Area Forecast Discussion
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098 FXUS61 KPBZ 181247 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 847 AM EDT Mon Sep 18 2017 .SYNOPSIS... High pressure centered over the region will bring a prolonged period of dry weather, along with unseasonably warm temperatures through the coming week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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With 8:45am update, made some minor changes to hourly temperatures that have been held down by fog. Evolution of fog looks good in the hourly grids, with fog expected to have burned off by 10-11am. Previous discussion follows. High pressure will continue to hold sway through the morning and into the daytime on Monday as a frontal boundary currently straddling Indiana into Michigan inches eastward. This front is set to run into a wall of high pressure and drier air aloft concurrent with its upper forcing shearing off rapidly northeastward toward Quebec. As this occurs, all convective activity currently along the front should translate well north of the area on Monday. Before that time, however, a clear overnight with very weak boundary layer flow will transition into a Monday with an increase in mid and high clouds as well as the current boundary layer moisture resulting in fairly pervasive cumulus development. However, with the surface trough impinging upon the western fringe of the area, easterly flow into the ridges will probably be weaker than in previous days. This would seemingly result in a lower chance of showers in the heat of the day in the terrain. Otherwise, continued elevated dewpoints due to a lack of afternoon ventilation spurred by cumulus development each and everyone one of the last couple days will result in saturated valleys through morning. This means a deja vu forecast for fog through sunrise. Even with a decent bit of cloud cover, a warm air mass already in place and at least some sun breaks through the day should result in yet another above normal afternoon as highs jump toward the lower 80s in most spots. Fries
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&& .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/... With the upper level pattern favoring ridging in the east and Jose moving closer to the coast, as well as deepening troughing in the west, fairly high speed SW flow will exist through most of the Midwest. One weak wave in the high speed flow will attempt again to impinge upon the region late Tuesday into Tuesday night. Again with this wave, shearing northward, a dry column, and a lack of upper support driving eastward make adding PoPs very difficult to do. PoPs for late Tuesday were adjusted to just below mention for rainfall, however cloud expectations were increased due to high projections of upper level moisture as the wave approaches. Regardless, warm SW flow off the deck, a humid boundary layer, and WAA will continue, thus well above normal readings will be common. Fries && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... A deepening upper trough in the west and retreating remnants of Jose will allow for heights to go through the roof in the eastern CONUS for the balance of the week. Low level flow looks to finally lose some of its easterly component, which should rid our area of the marine component and start to allow for more ample insolation. Likewise, deep layer southwesterly flow above the boundary layer should allow for 850 mb temperatures to approach 18C from Friday into the weekend (and possible beyond). This will allow for high temperatures to easily jump into no less than the mid 80s even with the shorter daytime hours as compared to mid-summer. That said, SuperBlend guidance is utterly ridiculously cool, and all bias-corrected guidance is taking several degrees of off explicit model/MOS output, hence both were summarily dismissed as statistical rubbish. As a result, the forecast was built entirely dry with very high reliance on adiabatic mixing of 850 mb temperatures from model guidance. This resulted in a continuation of far above normal readings through the entirety of the long term. Fries && .AVIATION /13Z MONDAY THROUGH FRIDAY/...
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While IFR/LIFR fog was still being observed as of 12Z, all fog is expected to depart local terminals by 15Z. VFR is expected under upper ridging for the rest of the TAF period, though a diurnal CU cig and increasing mid/high clouds are expected. .Outlook... Patchy morning fog restrictions are possible through Fri with ridging in place.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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