Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 200322 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1122 PM EDT Fri May 19 2017 .SYNOPSIS... High pressure off the southeast Atlantic Coast will continue to produce an unseasonably warm and humid southwest flow of air across the forecast area into tonight. This will combine with an approaching weak cold front to produce additional showers and storms especially over the mountains on Saturday. Unsettled weather will then continue through into early next week with shower chances again increasing ahead of another cold front arriving from the west by Monday. && .NEAR TERM /THROUGH SATURDAY/...
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As of 1115 PM EDT Friday... Upped pops over the west based on latest trends. High-res models/radar showing more agreement on nudging convection further southeast toward the SW Va mountains into the NC mountains overnight. Still should weaken with airmass stabilizingbut some decent instabilities remain south of line of convection in eastern KY toward the Cumberland Gap into the NC mountains. Expecting less thunder north of a Bluefield to Lexington VA line. Previous discussion from 1012 pm... A line of showers/thunderstorms shifting toward the Greenbrier/Summers County area. High-res models having a hard time keeping up with speed but have the general idea right of best threat of showers through the overnight to stay across the WV mountains into the Alleghanys and Mountain Empire. 00z RNK sounding showing SBCAPE of just under 1000 j/kg. RAP mesoanalysis indicating best CAPE across eastern KY south into NE TN. Storms over KY will have to be watched as they move into this unstable air through the next few hours, though with nighttime expect instability to weaken with time. Previous discussion from late afternoon... Overall shower/thunderstorm threat has ended, with lingering showers east of Staunton River SP and over the NC/TN border near Beech Mountain, NC. High-res models are keen on keeping most of the forecast area dry this evening, until convection upstream over northern KY/southern Ohio shifts east-southeast toward our WV mountains by midnight. Have updated pops to account for the little to no coverage, and may have to dry it even more per latest radar trends. Otherwise, forecast on track. Previous discussion from mid afternoon... Clusters of deeper convection continue to evolve mainly over southern/southwest sections in an area of convergence just south of a weak mid level wave passing to the north and on bottom of a weak residual surface trough. Latest short term models drive a loosely organized area of convection into eastern/southeast sections through late afternoon so upping pops for a few hours of likelys across the southern third into early evening. Otherwise still expecting coverage to fade after sunset if not sooner as best lift shifts back north closer to the surface cold front in the southern Ohio Valley. Some of this coverage may sneak back southeast into espcly northern portions of the area overnight but should be quite widely scattered at this point. However will leave in some low pops to cover this as well as for the potential to see another complex clip the northeast sections late. Should also see more patchy fog around espcly given coverage of convection from earlier. Lows in the muggy 60s overall. Front will gradually backdoor in from the northeast on Saturday but slower than earlier as models indicate building heights over top the low level cool pool that will attempt to slip back toward the Blue Ridge. This slower scenario would mean more instability developing ahead of the boundary espcly from just east of the Blue Ridge westward during the afternoon. Guidance shows a lobe of high 850 mb theta-e over the western half beneath good upper diffluence that could mean another round of more widespread showers and storms outside of the far northeast sections. Thus upped pops to higher chance/low likelys west and kept chance to low chance eastern sections. Expect low level northeast flow including lower dewpoints and stability to gradually shift west by late in the day but all dependent upon convective coverage and how much more it slows the boundary up. High temps quite tricky with potential for southern and southwest sections to zoom back into the 80s while the northeast remains stuck in the cooler 70s per latest warmer Mos.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY/... As of 300 PM EDT Friday... Surface front should finally spill westward into far western sections Saturday night in the wake of earlier convection before being bumped back slowly east on Sunday as the main upper trough to the west heads northeast. May see a lull in overall rain coverage Saturday night with mainly low clouds possibly persisting Blue Ridge and some drying across the northeast. Kept in some chance pops mainly mountains for now with only spotty showers out east. Expect any significant cooling to stay just to the north although some dewpoint drying could occur southwest to the eastern slopes per latest Nam. Otherwise lows still muggy...mainly low to mid 60s. Surface cold front associated with the upper trough to the west will drift east Sunday with its axis of deeper moisture working into the mountains by later in the day. Guidance shows quite an instability gradient from stability within deeper northeast flow across eastern sections to modest Cape values over the west where will be in the convergence zone of the residual front and lift ahead of the cold front. Therefore going to a gradient of increasing likely pops from west to east over the mountains Sunday including some thunder to mainly lower shower chances in the east in the afternoon. Highs should be much cooler as the wedge and clouds remain in place resulting in highs mostly lower to mid 70s at this point. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... As of 310 PM EDT Friday... 500 MB flattens during the first half of the week. Upper ridge remains over the southeast and southern Gulf of Mexico. A piece of the upper low redevelops and heads into the Ohio Valley by Thursday. ECMWF has best lift and good short wave crossing the Mid Atlantic region on Wednesday. A cold front passes through the area early Monday. A second front crosses through on Wednesday leading in a colder air mass over the area for Wednesday and Thursday. ECMWF shows the potential for some gusty winds behind Wednesday`s front. Expecting showers and thunderstorms along each of the front with the potential for heavy rain. Overall troffing and periods of rain will result in below normal temperatures for much of the week. Have trended toward cooler daytime temperatures for Monday through Friday. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... As of 710 PM EDT Friday... Quiet evening aviation wise now that convection has exited east. Will have to watch for fog formation overnight, especially where it rained. However, next upstream wave will bring some clouds back into the mix overnight which may hamper fog formation, or keeping it from getting dense. Confidence high that IFR vsbys will occur at BCB/LWB with MVFR LYH/DAN. Frontal driven storms over the Ohio Valley this evening may shift to near BLF/LWB after 04z, but confidence is low, so not adding them to the tafs. The front is forecast to enter the forecast area Saturday, entering the area backdoor style with a northeast push of wind Saturday and Saturday night. Models suggest that drier air may now be slower to push west of the Blue Ridge during the afternoon so added convection resulting in sub-VFR could occur after 18z, so added VCTS at LWB/BLF/BCB. May see some MVFR cigs in ROA/LYH once backdoor front move southwest. Extended Aviation Discussion... The front will then stall over or just south of the region early Sunday. With the front over the area, there will be an opportunity for added showers and thunderstorms, especially during the peak heating hours of the day over the western mountains by late Sunday. However expect combo of low clouds within the wedge and showers over the west to result in sub-VFR for most of Sunday. More widespread showers and storms may occur ahead of the front Sunday night with added poor flying conditions overnight. The front will cross the forecast area Monday, dry weather returning Monday night into Tuesday. Another front may then bring the next round of showers and subsequent MVFR by Wednesday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/PM/WP NEAR TERM...JH/WP SHORT TERM...JH LONG TERM...AMS AVIATION...JH/PM/WP

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