Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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511 FXUS61 KPBZ 040536 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 136 AM EDT Thu Jul 4 2024 .SYNOPSIS... A series of disturbances will create periods of scattered thunderstorms through Friday, offering low probabilities for localized flash flooding and gusty wind. Dry weather with seasonable temperature will return Saturday into Sunday. && .NEAR TERM /THROUGH TODAY/... KEY MESSAGES: - Isolated showers are expected through the overnight period. - Scattered showers and thunderstorms are likely Thursday, favoring locations along and south of I-70. These storms may pose a localized flash flood threat. ------------------------------------------------------------------- A broken line of showers continues to dissipate as it crosses southern portions of the area and outruns remaining instability. A few isolated showers and perhaps a rumble of thunder may continue overnight, favoring locations south of I-70. Otherwise, mostly cloudy skies are expected with patchy fog possible, especially across the PHD-ZZV area where thunderstorms occurred. Warm low temperatures approximately 10 degrees above average are expected. Broad west-southwest flow and a series of shortwaves amid a warm/humid environment will keep periodic showers and thunderstorms in the forecast today and Friday. Focus for activity will be along a stationary boundary lying along the I-70 corridor, with most convection occuring south of this boundary and a gradient of decreasing probabilities to the north. The good news for outdoor holiday activities is afternoon/evening coverage for storms, even south of the boundary, looks to remain isolated to scattered. Morning coverage looks low for most locations, with perhaps a stray shower or two popping up across the area. 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. Any flooding or severe wind threat will be maximized in the afternoon/evening period when surface-based instability will be maximized. These threats will trend down through the evening and overnight. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... KEY MESSAGES: - More widespread coverage is expected Friday, with damaging wind and flash flood threats remaining possible. ------------------------------------------------------------------- By 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 /06Z THURSDAY THROUGH MONDAY/... With convection over the last 6 hours, there were some terminals from PIT and south that received substantial rainfall and will likely assist in some MVFR/IFR cigs through dawn. While mid level cloud cover will likely keep from any fog developing, some cigs should be watched. These cigs will be slow to lift through the mid morning hours and as the case for the southern terminals, where the trough will layout, the lower layer will become a cu layer for thunderstorm development but mainly in the late afternoon and evening. Expect this convection to weaken after 00Z. Winds will be light and variable through the period with the exception of thunderstorms. .Outlook... Additional rounds of showers and thunderstorms (with occasional restrictions) are then expected episodically through early Sat as a cold front slowly crosses. VFR should return Sun amid high pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Rackley/Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...Shallenberger