Area Forecast Discussion
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000 FXUS61 KPBZ 211511 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1111 AM EDT Mon May 21 2018 .SYNOPSIS... Rain chances return late today through Tuesday as low pressure tracks to our north. The departure of a stubborn front will bring drier weather by Wednesday, with quiet and warm weather expected through Friday under high pressure. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Area of showers south of the Mason Dixon line have fizzled out due to mixing in of drier air and encountering subsidence. No changes to the current forecast as a dry afternoon is predicted. Previous discussion follows... The ever-present surface boundary currently lying just south of the CWA will get another northward push starting today as a warm front, courtesy of a surface wave along the boundary in the middle Mississippi Valley. The front will not make much northward progress by 00Z, and thus do not make much of a northward PoP push until late in the day. Best chances will lie in southeast Ohio, as well as a secondary maximum in the southeast counties with modest upslope effects. Warm air aloft should prevent much in the way of popup showers and storms initially, until the front lifts into the region. SPC has our southeast Ohio counties in a marginal severe risk for this afternoon and evening. CAMs suggest that the most likely scenario would be initial development in a more favorable air mass over IN/western OH with propagation into the CWA during the evening. A strong to severe wind gust or two would be possible if activity can congeal into multicell clusters/bowing segments. The lack of dry air aloft precludes a downburst risk, and overall wind field is a touch too weak to support persistent, rotating updrafts. Temperatures will run some 5 to 10 degrees above normal today, with much of the southern CWA getting into the lower 80s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... The surface low will continue its northeastward push, reaching the southern fringe of the Great Lakes by late tonight, and then western New York by Tuesday evening. Have continued likely PoPs for the Monday night/Tuesday period with a strong moisture punch of 1.5-1.75 inch PWAT values. Also, upper support will be provided from the RRQ of a 250mb jet over southeast Canada and an approaching upper trough. Locally heavy rain will be possible tonight given the high PWAT and relatively slow storm motion, but do not foresee a widespread flooding threat. Depending on how much instability can build up, the arrival of a cold front Tuesday afternoon/evening may present a slightly better risk of severe storms than today for the region as shear could be a bit more pronounced, supporting a gusty wind threat. Most of the area is under a day 2 marginal risk. The aforementioned trough should provide enough of a push to finally move the front away from the region by late Tuesday night or early Wednesday. Have PoPs decreasing from northwest to southeast as a result, ending precipitation by Wednesday evening at the latest. Temperatures will continue to run several degrees above normal through this period. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Highlights: - Dry weather to start - Trouble in the tropics - Wet second half of Memorial Day Weekend High pressure provides dry weather through the first half of Saturday as mid level ridging takes control over the eastern United States. With H5 heights around 582dm and H8 temps around 16C daytime highs should be well into the mid 80s outside of the mountains and perhaps north of I-80. Plenty of sunshine and warm temperatures between H6-H7 will put a cap on any cu from growing into a shower or storm across the higher terrain. The forecast gets messy Saturday afternoon through Memorial Day. A potential tropical system will slowly spin along the Gulf Coast states, while moisture is pumped north from the gulf on the windward side of the Appalachians. This in conjunction with an active jet stream brings several disturbances across during the aforementioned time frame. PWATS peak around 1.7" while warm cloud depths run near 12KFT. This spells potential for heavy rain and potential flooding if an any gets hits repeatedly. Right now, its too hard pinpoint location of showers with embedded thunder so nothing that meets confidence for insertion into the hazardous weather outlook. Severe thunderstorm threat appears low given the amount of clouds forecast. GEFS/GEPS remain in good agreement on the large scale synoptic system outside small location differences near the Gulf Coast. The timing of the shortwave troughs place highest QPF values in the mountains Saturday evening through Memorial Day. NAEFS pwats are in the low end of the probability of extremes using CFSR climo, thus for now do not see a high end event.
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&& .AVIATION /15Z MONDAY THROUGH FRIDAY/...
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VFR conditions are expected for most of today as high pressure slides E across the Ern Great Lakes. Mid/high clouds should increase ahead of an approaching warm front, and a few showers are possible S of I 70 this morning close to the front. A few thunderstorms are possible this aftn mainly across OH ports as the front begins to lift N toward the region, and daytime destabilization occurs. Mentioned a VCTS at ZZV. The front should continue its track N tonight with showers and ocnl MVFR conditions overspreading the region. OUTLOOK... Restrictions in showers/thunderstorms are likely Tue/Tue eve with a crossing cold front.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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