Area Forecast Discussion
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381 FXUS61 KPBZ 091824 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 124 PM EST Sat Dec 9 2017 .SYNOPSIS...
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Cold weather continues. Most locations will see a period of light snow tonight, early Monday morning, and again on Tuesday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Shortwave will pivot over the forecast area tonight but the overall strength of the system will weaken considerably with the jet core downstream the longwave axis and left entrance region over the forecast area. With weak dynamics for lift and relatively dry moisture profiles in the dendritic growth zone (roughly around 800-700mb tonight)...only see potential for a short period of light snow in most locations as the disturbance passes. A large percentage of the forecast area will see minimal accumulation (trace to 1"). Localized areas of up to 2" north of I-80...and higher sub- advisory amounts in the ridges where upslope flow on the backside of the system and boundary layer moisture co-located with the dendritic growth zone will keep things going a little longer before drier air works in and the inversion drops. A small handful of the typical spots in the ridges where snow development is highly favored may see accumulations >3", but by and large accumulations should will under 3"...even if snow to liquid ratios ended up being 25:1 (which is unlikely) based on expected QPF.
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&& .SHORT TERM /SUNDAY THROUGH TUESDAY/...
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Sunday afternoon and into the evening will remain dry until another weak wave quickly crosses overnight. Model consensus shows limited moisture to work with and given the quick passage...expect only very light snow accumulations. The persistent longwave pattern will be deepening Monday as the jet core enters the backside of the trough and strong shortwave drops into the base. At the surface, low pressure will cross the Great Lakes...over NY Monday night. Snow showers will spread across the forecast area Monday night as the associated front crosses. Lake effect and upslope will continue through Tuesday under cold northwesterly flow sets up.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Conditions for a continuing of heavy lake effect snow showers and squalls as well as upslope snows into the ridges continue to be fairly optimal right through Wednesday. While wind directions are difficult to pin down this far out, it certainly seems as though it will be more likely than not that winter headlines will be in the cards for lake effect/upslope snow. These likelihoods will be covered in the HWO for now, however the snow belt regions should be prepared for accumulating snow. As northwesterly flow starts to ebb by Thursday, another system looks to dive southeastward toward the area. Warm advection ahead of it suggests there is potential for some mixing with rain as precipitation develops, however with this system, the GFS is far warmer than the ECMWF. Behind this system, cold air again filters in the region to end the work week well below normal. Fries && .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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VFR conditions will prevail until moisture with the upper level shortwave approaches this eve. After this time, light snow will spread across the terminals, though moisture profiles are rather meager and suggest rather light snow rates - which would keep visibility being much of a concern outside of KFL and KDUJ. Instead, restrictions will be in the way of stratus with MVFR prevailing, though some brief IFR cannot be ruled out. A SW to W wind shift is expected overnight, with wind gusts picking up to 20kts due to steepening lapse rates in cold advection. Some improvement in cig height is anticipated tomorrow ahead of another fast moving shortwave. .Outlook... Scattered restrictions in light snow are expect Sunday night into Monday. The next chance for widespread restrictions will come with low pressure progged for Monday night/Tuesday.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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