Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 160100 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 900 PM EDT Wed Aug 15 2018 .SYNOPSIS... High pressure will bring overall fair weather to the Appalachians and central mid Atlantic region tonight. This high will then slide off to our east tomorrow and bring a chance for showers and thunderstorms back to the forecast. Low pressure over the Great Lakes will track east Friday and Saturday pushing a cold front into the mid Atlantic region, with a good chance for showers and thunderstorms through the weekend and into the first part of next week. && .NEAR TERM /THROUGH THURSDAY/... As of 845 PM EDT Wednesday... Spotty light showers just west of the region continue to fade this evening upon moving into weak ridging aloft and subsequent mid level dry air seen on evening raobs. Latest analysis also showing little in the way of instability so expect any residual light showers to fade later this evening as well as upstream convection that may approach late. However degree of high/mid clouds remains iffy overnight with swath of debris clouds likely to linger over the next few hours. This may limit fog formation at least early on so removed most mention until after midnight when expect some decrease in cloudiness. Also with dewpoints up slightly espcly east, bumped up lows a bit and if clouds linger over the west then may need to increase even more later on. Otherwise planning to stay dry overnight under partly cloudy skies west to mainly clear east, with lows ranging from the low 60s mountains to upper mid/upper 60s elsewhere. Previous discussion as of 245 PM EDT Wednesday... Radar is essentially devoid of returns early this afternoon but visible satellite imagery shows some good Cu towers as an approaching short wave works on some surface instability with marginal lapse rates aloft. Thus, expect a slight chance for widely scattered/isolated showers/thunder along and west of the Blue Ridge, primarily the southern Blue Ridge into the mountains of NC before any convective elements dissipate this early evening. Expect mid/high clouds upstream to move over the region tonight, but there are indications the clouds will be breaking up a bit as they go. With this in mind, will go a bit below guidance as expect there will be a few windows for radiational cooling to occur. This should also result in another round of valley fog west of the Blue Ridge tonight. Lows tonight look to be in the mid/upper 60s east of the Blue Ridge with upper 50s/around 60 to the west along with some cooler readings in the valleys. If clouds come in thicker than anticipated, will have to revisit the temperature and fog forecast. Surface high pressure will be drifting off to the east tomorrow, allowing for southwesterly return flow to develop. The best isentropic lift will follow the strongest 850mb winds up into the Ohio valley to our west, but there looks to be enough forcing for some scattered/widely scattered showers/thunder mainly along and west of the Ridge again tomorrow afternoon. Highs tomorrow will be a bit warmer with lower 90s east of the Ridge, mid/upper 80s to the west. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 300 PM EDT Wednesday... Fairly typical summertime pattern with weak flow aloft at the southern and central latitudes of the CONUS and stronger activity along and north of the Canadian border. Global models in general agreement however in trying to reestablish troughing in the eastern half of the CONUS as the subtropical ridge expands somewhat across the desert southwest. This will allow for increasing southwest flow aloft, increasing humidity and higher chances for mainly afternoon/evening convection both Friday and Saturday, The best chances for showers and thunderstorms will be in the west closer to the best upper support and deeper moisture but mesoscale interactions likely to support scattered storms elsewhere as well. Daytime high temps will be moderated by considerable cloudiness while reverse process in effect during the overnight yielding generally above normal lows. Humidity will again become more noticeable with dewpoints ranging from the mid-60s northwest to low 70s southeast. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 300 PM EDT Wednesday... Short-wave ridging or least zonal flow builds in for later Sunday into Monday as the first trough lifts out. Precipitation chances will decline somewhat Sunday and Monday but cannot remove pops entirely under a still moist and conditionally unstable air mass. Yet another trough is forecast to develop over the central U.S. early next week. This will be fairly amplified for what is still mid- summer, especially as advertised by the 12z ECMWF and CMC which spin up a fairly strong surface low (sub-1000 mb) for the season over the mid- to upper Mississippi Valley late Monday into Tuesday. This feature lifts north into the Great Lakes by Wednesday with a potentially broad shield of precipitation along and ahead of a frontal boundary over the central states and moving into parts of the Ohio valley and the western portions of our CWA Tue/Wed. GFS is considerably less aggressive with this feature but general pattern is similar. Either way precipitation chances will be on the increase early to mid-week. Little significant change in temperatures expected with no significant heat but plenty of humidity and fairly warm overnight temperatures owing to high moisture and clouds. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... As of 655 PM EDT Wednesday... Still looking at mainly VFR this evening with mainly some passing mid/high clouds after late afternoon cumulus fade. Main uncertainty is with the extent of these mid clouds overnight and the affect on radiational cooling that could lead to fog formation espcly in the valleys. Models continue to hint at some fog over the west late but probabilities remain low of seeing widespread fog/stratus given so much debris cloud around at least early on. Thus plan to back off low vsbys a bit but still appears a brief period of at least IFR vsbys/cigs possible at KLWB and KBCB with MVFR at KDAN toward daybreak. Any fog/stratus will burn off Thursday morning with VFR expected all sites into the afternoon. Widely scattered showers/thunder may develop Thursday afternoon but given better forcing to the west through most of the valid period wont include any mention at the TAF locations at this point. Winds will generally be light tonight before turning southwest at 5-10 knots Thursday afternoon. Continued medium confidence in sub-VFR tonight. High confidence other parameters through Thursday. Extended Discussion... Scattered afternoon and evening showers and storms will be possible at airports west of the Blue Ridge Thursday night. The next cold front and chance for more widespread showers and thunderstorms with associated MVFR conditions arrives on Friday and will keep chances of showers and thunderstorms through Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...JH/MBS SHORT TERM...PC LONG TERM...PC AVIATION...AMS/JH/MBS

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