Area Forecast Discussion
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000 FXUS61 KPBZ 201522 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1122 AM EDT Thu Jul 20 2017 .SYNOPSIS... Thunderstorm chances will escalate today with severe storms possible. Active weather remains in place through the weekend, with the risk of severe weather returning Saturday. && .NEAR TERM /THROUGH TONIGHT/...
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Two thunderstorm complexes...one over southern Ontario and another dropping across northern Indiana...are connected by a wavy frontal boundary near the southern Great Lakes shores. Neither of these MCSs are expected to impact our area, but additional thunderstorms are expected to fire along and ahead of the front later this afternoon and evening, with the bulk of the activity forming after 20-21Z. They will form in an air mass northwest of PIT with perhaps 1000-2000 J/kg of CAPE and 30-40 knots of effective bulk shear. This should be sufficient for a few strong to severe thunderstorms. Wind will be the primary threat, as wet bulb zero heights are too high, and CAPE aloft is too low, for much of a hail threat. An isolated tornado remains possible as well. Have continued with likely PoPs across the northern half of the CWA. Coverage and intensity should slowly fade after sunset, with a few scattered showers and storms remaining in the vicinity of the Mason/Dixon line by sunrise as the boundary slowly advances. Temperatures/dewpoints on track for now and made only minimal changes.
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&& .SHORT TERM /FRIDAY THROUGH SUNDAY/... The latest deterministic model trends are that this evenings convection and frontal passage will be decisive enough to drive the boundary south of the region for Friday. POPs for Friday were thus reduced, then revamped for the approach of another strong shortwave on Friday night, which may spawn more severe storms given the projected wind profile. Current timing does not favor that scenario, hence the marginal SPC outlook for the time frame. Models indicate a repetitive pattern for Saturday and cold frontal passage for Sunday. Likely POPs were thus maintained for the weekend along with the beginning of a downward temperature trend. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... The pattern of shortwaves crossing in zonal/northwest flow is expected to give way to Great Lakes-to-Northeastern-CONUS troughing during the first half of next week. Temperature will thus moderate back toward, and a few degrees under the average and rain chances will decline into mid week. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... High confidence forecast save for the onset and duration of thunderstorms this afternoon and early evening. These times could vary by 2-3 hours and flight category between 6-12Z Friday. An upper level disturbance crossing this afternoon will bring a line of strong to severe storms moving from north to south affecting likely all terminals if it develops like many of the high resolution models indicate. Inserted VCTS for all terminals starting around 20Z north and 0Z south of the mason dixon line. Brief restrictions to IFR vis can be expected if an airport is impacted by a storm. In wake of the storms, last 6-9 hours of forecast its hard to tell if MVFR fog will develop or will there be a canopy of stratocu or just VFR? For now, rolled with an optimistic forecast no cigs below 030. .OUTLOOK... Additional rounds of storms are expected through the weekend, and morning fog is possible as well. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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