Area Forecast Discussion
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000 FXUS61 KPBZ 091439 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 939 AM EST Fri Dec 9 2016 .SYNOPSIS... Occasional snow showers will continue through tonight, especially north of Pittsburgh, and will taper off on Saturday. Accumulating snow is expected for much of the region on Sunday. && .NEAR TERM /THROUGH TONIGHT/...
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Only subtle changes to POPs, as flow looks to waver through the afternoon. Previous temperatures and snowfall amounts look in good shape, and previous discussion follows. Core of the coldest 850mb temperatures now lies across the southern CWA and will continue to move south. Thus, although NW flow will continue at this level, temperature advection will be near neutral through the day. Low level flow becomes a bit better aligned in a WNW/NW direction later this morning into the afternoon, and still expect that this will be the period with the best overall accumulations. Made some slight upward adjustments to amounts in some locations, particularly along the northern CWA border and along the ridges. Still not quite enough for headlines at this time due to snowfall duration, but cannot rule out an issuance if a persistent band sets up. Forest County still has the best chance of this, but confidence was not high enough for an issuance at this time. Coverage/intensity of snow showers will slowly wane after 00Z as inversion heights lower and winds start to settle a bit more towards the west in the low levels. An additional 1-1.5 inches is possible north of I-80, with possibly up to an inch along the ridges, and less elsewhere. Temperatures will continue to run 5-10 degrees below normal.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY/... By daybreak Saturday, only the extreme northern edge of the forecast area will remain near the downlake moisture plume. Will linger chance PoPs in this area for now, but little additional accumulation is expected. Surface high pressure will bring dry weather through late Saturday evening, but the next system will already be approaching from the west. A complex system will move into the region by Sunday, stretching into the new work week. Modest isentropic lift along a weak warm front will lead to the onset of snow by daybreak Sunday. Models differ slightly with the placement of this initial band, but the mean of guidance centers the highest PoPs over the northern and western counties. This boundary will be the focus for light to moderate snow through Sunday afternoon, while a system organizes in the Midwest. An amplifying upper-level trough will push the deepening surface low through the southern Great Lakes Sunday night into Monday. As the warm front lifts north, we end up in the warm sector, with strong warm air advection. A non-diurnal temperature trend will bring a change from snow to rain Monday morning, at least for the southern half of the forecast area. Guidance has been inconsistent with the track of the low, subsequent warm air advection and precipitation types. At this time, chose to be a little general with a rain/snow mix Monday morning, until finer details can be hashed out. Regardless, accumulating snow is likely from Sunday afternoon into Monday, primarily north of Pittsburgh. There is also a possibility of pockets of freezing rain in the favorable mountain locations Monday morning, where easterly flow dams up the colder air. Will carry a mention in the HWO for this system. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... Any lingering shower activity behind the cold front Monday night should transition back to snow with falling temperatures. Transient high pressure will briefly lead to drier period into Tuesday. Largely zonal flow will then bring several disturbances through the latter part of next week. With significant guidance differences existing through this time, SuperBlend was relied on heavily. After near normal temperatures Monday, temperatures will drop back below normal through the end of next week. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/...
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Broad upper troughing and cold WNW flow should maintain mainly MVFR conditions through most of the TAF period. Scattered snow showers are also expected, though the best chance of local IFR conditions should be N of I 80 where some lake enhancement should occur. Gusty W winds should also persist today with a tight pressure gradient, though theses should diminish this evening. .OUTLOOK... Widespread restrictions are likely Sunday and Monday with crossing low pressure.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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