Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180200 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1000 PM EDT Fri Mar 17 2017 .SYNOPSIS... High pressure over the region will shift offshore this evening ahead of a warm front approaching from the south. This front will lift northeast through the area overnight before a trailing cold front pushes across from the west during Saturday. High pressure will follow the front on Monday, then another cold front crosses the Mid Atlantic region Monday night. && .NEAR TERM /THROUGH SATURDAY/...
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As of 940 PM EDT Friday... Undergoing a transition of wintery wx in the Alleghanys to thunderstorms over the New River Valley, though should see limited cloud to ground strikes as instability east of the Appalachians wanes. Also very dry air aloft in places with colder thermal structure allow for graupel/sleet to occur. This noted across the Lynchburg area as of 930pm. Radar showing bright banding/melting level around 4000-4500 AGL over Bedford County. Latest RAP13 showing area of moderate to heavier showers moving out of the piedmont between 03-04z, with mix of sleet/snow still possible until 1-2am EDT northeast of Lewisburg, WV to the Alleghanys of Bath County. Handling with SPS for now, as only getting minor accumulations. Temperatures running around freezing at LWB/HSP. Warm front situated from LEX-MWK this evening should head north of us into the mid-Atlantic overnight allowing temps to gradually warm above freezing. Models still favoring overnight higher pops across the mountains and south into the NC foothills and piedmont, as better jet energy shifts southward toward 12z Saturday. Previous discussion from mid afternoon... Initial swath of precip along the leading edge of the deeper warm advection aloft per latest model 850 mb temp gradient has pushed across the northwest sections where saw a period of snow where precip did reach the ground. Latest radar trends and HRRR suggest a break in coverage to take shape once this initial batch passes before deeper moisture ahead of the actual warm/cold front combo arrives by early this evening. This may bring another round of mix to far northwest sections before temps aloft surge above freezing later this evening. However some concern with dry air in that surface temps may still be close to freezing around LWB/HSP. Thus keeping in a mix with perhaps an inch or so of snow along the I-64 corridor but without much freezing rain mention or advisory headline at this point. Otherwise models suggest a decent slug of lift crossing the region espcly this evening before deeper moisture axis slides to the south late as the front folds southbound. Appears deep westerly flow could limit eastward expanse of rainfall but given a favorable jet aloft and lots of forecast diffluence expect momentum to carry rain farther east than usual. Therefore beefed up pops to push likelys out just east of the Blue Ridge tonight and high chances south/east. Even included some elevated thunder mention across the southwest per steep lapses and dynamics with QPF of up to one quarter inch east to three quarters west. Dropped lows below mos most spots given a chilly start and more evaporative cooling potential with lows close to freezing northwest and upper 30s/low 40s elsewhere before perhaps rising some late. Cold front crosses the region Saturday followed by increasing northwest flow and gradual drying by mid to late afternoon outside of the upslope northwest zones. However models suggest that a weak wave may form along the boundary over southern sections in advance of the strong dynamic shortwave trough that will arrive late. This may slow the exodus of the showers espcly southeast sections so left in decent chance pops south early on before switching to mostly upslope rain showers west during the afternoon. Expect to see enough clearing and warming before stronger cold advection arrives to help boost highs to around 50 far west to 55-60 Blue Ridge to mid 60s east. Will also turn windy as the 850 mb jet increases to 40+ knots under the onset of the stronger cold advection but below advisory levels per forecast high inversion levels and only weak subsidence.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 400 PM EDT Friday... Upslope snow showers should pick up Saturday night along and west of the Blue Ridge as an upper level trough pivots overhead. It appears that up to a couple inches of snow seems likely for western Greenbrier County tapering down to flurries in the New River Valley. Good cold air advection warrants pushing lows on Sunday morning below MOS guidance. Temperatures may struggle to increase initially during Sunday due to cloud cover in the mountains, but high pressure building from the north should allow skies to gradually clear by the afternoon. By Sunday night, this high will move over the Appalachian Mountains to allow another cold night with efficient radiational cooling. The upper level pattern becomes more zonal by Monday, and some ridging arrives from the southern Plains. Expect a good warm up on Monday, but clouds will steadily increase during the afternoon and evening from the northwest as a cold front approaches the Ohio River Valley. The 12Z GFS pushes this cold front into the CWA a little faster than the 00Z ECMWF during Monday night. There may be a lag in moisture arriving at the onset due to recovery from a cold and dry air mass from Sunday and Monday, so the slower ECMWF solution was favored. However, some rain showers will probably reach southeast West Virginia after midnight. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 400 PM EDT Friday... The cold front should move from northwest to southeast over the CWA on Tuesday. Meanwhile, another upper level trough will dig southward from eastern Canada to bring colder air behind the frontal passage. If the cold air arrives quickly enough, it could change the rain to snow in the higher elevations of southeast West Virginia and the northwest North Carolina mountains by Tuesday night. Cold air advection will continue through Wednesday as a strong high pressure area builds southeastward from the Great Lakes. Once overhead by Wednesday night, expect another cold night with temperatures well below freezing. This high should slide eastward toward the coast on Thursday, and the numerical models hint that some wedging may occur east of the Blue Ridge. A warm front will also approach from the west due to a potent low pressure system over the northern Plains on Friday, so the CWA should break free of the wedge with good southwesterly flow and a building upper level ridge. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... As of 755 PM EDT Friday... A warm front is generating significant isentropic lift over the region and driving the development of showers mainly west of the Blue Ridge as dry air to the east is generally preventing precipitation from reaching the ground. Mid/upper lapse rates are sufficient to support some convection as is evidenced by lightning upstream. Additionally, cold temperatures are keeping some mixed ptype across Greenbrier and Bath counties. Believe the best chances for precipitation at TAF sites west of the Ridge will be through about 06Z, with temperatures up north will rise enough for an all rain scenario at KLWb by around 03Z. The best chances for thunder look to be confines further south and west so will not introduce thunder into the TAFs, though this may have to be modified based on behavior of upstream convection. Expect little in the way of appreciable precipitation at eastern TAf sites. A cold front then looks poised to move through the region tomorrow. This will allow for a push of drier air to move in from the southwest with improving flight conditions. However westerly winds quickly become gusty, we will settle into an upslope/downslope pattern by the afternoon with a return to MVFR and some scattered showers in the west, but hold on to dry VFR conditions in the east. Extended Aviation Discussion... Gusty post frontal northwest winds along with upslope western mountain snow showers will develop Saturday night and continue into part of Sunday. Best chances for sub-VFR with snow showers at KBLF and perhaps KLWB will be Saturday night into Sunday morning. 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 into early Tuesday before improving conditions take shape into midweek. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/JH NEAR TERM...JH/WP SHORT TERM...PW LONG TERM...PW AVIATION...JH/MBS

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