Area Forecast Discussion
Issued by NWS Blacksburg, VA

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422 FXUS61 KRNK 261127 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 727 AM EDT Wed Jul 26 2017 .SYNOPSIS... High pressure over New York will be wedging southward over us today. The high moves southeast off the Delmarva tonight. A front will approach from the northwest Thursday afternoon, sliding across our area Friday afternoon into Friday night. && .NEAR TERM /THROUGH TONIGHT/... As of 715 AM EDT Wednesday... Update to forecast includes increasing cloud cover as low clouds have spread all the way into southeast WV per easterly fetch. Should see skies scatter out by midday/early afternoon under late July sunshine. Previous discussion from early morning... Overall seeing more low level moisture/clouds than most models predicted this morning, with latest surface analysis showing a decent easterly fetch in the pressure gradient over the Blue Ridge and points east while surface winds have amped up a bit in places like Mount Airy, NC out of the northeast. Have bumped up cloud cover to account for this. As far as today goes, showers should be isolated to widely scattered and confined to the Blue Ridge generally south of Blacksburg-Floyd, VA with best coverage across the Boone area and south with better low level moisture convergence and deeper moisture. Overall still looking at skies becoming mostly sunny across much of by late morning with scattered to broken cumulus this afternoon. With an easterly to southeast wind, temperatures should below normal for highs today, ranging from the mid 70s in the NC high country and higher terrain of Virginia, with upper 70s to lower 80s in the valleys, to mid 80s in the piedmont/foothills. Tonight, surface high shifts southeast and winds turn more south to southwest allowing dewpoints to creep back up. Limited showers in the southern Blue Ridge should fade by late evening. With flow more southerly should see less upslope induced stratus, though some of the models still indicating potential for stratus/stratocu along the Blue Ridge into the piedmont. Lows tonight will be in the mid to upper 60s across most areas, with patchy fog possible in the mountain valleys. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM EDT Tuesday... High pressure will weaken and slide east into the Atlantic ocean Thursday, as a cold front approaches from the west. The eastward progress of the frontal boundary will be slowed by the zonal flow aloft. The cold front should reach the mountains Thursday night into early Friday morning, then move east of the Blue Ridge Friday afternoon as an upper level low tracks across the Great Lakes into the Mid Atlantic region by Friday night. As the larger scale mid level trough deepens and expands Thursday, the combination of diurnal heating, low level convergence and orographical lift should generate scattered showers and thunderstorms across the mountains early Thursday afternoon. This convection will slowly drift eastward Thursday evening and Thursday night. SPC in the day 2 convective outlook continues to have much of the forecast area in a slight risk for severe thunderstorms. The primary threat is the potential for damaging winds and heavy rains. There remains some uncertainty on the coverage and potential of severe weather with NAM, GFS and ECMWF showing different solutions and timing. Differences abound with respect to amount, intensity, location of convection associated with this lead trough. The potential for severe weather is dependent on amount of instability (best instability north of us) and development of Ohio Valley Convection. Details will become clearer with time. High temperatures will be slightly warmer than normal Thursday with low to mid 80s expected west of the Blue Ridge and upper 80s to lower 90s in the east. Linger instabilities and a 30-40 knot low level jet could allow some strong storms to pass over the area Thursday night into Friday morning. Low temperatures Thursday night will range from the lower 60s in the mountains to the lower 70s in the piedmont. Showers and thunderstorms will spread east on Friday and reach the Piedmont by Friday night. The best dynamics with this front will remain north of our area over Pennsylvania and Maryland and move to along the New England coast Friday. However, scattered strong to severe thunderstorms may be possible across the foothills and the Piedmont. This is where the gfs and ecmwf paint the best helicity, capes and sfc computed lis. SPC Day 3 has a marginal to slight across our forecast area for Friday with the potential for organized fast-moving bands of storms. The main questions at this time revolve around timing of synoptic features. The severe potential could increase if the front is slower placing frontal passage during peaking heating Friday afternoon. Cloud cover and convection will result in cooler highs for Friday with readings from around 70 degrees in the western mountains to the mid 80s in the piedmont. By Midnight, thunderstorms should taper off leaving just lingering showers Friday night. Low temperatures Friday night into saturday morning will generally range from the upper 50s in the western mountains to the upper 60s in the piedmont. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 AM EDT Wednesday... The upper level trough will be overhead Saturday and move east Saturday night into Sunday. Heating under this cold pool may result in scattered diurnal showers to the region Saturday afternoon. High temperatures will be cooler than normal with reading from around 70 degrees in the mountains to the mid 80s in the piedmont. Surface high pressure will build southeast over the region Sunday. The high center will slide east into Midweek. This ridge of high pressure will keep the area cool and dry. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 724 AM EDT Wednesday... Low clouds and MVFR cigs worked all the way into WV this morning per a tighter gradient allowing for more upslope and easterly fetch of Atlantic moisture. Should see cigs start to lift to VFR and scatter out some by midday with BCB the last to go above MVFR at 18z. Should be mainly a VFR forecast, through tonight, Exception will be LWB fog still a possibility so not going any lower than 3sm, as another day of drying wx should limit fog. Aviation Extended Discussion... Should start to see a front approaching with better threat of showers/thunderstorms Thursday into Friday. Stronger storms and heavy rain possible in and around the mid-Atlantic/Ohio Valley region into the Carolinas this time frame so be prepared for sub-VFR at times. Outside of storms expect VFR conditions, with possible late night fog by Friday morning. Saturday looks drier with northwest flow, but could see lingering low end VFR/high end MVFR ceilings in SE WV along with a few added shra/tsra mainly southern sections Saturday afternoon. Expect widespread VFR to return Sunday under high pressure following the front. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...KK LONG TERM...KK/RCS AVIATION...AL/JH/WP

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