Area Forecast Discussion
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000 FXUS61 KPBZ 131953 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 253 PM EST Wed Dec 13 2017 .SYNOPSIS...
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Accumulating snow is forecast in most areas tonight as low pressure crosses. Snow showers linger on Thursday, with a break from the snow Thursday night into Friday. Below normal temperatures will continue into the weekend, with some moderation thereafter.
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&& .NEAR TERM /THROUGH THURSDAY/...
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Leading edge of isentropically- driven snow is racing into the CWA as of this writing. Models have been consistent with the track of the surface low across/near Pittsburgh through tonight, and with the track of the 850 mb low just to the north. Best dynamic support will remain in that region for the bulk of the event, with mid- level frontogenesis noted as well as some upper divergence from upper jets than cannot quite couple. Given the system being a clipper, overall system speed remains high and best support does not remain in place for an extended period of time. Still, the snow figures to be efficient with plenty of moisture in the dendritic growth layer through much of the night. Thus, an advisory-level accumulation remains appropriate north of Pittsburgh. Did up amounts slightly, with a 4-6 inch range now indicated at the maximum. Additions to the ongoing winter weather advisory were made for increased snow totals in a few cases, but also for the quick arrival of snow this afternoon which will impact the evening commute, especially on the major interstates. To the south of I-70, the partial intrusion of a dry slot plus lower snow ratios will hinder snow totals to generally 2 inches or less. Stratiform snow will transition to snow showers behind the departing surface low late tonight, and this is when the accumulation focus will shift toward the ridges as low level flow goes northwest. Much of the ridge accumulation will occur after 06Z, with activity scattering out fairly rapidly after sunrise as moisture collapses. Keeping a 2-4 inch range in the ridges. Wind gusts on the higher ridges bear watching, as instability could partially mix down 40-50 knot winds just off the surface in tight isobar packing behind the low. Past mid-morning, snow showers will slowly taper off with time as moisture continues to wane, but some light snow showers and/or flurries could continue through much of the day since the dendritic layer remains close to the ground. Minor changes to temperatures overall.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
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Flow will have backed a bit towards the west and southwest by Thursday evening, and as such expect virtually all of the snow shower activity to shut off by that time. Dry weather will continue through at least Friday morning with high pressure zipping by to the south. A weak shortwave will cross into the eastern Great Lakes Friday afternoon and track north of the region Friday night. Snow shower activity from this will commence Friday afternoon and linger into Saturday morning. The lack of a good moisture feed and overall weak forcing point to fairly light snow amounts, although an inch or two will be possible north of Pittsburgh over the period. Activity ends by evening. Temperatures remain below normal, but will start to moderate Saturday as 500 mb heights start to rise.
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&& .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
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Flow goes zonal over our area by Sunday as our trough lifts out and energy digs into the southwest U.S. This will result in continued temperature moderation towards more seasonal levels. The next system arrives on Sunday and will be mainly a rain producer from the southern branch of the jet stream. The pattern could remain unsettle thereafter with weak waves in the west- southwest flow aloft, with perhaps another cooldown by the middle of next week.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... Radar returns are increasing in coverage across western Ohio as of 1pm, although snow is not being observed farther south than Akron and Youngstown. Snow will continue to spread south and east during the afternoon hours. The one concern with determining how long it will take for visibilities to come down at local terminals is how long it takes for snow to overcome the dry air at the surface, with many locations currently reporting dewpoints in the single digits. While snow intensity may not ever be enough at Morgantown to result in IFR conditions, all other sites should have IFR/LIFR visibilities for several hours. Heaviest snow totals should fall between the Pennsylvania Turnpike and Interstate 80. The bulk of snowfall should be east of the region by sunrise, and conditions will slowly return to MVFR and VFR on Thursday. While winds this afternoon typically have some sort of a southerly component and some gusts up to 20 kt, winds will eventually veer to the northwest by Thursday morning. .Outlook... Next chance for restrictions is Friday into Saturday. && .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...Winter Weather Advisory from 7 PM this evening to 10 AM EST Thursday for MDZ001. OH...Winter Weather Advisory until 7 AM EST Thursday for OHZ039>041- 049-050. PA...Winter Weather Advisory until 7 AM EST Thursday for PAZ007>009- 013>016-020>023-029-031-073>075. Winter Weather Advisory from 7 PM this evening to 10 AM EST Thursday for PAZ076. WV...Winter Weather Advisory until 7 AM EST Thursday for WVZ001>003- 509-510. Winter Weather Advisory from 7 PM this evening to 10 AM EST Thursday for WVZ511>514.
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