Area Forecast Discussion
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000 FXUS61 KPBZ 270524 AAC AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 124 AM EDT Tue Jun 27 2017 .SYNOPSIS...
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Upper low pressure will maintain cool temperatures and the risk for showers or a storm today. Temperatures moderate the second half of the week. Dry Wednesday, showers and storms return Thursday and Friday.
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&& .NEAR TERM /THROUGH TODAY/...
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Two shortwave troughs will swing through overnight. The first will move into Central PA after 2am, the second will be right behind, reaching Erie, PA by dawn. The first is more elongated and weaker and is currently sustaining scattered showers ahead of it. The second is more compact and noticeable stronger and would expect most of its potential to be confined to the north in the lee of the Great Lakes. For the overnight period, kept low chance to slight chance PoPs spread out across most the region, then shifted PoPs to the north with the onset of sunrise. The first batch of showers, particularly the activity over the southern half of the area, is finding it hard to sustain structure as it moves to the east. It is encountering a dry(surface dewpoints in the 40s to lower 50s), and more stable atmosphere. The activity to the north is getting a boost from the aforementioned late night wave and the warm waters over Lake Erie. Temperatures overnight will again be below normal.
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&& .SHORT TERM /TONIGHT THROUGH THURSDAY/...
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Expect the risk for showers to dissipate across the southern half of the area during the morning hours, with the shortwave trough rapidly moving into upstate New York. Behind the exiting wave, winds will shift toward the NW and there will be a brief period of cold air advection. The main part of the cool pool aloft will be across northern counties. This destabilization, combined with a flow right off of Lake Erie, and a third wave moving across the Great Lakes, should allow for the redevelopment of scattered showers and storms across the north. With the cooler air aloft, cu should have no problem developing across most of the area, which will assist in keeping temperatures below normal. Upper level heights begin to rise tonight and broad high pressure will move into the Mid-Atlantic region on Wednesday morning. As the surface high speeds eastward, and the upper level ridge strengthens, flow in the lower and mid-levels will turn toward the southwest and allow for a much warmer air-mass to overspread the area. With lots of sun and warm air advection, a return to more normal temperatures is expect on Wednesday. The weak ridge will flatten Wednesday night, in response to the next shortwave trough moving from the Upper Midwest and then over Northern PA. Most of the energy from this wave will be used to weaken the ridge. This loss of large scale ascent, combined with the continued warming of temperatures aloft, will keep Wednesday night dry. Do expect to see and increase in high and mid-level clouds as the night progresses. On Thursday, the next upper level system will dig into the Western Great Lakes and the surface reflection will be positioned near the 500 low. A frontal boundary will extend eastward from the surface low, stretching across New York and into New England. In response to the Great Lakes system, heights will rise over the Upper Ohio Valley, which will keep energy rotating around the 500 low to the north of the region. The models are setting up an area of strong moisture convergence over the north on Thursday, which will likely lead to the development of showers and storms. Have included PoPs on Thursday, generally north of PIT, with likely PoPs over the far north. Temperatures on Thursday will continue to moderate and would expect gusty southwest winds as well.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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Great uncertainty in the long term portion of the forecast, as models are still trying to work out the details of the next large upper level system. With the system deepening over the weekend, positioned near the Western Great Lakes on Saturday, the southeastward movement has slowed in relation to previous model runs. Will rely heavily on blend of ensemble guidance to compose the long term.
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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Mainly VFR conditions are expected through the TAF period, through a crossing shortwave trough should result in scattered showers through the day mainly N of PIT. Mid level clouds should be replaced by CU by mid morning as convective temps are reached. A brief period of MVFR ceilings are possible for FKL/DUJ in the morning, though mixing should lift heights to VFR by afternoon. This mixing should also result in gusty W winds. .OUTLOOK... Restriction potential returns mainly N of PIT with an approaching cold front, with restrictions likely area wide Sat as the front crosses.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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