Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 182317 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 717 PM EDT Sat Mar 18 2017 .SYNOPSIS... An upper level area of low pressure and its associated cold front will cross the region from the west this evening before exiting overnight. High pressure will then follow the front for Sunday and Monday. A series of cold fronts will drop south across the area Tuesday into Wednesday with additional rounds of precipitation likely. && .NEAR TERM /THROUGH SUNDAY/... As of 625 PM EDT Saturday... Forecast on track, had some thunderstorms with sub-severe hail across the piedmont/foothills, and even over portions of the Roanoke and New River valley since 3pm. The strongest convection has now exited Halifax County. Cold front now lined up near the Blue Ridge as evidenced by a northwest shift in winds at Roanoke with gusts to 34kts. Will still see some limited thunder/hail threat in the east til about 8pm, while in the mountains we start to see some cold air moving into the mountains with rain changing to snow showers across the Greenbrier/Bath county higher terrain by 8pm. Winds with this initial fropa surge may gust as high as 45 mph, mainly in the higher elevations/foothills, but overall stay below advisory levels except possibly in elevations above 4000 ft in NC. No advisory planned. Previous discussion from early afternoon... Cold front still just west of the mountains should finally push east across the area this evening before exiting overnight. Already seeing clusters of mainly small hail producing convection due to cold air aloft, and expect this coverage to increase/organize a bit more upon heading east of the mountains over the next few hours despite only weak surface based instability. This in line with the latest HRRR and Rap solutions so running with highest chance pops eastern half into early this evening. 850 mb front beneath the passing strong mid level shortwave trough will follow the surface front across the mountains by sunset and work through the rest of the area this evening. This will cause northwest winds to quickly increase as well as deeper cold advection as the nose of the jet aloft punches in. However latest local scheme numbers suggest that winds, other than for a surge with the front, will overall stay below advisory levels given a 40ish knot jet under a rather steep inversion without really cold air as seen in past events. Thus pushed gusts to just below criteria southern Blue Ridge where best subsidence will reside overnight. Otherwise should see clearing develop east of the mountains this evening/overnight while upslope snow showers kick in out west where an inch or two of snow looks possible through Sunday morning. Kept lows on the warmer side of guidance, mostly 30s, given mixing beneath a not overly cold airmass. Upper cold pool will be slow to depart on Sunday with the core of the mid level shortwave energy not exiting to the southeast until Sunday afternoon. This in conjunction with high pressure building in from the west may keep more of a northerly flow in place espcly east where clouds could linger piedmont from late tonight through midday Sunday. However this along with dry air/subsidence should also tend to shutoff the upslope snow showers by midday if not sooner, with mainly sunny skies in between early on. Expect all except the far northwest to finally clear out during Sunday afternoon with winds diminishing a bit as the pressure gradient starts to weaken, but still quite blustery. High temps under the cold pool likely to struggle in the 40s to near 50 mountains, while recovering into the mid/upper 50s east given aid of downslope drying and warming of dry air. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 230 PM EDT Saturday... High pressure builds overhead in the wake of the exiting upper cold pool Sunday night before sliding to the south Monday in advance of the next upstream cold front. This will make for another cold Sunday night with lows in the 20s to lower 30s under good radiational cooling. Warmer air quickly returns Monday under westerly flow aloft and 850 mb temps jumping to near +10C by the end of the day. This combined with sunshine and clouds not increasing until afternoon supports highs mostly in the upper 50s to mid 60s with any isolated showers holding off across the far northwest until late. Deepening moisture/clouds continue to increase Monday night with added shower bands arriving across the western sections espcly after midnight. Otherwise mainly dry out east under strong downsloping flow aloft and better moisture convergence stuck over the far west. Should be milder under warming aloft and mixing with lows mostly in the 40s. Front will drift into the area Tuesday and perhaps linger southern sections Tuesday night before finally getting shoved to the south via passing stronger shortwave energy to the north on Wednesday. This scenario remains uncertain with guidance showing a possible weak wave along the boundary by Tuesday night which could result in more widespread precip into early Wednesday. Exactly where/if low pressure develops key to pops Tuesday afternoon into Wednesday with some solutions farther south and others leaving moisture around with colder air bleeding in from the north at the end. For now will continue mostly chance pops except a period of likelys late Tuesday into Tuesday night mainly southern/eastern half including some light snow far northwest toward daybreak Wednesday as deeper cold advection arrives. Models also indicate quite a bit of instability over the far southern sections late Tuesday so including a thunder mention there as well. Should finally see decreasing clouds from north to south by Wednesday afternoon but cooler with highs mainly 40s north/west to 50s elsewhere after a rather mild Tuesday. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 1245 PM EDT Saturday... Shortwave ridging will strengthen over the region later next week in the wake of a passing cold front to the south by Wednesday night. This will give rise to strong high pressure building southeast across the Great Lakes before wedging south down the Mid-Atlantic coast Thursday into Thursday night. However models remain uncertain in just how strong the wedge will be espcly in regards to low level moisture and subsequent low clouds. At this point appears the dry wedging wont be strong enough to scour out clouds along the southern Blue Ridge, but could see more clearing elsewhere given the closer proximity of the parent high just to the north. Otherwise will be chilly but dry into Thursday night. High then slides offshore later Thursday night allowing a weak warm front to shift north on Friday, in turn scouring the wedge under rebounding temps to more seasonal levels. Next round of shortwave energy heads out of the Rockies by the end of the week with an associated cold front approaching by next weekend. Timing of this boundary into the eastern ridging remains iffy but appears enough return of deep moisture to warrant a chance of showers mainly Saturday afternoon and overnight. Should also be all liquid with temps well above normal by Day7. && .AVIATION /23Z SATURDAY THROUGH THURSDAY/...
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As of 712 PM EDT Saturday... Looking at drying conditions east of the mountains this evening with cold front pushing across and out of the piedmont by 01z. Will see gusty winds across the mountains/foothills early on, with some gusts over 35 kts near TNB-HSP, but a little less at the taf sites. Should start to see some lower cigs working into BLF/LWB after 03z, with rain or snow showers starting up after 06z, changing to all snow showers by 09z. Appears most of the snow will be west or northwest of LWB/BLF so have no limited vsbys yet. Northerly flow will work in Sunday with cigs rising to VFR in the mountains by 12-15z. Not out of the question from LYH/DAN to have some mid/high clouds Sunday but nothing to affect aviation. Extended Aviation Discussion... High pressure building in on Monday should yield VFR all terminals to start the week. However moisture ahead of another cold front and associated weak low pressure may arrive by Monday night, with sub-VFR possible later Monday night mountains and all areas Tuesday into Tuesday night before improving conditions back to VFR take shape during Wednesday. By Thursday high pressure will wedge in from the northeast so will stay VFR though increasing clouds are expected by afternoon, but should stay VFR.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...JH/WP SHORT TERM...JH LONG TERM...JH AVIATION...AMS/JH/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.