Area Forecast Discussion
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000 FXUS61 KPBZ 271341 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 941 AM EDT Tue Sep 27 2016 .SYNOPSIS... An encroaching upper low will return rain chances for the latter half of the week. && .NEAR TERM /THROUGH TONIGHT/... The only changes made for the late morning update were some upward tweaks to wind speed as per the increasing pressure gradient between the Northern Great Lakes low and Mid Atlantic States high. The resulting south, to southwest wind has already neutralized cold advection in the wake of yesterdays front, and resuming warm advection should support highs near the seasonal averages despite the encroaching, cold upper low. Partial decoupling and a dry airmass should result in decent radiation tonight, so no major alterations were needed to already seasonably cool lows. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... The Great Lakes upper low is forecast to dig southward across the Upper Ohio Valley Wednesday, settling near KY/WV and cutting off from the upper level pattern through at least Friday. As models are coming into more consistent depictions, confidence in the forecast of showery weather with sub-average temperature is improving. The better chance for sustained rainfall is over Northwestern PA where a southeasterly wind will briefly support transport of deeper Atlantic moisture inland on Thursday. Overdone omega fields and lack of mid level convergence/frontogenetic forcing in the current models do not lend confidence to a heavy rain forecast, nor do ensemble means for the period. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... Most of the models lift the stubborn upper low from the middle Ohio Valley at the start of the period into the eastern Great Lakes by 12Z Sunday. Details of individual waves rotating around the low remain tricky at this distance, so kept PoPs fairly general, with a slow decreasing trend through the weekend. Expect Sunday night into the first portion of next week to be dry as a flattening ridge arrives. Near-climatological temperatures will edge back above normal by the end of the period with the departure of the upper low. SuperBlend values were slightly knocked back early in the period, but later numbers looked reasonable. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... General VFR is expected for the period with afternoon wind gusts of 15 to 20 kts in the tightening pressure gradient over the region. .OUTLOOK /WEDNESDAY THROUGH SATURDAY/... Upper-level low pressure will settle over the region for the rest of the week. Periodic restrictions in showers, with more sustain potential at DUG and FKL should be anticipated. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ 15 is the U.S. government's official web portal to all federal, state and local government web resources and services.