Area Forecast Discussion
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000 FXUS61 KPBZ 260730 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 330 AM EDT Wed Jul 26 2017 .SYNOPSIS...
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Today will be dry and a bit warmer. Showers and thunderstorms return Thursday and Friday due to a cold front and upper level low pressure system. Dry and seasonable weather returns this weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Quiet weather continues during this period as high pressure slides off to the east today. River valley fog will lift by mid-morning as the lack of cloud cover allows for decent heating to take place. Some fairly flat cumulus should pop up this afternoon, with generally dry mid levels. A return of southerly flow will allow for some warming today, with temperatures climbing back towards seasonal norms. Clouds will be on the increase tonight ahead of the next cold front/upper level wave to impact the region. Although upper level moisture increases, the mid levels remain dry through sunrise and the bulk of the lift remains off to the west, leading to a dry forecast. The clouds and a bit more mixing will allow low temperatures to rise back towards climatology as well.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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Forecast confidence for this period remains low, although the GFS and the ECMWF might be starting to settle on a preferred track for the main surface low. A shortwave digs across the western Great Lakes towards the upper Ohio Valley by Friday afternoon. While this happens, the surface wave travels near the Ohio River and just south of the Mason-Dixon line, reaching the east coast by Saturday morning. This track will keep the frontal boundary from crossing until late Thursday night/Friday morning, while the deepening shortwave crosses Friday afternoon/evening. What this means is an active period with plenty of opportunities for showers and thunderstorms, particularly across the southern CWA. Have the higher PoPs focused from Pittsburgh on south initially, then more southeast with time. Despite frontal passage by Friday, the crossing shortwave will provide support for precipitation during the afternoon and evening hours, despite the cooler air mass. Areas south and east of Pittsburgh are targeted with a slight risk of severe thunderstorms for Thursday afternoon and evening. While 0-6km bulk shear of 30-40 knots would be sufficient for some storm organization, instability appears to be in question. Much will depend on how much heating can occur on Thursday. The bigger risk may end up being flooding, as the heavier rain may target the wetter areas of the CWA. PWATs approaching 2 inches in spots plus warm cloud depths in excess of 12k feet could support plenty of downpours. Will mention both the severe and heavy rain threats in the HWO. Temperatures will sink back a bit below climatology behind the front by the end of this period.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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A few showers may linger into Saturday morning as the shortwave departs. Thereafter, Great Lakes high pressure will provide a few dry days along with seasonable temperatures as midlevel flow flattens. A front may approach from the northwest by the middle of next week, but the timing remains highly uncertain.
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&& .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... High pressure in control, so clear, calm and cool conditions will be ideal for valley fog development. As of the 06z issuance, already beginning to see some fog generation in some of the more favorable locations, and on experimental GOES-16 fog products. This is especially true across the north and in our southwest where temps have already matched the relatively low dewpoint readings. With all this in mind, opted for an aggressive approach to the forecast, dropping favorable locations to minimums by 09z. Outside of the main river valleys, some fog development is possible, but will be patchy and thus may not impact those terminals (PIT, MGW, AGC). Valley fog will dissipate after sunrise, giving way to VFR conditions. Clear skies will be marred only by some mid-level afternoon cu-development. Calm winds this morning will remain light and variable through the day. .OUTLOOK... Restriction chances return Thursday as low pressure impacts the Ohio Valley. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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