Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 080330 AFDCTP Area Forecast Discussion National Weather Service State College PA 1030 PM EST Thu Dec 7 2017 .SYNOPSIS...
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A wavy low pressure area may come close enough to affect southeastern areas Saturday, otherwise the region will remain dry. An upper trough will reinforce the cold air for Sunday followed by a number of weak Alberta-Clipper type systems that could keep us unsettled for much of next week.
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&& .NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
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The snow showers that brought some localized light accumulations earlier today, are now pretty much just a few leftover flurries as of 10 PM. A single lakeshore parallel LES snowband will remain near, or just a few miles to the north of the I-90 corridor in far NW PA. Latest HRRR suggests that the extreme southern edge of the band may affect far NW Warren county for a while this evening, but overall the bulk of the snow should remain north of the area. Accums over Warren county will be an inch or less. Elsewhere, central and eastern areas will see partly to mostly cloudy skies with little more than a stray flurry. Overnight lows in the mid teens to mid 20s will average a few deg below normal.
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&& .SHORT TERM /MIDNIGHT THROUGH 6 PM FRIDAY/... The mean boundary layer flow backs to the SW again by shortly after 05Z Friday, causing the persistent band of LES to shift north again into SWRN New York. As previously noted, tonight will be the best chance for snow accums across the far NW zones. Will let it top out at 2 or 3 inches in far NW Warren Co, less than inch elsewhere in the NW mtns. Elk county could even stay flurry-free as the fetch is rather poor to get any bands there. Any flurries and patchy 2-4SM light snow in the southwest/central counties during the evening will dissipate as weak forcing aloft moves off to the east. No additional accums are expected there. Clouds should break up. Mins should be into the teens west and L-M20s elsewhere, but will not drop too drastically with some wind still going through the night. It does seem like the gradient relaxes some on Friday (especially across southern PA) as a ridge of high pressure at the sfc extends from the Ohio River Valley to the Southern New England Coast, so expect there to be a little less westerly wind. Max temps will be 4-7F colder than Thursday`s. The old front off to the SE may continue to push cirrus over the SErn cos, but few other clouds will be found across the central and northern 2/3rds of the CWA. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Central PA will contend with two winter weather systems this weekend which could bring snow to different parts of the area. Temperatures will trend progressively colder through the weekend, with the coldest air of the season gradually taking hold by the middle of next week. The first system is a low pressure wave lifting north along a stalled frontal boundary draped from the Gulf Coast into the western Atlantic. 07/12z models have trended further northwest with the low track in response to a sharper upstream trough and more pronounced ridging downstream. This trend also resulted in a northwest shift in the precip shield which introduces low probs for snow as far west at the I-81 corridor. The 12z ECMWF is the farthest NW with its precip shield vs. GFS/WPC/NBM. The middle ground "edge" is probably somewhere between I-81 and I-95 at this time. Subtle shifts in the low track will make the difference in a potential period of light snow Saturday across the Lower Susquehanna Valley. If models continue to trend NW, snow risk will increase for places such as Harrisburg and Lancaster and may extend to the west of the Susq. River into interior parts of central PA. Continue to monitor the forecast. The second system is a clipper tracking eastward from the Great Lakes and eventually merging with the strengthening storm off the Northeast coast by the second half of the weekend. Snow showers with light accumulations are most likely over the higher terrain of the Alleghenies but may coat the ground quickly into parts of east-central PA. A period of lake effect and orographic snow showers should continue into Sunday with gusty winds and wind chills in the single digits and teens. Lake effect trajectories back to the west-southwest into Monday as the next shortwave digs southeast through the MS/OH Valley. There is a decent model spread in the low track and evolution of this system, but regardless of the details this feature should provide a good opportunity for most of the area to see some snow early next week. The coldest air of the season is forecast to arrive behind this system with a shot of arctic air and more lake effect snow lasting through midweek. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/... Bands of snow showers from the gusty westerly flow will continue through central PA through the first half of the evening. JST is seeing VLIFR cigs and vsbys. The snow bands are wavering though periods of IFR and lower will continue until lifting between 00Z to 03Z. Otherwise, widespread VFR conditions are anticipated for the rest of the night and into tomorrow as another ridge of high pressure will build over the PA airfields behind the cold front tonight. This will bring a diminishing westerly wind, and resulting VFR conditions across most, if not all, of the forecast area. Will have to watch KBFD and KJST, where upslope flow could potentially yield tempo MVFR to IFR cigs tonight into Friday morning. Outlook... Fri...No sig wx expected. Sat...Thickening clouds with late afternoon and nighttime snow showers/vis reductions poss Allegheny Plateau. Sun...AM snow showers/vis reductions poss Allegheny Plateau. Mon...PM light snow possible, mainly northwest Pa. Min night and Tuesday...Periods of snow and snow showers. Widespread MVFR likely, with periods of IFR and brief LIFR cigs and vsbys. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...Lambert LONG TERM...Steinbugl AVIATION...Lambert/Ceru

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