Area Forecast Discussion
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305 FXUS61 KPBZ 261134 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 734 AM EDT Mon Sep 26 2016 .SYNOPSIS... Showers and scattered thunderstorms can be expected with the passage of cold front today. && .NEAR TERM /THROUGH TONIGHT/... The only changes needed for the post dawn update were tweaks to cloud cover and wind based on the latest obs and model soundings. A deepening trough over the Great Lakes will pull a cold front 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 average low temperatures in the wake of the front. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... Temperature advection will be quickly neutralized on Tuesday, with warm advection resuming on the southeastern flank of Great Lakes low pressure. As such, temperatures were forecast near the 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 /11Z MONDAY THROUGH FRIDAY/... VFR will give way to condition deterioration this afternoon as a cold front sweeps across area terminals. General MVFR is anticipated with the feature, with IFR visibility in heavier convective activity. As mixing improves today, expect gusts of 15 to 20 kts, with higher values in any aforementioned convection. Improvement can be expected through the evening as subsidence and dry advection erode clouds and precip. Sufficient wind to prevent fog is anticipated overnight, with VFR continuing through Tuesday. .OUTLOOK /TUESDAY NIGHT THROUGH THURSDAY/... The next chance for restriction is expected Wednesday as upper level low pressure settles over the area. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ 15

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