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Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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740 FXUS61 KPBZ 171715 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 115 PM EDT Sat Aug 17 2024 .SYNOPSIS... A slow moving upper level system will promote rounds of showers and thunderstorms primarily each afternoon through Monday, with convection peaking Sunday afternoon. There is a low probability for severe weather this afternoon and evening. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - There is a low probability for strong to severe thunderstorms this afternoon and evening, favoring a wind and isolated flash flooding threat. ------------------------------------------------------------------- Latest WV imagery shows a slow-moving upper low currently centered over northern Lake Michigan will slowly shift east this weekend. By this afternoon, the approach of a pre-frontal trough and destabilization is likely to aid convective development along and ahead of a cold frontal boundary. Compared to Friday, diurnal heating looks to be a bit more robust today with colder and drier mid-levels. This should allow for MLCAPE values near 1000-2000 J/kg and more favorable mid-level lapse rates of 6-6.5 C/km. However, shear remains meager, with bulk shear values remaining below 30 kts. The primary threat with any stronger storms will be damaging wind. Overall confidence in the severe threat remains medium, due primarily to the potential for lingering cloud cover which could reduce afternoon destabilization. With weaker upper forcing and relatively weak shear, this would likely hamper robust storm organization. SPC has maintained the areawide marginal (1/5) risk for severe. 90th percentile PWATs (1.5-1.75") will contribute to an isolated/localized flash flooding threat. Waning instability after sunset and progression of the trough eastward will lead to waning precipitation chances after 06z, though some showers are likely to linger through the night. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... KEY MESSAGES: - Widespread convection is favored Sunday, but poses a more limited hazard risk. - Residual showers with cooler temperatures are likely on Monday, diminishing Monday evening. ------------------------------------------------------------------- By Sunday, the upper low/trough will be centered just to our north, allowing for lower convective temps and more widespread thunderstorms development in the afternoon. There is some uncertainty in favored locations due to slight variations in trough positioning that may create subsidence holes, but the overall pattern/environment should support on and off storms through the evening. The lack of strong instability despite 90th percentile PWATS and some forward motion of storms should preclude a flood threat. The trough continues east on Monday, leaving the area under cooler, northwest flow. Residual diurnally-driven showers are possible through the day, eventually diminishing Monday evening. Area temperatures will drop well below the daily average, resulting in daily highs in the 60s and lower 70s. && .LONG TERM /TUESDAY THROUGH SATURDAY/... KEY MESSAGES: - Long range trends favor dry weather and near normal temperature. ------------------------------------------------------------------- The region will remain under northwest flow on Tuesday, but with dry conditions. Residual cold air advection will lead to temperature around 10 degrees below the daily average. Long range analysis favors a continuation of the fairly amplified pattern of ridging over the Rockies and troughing along the east coast. This should position the region within the drier NW flow pattern where precipitation chances will be heavily reliant on strong shortwave movement over the ridge. Latest trends don`t favor this and thus suggest a prolonged period of dry weather and seasonable temperature Wednesday through the end of the week. && .AVIATION /17Z SATURDAY THROUGH WEDNESDAY/... As a surface trough approaches, more organized showers and thunderstorms are expected after 19z. Some may be severe with damaging wind and bring periodic VIS restrictions with heavy rain. Latest guidance still exhibits differences in overall coverage, so have introduced a TEMPO group for all sites during the most likely timeframe for thunder... primarily in the 19z to 04z timeframe with coverage increasing from west to east. A few showers may linger overnight with the passage of another weak surface trough. With lingering low-level moisture, probabilities increase overnight tonight after 06z for restrictions to MVFR and potentially IFR (40-60%), though guidance overdid restrictions a bit this morning as a whole, so erred slightly on the more conservative side introducing widespread low-end MVFR across the board, at least until we get a better idea where rainfall occurs. .Outlook... Periodic restrictions and showers and thunderstorms are possible through early Monday as low pressure slowly crosses the region. The greatest coverage of showers/thunderstorms will be in the afternoon and early evening. VFR returns by Tuesday under high pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Rackley/88 SHORT TERM...Rackley LONG TERM...Rackley/Frazier AVIATION...MLB