Area Forecast Discussion
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176 FXUS61 KPBZ 211350 AAB AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 950 AM 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/... A low-amplitude shortwave trough is taking advantage of the modest low-level instability evident in the 12Z KPBZ RAOB to generate isolated convection. Intensity of these showers will be limited by a strong inversion at H7. By mid-day, shortwave ridging may 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 wrn OH this morning 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 clear sfc boundary, broad PoPs were employed in the forecast this afternoon. Any showers and storms will weaken this evening with loss of heating. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... By Tuesday, strong low pressure is forecast to track across the Great Lakes, pulling a cold front toward the Ohio Valley. Showers and thunderstorms are expected as the front approaches, and as a prefrontal trough tracks across the area. Model-progged wind/shear profiles look favorable for a damaging wind potential with the storms, though warm mid-levels could initially limit instability. Outside of any storms, a tightening pressure gradient and mixing could result in 25-30 mph wind gusts. The prefrontal trough passage is timed to end the severe threat by Tuesday eve, with early Wednesday frontal passage heralding cooler temperatures. Building sfc high pressure should maintain the dry and cool weather Wed night. && .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 /14Z 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. && $$

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