Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 010317 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1117 PM EDT Fri Sep 30 2016 .SYNOPSIS... A strong upper level area of low pressure centered over Kentucky will slowly drift to the north later tonight into Saturday. This system will combine with a residual stationary front across the region to produce periods of showers and thunderstorms into late tonight for central and eastern Virginia. The low will move northeast, away from the region, resulting in drier weather this weekend. && .NEAR TERM /THROUGH SATURDAY/...
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As of 1110 PM Friday... Expect lingering showers over the Alleghany Highland toward Lynchburg through early overnight, while a shower or two also occurs in portions of Southeast WV where some deeper moisture convergence resides, though drier air aloft is keeping things mostly at bay. For the overnight we will see some clearing over the southern half of the forecast area roughly from Bluefield east to Danville, while clouds stick around in the Alleghanys over to Lynchburg corridor. Question again is fog formation and how widespread and dense it will become. Think will see fog in patches across most of the area where it clears but with some drier air it may vary at times. Still think dense fog will be a factor around dawn in the New River Valley, southern WV and portions of the VA/NC foothills east toward Southside Virginia. Another new weather issue will be rises along the main stem rivers. Given that 2-5+ inches of rain fell in portions of the Roanoke River basin, it looks like the river at Altavista and Randolph will go into minor flood Saturday. It will be close especially for Altavista, and right now the forecast takes it about 1/2 foot above flood stage which mainly affects pasture and low lying fields. No other major changes to the forecast with lows ranging from the upper 40s in the NC mountains to lower 60s across the Virginia Piedmont. Previous early evening discussion... Flash flood watch expired at 6pm. Coverage and intensity of showers has lessened today compared to earlier and yesterday. High-res models, radar and meso-analysis continues to paint the best shower threat from Greenbrier county WV southeast toward Lynchburg and Buckingham, VA through mid evening, then shifts the coverage further northeast overnight. Instability weakening to just a small area over southside Virginia into the NC Triangle area where SBCAPES at 23z were still in the 1000-2000 J/KG range. Shear still high but drier air aloft is acting to hinder some development. As we head into the overnight overall concern may switch to fog especially in areas that clear out, as ground is nearly saturated and airmass aloft is drying out. Could see potential dense fog advisory for portions of the area from southern WV into the New River Valley. Will monitor trends to see if materializes. Previous valid discussion from early this afternoon... For the overnight and into the day Saturday, the upper low will finally begin to lift north allowing drier air aloft to overspread the entire region from southwest to northeast. This should result in a continued decrease of shower coverage with time with the entire forecast area clearing out for Saturday. With diminishing cloud cover, temperatures should dip closer to the seasonal norm with temperatures falling into the 40s for North Carolina mountains and from the New River Valley west. Foothills should dip into the 50s...and low 60s farther north and east where clouds linger. For Saturday...temperatures expected to rebound into the 70s.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 330 PM EDT Friday... The closed low will continue to slowly migrate off to the northeast through the period as it continues to fill and open up, dragging a well occluded surface low with it. This will position our region essentially in the dry slot under a neutral thermal advection regime with slight warming aloft. This should yield essentially a dry forecast through the weekend. By Sunday night, high pressure pushing in form the upper midwest will nudge a cold front to our western doorstep before it stalls, but the best forcing and instability will be shearing off to our northwest and any chances for frontal precipitation will remain off to our west. The upper low will give way to ridging in the eastern US through the early part of next week, allowing a large area of high pressure to settle over New England and wedge down the east side of the Appalachians. Moisture will be lacking and isentropic lift over the wedge will not yet be appreciable do Monday looks to remain dry as well. Expect temperatures to be seasonable with highs near 80 east of the Blue Ridge and in the low/mid 70s west. Lows will range from well into the 40s in the valleys west of the Ridge to the upper 50s east. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 330 PM EDT Friday... The big variable mid to late week lies with the potential track of TS Matthew as it is expected to turn north and move up the Atlantic coast. The latest guidance indicates the tropical system will remain far enough to our east to keep direct effects of this system out of our region. However, the wedge will remain in place and the squeeze between the wedge and the tropical system will create enough overrunning to generate precipitation by late Tuesday/Tuesday night especially in the east and continuing through the end of the period. Temperatures in the wedge will remain cool and generally several degrees below normal. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... As of 720 PM EDT Friday... Showers may stick around a few more hours near a LWB-LYH corridor possibly near DAN/ROA as well. Overall terminals will be rainfree this period. Main concern heading into overnight will be fog and low clouds. Already seeing lower cigs at BLF. Drier air aloft working in from the south combined with very moist ground and light winds should favor fog formation. Think most sites will drop to IFR or worse after midnight, which will vary between fog and/or low stratus. Saturday, winds stay light but turn southwest. Fog and low clouds will be slow to lift but overall should be VFR everywhere by 15-17z. Extended aviation discussion... The deep upper level low will finally shift farther to the north by Saturday Night and away from the region on Sunday. The weather will trend back into a dry pattern with mainly VFR conditions next week, aside for river valley fog in the mountains resulting in brief period of late night early morning LIFR conditions at some of the mountain valley airports. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...PM/WP SHORT TERM...MBS LONG TERM...MBS AVIATION...PM/WP

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