Area Forecast Discussion
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000 FXUS61 KPBZ 231919 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 319 PM EDT Tue May 23 2017 .SYNOPSIS...
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Unsettled weather will return for the remainder of the week as an upper-level disturbance moves slowly across the Ohio Valley.
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&& .NEAR TERM /THROUGH WEDNESDAY NIGHT/...
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Weak echoes this morning on radar moved across the ridges with little fanfare, as the 12Z PBZ RAOB shows considerable dry air which helped to suppress precipitation from reaching the ground. A sharp contrast between cloudier conditions to the south and a thinner veil of cirrus to the north will persist for the next few hours before a shortwave trough approaches from the south and leads to increasing clouds area-wide late this afternoon. Rain showers now evident in srn WV will move northward with the associated shortwave trough, reaching the southern part of the forecast area by 00Z. PoPs were increased a bit in the southern zones, but nwd reach of this precipitation will be limited. A second wave will move nwd on Wednesday in the deep sly flow aloft, providing moisture and lift. Given this combination of ingredients, rain seems quite likely Wed afternoon and evening. The previous forecast depicted this weather well, and needed very little change. Temperature on Wed will see little difference to those today, as insolation may be limited by clouds but cloud cover overnight will limit radiational cooling effects and provide a warmer initial state.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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A strong upper-level low pressure system will meander from the Central Plains into the Ohio Valley late in the week, leading to a persistent active weather pattern through the end of the week. Although air temperature will decrease slightly into the upper 60s owing to cloud cover, cold air aloft associated with this low is expected to provide a modest increase in instability Thu and Fri, which will increase the chances for more-vigorous convection, especially as the low-level wind flow veers to more of a wly component.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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The slow-moving upper low will advance newd by Friday night, and an upper ridge will take hold briefly. Quiescent conditions will be relatively short-lived as the mid-level ridge axis progresses quickly ewd. The net effect will be a return to deep swly flow aloft for the weekend. This will bring Gulf moisture toward the area again, resulting in increasing temperature and humidity and increasing convective chances at least through Memorial Day.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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VFR conditions are expected through the evening as only high clouds build into the area. The coastal low pressure system will begin to spread light rain into the area tonight, but no visibility restrictions are expected. Ceilings may begin to fall to near MVFR near daybreak Wednesday. Wind will remain light and from the east-southeast through the period. .Outlook... Restrictions are likely late Wed thru Thu and are possible Thu night thru Sat with crossing low pressure.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ Kramar/TAX

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