Area Forecast Discussion
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000 FXUS61 KPBZ 250917 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 517 AM EDT Mon Sep 25 2017 .SYNOPSIS... High pressure will maintain dry and warm weather into mid week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Cirrus has started to really cover much of the area early this morning as it advanced from the south overnight. This seems to be upper level moisture feeding off of Maria that is being sandwiched between the ridge dominating just to our northeast and a weak upper low along the Gulf of Mexico coast. This will likely have two impacts. First of all, it will keep things fairly warm through sunrise by limiting the last of the radiational cooling we would otherwise have, and second, it will incrementally decrease daytime insolation. This will yield a slightly tighter diurnal temperature curve. As a result, filtered sun will mean highs just a degree or two lower than yesterday yet still within eyeshot of 90F. Fries && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/... One weak jet streak that will has had cirrus advecting northward into our area will peel off to the east by Tuesday. This will allow for skies to clear yet again. With better insolation, a fall off of about 1C in 850 mb temperatures and loss of about 10 dam in 500 mb heights will likely be offset. Thus, highs will trend toward the same numbers on Tuesday as Monday, which will continue the ridiculously above normal trend. By Wednesday, the pattern looks set to finally start to break down as an upper trough starts to shear off to the northeast as it lifts through the Great Lakes. Moisture below the upper levels is exceedingly modest with the diffuse H5 wave that moves across the area largely beyond the diurnal maximum on instability. Thus, while fairly impressive temperature falls will be noted with the front, an utter dearth of moisture in the column combined with forcing anywhere beyond the boundary layer pushing well to the north of the area will mean what looks like a largely dry frontal passage. Some slight chance PoPs were added for the northern fringe of the area, but it would seem most areas should remain dry through the frontal passage. By Thursday, cyclonic flow and constant cold advection will have dropped 850 mb temperatures roughly 10C from their levels earlier in the week. As such, highs will be struggling to reach 70F even as dry weather continues. Fries && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... Further changing of the pattern looks likely in the long term. While post-frontal cyclonic flow will continue through the remainder of the week, a much deeper upper level system will arrive for the weekend. Substantial cooling seems likely with this system in the mid-levels as it transits the Great Lakes and heads into the northeastern CONUS. As a result, instability will increase markedly and mid-level moisture will finally arrive. Shower chances maximize with its passage on Saturday likewise. Saturday`s system and increase in clouds will drop temperatures back toward their coldest point of recent memory. Without much in the way of sunshine and as 850 mb temperatures drop toward +3 or +4C in the daytime, highs much beyond the mid 60s in the lower elevations seem unrealistic. Even still, this will only be a couple of degrees above normal for one day after a stretch of consistent above normal days that will have been going on since September 13. Fries && .AVIATION /09Z MONDAY THROUGH FRIDAY/... Other than localized morning fog, high pressure will maintain light wind and VFR through the TAF period. .Outlook... Restrictions are possible with cold fronts Wed night and Fri. && .CLIMATE...
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While we will not be quite as warm as over the weekend, temperatures will still be 15 or more degrees above normal this aftenroon. Here are the local record high temperatures for Monday: PIT: 92 (1881, 1900) ZZV: 94 (1908) MGW: 93 (1930) DUJ: 87 (2007) HLG: 91 (1934) PHD: 91 (2007)
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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