Area Forecast Discussion
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000 FXUS61 KPBZ 211716 AAC AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 116 PM EDT Mon Aug 21 2017 .SYNOPSIS... A sequence of weak upper-level disturbances will provide isolated showers and thunderstorms today. Widespread showers and thunderstorms are expected on Tuesday as a cold front crosses the region. && .NEAR TERM /THROUGH TONIGHT/... Convection from this morning that took advantage of the modest instability noted in the 12Z sounding has subsided as the low- amplitude trough that supported it continues to move ewd. Shortwave ridging will spell a brief erosion of convective cloud cover, though cirrus may still provide at least a partial obscuration of the sky during peak eclipse viewing. A second, weak shortwave trough over central OH will advance ewd this afternoon and may provide a second round of modest convection as low-level warm advection weakens the H7 inversion. Lacking any focused sfc boundary, broad PoPs were employed in the forecast this afternoon along the diffuse warm front. Any showers and storms will weaken this evening with loss of heating, and some clearing is expected in the wake of the associated shortwave trough. && .SHORT TERM /TUESDAY 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 SUNDAY/... Broad surface high pressure under an ern-CONUS trough is progged to support a dry and cooler-than-average air mass through the period. && .AVIATION /17Z MONDAY THROUGH FRIDAY/... General VFR is expected for the period although a crossing shortwave may spawn isold to sct convection. Expect rapid deterioration of conditions on Tuesday as widespread precip will herald the advance of cold front. .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. && $$ Update...Kramar

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