Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 292039 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 439 PM EDT Thu Sep 29 2016 .SYNOPSIS...
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A strong upper level area of low pressure will remain just west of the mountains today into Friday. This system will combine with a residual stationary front across the region to produce periods of showers and thunderstorms into Friday night. The low will move northeast, away from the region, resulting in drier weather this weekend.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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As of 430 PM EDT Thursday... Upper low was along the Ohio River as seen in all satellite loops. A well defined area of mid level drying over the central and southern Appalachians into the eastern Great Lakes. The upper low is forecast to drift southeast into Kentucky then loop back into Indiana. Good consensus in the guidance with the track of the low. As a result there will be little change in the weather pattern tonight or Friday. Surface through low level winds will keep dew points in the 60s in all but the southwest tip of Virginia and extreme western North Carolina. This will fill low clouds and fog in over the foothills and to the east. The western edge of multiple bands of showers and thunderstorms will gradually move northeast tonight and Friday. Have taken a blend of bias corrected MET and MAV guidance for lows tonight. Areas closer to the upper low, west of Bluefield and Wilkesboro will have the coolest temperatures overnight. Highs on Friday will very dependent on cloud cover, similar to today. Locations that have more sunshine will be close to 80 degrees. Spots that stay in the low clouds longer may only reach the lower 70s.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY NIGHT/...
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As of 330 PM EDT Thursday... The closed low over the Ohio valley that has been dominating the upper level pattern will slowly pull up to the Great Lakes region as it starts to 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 a weekend forecast devoid of significant precipitation though an isolated shower may still be possible. By sunday night, high pressure pushing in form the upper midwest will nudge a cold front to our western doorstep but the best forcing and instability will be shearing off to our northwest so the chances for any frontal precipitation encroaching Sunday night are low.
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&& .LONG TERM /MONDAY THROUGH THURSDAY/...
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As of 330 PM EDT Thursday... The upper low will give way to ridging in the eastern US through the early part of next week. This stall the approaching front and allow a large area of high pressure to settle over New England and wedge down the east side of the Appalachians. The big variable lies with the potential track of TS Matthew as it is expected to turn north and move up the Atlantic coast. The exact track of Matthew will determine how much, if any, precipitation it can push into the region from the east and how much overrunning precipitation will develop as it interacts with the wedge. Right now, the most likely scenario is for some light overrunning precipitation to develop by Tuesday and increase a bit into Wednesday especially in the east, with any significant effects form Matthew remaining to our east.
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&& .AVIATION /20Z THURSDAY THROUGH TUESDAY/... As of 215 PM EDT Thursday... Low clouds along the Blue Ridge an in the foothills of Virginia and North Carolina have either lifted to MVFR or eroded as of the 18Z start of the TAF forecast period. Scattered thunderstorms have already developed. The best probability of precipitation will be in three main bands. The first will be from the Tennessee/North Carolina border north into central West Virginia. Another band of storms will line up from the North Carolina foothills into southeast West Virginia. Confidence is lower in the formation of storms farther east but this bans would be mainly east of a KDAN to KLYH line. The environment favorable for hail this afternoon and evening, with the best probability of any hail possibly impacting an airport would be at KLWB or KBLF. Best concentration shifts into central and northern Virginia late tonight. This should again allow for areas of MVFR to IFR ceilings to fill in again with fog overnight. With little movement of the low pressure system at the surface or upper levels, confidence is high in the persistent easterly upslope winds through 12Z/8AM. Have added LLWS in for KLWB late tonight. Similar to today, improvement in conditions will be slow after sunrise. Ceilings are likely to not reach VFR until after 15Z/11AM. Extended aviation discussion... A deep upper low will remain over the Ohio and Tennessee Valleys into Friday night with a slow drift to the northeast on Saturday. This will keep variable clouds, MVFR cigs, and periods of -SHRA across the region through much of the period. Should finally see VFR return during Saturday and continue into Monday as the upper low lifts northeast and weak high pressure builds in. && .HYDROLOGY...
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As of 430 PM EDT Thursday... Development of thunderstorms had been early this afternoon mainly over the mountains. Storms were lining up and moving from south to north. MSAS analysis showed most unstable air was over the northwest North Carolina mountains and from central North Carolina into eastern Virginia. Highest precipitable water values were east of Lynchburg and Danville. Until the threat of thunderstorms diminishes after sunset, will keep the flash flood watch going.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Flash Flood Watch until 6 PM EDT this evening for VAZ024-035- 044>047-058-059. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...MBS LONG TERM...MBS AVIATION...AMS/JH HYDROLOGY...JH

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