Area Forecast Discussion
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000 FXUS61 KPBZ 071025 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 525 AM EST Wed Dec 7 2016 .SYNOPSIS... High pressure provides dry weather today. A Thursday cold front will bring much colder temperatures and snow shower chances into the upcoming weekend. && .NEAR TERM /THROUGH TONIGHT/... 520 AM...forecast mostly on track. Did tweak sky cover to bring in cloud breakup a bit quicker based on satellite loops. Pockets of freezing drizzle may linger for an hour or two on the ridges, but should end fairly soon with drier air moving in. Previous discussion... Front has progressed across most of the CWA, bringing a wind shift and falling dewpoints along with it. Lingering drizzle should pull east with the front by 12Z. Cannot rule out an isolated pocket or two of freezing drizzle in the deeper valleys, but it would be brief. Otherwise, dry weather is forecast with high pressure building in for a brief visit. Ceilings will continue to lift and lower clouds will break with time, although mid and upper clouds will develop later in the day in southwest flow aloft. Temperatures will remain a few degrees below seasonal norms. As an upper low spins across Ontario tonight, a shortwave trough will begin to drop across the Great Lakes. Clouds will slowly thicken and lower tonight, but with little low-level moisture, snow shower activity will be very limited at best, with the ridges perhaps seeing isolated activity by sunrise in developing upslope flow. Seasonable low temperatures are expected. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... An upper-level low will advance east into Quebec Thursday, allowing much colder air to wrap in behind, invading our area from the west. Very little moisture exists along the mid-level cold front, so initial precipitation chances will be minimal through Thursday afternoon, but a slight wind shift will bring lake-effect and upslope snow that could extend into the early weekend. Although cold advection will be ongoing, the coldest air will pour in later Thursday afternoon with a mid-level trough. This will steepen lapse rates through the mid-levels and increase the boundary layer height. Veering winds behind the trough axis will seep Great Lakes moisture in across the northern 1/3 of the forecast area, eventually extending southward into the Ridges. Deep northwest flow will spread snow showers initially confined to our northern reaches southward, nearing the Pennsylvania Turnpike Friday afternoon. Snow showers will be ongoing through much of the day Friday for the northern 1/3 as well as into the Ridges. These areas stand to see the best chance of accumulating snowfall, albeit over a fairly long duration. For now, will carry a mention of accumulating snow in the HWO for these counties. With a less favorable wind setup and less moisture availability for most of the event, eastern OH, northern WV (outside of the mountains), and much of southwestern PA should see little to no accumulation. The shot of much colder air will hold temperatures 5-10 degrees below the averages. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Surface high pressure will briefly settle over the area Saturday, bringing an end to any remaining light snow showers. Drier weather will remain fleeting, however, as zonal flow aloft will quickly advance the next system into the lower Great Lakes. Models currently having a difficult time latching onto this system, leaving the track in limbo. The track of the low will play a vital role in determining the level of warm air advection and subsequent precipitation types Sunday into Monday. Regardless of the exact path, the setup is favorable for tapping into Gulf moisture to spread along the trailing boundary. Superblend was largely utilized for this system, including the inclusion of likely PoPs Sunday night. After the early week system, models differ slightly on smaller disturbances through the upper-level pattern. One thing that is fairly certain, however, is that the cold air will stay through next week, continually re-enforced by mean northwest flow aloft. Middle of next week should feature temperatures that are well-below average. && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/... Ceilings are lifting in the wake of the frontal boundary which crossed overnight. Expect this trend to continue, with all areas achieving VFR later this morning or by midday. High pressure will keep flight conditions favorable through the TAF period, with mid and high clouds dominating tonight. After the initial gusts behind the front, west winds 10 knots or less will settle towards a southwesterly direction tonight. .OUTLOOK... Periodic restrictions are likely for the rest of the week as a strong cold front sweeps the region. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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