Area Forecast Discussion
Issued by NWS Blacksburg, VA

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886 FXUS61 KRNK 090459 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1159 PM EST Fri Dec 8 2017 .SYNOPSIS... Low pressure over northern Florida will move northeast along the southeast Atlantic Coast tonight, then off the Mid-Atlantic Coast Saturday. Greatest snowfall accumulations are expected along the Blue Ridge and into the North Carolina and Virginia Piedmont. A strong Canadian Cold front associated with colder air will cross the eastern United States Saturday night into Sunday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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As of 1150 PM EST Friday... Seeing a break in the snow across much of southwest Virginia and northern North Carolina. Expect this will be filling back into before 4AM. Based timing on the Hi-ResNMM along with the HRRR and RAP. A Winter Storm Warning remains in effect for all counties along and east of the Blue Ridge, with the line in the sand drawn near Interstate 81 where there will be a sharp cutoff with respect to where it snows and where it does not snow... basically 95 percent of the precipitation from this system occurring east of I-81. Overall synoptic pattern shows a full latitude long wave trough over the eastern CONUS with a strong shortwave ejecting out of the base of the trough from the Gulf of Mexico. Conveyor belt of deep moisture exists on the east side of this trough, and as the short wave becomes negatively tilted, this moisture is getting pushed northwest into the cold airmass that resides over the region. With P-type not really a player for our forecast area (primarily snow anticipated), challenge remains forecast QPF with models indicating liquid equivalent amounts of a half inch /0.50/ to /1.00/ along and east of the Blue Ridge. A 10:1 conversion of these amounts suggests 5 to 10 inches of snow, and in spite of the melting that is occurring due to the warm ground, the official forecast has trended toward those higher numbers. Periods of snow, heavy at times will continue through the night and into early Saturday. It appears the strongest deformation, dynamic lift, from this system is going to shift from the NC mountains where it snowed for most of the day Friday, to across the NC/VA Piedmont. As such, do not be surprised to see 1 to 2 inch an hour rates develop for a period of time. Temperatures through tonight will remain at or below freezing, hugging the freezing mark across the Piedmont, and into the 20s along and west of the Blue Ridge. Little rise is expected Saturday in-spite of the snow coming to an end. Model trends suggests the snow to end from west to east with the majority of the accumulation done by mid-day. Attention will then turn toward a cold front that will cross the area from the northwest.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY NIGHT/... As of 100 PM EST Friday... As the coastal low pulls away from the region late Saturday, a cold front will move through the region Saturday evening. This will bring a reinforcing shot of cold air to the Appalachians and central mid Atlantic region and set the stage for upslope snow showers west of the Blue Ridge with a few inches of fluffy snow expected at the higher elevations. The low level wind field will also amplify considerably with very blustery conditions leading to areas of blowing snow and low wind chill values. Accumulating snow showers will taper off to flurries Sunday morning but blustery conditions look to continue through the first part of next week as the wind field remains energized by numerous short waves zipping through fast upper level flow. Temperatures will remain well below normal into the first part of next week. Many locations will see departures of 10 to 15 degrees below seasonal norms. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 100 PM EST Friday... Amplified upper pattern featuring a western ridge and eastern trof will persist through next week, though some deamplification looks to occur toward the end of the week. The main storm track will keep areas of low pressure moving from the Great Lakes into New England with trailing cold fronts pushing reinforcing shots of cold air into the Appalachians with occasional bouts of snow showers west of the Blue Ridge. The fast moving pattern will also keep a good amount of energy in the low level wind field with blustery conditions through the period. With little change to the cold pattern in place, expect temperatures to remain well below normal through the upcoming week. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
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As of 1150 PM EST Friday... Medium to high confidence that snow will fill back in over the central Appalachians by 10Z/5AM with MVFR to IFR visibility due to fog and snow. Axis of heaviest snow will remain east of the BLue Ridge overnight. KDAN airport has the potential for another 2 to 4 inches of snow before Saturday afternoon. North and west of the sharp precipitation gradient conditions will be VFR through Saturday morning. Expect improving conditions after 09/18Z from west to east, as low pressure begins to drift away from the region and winds become northwest. Medium confidence on this timing. Shortly after noon a clipper will cross the Appalachians, increasing the winds and bringing MVFR clouds to the mountains, including at KLWB and KBLF. Snow showers will persist overnight in the mountains with MVFR, and at times IFR, visibilities. Wind gusts up to 20-35 knots are likely at higher elevations by the 06Z end of the TAF forecast period. Extended Discussion... Strong northwest winds will continue into early Sunday. VFR conditions then return Sunday evening through Monday. Next chance for sub-VFR conditions is with a clipper system Tuesday, particularly in the western mountains.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Weather Advisory until 4 PM EST Saturday for VAZ009- 012>014-022>024. Winter Storm Warning until 4 PM EST Saturday for VAZ015>017- 032>035-043>047-058-059. NC...Winter Storm Warning until 4 PM EST Saturday for NCZ001>006- 018>020. WV...None. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...MBS LONG TERM...MBS AVIATION...AMS/NF

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