Area Forecast Discussion
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848 FXUS61 KPBZ 231836 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 236 PM EDT SAT JUL 23 2016 .SYNOPSIS... Hot and humid conditions will continue. The best chance for showers and thunderstorms will return on Monday with the passage of a weak cold front. && .NEAR TERM /THROUGH TONIGHT/... Weak boundary, indicated mainly from a wind shift in surface obs and lower dewpoints over Northwestern PA and NY, is bisecting the CWA. This may be the focus for the development of widely scattered thunderstorms today, with plenty of instability, weak shear, and the support of a passing short wave. This continues to be progged by the hi-res models. Will maintain low chance pops from about Pittsburgh southward, where the best low level moisture resides. Question remains whether storms will develop before the drier air aloft is advected and mixed to the surface, precluding development. Otherwise, most locations will still exceed 90 today. Slightly lower dewpoints should help to relieve some of the high heat indices, especially north but some values will still approach 100 in Ohio where low level moisture remains. Thus, no change was made to the heat advisory. Model guidance suggests that these drier dewpoints will never fully make it across the entire region before southerly flow returns ahead of the next front Sunday. But, this should be sufficient enough to provide a cooler night, for the northern half of the region, than previous nights. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Upper ridge will build eastward briefly on Sunday, with a weak shortwave crossing the lower Great lakes in advance of a front that is progged to cross on Monday. Anticipate that most of Sunday should remain dry, with warm and humid conditions continuing. 591dam heights build overhead, so again anticipate temperatures exceeding 90 although some high clouds may limit heating for the northwesternmost zones. An upper-level trough and its associated front will approach from the west early Monday. Based the current model run timing, some precipitation may already be moving into the area Monday morning, which may limit the threat for any strong to severe storms despite instability and moderate shear. For now, agree with SPCs analysis of a Marginal Risk for the region. Ahead of the boundary, where we remain cloud free early, temperatures should still warm well into the 80`s and approach 90. Front will stall just south of the PA/MD border by Monday night and we will remain in zonal flow. This could lead to lingering chances of showers/storms, mainly along the terrain on Tuesday. While dewpoints will be lower, it should still be another day of mid-80 temperatures. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... Zonal flow will be replaced by weak troughing over the eastern CONUS for the end of the week. With several shortwaves progged to pass in the upper level pattern, but differences in the deterministic models, have opted to stay close to a blend of guidance with near or slightly above normal temperatures forecast. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... vfr conditions this afternoon. Some lower dewpoint air in moving in in the northern airports like KDUJ and KFKL. it will gradually move southward. In airports from KZZV to KPIT to KLBE and south, there is a chance of an isolated thunderstorm after 19Z as the drier air acts as a lifting mechanism. some mvfr restrictions in the early morning hours sunday possible at in airports from KZZV to KPIT to KLBE and south. .OUTLOOK /SATURDAY THROUGH WEDNESDAY/... Restrictions will be possible late Sunday and Monday with the approach and passage of a weak cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...Heat Advisory until 8 PM EDT this evening FOR OHZ048-057>059- 068-069. PA...None. WV...Heat Advisory until 8 PM EDT this evening FOR WVZ004-012. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.