Area Forecast Discussion
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000 FXUS61 KPBZ 161742 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1242 PM EST Sat Dec 16 2017 .SYNOPSIS... Light snow north of Pittsburgh will taper off this afternoon. Temperatures will begin to moderate to near seasonal averages. && .NEAR TERM /THROUGH TONIGHT/... Area of isentropic lift is supporting the snow that is ongoing this morning over the region, with a northerly shift over the last several hours. Expect snow continue through at least mid day over our northern zones as convergence and moisture aoa 750mb is squarely in the dendritic zone, though the best rates reside just outside our forecast area. Made only minor adjustments to the snow forecast with another inch or so possible. Further south, building high pressure and warm advection should allow for clearing skies and warming temperatures, at least to near seasonal averages. Cloud cover will likely remain locked in north of I-80 which will lead to a tight temperature gradient across the region today. Building ridge will lend to a quiet night tonight. Warmth aloft should hold temperatures up slightly, given mostly clear skies and light wind - though it doesn`t appear we will fully decouple. Stayed close to persistence for lows. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Despite brief ridging aloft locally, a wave ejecting out of the southern Plains will ride over the ridge Sunday afternoon bringing light precipitation back to the area. The weakening disturbance will stream southern moisture northward along an axis of modest isentropic ascent. Models still differ on the placement of the main precipitation band Sunday, but more importantly on the boundary layer temperatures and subsequent precipitation types. Will continue to use a blend for the placement of high chance PoPs and will keep p-types fairly broad. Regardless of precipitation type, this system looks to have relative minor impact on the forecast area. The weak wave will depart quickly to the east Sunday night, leaving a period of mostly zonal flow aloft. Monday and Tuesday`s precipitation forecast appear a bit nebulous at this time. With abundant low-level moisture left below a strong mid- level inversion, it looks as if clouds and light precipitation or drizzle could plague the area in the beginning of the week. With a lack of organized ascent, precipitation chances will hinge on weak waves passing through the zonal flow. Will follow the previous forecast and continue to keep PoPs in the neighborhood of climatology. Temperatures will continue to warm to above average values Monday and Tuesday, despite continuous cloud cover expected. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... A broad trough will drop into the central CONUS Tuesday night sweeping a cold front through the area. This could re-invigorate showers Tuesday night into Wednesday, but will help drive temperatures back to near-normal values. Upper-level flow returns to zonal behind the front, bringing a drier and warmer trend until the latter part of the week. Models still have another system/cold front for Friday, but strength and placement of the low have changed with newest guidance. Will hold close to the SuperBlend for precipitation details, and look for clarity in the coming guidance packages. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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Near and north of I-80, MVFR ceilings will linger through most of the period as clouds remain locked in. Snow showers may still produce brief MVFR/IFR visibilities until mostly shutting off by 00Z. Ceilings may drop to IFR during the overnight/early hours for a period before lifting by mid-morning once mixing kicks in. Further south, building high pressure will keep conditions VFR through the period. Mid clouds will mostly clear out this afternoon, with scattered clouds at most tonight. Overcast conditions may return by midday Sunday ahead of a weak disturbance, with most light precipitation holding off until after 18Z. .Outlook... Restrictions are possible from Sunday night through Tuesday, as abundant low-level moisture may become trapped underneath an inversion for an extended period. IFR conditions are possible at times.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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