Area Forecast Discussion
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000 FXUS61 KPBZ 110553 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1242 AM EST Sun Dec 11 2016 .SYNOPSIS...
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Snow will overspread the area through Sunday with many areas changing to rain or a wintry mix by the evening. Much colder air arrives late in the week.
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&& .NEAR TERM /THROUGH TODAY/...
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Widespread virga is quickly encompassing the area early this morning as evidenced by the regional radar mosaic. Model soundings indicate a fair amount of dry air below 5 kft will need to be overcome, however the multi-model consensus indicates decent moisture transport above this layer in the 285-295K layer with condensation pressure deficits crashing through the floor. As such, snow should quickly start to develop in Ohio and move eastward early this morning. Once the layer below 5 kft becomes saturated, snow to liquid ratios should quickly increase to 13-15 to 1 given a very impressive depth of saturation in the dendritic growth layer north of the advancing warm front. This should lead to several hours with deep layer isentropic ascent and strong ice crystal growth potential. While QPF from all models is fairly modest, efficient growth should allow most areas in the CWA north of I-70 to manage at least an inch by daybreak. However, the cutoff in precipitation should be pretty start should of I-68, so those areas may see little/no snowfall with the warm front. As the warm front rides northward during the daytime hours today, dry air in the boundary layer will accompany the northward migration of the pre-frontal isentropic ascent. Thus, most areas will simply stop snowing behind the warm front with a seemingly lower chance of an immediate changeover to rain compared to what the forecast implied this time yesterday. Once in the warm sector, PoPs were thus reduced decidedly generally south of Pittsburgh this afternoon as temperatures warm toward/above freezing in these areas. Fries
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY/... Highest snow totals were placed across the northern counties where best lift and moisture will reside into Sunday evening and the winter weather advisory will continue. As surface low shifts north expect enough warming aloft to change precip over to rain across the south, with a period of freezing rain possible north of Pittsburgh and in the ridges. With less snow expected across the southern ridges, no headline was issued at this time, with any freezing precip not expected until Sunday night. Still expect all precip to mix with or change to plain rain before sunrise Monday, as southwest flow ahead of an approaching cold front warms the column. Temperatures will then level off Monday as the front sweeps east with rain and or snow showers ending. An arctic front will then be approaching Tuesday with low chance POPs for snow showers ahead of the front. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Upper troughing and cold W-WSW flow should persist across the eastern CONUS through Friday maintaining the chance for lake enhanced and upslope snow showers. Some accumulation is likely with a 13+ degree temperature difference between the lake and 850hpa. With uncertainty in band placement, have just upped PoPs for the likely locations through Saturday morning. A less amplified pattern sets up for the weekend through early next week, with several crossing shortwaves progged. Differences in the evolution of these systems prompted the use of the superblend for much of this timeframe. Much below average temperatures are expected to moderate by early next week. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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Current VFR conditions will begin to deteriorate this morning as widespread light snow commences along the warm front. Reduction in visibilities and ceilings will spread northward, engulfing the area by about 12z. The southern edge will quickly lift northward later this morning, meaning southern ports of KMGW, and to a lesser extent KLBE/KHLG will see improvement by mid morning. Along the north, the snow will reside for most of the day, keeping low MVFR or IFR restrictions in through the period. Between these areas, some improvement from MVFR will be seen, but to what extent remains in question. Cold front approaches late Sunday bringing at least a mix of rain and snow. There is at least some potential for freezing rain along the leading edge of the rain/snow mix, but confidence is too low for TAF inclusion at this time. Best chances for freezing rain would be for KDUJ/KFKL 03-09Z Monday. .OUTLOOK... Restrictions are likely to continue through Monday, returning again Wednesday, with crossing areas of low pressure.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...Winter Weather Advisory until 4 AM EST Monday FOR PAZ007>009- 013>016-022-023. WV...None. && $$

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