Area Forecast Discussion
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000 FXUS61 KPBZ 201759 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 159 PM EDT FRI MAY 20 2016 .SYNOPSIS...
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Low pressure will bring rain tonight and Saturday, with a few lingering showers into Sunday. Dry conditions and a warming trend in temperatures are expected during the first half of next week.
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&& .NEAR TERM /THROUGH SATURDAY/...
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A veil of cirrus currently covers the CWA as the 500 mb ridge axis crosses. Rain has progressed to a point just southwest of Cincinnati. Recent hi-res model runs have slowed down the arrival of precipitation to mainly past 00Z. This makes sense given the dry airmass in place and the more NNE trajectory of the better moisture and lift. Will be backing off on PoPs for a few hours as a result. Still, there is still enough model support to justify categorical PoPs across most of the CWA tonight. We expect a surface low tracking across the Ohio Valley to open into an inverted trough across West Virginia on Saturday, with a new coastal low taking over. While the best push of moisture still remains off to the southeast, a secondary precipitable water maximum crosses our area with the surface low and ahead of the 500 mb trough. This will lead to a soaking rain for much of the southeastern CWA with rain totals of 1 inch or more. Amounts will taper off to the north and west. Think rainfall rates and the overall lack of convection will preclude a large-scale flooding threat, but can`t rule out isolated issues in the southern CWA where FFG values are a bit lower. The steadier synoptic rainfall will degenerate into showers as time goes on Saturday with the arrival of the upper trough. PoPs and rainfall rates fall off a bit as a result, but dry weather can`t be guaranteed at any point during the day. A small diurnal range in temperature is forecast for the period given the wet conditions. Used a blend of guidance for the values. CL
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&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY/... Models show good consensus through the short term in tracking a surface low across southern portions of the forecast area overnight and Saturday. Moisture advection will ramp up overnight and expect rain to have spread across the forecast area by midnight. Isentropic analysis shows respectable synoptic forcing but particularly over southern and eastern zones. Have increased forecast rain amounts over these areas based on latest model and WPC guidance with an inch or more across southern fringes of the forecast area and decreasing to a little over a quarter inch to the north. Based on latest FFG do not anticipate any major water issues but southern locations could see isolated minor flooding of streams and creeks after midnight when the brunt of the rainfall is expected. Showers may linger across the region Saturday night and Sunday as a building ridge over the central CONUS, deepens the trough over the east, with a projected shortwave moving through the trough. Generally kept the chance pops relegated to the east, where better moisture and ascent are forecast. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Overall models show average agreement and continuity with previous runs with regards to the central conus ridge shifting to the east and bringing a warming trend in temperatures to the region. Have maintained a dry forecast through the first half of the week until flow shifts to the southwest and moisture advection increases. && .AVIATION /17Z FRIDAY THROUGH TUESDAY/...
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VFR conditions will continue through the evening, although clouds will be lowering and thickening with time ahead of approaching low pressure. Rain will overspread the region tonight, with an areawide drop through MVFR towards IFR conditions by Saturday morning. Rainfall will taper off to showers as time progresses on Saturday, but IFR to possibly even LIFR ceilings will persist through most of the day as an upper level trough crosses. .OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/... Restrictions are likely to continue into Saturday night, with improvement on Sunday.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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