Area Forecast Discussion
Issued by NWS Blacksburg, VA

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389 FXUS61 KRNK 062338 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 638 PM EST Tue Dec 6 2016 .SYNOPSIS... Low pressure will pass northeast of the region and weaken overnight. A weak cold front trailing this system should move across the area late tonight into early Wednesday. High pressure builds east in the wake of this front by Wednesday afternoon followed by a stronger cold front that should cross the region on Thursday. && .NEAR TERM /THROUGH WEDNESDAY/... As of 230 PM EST Tuesday... Low pressure in Eastern Kentucky this afternoon will continue to weaken as it marches northeast tonight. Meanwhile, Coastal low off the North Carolina will deepen tonight and push out into the Atlantic ocean overnight into Wednesday. The best dynamic lift will occur this afternoon into this evening ahead of a negatively tilted shortwave trough lifting northeast through the southern Appalachians. After the surge of PVA passes, then precipitation will wane with rain tapering off from southwest to northeast. Water vapor loop showed drier air pushing in from the southwest this afternoon into tonight. Gradual clearing will follow for most of the CWA tonight as winds become northerly behind the departing storm system. Lingering clouds and light precipitation will be found across the mountains, with potential for drizzle and or freezing drizzle for the West Virginia Highlands. Used a blend of NAM and continuity to capture the pops for tonight. Utilized the SREF temperature profiles to shape the weather grids. Added areas of fog especially in the east tonight. Low temperatures tonight will range from around 30 degrees in northwest Greenbrier county to the upper 30s in the Piedmont. Light wintry mix of lingering precipitation across western slopes of Greenbrier County Wednesday morning will taper off by afternoon. High temperatures will vary from around 40 degrees in the northwest mountains of Southeast West Virginia to the mid and upper 50s in the Piedmont. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 245 PM EST Tuesday... Brief quiet period under zonal flow aloft Wednesday night will quickly transition to one of eastern troughiness with a subsequent Arctic front crossing the region from northwest to southeast on Thursday. Models remain rather inconsistent in the degree of return moisture ahead of the boundary starting later Wednesday night and with the actual 850 mb front Thursday. Not seeing a lot of support to include much precip but given some slight backing as well as possible slowing of the front, think prudent to keep in some low pop mention espcly southwest sections under the tail of a passing jet streak. This would consist of mainly a rain/snow shower mix to just spotty rain showers south/east pending timing of the cold advection, followed by a switch to mainly post frontal upslope snow showers later in the day. Kept temps mostly in the 30s Wednesday night as clouds/mixing increase with a range of highs from steady mid 30s northwest, to 40-45 Blue Ridge, to low 50s southeast Thursday pending timing of the actual frontal passage. Cold advection will dominate the remainder of the period as strong northwest flow continues ahead of high pressure building slowly east from the central U.S. Guidance remains in line in showing winds just below advisory levels most spots Thursday night into Friday while dropping 850 mb temps down to as low as -15C mountains. However with the core of the Arctic air sliding by to the north, should be warmer out east of the ridges given less pronounced digging of the trough off latest runs. This would support blustery lows in the mid/upper teens mountains to low/mid 20s east with western wind chills zero to 10 above. Appears to be just enough low level moisture coinciding with the coldest air aloft and stronger upslope flow to result in periods of snow showers mainly far northwest. However since coverage iffy given such mixed/dry air, only including a low pop northwest slopes into Friday for now. Otherwise expecting a mainly sunny but cold and continued blustery day Friday outside of the upslope western zones where more clouds may persist. Appears highs will stay below freezing for much of the mountains Friday, while rebounding into the 30s to around 40 piedmont where cold advection offset by downsloping flow will occur. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 130 PM EST Tuesday... Upper trough lifts out Friday night allowing cold surface high pressure to build overhead by Saturday morning. This should bring diminishing winds overnight but also good radiational cooling within the residual piece of Arctic air in place. Still some potential to see warm advection high clouds invade late Friday night into Saturday morning which could keep readings from bottoming out. Thus running with mostly clear and lows teens mountains to upper teens/low 20s east for now. Surface high should cross the region Saturday with a fast zonal flow regime developing that will continue into early next week. Exodus of the cold pool aloft should allow for gradual moderation in temps into the 30s to lower 40s Saturday before much stronger warm advection on southwest flow develops Sunday into Monday ahead of an approaching upstream cold front. Latest models have slowed down the eastward progression of deeper moisture with this initial front similar to the earlier ECMWF with most pops holding off until Sunday night or Monday. This should be after warming aloft has won out with mostly chance rain/showers with perhaps some snow mixed in far west/northwest. Lots of uncertainty moving ahead toward midweek in whether or not a punch of dry air follows this boundary before the next northern stream wave approaches Tuesday, or does it stall with moisture returning back north. For now will dry things out on day7 per WPC and latest 12Z ECMWF with overall temps 40s west to 50s north Monday/Tuesday. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 625 PM EST Tuesday... Poor flying conditions expected to persist through tonight with improvements on Wednesday. Widespread rainfall from earlier has tapered to mainly drizzle this evening under developing areas of fog that will likely persist much of the night. Thus still expecting periods of IFR at most terminals overnight with potential for LIFR vcnty of the mountains, with ridges obscured in stratus. A weak secondary cold front will cross the western mountains overnight allowing for a gradual transition to elevation snow showers in West Va, with drying elsewhere toward daybreak as deeper northwest flow develops. Better drying will continue early Wednesday resulting in a return to VFR along/east of the Blue Ridge Wednesday morning, with improving conditions likely delayed until afternoon at KBLF/KLWB given residual low level upslope moisture. Should finally see all sites become VFR during Wednesday afternoon under some high clouds and northwest winds at 5-15 kts, perhaps gusting to near 20 kts at times over the mountains. Low to medium confidence in ceilings, visibilities and winds during the taf period. Extended aviation discussion... Clouds and possibly a few showers may return Wednesday night in advance of an approaching Arctic front that is expected to move through the region Thursday. Limited moisture may result in a few rain or western snow showers in advance of the boundary Thursday morning. However upslope conditions should support snow showers across the mountains behind the front Thursday afternoon into Friday along with a significant surge of cold air. This will lead to VFR conditions east of the Blue Ridge through much of the period beyond Thursday, but MVFR conditions may linger into Friday across the West Va sites. West to northwest winds behind the front will be strong into Friday with gusts likely topping 25-30 kts at times. Winds and any residual low level cloud cover should quickly fade by Saturday as high pressure builds overhead making for overall VFR conditions this weekend ahead of the next cold front that wont arrive until early next week. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...KK NEAR TERM...KK SHORT TERM...JH LONG TERM...JH AVIATION...JH/KK/PM

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