Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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145 FXUS61 KPBZ 041730 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 130 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 /THROUGH TONIGHT/... 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. ------------------------------------------------------------------- 1pm update... Latest analysis shows weak convergence along a rough W-E line near I-80 that has led to scattered showers and low probabilities thunderstorms. Farther out west, a notable area of vort advection is maintaining a shield of mostly moderate rain showers and developing new convection along its southern flank. Based on mesoanalysis showing ~1500 J/kg SBCAPE with breaks in area cloud cover likely offering further destabilization, the expectation is for persistence of ongoing storms with an uptick in coverage favoring the I-80 corridor PLUS south of I-70 through 4pm this afternoon. Weak model handling of current situation suggests a continuation of updating priors is required to best project future anticipation. Overall threats are similar to prior discussions, as high PWAT and weak steering flow makes localized flash flooding the primary concern while low probabilities for damaging wind remain. Previous 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 through this evening 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 later tonight ahead of the approaching trough. However, variation in outcomes is high as daytime convective evolution could alter the model-expected environment tonight. 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 /FRIDAY 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 /18Z 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...Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...Cermak