Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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038 FXUS61 KPBZ 042149 AAA AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 549 PM 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 /UNTIL 6 AM FRIDAY MORNING/... KEY MESSAGES: - Probabilities increasing for afternoon/evening showers and thunderstorms for many locations beyond the previously messaged I-70 south region. - Localized flash flooding with slow moving convection is primary concern with a more limited damaging wind threat. ------------------------------------------------------------------- 545 pm update... An MCV was crossing eastern OH, with a cluster of showers/thunderstorms associated with it. THe overall trend has been a slow weakening, with satellite cloud tops warming and a decrease in radar estimated rainfall rates. We will still monitor for training/localized flooding issues as this cluster of showers and storms tracks across the region, mainly north of PIT. The other area of showers/storms was across northern WV. Overall, ML CAPE values have decreased in this area, and satellite shows warming cloud tops. Updated near term POPs based on the latest radar trends. 345pm update... Showers and isolated thunderstorms (mainly south of the forecast area) continue to travel east ahead of a noted area of positive vorticity advection. While this feature is now expected to continue east and provide lift for convection, weak lapse rates and diminished instability from cloud cover ahead of the wave should limit the severe threat. Localized flash flooding remains a concern, but cells with higher rainfall rates remain very isolated (or south of region) while forward movement remains fast enough to mitigate risk (plus dry antecedent surface conditions). The one area of some concern through 7pm are portions of Preston/Tucker Counties where a greater concentration of stronger cells are aiming toward and some convergence is seen. The expectation is for a lull behind the passing wave as a result of subsidence, which could aid hopes for firework displays this evening. That said, there remains signal for a secondary shortwave to reignite storms around 00z across western/central OH and move east; that bears monitoring for 9pm firework displays across eastern OH. Rest of the Discussion... Broad surface high pressure parked over the southeast and upper ridging across the East Coast keep warm and humid conditions in the region that will lead to scattered to occasionally numerous showers and thunderstorms through this evening. The main concern is localized flash flooding due to near- record PWAT values, enough column shear, moderate instability (around 1500 J/kg), and weak steering flow. Weak lapse rates and lack of strong forcing precludes any flood watch issuance as well as limits probability of a damaging wind threat (in the form of wet microbursts). These threats will trend down through the evening and overnight. Hi-res models suggest increasing coverage of showers and thunderstorms areawide is expected after 00z/8pm across western Ohio that will move east ahead of a secondary shortwave. However, variation in outcomes is high as daytime convective evolution could alter the model- expected environment tonight. Severe is not expected, though some there could be enough low- level modifications to create a very low probability wind/tornado threat. Flash flooding risks will remain given unchanged environment. Have outdoor holiday plans? We recommend checking in on the radar and forecast every now and then this afternoon in case rain is moving your way. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... KEY MESSAGES: - More widespread coverage is expected Friday, with damaging wind and flash flood threats remaining possible. - Dry and more seasonable weather returns on Saturday. ------------------------------------------------------------------- A more organized shortwave and surface low pressure crossing the Great Lakes will lift the stationary boundary northward as a warm front and push a late-day cold front through the region. Breaks in cloud coverage and weak cooling aloft should help destabilize the otherwise unchanged environment (modest CAPE, moderate shear, weak lapse rates, high PWAT values). The expectation is for greater shower and thunderstorm coverage during the afternoon and evening Friday ahead of each boundary, with damaging wind and localized flash flooding threats possible. Improved forcing and instability should be negated by stronger storm flow to leave the overall flash flood threat similar to that seen today. Passage of the surface cold front and upper shortwave will diminish storm chances Friday night, with dry and seasonable weather returning on Saturday. && .LONG TERM /SUNDAY THROUGH THURSDAY/... KEY MESSAGES: - High probability for dry weather and slightly above average temperature the rest of the weekend. - Unsettled weather returns Tuesday through at least mid-week. ------------------------------------------------------------------- Confidence remains high in dry weather continuing through the weekend as surface ridging remains over the Ohio Valley and upper troughing persists over the Central Plains. Temperatures should remain near-normal on Sunday, but increasing return flow and warm advection on Monday ahead of the next low pressure system will drive daily highs back above-normal. Ensembles indicate more active weather Tuesday into mid-week as low pressure crosses and upper troughing sets up across the East. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... Ceilings have generally lifted to VFR/MVFR to start the TAF period, with additional improvement expected through the remainder of the afternoon. Scattered showers and thunderstorms are expected to move across the area through late afternoon and early evening, and then possibly a second round overnight. Still a fair amount of uncertainty regarding coverage, prompting VC in TAFs except in a few scenarios where there is greater confidence in at least enough coverage to expect impact to a terminal (in which cases TEMPOs were substituted). Winds remain light and variable (generally out of the southwest) outside of thunderstorms. Gusty winds and restrictions can be expected in and around storms. There is growing confidence in the return of low cigs Friday morning, especially in areas that see heavy rain today/tonight. .Outlook... Additional rounds of showers and thunderstorms (with occasional restrictions) are 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...WM/Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...Cermak/Kramar/Shallenberger