Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 280611 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 211 AM EDT Thu Jul 28 2016 .SYNOPSIS... A wavy front will be nearly stationary from the Mid Atlantic region to the mid Mississippi Valley through the end of the week. Weak impulses tracking along the front will combine with deep moisture to produce periodic rounds of showers and thunderstorms. && .NEAR TERM /THROUGH TODAY/... As of 945 PM EDT Wednesday... Atmosphere has generally been worked over in terms of instability needed for showers/storms. There may be lingering showers and a few isolated storms overnight but with significantly reduced intensity due to loss of daytime heating and reduction in available CAPE. Today`s rainfall will lead to patchy fog overnight otherwise the main theme for the overnight will be the high dewpoints (lower 70s most areas and muggy conditions) and a continuation of the muggy conditions. As we head to Thursday, models continue to advertise decent shortwave moving from the TN Valley into the eastern Ohio Valley. Better upper support with backing winds suggests that higher threat of showers and storms occurs over the mountains, though further east is limited some. Any cloud cover tonight into Thursday from blow off of upstream convection may inhibit stronger storms in the west, but should be more sunshine in the east. The Storm Prediction Center Day 2 has a slight risk of severe storms in our piedmont counties Thursday and marginal elsewhere. Looking for highs on Thursday to range from the lower to mid 80s west to lower to mid 90s east. && .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... As of 330 PM EDT Wednesday... Overall synoptic pattern shows upper ridge across the western states with broad trough developing across the MS/OH valley as fairly strong short-wave helps to amplify the trough. This will spin up a weak surface low...currently forecast by the consensus of models to pass just to our northwest Thursday night and Friday with an axis of very high PWATS and the potential for significant rainfall mainly to our north and west. QPF ranges from less than 0.25 inches far southeast CWA up to possibly 1.50 inches far northwest. Recently issued WPC Day 2 (12z Thu-12z Fri) Excessive Rainfall outlook show an area of slight chance for excessive rainfall mainly north and west as well. Cannot rule out some hydro issues in our northern counties with this much rainfall but better likelihood north of the CWA where some Flood Watches have been or are likely to be issued. At this point no Flood Watches for our area but will have to monitor closely for any southward shifts in the expected area of heaviest rainfall. Partial clearing Friday into the weekend with little significant change in the overall pattern. Maintaining diurnal thunderstorm chances in the still moist and unstable air mass. Temperatures near to slightly above seasonal normals. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 330 PM EDT Wednesday... The generalized pattern over the CONUS will be slow to change in the extended period as upper ridge builds over the western states an broad troughing takes hold across the eastern U.S. Expect several shortwaves will crest the western ridge and help to amplify the eastern trough early in the period. Meanwhile a surface frontal boundary will persist in the vicinity of the mid-Atlantic through the period oscillating somewhat north and south in response to short- wave activity and modified by rounds of mainly afternoon/evening convection. The air mass will remain warm and humid through the period with daily highs near to slightly above normal and lows above normal due to the high humidity and considerable cloudiness at times. By Wednesday indications are that H5 heights will begin to rise again with somewhat drier and hotter conditions for mid-week period. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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As of 200 AM EDT Thursday... Area of showers and thunderstorms with MVFR ceilings and visibilities over eastern Kentucky and southwest Virginia will continue to move northeast this morning. Along the Blue Ridge and into the piedmont of Virginia and North Carolina areas of fog and stratus will develop. Observations showed high surface dew points with little to no dew point depression. High confidence of IFR to LIFR fog at KBCB and KLWB this morning. Medium confidence how far visibilities will drop at KBLF and KROA. The fog will dissipate after sunrise with VFR visibility by 14Z/10AM. May take longer for ceilings to lift back to VFR. Storms will develop over the mountains during the early afternoon and then move east into the foothills and piedmont during the mid- late afternoon. There is a high likelihood for VCTS for all of the flight terminals in the central Appalachians this afternoon but timing of MVFR conditions too uncertain to include in the bodyof the TAFs at this time. Bufkit showed a favorable shear profile for more organized storms and the potential for microburst winds within the thunderstorm cores leading to isolated surface gusts of 30-50kts. Coverage of thunderstorms will diminish after sunset in the piedmont. Scattered showers will continue in the mountains overnight. Models suggested ceilings will lower to MVFR with deep westerly winds around 06Z. Have not lowered the ceilings in the TAFS at this point. Extended aviation discussion... An upper ridge of high pressure will remain just south of the area and a residual frontal boundary will remain over the area through Monday. This will allow for periodic, mainly diurnally driven, deep convection. A more widespread sub-VFR potential exists into Friday per a strong wave of low pressure which will ripple east along a stalled front. After the passage of this wave, some decrease in coverage of precipiation is expected over the weekend. In addition to the thunderstorm threat, late night and early morning fog will likely occur at the usual valley locations.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...PM/WP SHORT TERM...PC LONG TERM...PC AVIATION...AMS/PM

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