Area Forecast Discussion
Issued by NWS Blacksburg, VA

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390 FXUS61 KRNK 291119 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 719 AM EDT Thu Sep 29 2016 .SYNOPSIS... 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 today into Friday night. The low will move northeast, away from the region, resulting in drier weather this weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 240 AM EDT Thursday... Appears another active day in store espcly this afternoon as the upper low to the northwest digs toward the Tennessee Valley and another impulse aloft rotates through from the southwest. This looks to again play tag with the stalled surface low and occluded boundary stuck along the Blue Ridge. Bands of added convection likely to take shape across the eastern half as this occurs per latest Cam solutions with coverage rotating north/northwest into northern sections through the evening. However exactly where this takes place and how fast in question given early showers, and idea that this initial axis will shift east, followed by low clouds that may tend to limit instability later on within low level easterly flow. Think best chances of deeper convection will occur just south of the boundary/triple point and perhaps even out west where will have a band under the upper low arriving late. Although lapses likely to be weaker today unless more heating occurs, added cooling aloft and deeper low level southeast flow turning southwest aloft while strengthening supports added severe hail/wind potential. This espcly along/southeast of the boundary near Highway 460 where shear parameters best. Thus after a likely early morning lull as supported by the latest HRRR expect enough coverage to keep overall likely/cat pops in all except the far sw where a weak dry slot may hold. Highest QPF looks to also reside across the easternmost counties with this axis swinging back toward the Virginia Highlands later today. May add Rockbridge to the watch given pockets of heavier rainfall overnight and possible added training bands today. Highs mostly 70s although could get to around 80 southeast if more sunshine develops, while some spots across the north and east may get stuck in the 60s if clouds persist. Upper low should begin to pivot slowly north/northeast overnight allowing the eastern conveyor belt of deep moisture/convergence to lift a bit farther to the northeast late ahead of the residual surface front. This may also push somewhat drier air aloft into western sections late as the weak surface low along the Blue Ridge retrogrades back westward, and a secondary cold front edges east across the far west. Appears loss of instability should again help reduce thunder chances after this evening but lingering heavy rain threat likely to continue at least northeast third through late tonight. Therefore keeping a gradient of likely or higher pops mainly along/east of the Blue Ridge overnight and chances elsewhere given expected slower exodus of deeper moisture. Low temps mainly 50s mountains to mid 60s out east.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 230 AM EDT Thursday... A very large closed low will wobble over the southern Ohio Valley through Saturday night. Through each period, precipitation coverage will become smaller and smaller as dry air gets wrapped into this low. Dry air will start moving over the the southern Appalachains Friday morning, then works north through the day. Rain showers will begin to taper off from south to north behind a short wave axis, finally exiting the Alleghany Highlands and the Hill City of Lynchburg late Friday evening. Even though mid and high levels will remain relatively dry Saturday, low level moisture and afternoon heating may produce a few shallow dark base clouds and a few showers. Overall coverage of showers and measurable rain will be less than 10 percent Saturday afternoon. Temperatures will remain seasonal Friday into the weekend with highs ranging in the 70s, some 60s along ridge tops and lows into the 50s. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 320 PM EDT Wednesday... Closed upper low will lift northeast and reach the St. Lawrence river valley by Sunday night. Then, the low center will open up and weaken as it moves across New England Monday and moves into the Atlantic ocean on Tuesday. The exact evolution of the large scale patterns will affect the eventual track of what is forecasted by NHC to be Hurricane Matthew. The storm may threaten the southeast coast next week. This is being monitored by the NHC and WPC. For much of the extended ISC grids leaned towards WPC which was a blend of the 00Z GFS/GEFS MEAN/ECMWF ENS MEAN. Temperatures will start cooler for Saturday with continued improvement as precip/cloudcover comes to an end, then temperatures begin to moderate Sunday into Wednesday. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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As of 705 AM EDT Thursday... Much of the region has basically dry slotted early this morning with a void in showers between bands just east of the region and weaker showers to the west. However in the wake of the rainfall seeing widespread sub-VFR with IFR in spots that will likely persist into mid morning and perhaps early afternoon east of the Blue Ridge per weak easterly flow. Also vsbys may continue to lower in developing dense fog with MVFR to IFR restrictions possible this morning including some spotty light rain or drizzle. Should see some slow improvement in cigs/vsbys by afternoon with a gradual return to VFR mainly across the west where moisture is a bit more shallow. Once any heating develops should see more showers and possible storms redevelop in bands this afternoon with the best chances along the KHSP-KLYH-KDAN corridor, and then around KBLF/KLWB later in the day. Therefore will focus the more widespread prevailing sub-VFR in these areas with more vicinity mention elsewhere pending the degree of heating. Showers and storms again look to linger into this evening with the best concentration shifting into northern sections overnight before fading. This should again allow for areas of MVFR in shra/tsra this evening, then widespread sub-VFR in fog/stratus overnight. Extended aviation discussion... A deep upper low will remain over the Ohio and Tennessee Valleys Friday into Friday night. 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 north and weak high pressure builds in.
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&& .HYDROLOGY...
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As of 700 AM EDT Thursday... Showers and thunderstorms during Wednesday/Wednesday evening brought locally heavy rainfall of 1 to 3 inches in spots, espcly along the Virginia/North Carolina border. Other areas of isolated heavy rainfall occurred along/east of the Blue Ridge in Virginia. Added bands of showers and storms could redevelop across eastern sections, as well as over the western mountains as an upper level low drifts to the southeast today. Locally heavy downpours could result in another 1-2 inches of rain across eastern locations with a half to one inch over the west. The heaviest rainfall may end up across the southern Shenandoah valley region this evening as bands tend to merge. Thus the flash flash watch continues for a few far eastern counties northwest to Rockbridge county where the best potential exists for heavier rainfall capable of producing flooding or flash flooding. Rises along mainstem rivers could reach half bankfull or more in spots, mainly over eastern sections, where heavier QPF may continue and runoff will be best.
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&& .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Flash Flood Watch until 6 PM EDT this evening for VAZ024-035- 044>047-058-059. NC...None. WV...None.
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&& $$ SYNOPSIS...AMS/JH NEAR TERM...JH SHORT TERM...RCS LONG TERM...KK AVIATION...AMS/JH/WP HYDROLOGY...JH

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