Area Forecast Discussion
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000 FXUS61 KPBZ 142027 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 327 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 /THROUGH THURSDAY/...
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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. 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.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SUNDAY NIGHT/...
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Surface low pressure will move through the Ohio Valley Thursday night, dragging a cold front across the area. The period of heaviest rainfall is expected to be Thursday night, with rainfall rates decreasing on Friday; heaviest rainfall should occur along the Mason-Dixon line in southwestern Pennsylvania and northern West Virginia. See the hydrology section below for more information. Confidence was high enough to issue an areal flood watch in addition to the flood watch at individual river points. As precipitation ends Friday, there could be a brief period of snow, but any accumulation would be minimal. The better chance for snow accumulation will occur with a quick moving storm Saturday afternoon and evening. While the center of the low pressure system will pass well to the southeast, precipitation could spread across the area and change from rain to snow. Models are still varying in how the storm is depicted, and it`s too far to nail down any details. High pressure will briefly move into the region for Sunday, yielding dry conditions.
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&& .LONG TERM /MONDAY THROUGH WEDNESDAY/... Deep swly flow will persist in the ern and central CONUS through much of next week as an H5 trough becomes entrenched in the swrn CONUS and upper high pressure persists in the wrn Atlantic. This stagnant upper- air pattern will support strong return flow, warm advection and an omnipresent frontal boundary, with multiple rounds of rain/showers beginning Mon morning and continuing through much of the week. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... 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. && .HYDROLOGY...
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Rises on Mon and Ohio Rivers and their tributaries are expected later this week... 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. 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.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...Flood Watch from Thursday evening through Friday afternoon for MDZ001. OH...Flood Watch from Thursday evening through Friday afternoon for OHZ059-068-069. PA...Flood Watch from Thursday evening through Friday afternoon for PAZ021-029-031-073>076. WV...Flood Watch from Thursday evening through Friday afternoon for WVZ001>004-012-021-509>514.
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&& $$

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