Area Forecast Discussion
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000 FXUS61 KPBZ 231744 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 144 PM EDT Tue May 23 2017 .SYNOPSIS... High pressure will provide a dry Tuesday with seasonal temperatures, but unsettled weather will return on Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 12Z PBZ RAOB shows considerable dry air through a deep layer, which will help suppress precipitation from reaching the ground, despite echoes on radar in the far-southern zones. 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. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/... Models appear to be congregating around a solution depicting a low-amplitude shortwave trough generating light rain tonight in at least the southern half of the forecast area. While some of the initial precipitation will be expended in saturating the column, it seems prudent to include PoPs through the overnight period south of I-80. By morning, the focus for rain will become increasingly associated with the deepening surface low pressure system in Ohio, and the PoP footprint shifts accordingly. Model solutions have had substantial difficulty over the past few days managing the depiction of the digging and deepening of the mid/upper lower from the upper Mississippi Valley toward the Ohio Valley. However, the 00z cycle tonight has favored a timing of deeper moisture into the area generally around Wednesday afternoon across much of the area. This will allow for an unusual temperature spread with the warmest readings northeast and coldest southwest on Wednesday. However, while forcing with the incoming system is impressive, instability is not. Thus, while moderate rainfall amounts will be possible, thunder chances remain rather subdued. The upper low takes its sweet time migrating across the area from Wednesday night into Friday. This will bring a decent chunk of 500 mb cold air over the CWA. As such, a lowering of convective temperatures will mean abundant cloud cover and shower chances remaining across the CWA through the remainder of the work week. Temperatures meanwhile will be below normal. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... While the slow-moving upper low will have advanced northeast of the area by Friday night, and upper ridging will be briefly holding sway over the area, the interlude of quiescent conditions will be relatively short. The mid-level ridge axis looks to kick east of the area quickly on the consensus with deeper southwesterly flow aloft returning for the weekend. This will bring Gulf moisture toward the area again, resulting in increasing temperature and humidity as it occurs. Shower chances will increase through the weekend as deep moisture encroaches, however warmer temperatures should prevail at least until early next week as the highly amplified pattern continues to persist, and the next sprawling upper low looks to take until at least Tuesday to arrive in our area. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... 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. Winds 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. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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