Area Forecast Discussion
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000 FXUS61 KPBZ 141734 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1234 PM EST Wed Feb 14 2018 .SYNOPSIS... A series of upper air disturbances will result in a several day period of wet weather. Widespread rain is expected with a late Thursday and Friday cold front. Rivers and streams could become swollen as a result. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Regional radar mosaic portrays rain developing and moving into the region. It will take until early afternoon before measurable precipitation is observed. Elevated instability exists this afternoon over northern West Virginia and southwestern Pennsylvania, however despite the region being outlook in general thunder, elected to keep it out of the forecast. If it occurs, it will be slight chance at best. Looking at the current lightning mapper not see any strokes as of yet. The greatest aerial coverage of showers will be around 0Z plus and minus a few hours correlating well the period of 305K isentropic upglide and low level convergence in response to a 60kt H8 jet. Focused pops south of I-80 with categorical and a touch lower numbers points north. Overall rainfall amounts will be less than three tenths of an inch with most locations experiencing less than a tenth of an inch.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... The crossing wave should continue to result in rain through the evening, though a lack of significant upper support should limit rainfall amounts to a half inch or less. Rain chances should taper off overnight as the wave exits, though with ascent in warm advection and low level moisture in place some patchy light rain is possible through Thursday morning. A shortwave and associated sfc low is progged to track from the Mid MS Valley region to the Upper OH Valley region by late Thu/Thu night. Widespread rain is expected with the wave with jet enhanced ascent and deep layer moisture. The low is progged to track across PA Thu night/early Fri, dragging a cold front across the area. Rainfall totals of generally 1-2 inches are expected, with the highest amounts from PIT south across the Monongahela Basin. After coordination with surrounding offices, will maintain an HWO mention of a possible flood watch and elevated rivers, and see what the morning RFC river progs show. Precip should taper off after FROPA Friday, and could briefly mix with snow before ending. High pressure should build in Friday night through early Sat with dry weather expected. Models differ in run to run consistency in the handling of a srn stream wave tracking through the MS/TN/OH Valley Sat. Increased chance POPs for snow for most of the area, though significant uncertainty remains in the details. After temperatures 20-25 degrees above average on Thursday, readings should return to seasonal levels by Fri night/Sat. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... A deepening Wrn CONUS trough should result in SW flow and above average temperatures through the period. Shortwaves embedded in the flow, and a slow moving sfc boundary should also result in periodic rain chances. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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High confidence forecast with CIGS and precipitation type this afternoon through the overnight. CIGS could lift to MVFR earlier than forecast Thursday morning. Showers will increase in coverage this afternoon dropping conditions to IFR and they will hold there for most of the night. Improvement will occur after midnight as conditions lift to MVFR save for FKL and DUJ where drizzle and stratus could hold.
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&& .HYDROLOGY... ...Rise on Mon and Ohio rivers later this week are expected along with their tributaries... A two to three day period of rainfall will lead to swollen streams and creeks especially across southwestern Pennsylvania and northern West Virginia. Overall rainfall amounts in the aforementioned area will be around two inches, which falls below 24 hour flash flood guidance. We could see higher amounts due to terrain effects. A flood watch may be needed later today if forecast amounts increase. The greatest period of QPF will be 0Z-12Z Friday, however feel NCEP suite is a little overdone with QPF due to overplaying warm advection and centering it on the nose of the low level jet. Meanwhile, mid and upper level jet position support ageostrophic subsidence which would offset low level forcing. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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