Area Forecast Discussion
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000 FXUS61 KPBZ 260750 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 350 AM EDT Mon Sep 26 2016 .SYNOPSIS...
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Showers and scattered thunderstorms can be expected with the passage of cold front today. More seasonable temperatures are expected for the rest of the week.
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&& .NEAR TERM /THROUGH TONIGHT/... Deepening trough over the Great Lakes will push a cold front, currently analyzed over eastern Indiana, across the Upper Ohio valley this afternoon. Model consensus on timing is relatively good between the deterministic models and the hi res short term guidance. As such, very little adjustment was needed to categorical probabilities with strengthening support for thunderstorms as the boundary approaches southwestern PA/northern WV. This will be where surface instability is likely to be the highest based on the boundary`s timing, and less cloud cover. The NAM is the most robust with it`s CAPE/dewpoints compared to other model guidance, including the RAP and HRRR soundings, which it tends to overdue in most convective scenarios. However, with deep layer shear present and at least modest cape of 500j/kg, some strong to severe storms may be possible which is supported by the spc marginal risk over the aforementioned region. Strong southerly flow and sunshine in advance of the boundary should allow for temperatures to warm above seasonal averages this afternoon followed by normal low temperatures with the fronts passage progged to be east of the ridges by midnight. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... Temperature advection will be rather weak on Tuesday with southwesterly flow expected aloft with the upper trough still situated over the northern Great Lakes and high pressure present at the surface. Thus, temperatures were forecast just below seasonal averages. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Most of this period will be dominated by the closed upper low...which will dive from Michigan into the central Ohio Valley by Thursday and linger as a cutoff through at least Friday. Models are beginning to converge on this scenario, with the lagging GFS finally coming around. As such, mostly chance PoPs were maintained through the remainder of the work week for scattered showers. Timing of shortwaves around the upper low remains tricky at this distance. Given the upper low representing a pattern change, felt the SuperBlend temperatures were a bit too high and knocked them back a couple of degrees early on, keeping daytime values a bit below climatology. The upper low should begin to lift out by next weekend as midlevel heights build over the lower Ohio Valley. This will bring dry weather back by Sunday, as well as allow temperatures to recover back to seasonal levels. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Mostly VFR conditions are forecast through midday. The lone exception may be near DUJ around sunrise, as some low clouds try to creep up the ridges on southeast upslope flow. Handling with a MVFR TEMPO for now but may need to adjust depending on satellite trends. Conditions will deteriorate during the afternoon with the approach and passage of a cold front. A short period of MVFR or even IFR visibilities in showers or thunderstorms is expected, but timing remains a bit problematic still. Used VCTS and expect to refine timing in future updates. Some of the storms may be strong, with heavy rain and gusty winds. Behind the front, MVFR ceilings will linger for a few hours into the evening hours, until drier air sweeps in from the west, allowing for clearing skies. .OUTLOOK /MONDAY NIGHT THROUGH THURSDAY/... The next chance for restriction is expected by Wednesday as upper level low pressure settles into the area. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.