Area Forecast Discussion
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323 FXUS61 KPBZ 270941 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 541 AM EDT Thu Apr 27 2017 .SYNOPSIS... A very warm day on tap. Showers and storms return this afternoon ahead of a cold front. Unsettled but warm weather through the weekend, && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A cold front associated with an occluding system will cross the CWA during the late afternoon/early evening. Latest models runs are increasing the eastward speed of the system, so have sped up the onset of PoPs today. This appears to be mostly related to a faster and stronger shortwave trough, which will more efficiently break down the eastern ridge. Energy aloft splits this afternoon with the best dynamics spinning northward toward the Great Lakes surface low. As this large scale ascent rushes northward, models are showing a decrease in intensity and coverage of the convection ahead of the front. Atmosphere does destabilize ahead of the boundary, but the best instability remains aloft. Additionally, convection that does develop will be sustained by the well sheared environment. The greatest threat today remains damaging winds and large hail. A couple of elements will be working against the development of strong storms. First, pre-frontal upper and mid-level clouds, and second, the very warm air aloft. Any cooling aloft is closely linked to the surface front, so this leads me to believe that any strong convection will also be tied to FROPA. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... Cold front and associated convection will quickly exit to the east this evening. Dry weather returns Friday with high pressure. Any cooler air behind today`s front will be quickly ejected to the north as strong warm air advection takes over. Eastern ridge will try to build late Friday, but will be shunted by a series of upper level waves which will ride over the top of the rising heights. These wave will bring showers and storms back to the area late Friday night and Saturday. Seeing discrepancies in models solutions on Saturday with the position and timing of the shortwaves. Have leaned toward a more northern track, which complies with slowly rising 500mb heights on Saturday. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... An active pattern is figured for the remainder of the weekend into early next week. A few shortwaves will cross in continued moist southwest flow along the front of a broad trough, leading to rain chances again on Sunday. Timing remains tricky, but Saturday night currently looks to be the period with the lowest coverage in the warm sector. Temperatures remain above normal. The trough lifts out as a closed upper low into the Great Lakes by Monday, pushing a fairly strong boundary across us. Given system strength, the amount of moisture, and a possibly negative tilt to the upper trough, strong storms appear possible. Behind this system, quieter weather and seasonable temperatures are expected into the middle of next week. && .AVIATION /10Z THURSDAY THROUGH MONDAY/...
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VFR conditions are forecast for the morning hours, although clouds will be thickening with time ahead of an approaching cold front. Winds will pick up out of the south and gust to 20 to 25 knots once mixing gets going. Timing for the frontal passage will be between roughly 18Z and 02Z, with showers and thunderstorms along and ahead. Coded up a period of MVFR showers with VCTS, with exact timing still a bit uncertain, but brief IFR conditions will be possible in any downpours. Stronger wind gusts are also possible in the strongest storms. Behind the front, winds will diminish and MVFR ceilings will linger. Considered adding fog, but think it will be patchy at best as boundary layer should remain fairly mixed overall. .Outlook... Occasional restrictions are possible this weekend along a stalled frontal boundary. Better restriction chances arrive with a strong cold front Sunday night into Monday.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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