Area Forecast Discussion
Issued by NWS Blacksburg, VA

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664 FXUS61 KRNK 181907 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 307 PM EDT Fri Aug 18 2017 .SYNOPSIS... A weak cold front will cross the mountains from the west this evening before sliding southeast of the region overnight. The front will remain over the Carolinas Saturday into Sunday before dissipating. High pressure works in from the Ohio Valley during the weekend, then overhead Monday resulting in drier weather across the region. && .NEAR TERM /THROUGH SATURDAY/... As of 245 PM EDT Friday... Surface cold front now just west of the mountains will slide slowly east reaching the Blue Ridge late this evening before exiting to the southeast overnight. Best instability remains across eastern sections where the flow has backed a bit and dewpoints remain higher. Elsewhere rather well mixed westerly flow has tended to limit convergence/development with more widely scattered coverage expected through late afternoon over the mountains. Best coverage including isolated severe potential appears across the piedmont espcly northeast sections where slightly stronger winds aloft under a passing vort tail may enhance bands a bit. Thus keeping low likely to chance pops mainly east into early evening with most showers out of the southeast around midnight as seen off the latest HRRR. Weak cool advection along with slightly lower dewpoint air will follow the front in from the northwest by morning allowing lows to dip well into the 60s mountains, while lingering closer to 70 southeast. Fog likely limited to the deeper valleys and eastern sections that possibly see more showers through early evening. Front sags into the Carolinas before stalling Saturday in advance of the next shortwave trough that will approach the region during the afternoon. This should basically put the area in between deeper moisture to the southeast, and lift beneath the cold pool with the shortwave crossing the Ohio Valley. Latest guidance supports an overall dry scenario with dry air aloft off forecast soundings, and low level northwest flow beneath rather meager instability Saturday afternoon. Cant totally rule out a sprinkle or shower reaching the far northwest counties late in the day but not enough to include a pop mention for now. Otherwise partly to mostly sunny and a bit less humid with highs still 80s to near 90 east, as weak downslope offsets slight cooling aloft. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 240 PM EDT Friday... An upper level trough will pivot over the region Saturday night. Not much cool air is behind this trough, therefore temperatures Sunday will warm back above normal with mid 80s west to near 90F east. The only notable change will be slightly drier air (dew points in the low 60s west to upper 60s east) with a westerly breeze. Dry high pressure with increasing heights aloft will continue to keep most of the region dry through Monday night. Some low level moisture may creep into the area from the south Monday. This moisture and upslope flow may generate a few storms across the North Carolina High Country late in the afternoon, fading in the evening. Under mostly sunny skies, temperatures will warm a little above normal Monday with 80s west to lower 90s east. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 255 PM EDT Friday... A western Atlantic upper level ridge will track westward over the Gulf states through early next week. This ridge will push temperatures 5F to 10F warmer than normal. With an increase in heat and humidity, scattered showers and thunderstorms are expected Tuesday afternoon across the mountains and then moving and fading across the foothills in the evening. On Wednesday, models are wanting to bring a cold front south into the Gulf states, pushing the upper level ridge into the Gulf. Considering climatology for the time of year, models look to be over zealous with moving this front into a hot and humid air mass. I would not be surprised to see a slowing trend with the frontal passage being more towards Thursday. For now, kept timing close to guidance while keeping PoPs low. Until the front clears the area, temperatures will stay 5F to 10F warmer normal. Following the front, temperatures will be 5F or cooler than normal. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... As of 1240 PM EDT Friday... Most showers with isolated storms continue to linger across the far western areas, mainly just west of KBLF-KLWB early this afternoon where seeing pockets of MVFR cigs. Latest models continue to develop showers/storms across and espcly east of the mountains this afternoon into early evening ahead of the upstream cold front. Appears most of this will initially be scattered in nature over the west before perhaps organizing into more bands/clusters along/east of the Blue Ridge by mid afternoon. Shra/tsra should then push into eastern sections by early this evening prior to exiting shortly after 00z/8 PM if not sooner. Thus running with mostly VCTS/VCSH at all locations with tempo groups for lower MVFR conditions in showers across the west, and deeper convection east where IFR vsbys may occur. Appears fog will be stuck in the valleys and eastern locations that see heavier rainfall this afternoon although uncertain given gradual advection of dry air late. For now included sub- VFR in fog at KLWB/KBCB/KLYH late tonight while leaving out elsewhere. Some stratus also possible with the fog and perhaps even at KBLF with weak upslope flow. Outside of convection, winds will be mainly west to southwest at 5-15 kts ahead of the front this afternoon before turning light/variable overnight. Weak high pressure will build into the area Saturday bringing VFR conditions under northwest winds at 5-10 kts. Extended Aviation Discussion... Mainly VFR conditions for the second half of weekend under weak high pressure. Scattered thunderstorms and periods of MVFR conditions return next week, with late night/early morning fog possible almost any day. Better potential for sub-VFR will come Wednesday when more widespread showers and storms arrive with the next cold front. && .EQUIPMENT... As of 400 AM EDT Friday Aug 18th... KFCX doppler radar expected to be down for the rest of the month due to a failing bull gear. Technicians are working on the radar, through next week and the radar will most likely stay down completely as the repairs are being made. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RCS LONG TERM...RCS AVIATION...JH/RAB/WP EQUIPMENT...RAB/WERT/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.