Area Forecast Discussion
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000 FXUS61 KPBZ 150810 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 310 AM EST Fri Dec 15 2017 .SYNOPSIS... Cold with another round of snow showers expected this evening, mostly north of Pittsburgh. Some temperature moderation is then expected over the weekend. && .NEAR TERM /THROUGH TONIGHT/... Latest GOES-16 nighttime microphysics channel showing clear distinction between the thin high cirrus over much of the area, and two areas of low clouds straddling our north and south boundaries. The southern stratus is expected to creep back northward through the morning, clinging to the ridges, perhaps insulating these locations and keeping temperatures a few degrees warmer than the rest of the area only marginally obscured by the high cirrus. The GOES-16 Simple Water Vapor RGB shows our next disturbance quite well, currently entering northern Wisconsin. This wave will cross the western Great Lakes today, deepening the upper- level trough and surface low under favorable upper-level jet dynamics. Although the system lacks deep moisture, it will acquire some low-level moisture on its journey through the Great Lake aggregate. Steepening lapse rates under mid-level cooling will help fuel snow showers as they enter our northwestern zones this evening. Most of this activity will stay north of Pittsburgh and probably north of I-80, but there will be potential for accumulating snow showers south to the PGH metro area. Current timing would be after the evening rush. A quick 1-2" is possible across the northern tier of counties, with a marked decrease expected traveling south. Snow showers will likely taper down after the passage of this wave near midnight tonight. However, a developing low-level jet and an injection of mid-level moisture will allow for some re- invigoration of snow showers Saturday morning. This evolution is represented well in the bevy of high-res models at our disposal. This activity will likely stay north of the developing mid-level warmfront, or roughly north of Pittsburgh. Another inch or so could be the result of these showers. All told, the roughly 24-30hr snow total will likely remain under Advisory levels, with the northernmost counties the most likely to flirt with the 3" mark. Elsewhere, and inch or less is expected. In addition to the snow, the aforementioned strengthening low- level jet will bring wind gust to the ridges that could near Wind Advisory levels tonight. Current forecast remains just below the Advisory threshold, although this will need to be monitored through today. Regardless, the increased wind tonight will bring a bite to the already cold air in place. Wind chills will commonly be in the low teens to single digits, colder in the higher terrain. && .SHORT TERM /SATURDAY/... Residual snow showers may linger into Sat, but will decrease in coverage as warmer air invades the region and heights rise. Flow will become zonal by Sun in the Great Lakes region as a shortwave trough strengthens in the swrn CONUS. Ahead of this system, warm-air advection will help restore temperature to near-seasonal values during the weekend and into next week. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... An impulse ejected from the trough in the swrn CONUS may bring light rain to the region on Sun afternoon-evening, but it will be a decaying system by the time it approaches the Great Lakes. A better chance for precipitation comes mid-week as the swrn CONUS trough phases into a nrn stream disturbance and drives a cold front through the region. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... General VFR is expected through the day. Snow showers mainly north of KPIT will develop night with the best chance of IFR at KFKL/KDUJ. Analogs put the chance of LIFR at these ports between 40 and 50%. Snow is expected at FKL and possibly at DUJ Friday afternoon with visibility restrictions. .Outlook... Next chance for restrictions is late Friday into Saturday. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.