Area Forecast Discussion
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000 FXUS61 KPBZ 291425 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1025 AM EDT Thu Sep 29 2016 .SYNOPSIS... Upper level low pressure will bring rain to our region for the rest of the week. && .NEAR TERM /THROUGH TONIGHT/... The late morning update feature the addition of a flash flood watch for Eastern Preston, Tucker, and Garrett Counties, as well as HWO severe mention for high shear/better instability potential areas to the south and west of Pittsburgh. Deep, mature, stacked low pressure continues to spin over the Mid Ohio Valley with surface occluded front objectively analyzed as curving across Central WV. The systems mid level dry slot as shunted widespread rain toward, and north of the I 80 corridor into the mid level convergence zone. The Atlantic moisture stream is still expected to develop generally north of the PA turnpike, so no changes were made to categorical POPs across those areas. Convective development into Tucker, Garrett, and Preston counties will provide the main heavy rain/high water threat into Friday given flash flood guidance and upslope enhancement. Reduced cloud cover as per the latest visible images will aid in destabilization today. A flash flood watch was thus issued for those areas, especially in light of the band of 2 to 3 inch rainfall which fell on the eastern slopes last night. In addition, expect convection along the aforementioned front to become a player today with SPC marginal risk maintained, and dependant on cloud cover/instability magnitude for areas south of the PA turnpike. These areas will be closely monitored for severe given the magnitude of deep layer shear on the eastern flank of the low. A hazardous weather outlook mention was thus included for this potential also. The potential for high downslope wind gusts from the Morgantown- to-Latrobe vicinities will also be monitored given inversion levels and low level jet expectations, but current limitations based on surface wind orientation as per development of the surface low along the aforementioned front to the south have provided some decision time. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... Rain and gusty winds will linger through Saturday as the nearly stationary mature low pressure system gradually fills. A strong 60kt+ jet at 850mb is progged to stream across our southeast ridges through Friday morning. Still some questions as to the orthogonal flow and just how much of this wind will be able to break to the surface, so at the moment, the near Advisory gusts and HWO mention were maintained from previous forecast. Strong downsloping flow will continue through the day Friday as the parent low moves very little. This, along with the deep Atlantic moisture feed and convergence zone lifting north will result in a relative minima in shower activity just west of the ridges through center of the forecast area. This rain shadow effect is reflected in most operational model qpf fields and PoPs and WPC collaborated qpf have been trimmed back accordingly. As the low dislodges and slowly creeps northward Saturday, the dry slot wrapping around the eastern edge of the circulation will push into our area. This will bring an end to any organized rain bands, leaving only scattered, light rain showers mainly across the north. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... Lingering low pressure system will slowly drift over the southern Great Lakes Sunday into Monday. While this will keep rain chances in the forecast across the north, the aforementioned dry air will erode residual moisture. By Tuesday, the low will finally move east of the area, and high pressure will build into our west. This will bring a return to drier and warmer conditions with temperatures returning to above-average through the end of the week. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... An upper low aloft will pull deeper moisture across the ports today with low MVFR across northern terminals becoming IFR as widespread showers move in late this morning. Elsewhere conditions will deteriorate to MVFR or remain so through the day with showers and isolated thunderstorms after 16Z. East winds will strengthen with gusts over 20kts most locations through the afternoon. .OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... Periodic restrictions can be expected into the weekend as the upper level low lingers, then slowly lifts north of the region. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flash Flood Watch through Friday afternoon FOR MDZ001. OH...None. PA...None. WV...Flash Flood Watch through Friday afternoon FOR WVZ512>514. && $$ 15

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