Area Forecast Discussion
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379 FXUS61 KPBZ 100908 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 408 AM EST Sat Dec 10 2016 .SYNOPSIS... Lake effect snow will wind down north of I-80 this morning with a few breaks in the clouds across the area. Cold air will remain in place in advance of the next system that will affect the area tonight through Monday with snow, rain, and the potential of a wintry mix before much colder air arrives late in the week. && .NEAR TERM /THROUGH TONIGHT/...
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Fairly unstable lapse rates remain through the dendritic layer this morning with near saturation also noted in RAP soundings through the layer. This is resulting in flurries across much of the area from Pittsburgh southward, which should dissipate as the morning goes on as drier air encroaches from the southwest. Likewise farther north, lake effect snow bands that had resided over Mercer and Venango County all night due to persistent NW flow through the dendritic layer even with southwesterly surface flow have gradually moved northward as 850 mb flow turns more westerly and eventually southwesterly today. This should end accumulating snow in these areas, and the previous lake effect snow advisory was thus dropped. Some breaking up of clouds will be likely during the daytime today as time height sections reflect a drier column with surface flow favoring a southerly component. With that in mind, high temperatures may manage to muster a bit more upward mobility than in previous days even as no areas seem poised to challenge freezing. The next system starts to affect the area after midnight tonight with isentropic ascent increasing in the 285-295K layer. GFS/NAM/SREF reflections of lift all favor a band of modest moisture transport in the layer focused first over the southern periphery of the area, then transiting slowly northward as warmer air advances northward into the Ohio Valley. Consensus QPF favors roughly a tenth of liquid equivalent as this crosses with a solidly below freezing column and an impressive depth of saturation and lift through the dendritic layer. Thus a general inch or two of snowfall seem likely as this area of isentropic ascent in advance of a northward migrating warm front seems likely overnight tonight into Sunday morning for most areas. Fries
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&& .SHORT TERM /SUNDAY THROUGH TUESDAY/... High pressure will begin to move east Saturday with flow becoming westerly as weak shortwave exits. Temperatures will continue well below average. Complex low pressure will approach Sunday and move across the Great Lakes Monday. Warm advection snow will develop across the region Sunday and continue into Sunday evening, before mixing briefly with freezing rain and then changing to plain rain except for areas north of I-80 where cold air will hang in until mid morning Monday. With surface low so far west, warm air should be able to move north fairly quickly, keeping snow accumulations in check for the most part. Best estimate for now is 4-6 inches north of SR 422 in PA, with only an inch or two across Pittsburgh. Areas south of Pittsburgh will have little in the way of accumulation. Some light icing possible mainly in the ridges for a time Sunday night. Warm advection will push temperatures into the upper 30s to mid 40s Monday before a cold front drops temperatures back toward normal in the afternoon. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... Main feature will be an arctic cold front Tuesday night crossing east of the ridges early Wednesday. Temperatures will be 15 to 20 degrees below average through late week. While snow showers will be scattered mainly across the north, no significant snow is expected. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... Lake effect snow bands will continue to impact KFKL and KDUJ into the dawn hours. Elsewhere, MVFR cigs will gradually improve to VFR today as drier air arrives from the SW. The next system will roll into the area tonight with snow overspreading all sites near the end of the TAF valid period. .OUTLOOK... Widespread restrictions are likely Sunday and Monday, and again Wednesday, with crossing areas of low pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...None. OH...None. PA...None. WV...None.
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&& $$

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