as a result. Adjusted cloud grids to reflect this with only minor impacts on high temps. Mid-high moisture increasing ahead of Alberta Clipper to swing southeast across the lower Grt Lks today, spreading perhaps a bit of light snow across the northwest counties by late in the day. Meanwhile, marine layer stratus will hold sway over the eastern part of the forecast area. Temps will moderate a bit in WAA regime ahead of clipper, but thickening cloud cover will temper the warm up. NBM/SuperBlend indicating highs in the 20s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... All short range guidance takes weakening clipper across the eastern Grt Lks tonight, a track unfavorable for much snow in central Pa. Weak WAA, combined with orographic enhancement, may produce up to an inch or two across the northern mountains by dawn, with little if any snow across the southeast counties. An examination of omega fields supports fairly high snow/water ratios, with much of the lift occurring with dendritic growth zone. A weak secondary low tracking from the southern Appalachians to the Mid Atlantic coast, combined with frontogenetic forcing resulting from jet streak entrance circulation, could potentially produce several inches of additional accumulation across the southeast portion of the forecast area Tuesday/Tuesday night. 00Z models are placing the band of strongest 850-700mb fgen along the I-81 corridor, where 00Z ensemble mean qpf is supporting advisory type snows from Harrisburg northeast into the Poconos. Have opted to hold off on any headlines until the event is captured by high res HREFV2 ensemble and we can pin down the threat area and snow amounts with greater certainty. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... A reinforcing shot of cold air will work into the region by Wednesday, as deep upper trough swings through the region. Surface ridging over the area indicates there will be very limited lake effect activity, and mostly sunny skies east of the mountains Wed/Thursday. 00Z NAEFS and ECENS continue to advertise a pattern change by late in the forecast period, with upper trough lifting out and an anomalous upper ridge building over the eastern conus by next weekend. Return southwest flow and above normal temperatures appear very likely by next weekend, as surface high passes off the east coast and anomalous 850 temps surge into the region. && .AVIATION /16Z MONDAY THROUGH FRIDAY/...
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MVFR ceilings ovr the Susq Valley as Atlantic moisture trapped under an inversion spreads westward. This restriction will persist through at least the evening before lifting to VFR overnight. An Alberta Clipper will swing southeast across the lower Great Lakes later today and tonight, spreading a thickening mid-deck across the state. Clouds and visibility will lower to MVFR by 00z over the NW mountains and encompass the NW half of CWA by 06z with IFR working into the NW mountains. This will be accompanied by light snow across the northwest counties by late in the day and the NW half tonight. A weak secondary low Tuesday through Tuesday night will shift MVFR to IFR restrictions to eastern areas in light snow, with more scattered snow showers (and thus more scattered restrictions) for western areas. As deep upper trough swings through the region Wednesday, ceiling restrictions again shift back to the western higher terrain along with scattered snow showers. Otherwise, primarily VFR conditions will prevail. Thursday looks to be breezy with gusts to 15-25 mph. Outlook... Tue...Restrictions in light snow mainly SE half. Lingering snow showers with intermittant restrictions over the NW half. Wed...VFR SE half, but ceiling reductions and intermittent vsby restrictions across the Northern and Western mtns as a result of isolated snow showers. Thu-Fri...Mainly VFR.
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&& .HYDROLOGY... Flood watch has been allowed to expire for the Lower Main Stem of the Susquehanna. River gages have begun to falling at Harrisburg and Marietta, and the threat of ice jam flooding is diminishing. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald NEAR TERM...DeVoir/Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Fitzgerald AVIATION...DeVoir/RXR HYDROLOGY...

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