Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180556 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 156 AM EDT Tue Jul 18 2017 .SYNOPSIS...
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An upper level trough should head toward the coast later today and could spark isolated showers and thunderstorms in the mountains. High pressure will bring drier conditions later in the week. Upper level ridging should make it quite hot and humid by Friday and the upcoming weekend.
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&& .NEAR TERM /THROUGH TODAY/...
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As of 155 AM EDT Monday... Expect with some overnight clearing to again see fog development espcly where earlier heavy rainfall occurred and across the western mountain valleys. Left temps similar to previous with overall lows in the 60s. For Tuesday...any overnight fog should burn off with partly sunny skies. Skies should fill in with cumulus readily associated with cold pocket of air aloft (-12C at 500 mb). Related mid-level trough should be slowly moving eastward into coastal NC through the daylight hours, leaving the forecast area on the northern side of the trough. Thus it appears forcing likely to be being even more limited than today. Though the 12z/17th GFS and ECMWF solutions try to paint much of the forecast area with some light QPF, it`s not clear if the coverage will be that widespread. Differential heating along the terrain may be the only substantive source of lift. Started with the global model PoPs but also blended some of the available mesoscale models to show the spatial coverage variation. Namely: isolated/slight chance PoPs for the VA/upper NC Piedmont and in southeastern WV, scattered/chance PoPs along the Blue Ridge. As the case today, storms should be slow moving in a weak shear environment, but weaker lapse rates should keep thunderstorms more general/garden-variety. Highs in the upper 70s/mid 80s mtns with low 90s confined to the Piedmont.
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&& .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 326 PM EDT Monday... You can expect an increase in temperatures this period as the axis of the upper trough moves from the piedmont of VA/NC east to the Atlantic coast. 5h heights will stay mainly in the 591 DM range, while 8h temps rise from +18C to +20-22C. At the sfc, high pressure is going to be in place over the southern Appalachians, with lee trough in the piedmont. Weak convergence along the Blue Ridge and differential heating may lead to isolate to widely scattered storms Wednesday afternoon/evening. Appears subsidence behind the trough may limit coverage. More subsidence/drying aloft will keep any convection at bay Thursday so expect a mostly sunny/hot day, with highs in the mid 80s to near 90 mountains, to lower to mid 90s foothills/piedmont. Heat indices should not be an issue as dewpoints will be in the lower to mid 60s. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 325 PM EDT Sunday... Keeping the theme of hot and humid with daily threat of storms. Will be on the northern periphery of upper high, so any convection on the southern belt of the westerlies may scrape our area in the Fri-Sun time frame. Models diverge Monday with new ECMWF showing a trough digging through the Ohio Valley which is more favorable for convection. The GFS showing less amplification with better ridge over the southeast. With this being 7 days out will keep token low chance pops in mainly west. Saturday-Sunday appear to be hottest days with 8h temps around +24C. Looking at upper 80s to around 90 west, to mid to upper 90s east. Convection and any upstream blowoff of high clouds may inhibit this though. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 155 AM EDT Tuesday... An upper level trough will pass overhead during the early morning hours. Light to calm winds are already situated throughout the region with some spots have wet ground due to recent rainfall. With convection from the previous evening now dissipated and skies clearing, the setup for fog seems quite likely for all TAF sites except for ROA where no rain was observed. Highest confidence for IFR conditions is in place for BCB and LWB where even LIFR is possible toward sunrise. Fairly high confidence exists for DAN and LYH with IFR due to more surface moisture given the lower spread in temperatures and dewpoints. BLF fog is questionable at this point given the higher spread between temperature and dewpoint, and it could be more borderline IFR to just MVFR if any develops. Any overnight fog should quickly dissipate after sunrise on Tuesday morning. VFR conditions should prevail through the remainder of the TAF forecast period. Some cumulus/stratocumulus development is likely by the afternoon, and there is a potential for isolated showers and thunderstorms. The limited coverage and extent of this convection makes it too uncertain for any mention of thunder, but VCSH was given to BCB as that site has the highest chance for any activity compared to the other TAF sites. Whatever activity does form should vanish by Tuesday night. Aviation Extended Discussion... The upper level trough will head offshore by Wednesday, which will open our region to a large upper level ridge moving eastward from the Plains. Convective activity should become even more sparse as capping takes place aloft. Overall, it appears that VFR conditions will primarily reign through the daytime hours. There could be some MVFR/IFR fog and ceilings during the early morning hours in the cooler mountain valleys like LWB. Hot and humid weather will prevail through the end of the week.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PW NEAR TERM...AL/JH SHORT TERM...WP LONG TERM...WP AVIATION...PW

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