Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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766 FXUS61 KPBZ 200945 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 545 AM EDT Fri Sep 20 2024 .SYNOPSIS... Seasonably hot weather is expected through the weekend with a marginal chance of severe storms Saturday, mainly east of I-79. A wetter pattern is becoming increasingly likely next week. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Seasonably hot weather; record breaking heat potential for New Philadelphia and DuBois. ------------------------------------------------------------------- Any lingering fog is expected to clear rapidly beyond sunrise with mixing. Temperatures are expected to climb rapidly into the day today with upper ridging and surface southerly flow under high pressure. With how warm conditions have been, it is difficult to believe the average high for Pittsburgh this time of year is 74. With temperatures forecast to climb into the 80s (and even 90s for eastern Ohio), highs will be around 10 to 15 degrees above average. New Philadelphia has a shot at beating their record high of 89F (2002), and DuBois may approach their record high of 84F (1965). Temperatures will cool under clear skies tomorrow night, but should be limited by dew points and light winds. This will keep lows slightly above average. Fog appears less likely overnight save insulated valleys with larger dew point depressions and some winds. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... KEY MESSAGES: - Marginal severe storm potential, mainly east of I-79 with the primary threat being damaging winds. --------------------------------------------------------------------- Guidance still remains optimistic on precipitation chances Saturday for western Pennsylvania and eastern Ohio as a shortwave overtops and flattens an eastern ridge. This will act to cool upper levels and keep daytime highs slightly cooler than the day prior, but the main question remains severe potential. First, the environment looks favorable for low-end severe threats. Probabilities of at least 1000 J/kg of SBCAPE are up to 50% to 75%, while chances of 30kts to 40kts of shear in the 0-6km layer remain elevated, though most of the shear is confined to the mid-levels. Mid-level dry air in shortwave induced subsidence is also likely to supply as much as 800-1000 J/kg DCAPE. This suggests winds remain the primary threat. So the main question for development is not the environment, but rather the forcing. There is still spread in the intensity and timing of the mid- level vort max. Passage could be as reasonable early as 14Z and as late as 22Z. The later the passage time, the more the wave will be able to utilize instability, and thus, the higher chance of severe weather. The second uncertainty is intensity. The forcing will need to be strong enough to overcome mid-level dry air. A number of CAMs suggest this, but roughly an equal number rely on orographic help, leaving the primary threat east of the forecast area. These uncertainties have justified the maintenance of a marginal risk for severe weather. Chances of any rain with this wave range from 50% in eastern Ohio to 90% east of Pittsburgh. Despite this, chances of 0.25" of rain only maximize at 50% to 60% in western Pennsylvania. This will do little in the ways of drought relief. Rain chances taper overnight as the wave passes to the east and subsidence fills in behind. Fog is possible Saturday night and Sunday morning given calm, clear conditions and recent rainfall. && .LONG TERM /SUNDAY THROUGH THURSDAY/... KEY MESSAGES: - Hot and dry Sunday. - Precipitation chances encroaching for the rest of the week with moderating temperatures. ------------------------------------------------------------------- There remains high confidence in brief ridging Sunday which will allow high temperatures to remain well above average. Chances of topping 90F are 20% to 40% in eastern Ohio, with 80s forecast elsewhere. By Monday, there is more agreement that the ridge axis flattens to quasi-zonal flow, but uncertainties in the 500mb flow snowball by mid-week. All clustered guidance indicates some troughing, however, roughly 40% of global ensemble membership has a positively tilted Midwest trough, while 60% has a neutral eastern trough by the middle of next week. A Midwest trough would be more conducive to low tracks over our area and more precipitation, while a eastern trough still allows precipitation chances, but the main QPF axis would be toward the eastern seaboard. However you cut the cards, this is the best shot of notable rain this month, with chances of greater than an inch of QPF 50% for eastern Ohio and northern West Virginia and 60% to 70% in western Pennsylvania. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... Patchy early morning fog is possible with efficient radiational cooling and light winds, primarily for FKL/DUJ but also possibly around MGW/LBE (though generally shorter duration and less dense at the latter terminals). Otherwise, VFR and light winds are expected throughout the TAF period. Scattered diurnal CU should develop during late morning and afternoon with bases starting in the 3-5kft range, gradually lifting to 6-8kft before dissipating around sunset. .Outlook... Low chances for restrictions in thunderstorms are possible Saturday with a crossing shortwave trough. VFR returns Sunday under high pressure before restriction potential returns early next week with an approaching warm front. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Milcarek NEAR TERM...Milcarek SHORT TERM...Milcarek LONG TERM...Milcarek AVIATION...Cermak/Hefferan/22