827 FXUS61 KPBZ 300538 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 138 AM EDT Fri Jun 30 2023 .SYNOPSIS... Haze and smoke from Canadian wildfires will impact area air quality and reduce visibilities. Those impacts should improve as thunderstorm chances increase with a series of shortwaves through the weekend. && .NEAR TERM /THROUGH TODAY/... Overnight period in good shape. No major changes needed. An upper level ridge will slowly build in from the west today. This will allow a warmer and more stable airmass to begin to spread across the region. Still seeing differences in model solutions for today in terms of timing and placement of afternoon convection. A weak shortwave trough will drift southeastward across the Upper Ohio Valley this afternoon in the persistent NW flow aloft. This upper level wave will be the focus for the initiation of afternoon convection. The real question is where and when? Models are not placing an abundance of deep moisture over the region this afternoon pushing that further east. Warming temperatures aloft are providing a cap and atmospheric buoyancy is relatively low, the overall wind field is weak as is the shear. It appears that the best locations for storms this afternoon would be east of Pittsburgh where an area of low and mid-level convergence will develop during the afternoon. Temperatures today will also be tricky as the smoke has been limiting sunshine, and limiting mixing. The latest near surface smoke model is showing a decrease in smoke today, which would make sense given the expected synoptic pattern. With this in mind, have raised temperatures a few degrees from Thursday's highs. && .SHORT TERM /TONIGHT THROUGH SUNDAY/... The Upper Ohio River Valley will be situated just to the east of a ridge axis centered over the southern Mississippi River Valley and broad troughing over the northern Great Lakes through Saturday night. Weak shortwaves rounding the trough base and ridge top and the progression eastward combined with convective progression setting surfaces boundaries will largely dictate the forecast outcome during this period. For Saturday, forecast uncertainty only increases with continued reliance of upstream convection timing and eastward progression. This low confidence forecast period should feature another shortwave passage with a weak sfc trough, either arriving during the morning hours with a decaying MCS, or arriving in the afternoon to foster greater thunderstorm generation (and higher severe threat). Location of greatest instability will likely remain south of the Mason-Dixon line as warm/moist air struggles to advance northward, meaning the day's severe potential may be limited to locations south of Pittsburgh. However, the later shortwave arrival time may offer greater destabilization that fosters a greater damaging wind threat for the region. Temperature will generally hover near to slightly above seasonal averages during this period (earlier convective timing and/or excessive cloud cover could cause temperature to fall a few degrees below current forecasted levels). Weak quasi-zonal flow will remain over the Upper Ohio River Valley region Sunday ahead of a developing upper trough over the Central Plains. Approach of shortwaves ahead of that trough within the relatively unchanged environment will offer additional shower and thunderstorm chances, favoring Sunday afternoon and evening hours. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Ensembles agree that the Central Plains trough will cross the region Monday, offering additional thunderstorm chances will a drop in potential for severe storms as temperature hovers at or slightly below the daily average. There will be some uncertainty with how quickly that trough exits the region, but ensembles favor a dry and seasonable warm pattern to develop after it does with development of high pressure and weak ridging. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... MVFR/IFR visbys persist through tonight due to lingering Canadian wildfire smoke. Skies finally begin to clear out from west to east later this morning as winds shift aloft ahead of the next approaching low pressure system. Should see conditions improve to VFR at area terminals by early this afternoon. Coverage of showers and thunderstorms this afternoon is likely to be less than previously anticipated. Latest guidance keeps much of the area capped this afternoon, with greatest chances for convection along the ridges. Kept PROB30 -TSRA groups for LBE and DUJ, but removed for other sites given low probability. Winds remain generally light and primarily out of the west or southwest through the TAF period. .OUTLOOK... Shower and thunderstorm activity continues through the weekend and into early next week as a low pressure system slows over the local area. As a result, will see a continued potential for local/temporary restrictions to impacted terminals through the medium range outlook. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...22 NEAR TERM...22 SHORT TERM...Frazier LONG TERM...Frazier AVIATION...Rackley