Area Forecast Discussion
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306 FXUS61 KPBZ 090909 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 409 AM EST Fri Dec 9 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Broken lake effect band currently extends across Mercer and northern Butler Counties and into northern Clarion. Upped PoPs/snow amounts a bit in this area to handle this band. Will continue to monitor this area to see if it persists, although hi-res models suggest that it will not. 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 SUNDAY/...
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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.
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&& .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... 12Z GFS/ECMWF are in relatively good agreement that a warm front will lift across the region Sunday night into Monday, and until the entire region is in the warm sector, a period of freezing rain could be possible before snow changes over to rain. Did not have enough confidence in this to include freezing rain in the forecast at this time. The surge of warm air should bring temperatures back towards normal on Monday. Model agreement drops after the cold front moves through Monday night, and while models both show high pressure developing in the Plains and a storm system moving up the East Coast, the differences in where those systems track result in little agreement on precipitation, and have stayed close to the SuperBlend with chance pops through much of the rest of the forecast. After Monday`s near normal temperatures, temperatures will drop back below normal, with another reinforcing shot of cold air likely to drop many locations into the single digits Wednesday night and keep some locations in the teens on Thursday. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/... Expect that ceilings will be MVFR through most of the next 24 hours over the region, but periods of VFR, especially at the start of the TAF period, will remain possible. Snow showers will continue as well, with mainly VFR to MVFR visibilities overnight. Expect coverage and intensity to pick up a bit after 12Z, with occasional IFR visibilities becoming more likely along/north of I-80 and along the ridges. Cannot rule out a brief dip to IFR elsewhere as well. Wind gusts between 15 and 25 knots out of the west will continue through tomorrow afternoon, with some diminishment tomorrow evening. .OUTLOOK... Restrictions are likely through early Saturday under upper troughing, and again Sunday and Monday with crossing low pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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