Area Forecast Discussion
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000 FXUS61 KPBZ 220101 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 901 PM EDT Mon Aug 21 2017 .SYNOPSIS... Quiescent conditions will continue through Tuesday morning. Widespread showers and thunderstorms are expected on Tuesday as a cold front crosses the region. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... A rather pervasive cirrus shield has advanced eastward over much of the CWA through the evening hours. Further, the earlier diffuse dewpoint gradient has really become a non-factor. Thus, with nighttime stabilization occurring, a lack of a focusing/lifting mechanism, and convective blow off overspreading the area, further convection development is unlikely. PoPs have been limited to the north of I-80 realm for the next few hours before the bulk of the overnight hours become dry. As convective blow off seems poised to remain over the area for much of the night, lows will have difficulty dropping all that far from the current readings. Thus, an above normal night looks to be in store with soupy conditions. Fries && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... A strong upper low will dig into the Great Lakes on Tue and acquire a neutral to negative tilt through the day in concert with the movement of a mid-level jet maximum. The system`s associated cold front will approach the Ohio Valley during the early evening, but a prefrontal trough is expected to be the focus for daytime convection in the area. Abundant low-level moisture, steepening lapse rates and strong effective bulk shear will support the development of strong to severe thunderstorms by early afternoon along the sharpening sfc trough. CAPE on the order of 2000 J/kg and effective shear of 40-50kt will promote organized, severe convection. Given the deep-layer shear orientation roughly parallel to the sfc feature, storms should congeal quickly into an intense convective line that will move sewd into the instability axis. Damaging wind gusts will be the primary threat, but hail also is possible in more intense, cellular updrafts ahead of the line. Storms will exit sewd by early evening with rain lingering into the evening behind the storms as the cold front traverses the region. High pressure will build in on Wed/Wed eve, with little chance of rain as dry air invades. && .LONG TERM /THURSDAY THROUGH MONDAY/... Although ensembles still show spread in their upper pattern solutions, it appears that broad surface high pressure under an ern-CONUS trough/midwestern ridge pattern is progged to support a generally-dry air mass through the period. Daily temperatures below climatological average can be expected through early next week. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... A few scattered showers and thunderstorms will continue through 01Z or so near/north of I-80, and have included VCTS at FKL/DUJ as a result. After these dissipate with the loss of daytime heating, mainly high clouds are expected overnight. Fog does not appear to be much of a threat given the warm overnight temperatures which will not allow crossover values to be reached. As a cold front approaches on Tuesday, showers and thunderstorms will become more numerous from late morning on. Hinted at flight condition deterioration with VCTS and a drop to MVFR visibilities at several terminals during the afternoon. IFR conditions are certainly possible, as are strong wind gusts, but timing will need to be refined. Expect prevailing winds outside of convection to increase to gust to between 15 and 25 knots out of the southwest during the afternoon. .Outlook... With passage of an early Wed cold front, general VFR can be expected for the remainder of the week. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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