Area Forecast Discussion
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000 FXUS61 KPBZ 172039 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 339 PM EST Fri Nov 17 2017 .SYNOPSIS...
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High pressure will slide to the east tonight, with rain chances increasing ahead of approaching low pressure and a cold front. Expect gusty wind with the passage of the front tomorrow evening with snow showers possible on Sunday.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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High clouds will continue to spread over the region in advance of low pressure, progged to approach tomorrow. A shortwave riding along the warm front will bring the first round of rain to the area overnight, with little change in the PoP forecast based on the latest hi res model guidance and forecast trends. Despite an early decline in temperatures with minimal cloud cover, strong warm advection should slow the fall with some gradual warming expected after midnight.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
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Periods of rain will continue on Saturday as the trough amplifies over the Ohio Valley and shortwaves ride along in southwest flow. PoPs will be highest where the warm front resides, before it shifts north of the entire region. There may be a lull in the precip ahead of the actual cold front, but for now, did not get that specific with timing. While a very strong low level jet will be present with wind 50+ kts, a capping inversion looks to keep much of this from translating to the ground, at least until the cold frontal passage Saturday evening. Once the front passes, the strongest winds aloft will shift east, however steepening lapse rates in cold advection may allow for gusts to 40kts, with higher gusts possible in the terrain. Still, it looks likely the best chance for headline- criteria gusts may be in the terrain Saturday night. Will maintain the mention in the HWO for now. Upper trough will pivot across the region on Sunday with cold northwest flow resuming and snow showers expected. Have strayed little from the previous forecast, which holds the highest PoPs in the snow belt north of I-80 and in the mountains of PA/WV/MD where lake enhancement/upslope is anticipated. Still thinking 2-3 is reasonable, though some higher amounts may be possible. Depth of saturation will quickly fall below the prime snow growth zone in building subsidence in the terrain, which should keep rates down. Snow showers will continue through Sunday night as another reinforcing shortwave digs across the region. Conditions should begin to improve on Monday, as a surface high builds eastward and winds back toward the west.
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&& .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
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Weak ridging will continue until the passage of a weak front midweek. The deterministic guidance is rather unimpressive with the front and much of the lift will be situated well to the north, where the low is expected to pass. Broad troughing than remains in place through the end of the week. Other than some cool temperatures, will keep pops low based on the model blend.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... With the dissipation of the lower clouds from this morning, VFR flight conditions are expected through the remainder of the afternoon and into the evening hours, with only mid and high clouds expected. Starting around midnight, a developing low level jet will create ideal conditions for low level wind shear, with 40 to 50 knot winds trapped above an inversion just off of the surface. LLWS has thus been added to all TAFs. Rain will arrive in the hours leading up to sunrise ahead of an advancing warm front. Restrictions will likely arrive after 12Z, with ceilings and visibility dropping to MVFR at times as the rain becomes more widespread. IFR will be possible towards the end of the TAF period at FKL/DUJ. The stronger winds will remain just off the surface, but some gusts out of the southwest at 20 to 25 knots are expected by midday. .Outlook... Restrictions are likely with a Sat cold front and with Sun upper troughing and cold NW flow. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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