Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 041459 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 959 AM EST Sun Dec 4 2016 .SYNOPSIS... High pressure shifts northeast today. A couple of upper disturbances will lift northeast across our area today into tonight. The main system shifts across the Gulf Coast states into the mid-Atlantic Tuesday. A strong cold front enters the area Thursday with much colder temperatures expected to end the workweek. && .NEAR TERM /THROUGH TONIGHT/... As of 955 AM EST Sunday... Light precipitation continues to make gradual progression northeast into and through the region. Temperatures across the southwest portions of the area are slowly rising into the middle 30s. Pockets of sleet and/or snow are gradually decreasing in coverage across this portion of the area with plain rain becoming dominate. However, as the leading edge of the precipitation saturates the low levels of the atmosphere, and both temperature and dew point trends towards a sub-zero C wet-bulb, some light sleet and snow will continue to be possible around and a few hours after the onset of the precipitation. By the time the leading edge reaches northern parts of the region this afternoon, most areas will receive only rain. The exception will be the higher ridges of the Alleghany Highlands where sleet will be possible. As of 648 am EST Sunday... Rain and some snow finally making it into the NC mountains/foothills, and as far northeast as Smyth County VA. Weather cams showing a coating of snow at Beech Mountain NC. Have highlighted the higher elevations from Tazewell to Watauga for light snow coating the roads. Models still favor mainly rain with snow/sleet mixture at times. Temperatures/dewpoints show wet bulb within 32F. Confident that wintry precip will be limited to higher terrain with some lower elevations along I-81 from Abingdon to Wytheville potentially seeing some snow/sleet but to no impact. Bump pops up across the southwest CWA to account for latest radar and high-res model trends. By lunchtime, precip, mainly rain should be as far northeast as Bluefield to Radford to Stuart to Danbury, with more patchy rain to perhaps Roanoke and Danville. Previous discussion from early this morning... Have not seen any precip in our local observations but seeing light rain reported just south of Wilkes County NC over the Interstate 40 corridor. Airmass will be moistening from top to bottom right through the day. Models are similar in timing for precip to move into the mountains/foothills of NC/SW VA by 12z then isentropic lift and upper forcing accelerate east-northeast through the afternoon. Main concern this morning is with ptype. Noticing a bit cooler than earlier forecast, so will lean more toward snow/sleet southwest then rain, as opposed to freezing rain. Still amounts will be very light but could see a tenth of an inch of snow in the higher terrain of NW NC into far SW VA, maybe even some of the lower elevations may see some light coating. Still for temperatures and ground/road sfcs there should not enough to cause any problems. Expect the precip to chase the cooler air north where the leading edge will be a mixture of rain/snow/sleet before switching to all rain. Could still remain wintry mix over the Alleghanys of Bath into Greenbrier through tonight. Overall will be limited in winter precip so no headlines planned as amounts and coverage are very small/negligible. One upper vort moves north this morning, then another wave shifts from the Southern Appalachians around midday to the Southwest VA mountains this evening. Appears the southern tier of the forecast area south of Highway 460 should see occasional rain, while the northern extent along I-64 to north of Amherst will still have a fair chance of rain, but not as much. This will change this evening as northern stream shortwave heads east and the northern CWA gets into better lift with right entrance upper jet moving from KY to the Northern VA. Expect likely pops for rain across the east then shifting to dry solution of the EC/NAM across the southern tier late, with overnight pops ranging from slight chance NC foothills into the New River Valley to high chance to low likely east of a Lynchburg to Greensboro line and also across the western cwa from Tazewell to Lewisburg with shortwave energy moving in. By dawn we should be mostly dry with possible drizzle left over most areas with still some light rain in the piedmont of VA east of Lynchburg, and across the mountains. Still need to watch for potential freezing rain and/or freezing drizzle in the higher terrain/eastern slopes of the Alleghanys of Bath county and Greenbrier. Forecast temps suggest no lower than 32F expected, so very limited. As for temperatures this period since we are dropping cooler this morning and with precip coming in this morning, the highs were trimmed some along and either side of the Blue Ridge. These areas will be hard pressed to reach above 40f, while further west and east temps should manage to flirt with mid 40s. Tonight, as we keep clouds and rain around temps will be dropping slowly and ranging from the lower 30s Alleghanys and Blue Ridge north of the James River, to mid to upper 30s elsewhere. