Area Forecast Discussion
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000 FXUS61 KPBZ 172153 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 553 PM EDT Thu May 17 2018 .SYNOPSIS... Periodic rain will continue to affect the Upper Ohio Region into next week. && .NEAR TERM /THROUGH FRIDAY NIGHT/... The weather pattern will be characterized by a slow-moving cutoff low in the Midwestern CONUS, which will help to maintain sly flow aloft along the spine of the Appalachians through the remainder of the week. The fringe of a plume of Gulf moisture advecting newd on that sly wind aloft is grazing the ridge zones this afternoon, while insolation into the moist boundary layer elsewhere has provided enough CAPE (500-750 J/kg) to initiate convection in the deep enely lower-level flow swd from IDI-ZZV. Amid the deep moisture and high PWAT, deep convection can be expected to produce efficient rain, which could become locally problematic owing to slow storm motion. However, the main flood concern during the next 24 hours will remain in the ridges, where upslope ely flow and a series of shortwave troughs will enhance rainfall especially overnight into Fri. The wrn edge of the Flood Watch was trimmed earlier this afternoon as confidence has increased in the heaviest, most- prolonged rainfall being confined primarily to the ridge zones (where locally 2-3 in are possible). A sharp gradient in rain totals is expected with wwd extent. Outside of cloud cover, temperature today has recovered into the upper 70s and lower 80s. As cloud cover will be quite abundant on Fri and precipitation in broader coverage, the diurnal temperature change will be muted. Maxima in the low-mid 70s are forecasted for Fri. The NAM and GFS (to a lesser extent) suggest renewed moderate rainfall late Fri night, with the arrival of dry air aloft bringing an end by early Sat morning. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... The closed low will phase back into the stronger flow aloft on Sat, which will lead to its approach and enhancement to both the upper-level flow and the upward motion in the Ohio Valley both Sat and Sun. With a very moist boundary layer in place, any diurnal heating will generate instability quickly in a modestly-sheared air mass. Differences in the depiction of forecast soundings exist during this timeframe, but it seems a possibility that both flooding and severe thunderstorms could return to the region over the weekend as a modified EML advects from the Plains into the Ohio Valley region. && .LONG TERM /MONDAY THROUGH THURSDAY/... In the wake of the weekend wave, a frontal boundary appears poised to stall in the region once again early next week as mid-level lapse rates steepen aloft. Such a pattern will lead to rounds of showers and thunderstorms on Mon and Tue before the front is driven swd and high pressure returns mid-late week. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/...
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VFR will carry into tonight under light northeasterly flow. Increasing high clouds will preclude possibility of fog development tonight. Strong south-to-north surge in moisture will occur after 12Z, accompanied by MVFR ceilings and the threat of rainfall. Thunder chances too low with weak instability and warm-rain processes to warrant mention in the TAFs at this time. Wind will remain light from the northeast to east, with speeds increasing to 8-10 kts after 12Z. OUTLOOK... Periodic restrictions are likely into early next week as the area remains under the influence of moist upper troughing.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flood Watch through Friday evening for MDZ001. OH...None. PA...Flood Watch through Friday evening for PAZ074-076. WV...Flood Watch through Friday evening for WVZ510>514. && $$

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