Area Forecast Discussion
Issued by NWS Blacksburg, VA

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247 FXUS61 KRNK 290511 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 111 AM EDT Thu Sep 29 2016 .SYNOPSIS... A strong upper level area of low pressure will moving from the Great Lakes to the Tennessee Valley tonight and Friday. This system will combine with a low pressure system over the Mid Atlantic region to produce several periods of showers and thunderstorms tonight through Friday night. The low will move northeast, away from the region, resulting in drier weather this weekend. && .NEAR TERM /THROUGH TODAY/... As of 935 PM EDT Wednesday... Severe Thunderstorm Watch 488 will be allowed to expire at 10pm. Still with high shear environment and upper level support isolated large hail will be a threat along/east of the Blue Ridge for a few more hours. Starting to watch for hydro concerns, and current flash flood watch covers the area we are most concerned about overnight into Thursday. Could possibly see it being extended west toward Roanoke, but will wait and see how the heavier rains set up over the next several hours. Previous evening discussion... Cleared portions of Severe Thunderstorm Watch 488 roughly west of a line from Lynchburg to Martinsville to Yadkinville. Best instability resides east of this line, but especially over central NC. Still seeing good shear values along and east of the Blue Ridge. HRRR shows redevelopment this evening over the foothills of NC north into the New River and Roanoke Valleys. Will have to watch for isolated wind issues, but given loss of heating threat should stay isolated. Previous discussion from mid afternoon... Closed upper low over Michigan will fill slightly and move south into southern Indiana by Thursday morning. Strongest vorticity advection reaches the central Appalachians late tonight. Cold pool aloft also moves over the mountains late tonight and Thursday with 500 mb temperatures down to -20 in far southwest Virginia. Diffluence aloft will also produce some lift with the central and eastern Virginia within the right rear quadrant of the upper jet overnight. With the abundant lift and moisture east of the Blue Ridge, will be increasing probability of precipitation on Thursday. A surface cold front with associated with the upper low will approach the Appalachians Thursday morning. Models bring a chance of showers into southwest Virginia with this feature by Thursday afternoon. By late Thursday this front will merge with the main surface low over Virginia. Best instability and most favorable shear profiles are in the piedmont this afternoon and tonight. In locations with heating the convective available potential energy may reach 2500 J/KG this afternoon. The enhanced low level winds will be along the boundary north of a HSP to FVX line. Have kept maximum temperatures below guidance on Thursday based on the amount of rain and cloud cover expected. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... As of 320 PM EDT Wednesday... A closed upper low centered near SDF Thursday evening will stall across the Ohio River Basin through Friday night. At the same time, a series of disturbances, including complex frontal system will interact with the deep atlantic moisture and pulse along the mid Atlantic Seaboard. As a result, scattered to numerous showers and thunderstorms will continue around the low and along the boundary. Some of the thunderstorms could be strong with gusty winds,hail and heavy downpours Thursday evening into Thursday night. The swody2 has placed much of the CWA in Marginal risk of severe with main threat being hail and gusty wind. Convection is expected to diminish with the loss of daytime heating and the subsequent instability axis overnight Thursday into Friday morning. Low temperatures Thursday night will range from the upper 40s in the mountains to the lower 60s in the Piedmont. Considerable clouds with scattered showers and a few thunderstorms will continue Friday. High temperatures Friday will remain relatively cool with readings from the mid 60s in the Mountain to the mid 70s in the Piedmont. Isolated to scattered showers will continue Friday night. The Best chances for rain will occur across the North. Low temperatures friday night will vary from the mid 40s in the western Mountains to the upper 50s in the Piedmont. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 320 PM EDT Wednesday... Closed upper low centered near Saturday morning 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 /06Z THURSDAY THROUGH MONDAY/...
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As of 1257 AM EDT Thursday... Bands of convection persist across parts of the region tonight, with the best coverage along/east of the Blue Ridge. Expect lingering coverage to perhaps impact all locations excluding KBLF overnight but too iffy to include much more than a VCSH or tempo group through daybreak. Otherwise looking at VFR to MVFR cigs with pockets of IFR mainly around KLYH and where showers/clouds may fade allowing for fog formation to take shape. As an upper low moves south of the Great Lakes Thursday...a cold front will approach the Appalachians from the west. This front will merge with a stationary low pressure system over Virginia on Thursday. This will result in added rounds of showers and storms espcly during the afternoon with perhaps a lull during the morning. Appears cigs may also rise to MVFR to VFR by midday before convection redevelops espcly in a band across the east and another with the front approaching from the west. Still uncertain with overall coverage but given high probability will include a prevailing group in spots with vicinity mention elsewhere. Extended aviation discussion... A deep upper low will remain over the Ohio and Tennessee Valleys through 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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VA...Flash Flood Watch through this afternoon for VAZ035-044>047- 058-059. NC...None. WV...None.
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&& $$ SYNOPSIS...AMS NEAR TERM...AMS/WP SHORT TERM...KK LONG TERM...KK AVIATION...AMS/JH/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.