Area Forecast Discussion
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228 FXUS61 KPBZ 180002 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 702 PM EST Fri Nov 17 2017 .SYNOPSIS...
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High pressure will slide to the east tonight, with rain chances increasing Saturday ahead of approaching low pressure and a cold front. Snow showers are likely on Sunday.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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The eve update featured adjustments to hourly temperature trends as radiation has supported a more rapid drop than expected. That trend will be reversed as warm advection, and associated high and mid level clouds will spread over the region tonight with the approach of a shortwave in developing WSW flow aloft. That system will bring the first round of rain to the area during the predawn hours. Little change in the PoP forecast was needed as per the latest hi res model guidance and forecast trends.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... 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. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... 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. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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Expect condition degradation on Saturday beginning around midnight as low level wind shear results from low inversion levels and a developing low level jet in a tightening pressure gradient. Rain development is expected during the predawn hours, but cig and vsby reductions are not expected until after daybreak, with IFR likely for afternoon and evening at FKL and DUJ. Wind gusts to 25 kt will also plague all terminals. Cold frontal passage can be expected around midnight Sunday. .Outlook... Restrictions are likely with Sun upper troughing and cold NW flow.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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