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 430 AM EST Sunday... High pressure building into the Ohio valley will bring an end to any lingering precipitation on Monday. This high will then move into New England and wedge down the east slopes of the Appalachians as a surface low being driven my an upper trof moving out of Texas approaches from the southwest. There will be significant isentropic lift with this system as it moves through and synthetic water vapor imagery continues to show deep moisture transport in a plume emanating from the tropical Pacific. These ingredients will combine to spread a cold, soaking rain across the region from the southwest starting Monday night and continuing through Tuesday, along with gusty winds at the higher elevations from the northwest mountains of North Carolina up through the Mountain Empire of Virginia into western Greenbrier county. Hydro concerns remain low as total QPF amounts through late Tuesday are expected to generally be around one inch and the region is still recovering from a very dry fall season. As high pressure builds in and northwest winds pick up Tuesday night, some upslope showers are expected west of the Blue Ridge with some wet snow mixing in for western Greenbrier county during the predawn hours of Wednesday. Any lingering upslope rain/snow showers will end Wednesday morning with improving conditions into the afternoon. Temperatures are generally expected to be at to a bit above normal on both Monday and Wednesday, but Tuesday will feature temperatures well below normal in the heart of the wedge with warmer readings mainly along the western periphery of the wedge. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 200 PM EST Saturday... Very strong cold front associated with the 500 mb trough will cross the region Thursday with some timing differences in models as slightly faster trends continue. Lobe of deeper moisture right along the front may bring a band of showers west, with a quick change to snow showers far west as seen with similar arctic fronts in the past. Some of this coverage may even spill east of the mountains in liquid form so running with decent to high chance pops west and slight coverage east. Pending timing, temps to fall from west to east by afternoon with the core of the cold air arriving Friday into Friday night under strong northwest winds, and lingering snow showers despite very dry air by weeks end. Gradient given depth of the cold advection perhaps enough to warrant advisory level winds in spots over the mountains otherwise very cold. Appears highs wont get out of the 20s to around 30 mountains Friday and 30s east with lows teens most spots Friday night and even single digits in the deeper valleys. This should also push wind chills to around zero if not colder in spots by early Saturday. Thermal trough including the coldest air aloft will lift out by Saturday but still highs only 30s to low 40s despite sunshine. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... As of 640 AM EST Sunday... Mid and high clouds already had overspread the forecast area. Lower cigs and precip are making inroads toward BLF/BCB, but will not get at these sites till about 18-20z. Appears best shift in precip will stay over the NC/Southern VA area today but will still see some precip in all areas by this evening. Will see mainly VFR this morning, then sinking to MVFR this afternoon and IFR after 23z. Will keep ptype all rain at the taf sites as any winter precip will be mainly confined to elevations above 3000-3500 ft, though BLF/LWB/BCB could see some sleet this morning/early afternoon. Overnight will see precip start to fade as wave aloft moves away. Will be cloudy still and with wet ground and light enough winds, expect some fog/stratus. Models all favor IFR or worse at all sites during the night til 12z Monday. High confidence in cigs today/tonight with medium to low confidence on vsbys. Extended aviation discussion... A break in the rain into Monday may allow for some VFR with sub- VFR returning late Monday night ahead of low pressure moving into the Tennessee Valley with widespread rain expected into Tuesday. Expect a bit of improvement after Tuesday as front moves offshore with another front entering from the west, with mainly VFR expected then though some MVFR cigs BLF/LWB lingering with good upslope flow behind an Arctic cold front. && .EQUIPMENT... As of 645 am EST Sunday... Phone company informed us that broadcast from Wythe County weather radio transmitter, WZ2500, should be available and the line is clean. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/WP NEAR TERM...DS/WP SHORT TERM...MBS LONG TERM...JH AVIATION...RAB/WP EQUIPMENT...WP is the U.S. government's official web portal to all federal, state and local government web resources and services.