Area Forecast Discussion
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000 FXUS61 KPBZ 281201 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 801 AM EDT Fri Apr 28 2017 .SYNOPSIS... A break in the activity today under high pressure. Unsettled but warm weather expected for the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Morning update to remove patchy fog and adjust sky grids into the afternoon. No other changes, and previous discussion follows. Dry weather returns today under high pressure. The cool air this morning, will quickly eject to the north as strong warm air advection takes over.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... Low confidence forecast through much of the weekend due to differences in model solutions. Models are having a difficult time determining the position and timing of a warm front on Saturday and also the extent and strength of Eastern CONUS ridge. The upper levels will show a slow increase in 500mb heights beginning tonight and continuing through most of Saturday night. This is in response to a large and vigorous upper level system which will dig into the Southern Plains over the weekend. Zonal flow this evening will be replace by the building eastern ridge overnight. As the zonal flow is pushed northward a series of shortwaves will rush north of the building ridge, bringing another chance for showers and storms tonight and Saturday. Models seem to be really suffering from convective feedback tonight, and late on Saturday, particularly with the NAM solution. One thing the models do somewhat agree on, most of the precipitation tonight and Saturday will be over the northern half of the region, north of the surface warm front. Discrepancies again arise Saturday night and Sunday. At this point it seems like the NAM has a better handle on the overall pattern as rather strong ridge will be in place over the area and we will be well into the warm sector. This would provide a more stable atmosphere and limit the prospects for widespread showers and storms Saturday night and through much of Sunday. The other question is convective threats with the shortwave tonight and then on Saturday afternoon. Interestingly enough, the best lift will ride north of the unstable air, particularly tonight which will limit storm coverage and intensity. Could see more bebop type of situation on Saturday under the building ridge. Again, will lean closer to NAM solution Saturday night and Sunday as it is showing a better solution to the overall pattern. The key for the weekend will be the timing and movement of the rather well defined warm front. How far north will it push on Saturday and Sunday and how long will it take for it to move north of the region. Warm temperatures are expected through the entire weekend. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Eastern ridge finally begins to break down on Monday, as deep upper level system spins northward from the plains/Midwest on Sunday, toward the Great Lakes by Monday night. The 500 low will eventually move across Southern Canada Tuesday and Wednesday. The surface reflection will move directly under the 500 low and swing the occluded front through the Upper Ohio Valley late Monday/Monday night. This will increase the risk for showers and storms. A cooler and unsettled pattern will continue through Midweek. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... Patches of IFR fog and MVFR clouds will linger for a few more hours, with most fog south of the Mason-Dixon line and the low clouds further north. After 14Z or so, VFR conditions are expected for the rest of the day under high pressure, with high clouds and light winds becoming more southerly with time. Moisture increases after 00Z as a warm front lifts back north. Clouds will lower with time, with MVFR ceilings showing up northwest of PIT by sunrise. Showers and a few thunderstorms are expected as well, with thunder chances too low to include yet, but brief IFR visibilities are possible late tonight. .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. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.