Area Forecast Discussion
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000 FXUS61 KPBZ 060908 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 408 AM EST Tue Dec 6 2016 .SYNOPSIS... Low pressure is expected to spread precipitation across the region Tuesday. A Thursday cold front will return snow shower chances and much colder temperatures for the end of the week. && .NEAR TERM /THROUGH TONIGHT/...
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Weakening low pressure and an associated shortwave will track across the Ohio Valley today. A new coastal low will form off of Virginia by 00Z, with the original low opening up over the CWA. Precipitation is expected areawide as strong isentropic lift combines with PWAT values approaching one inch and a strong low level jet. With slightly slower timing, most of the precipitation outside of the advisory area will be in the form of rain, although a few brief pockets of freezing rain cannot be totally ruled out at onset. In the advisory area in the higher terrain, strong southeast upslope flow will keep colder low level air in place, while a warm layer aloft allows for sufficient melting to produce a freezing rain threat. Sleet is also a possibility early due to evaporative cooling. The freezing rain threat will continue through the afternoon, ending when low-level flow veers southwest by the evening. Across the far northeast, temperature profiles will favor a change to snow this afternoon, and continuing into tonight, with some accumulation of an inch or so. Sleet and a little freezing rain are possible here too, but confidence is not high enough for a headline. Another concern is wind gusts associated with the low-level jet this evening. On the ridges, gusts of 30 to 40 MPH are possible. There are some signs of possible downslope enhancement in Fayette/Westmoreland counties with reverse wind shear above the ridgetops, but confidence is low. Steady precipitation will pull off to the east fairly rapidly this evening as the coastal low pulls away. Upper level moisture is lost by midnight across most of the area, meaning that drizzle or freezing drizzle may be a concern late tonight.
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Dry weather is forecast for Wednesday as surface high pressure pays a brief visit, although temperatures will remain a touch below normal. The next cold front is still expected to cross on Thursday, bringing the coldest air of the season thus far. Kept the idea of high chance/low likely PoPs for snow showers behind the front in the developing mid-level trough. Lake enhancement does not appear likely with generally WSW flow, although some minor accumulation is possible, especially north of Pittsburgh. Temperatures will tumble towards values well below normal.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Upper troughing and cold W-WSW flow should persist across the eastern CONUS through Friday maintaining the chance for lake enhanced and upslope snow showers. Some accumulation is likely with a 13+ degree temperature difference between the lake and 850hpa. But with uncertainty in band placement, have just upped PoPs for the likely locations through Saturday morning. A less amplified pattern sets up for the weekend through early next week, with several crossing shortwaves progged. Differences in the evolution of these systems prompted the use of the superblend for much of this timeframe. Much below average temperatures are expected to moderate by early next week. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... VFR will prevail through the early morning hours before deeper moisture associated with a northeastward traversing low pressure approaches. Most if not all of the model guidance then deteriorates conditions to MVFR and eventually IFR as moisture spreads across the terminals. Strong warming aloft should support a mainly rain event across the TAF sites, save for KFKL and KDUJ where a period of wintry mix may occur for several hours. There may be some frozen precipitation at onset further south depending on how quickly we can saturate, but with low confidence, this was not mentioned in the TAFs at this time. An ese wind is expected through much of the day, veering to southwesterly and westerly as the coastal low becomes the primary low pressure system. Some low level wind shear may be possible at KLBE with a strong low level jet in place early this morning, before we start mixing, but will wait to see if this materializes as much of the bufkit guidance shows some mixing will occur. .OUTLOOK... Improvements look possible on Wednesday before the next cold front brings the chance for both cig and vsby restrictions in snow showers. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Weather Advisory until 10 PM EST this evening FOR MDZ001. OH...None. PA...Winter Weather Advisory until 10 PM EST this evening FOR PAZ074-076. WV...Winter Weather Advisory until 10 PM EST this evening FOR WVZ512>514. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.