Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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650 FXUS61 KPBZ 032129 AAA AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 529 PM EDT Wed Jul 3 2024 .SYNOPSIS... A series of disturbances will create periods of scattered thunderstorms tonight through Friday, offering low probabilities for localized flash flooding and gusty wind. Dry weather with seasonable temperature are expected to return Saturday into Sunday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... KEY MESSAGES: - Isolated to scattered showers and thunderstorms expected through the overnight period. - There is a narrow window this evening for a damaging wind threat across eastern OH into northwest PA. ------------------------------------------------------------------- As of 130pm, convection was initiating along a broken line from Cleveland, OH back towards eastern IN within a localized SBCAPE maxima and just ahead of noted mid-level vorticity advection. A warm, moist environment ahead of this line is characterized by rising PWAT values (trending above 90th percentile), 30kts effective shear, 1000-1500 J/kg SBCAPE and strong low-level lapse rates. This should support continued upscale convective growth as the storm axis approaches eastern OH to northwest PA zones between 4-5pm, generally forming a broken line of thunderstorms. Despite middling mid- level lapse rates and weak surface convergence, that environment could support wet microbursts; the window of hazardous weather opportunity will be narrow though (~4pm-9pm) as surface based instability wanes and the upper shortwave lifts NE of the region. Otherwise, the rest of the afternoon hours will see hot and humid conditions increase, raising area heat indices into the 90s (probabilities of reaching/exceeding 100 deg F is too low for mention). The loss of daytime heating and upper support will see convective coverage wane overnight while a surface boundary slowly shifts southeast into the region. Broad ascent within southwest flow over a warm, moist environment is expected to maintain isolated to scattered thunderstorms with limited impacts. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... KEY MESSAGES: - Scattered to numerous showers and thunderstorms are likely Thursday, favoring locations along and south of I-70. These storms may pose a localized flash flood threat. - More widespread coverage is expected Friday, with damaging wind and flash flood threats remaining possible. ------------------------------------------------------------------- Broad west southwest flow will remain in place over the Upper Ohio River Valley region as the main trough axis sits over the Central Plains Thursday and Friday. A series of shortwaves will traverse the region within this flow and tap into the warm, humid environment to create periodic shower and thunderstorm chances. For Thursday, a stationary boundary laying roughly along the I-70 corridor will serve as a focus for convective development throughout the day; areas to the south are thus more likely to see convection while a gradient of decreasing probabilities exist to the north. Modest instability (around 1000 J/KG), weak lapse rates, and weak forcing should limit concerns for damaging wind and localized flash flooding but low probabilities remain given near record PWAT values, enough column shear, and potential for some storm training with parallel storm flow and surface boundary. The afternoon to evening period, where surface based instability is maximized, is likely when those threats are maximized before trending down overnight. For Friday, a more organized shortwave will lift the stationary boundary northward as a warm front and push through a late day cold front. Increases in storm motion and lack of parallel boundary flow should temper flash flood risks, otherwise the environment should resemble that of Thursday`s but for most of the forecast region. The afternoon/evening timeframe remains the most likely period of impact of hazardous weather. Passage of the surface cold front and upper shortwave will diminish storm chances Friday night and initiate a period of drier and more seasonable weather. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... KEY MESSAGES: - High probability for dry weather and slightly above average temperature the rest of the weekend. ------------------------------------------------------------------- Confidence remains high as ensembles show strong agreement of dry and seasonable weather developing Saturday and Sunday. This is a result of upper troughing persisting over the Central Plains and the Upper Ohio River Valley within the dry slot of southwest flow (plus surface ridging). Expect near to slightly above average temperature Saturday and Sunday before temperature returns well above normal Monday (think upper 80s to lower 90s) as warm, moist advection increases ahead of the next low pressure system set to cross Tuesday into Wednesday. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... A broken line of showers/storms has developed from near Erie to west of Cincinnati, which is making slow ewd progress late this afternoon. These storms are entering a region of lesser buoyancy across wrn PA, so the expectation is that the nrn segment of the line will slowly decrease in intensity and erode while the swrn section of the line may retain some modest intensity. TAFs were updated to reflect a briefer window for potential tstm proximity at sites, and to decrease the prolonged nature of showers overnight tonight at many terminals. Restrictions settle in Thursday morning around and following sunrise, with MVFR (potentially IFR) cigs beginning as early as ~10Z, lasting through much of the morning before heating/mixing allows cloud bases to lift to VFR around the tail end of the current TAF period. .Outlook... Ceiling restrictions gradually improve late Thursday morning into the afternoon. Additional rounds of showers and thunderstorms (with occasional restrictions) are then expected Thursday afternoon through early Saturday as the front slowly crosses. VFR should return Sunday under high pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...Cermak/Kramar/Rackley