UPDATE 8:20 AM, 12/9/2018: Bands of heavy snow with visibilities dropping under 1/4 mile at times are lifting north from North Carolina into Southwest Virginia. These bands contain snowfall rates of 1 to 2 inches per hour. Snow totals have already topped 10 inches in parts of northwest North Carolina and are in the 6-8 range just across the state line in Virginia, with 2+ inches near Roanoke and the leading edge of accumulating snow near I-64. Widespread amounts of 10 or more inches continue to appear likely at least as far north as Roanoke and possibly another 15-30 miles northward, and some locations especially near the North Carolina line may approach or even exceed 20 inches. This particular early December snow event appears as if it will max out its potential in our region, possibly rivaling the Dec. 18-19 storm of 9 years ago. END UPDATE
UPDATE 4 AM, 12/9/2018: The snowstorm has begun for most locations along and south of the U.S. 460 corridor, including the Roanoke and New River valleys, and will soon begin at many areas to the north. Snow will continue for many hours, likely into early evening, varying in intensity but often moderate to occasionally heavy, with 1- to 2-inch per hour rates developing at times (keep an ear out for thunder, especially south and southeast of Roanoke). Many if not all locations from Roanoke south will end up with close to or just above a foot or so out of this, I do believe -- let's say 10-15 inches, with some localized higher amounts up to 2 feet. And some northward to the I-64 corridor may get there, too -- 5-12 inches in that zone, a wider span for a possible dropoff toward the north and a bit more uncertainty. Travel conditions will deteriorate rapidly from south to north in the next few hours. I hope you don't have to be anywhere on this snowy Sunday morning, and can either enjoy or endure this at home. END UPDATE
The morning light will likely reveal a whitening landscape across the region from the Roanoke and New River valleys southwestward, as a complex storm system moving over the South likely deals a potent punch of heavy snow to our region on Sunday.
The lift provided by an upper-level southern stream wave will lift abundant Gulf of Mexico moisture northward, later also wrapping in western Atlantic moisture, for rapidly developing snow over our region in the pre-dawn hours of Sunday, with moderate to occasionally heavy snow continuing throughout the daylight hours on Sunday. Snowfall rates of 1 to 2 inches per hour are possible at times, maybe even 3 inches per hour for a short time in the heaviest banding.
The atmosphere is extremely dry in the layers right above the surface, and this will take some time to saturate before we see snowflakes at the surface, but this may well happen as early as 3-4 a.m. in the New River and Roanoke valleys based on many short-range models, almost certainly before sunrise.
No matter the media or meteorology source, expectations have generally gone up during the day Saturday as additional data has revealed the storm on a track and with the dynamics to lift moisture robustly farther to the north against the high pressure system delivering the cold, dry air necessary to keep it mostly or all snow.
My expectations are 8-14 inches from the U.S. 460 corridor (Blacksburg-Roanoke-Bedford) southward to the Virginia state line, with some spots of up to 20 inches. Generally there will be more potential for greater amounts the farther south you go, but snowfall never spreads out that evenly in our complex terrain, and there may well be small-scale heavy bands that dump bigger amounts over localized areas for longer.
From the 460 corridor north to I-64 (Covington-Lexington-Buena Vista), I'm expecting 4-10 inches -- again, generally more south and less north, but with some variations. Beyond that snowfall amounts, with a pretty big drop off from around 3 inches to nothing in 15-30 miles somewhere north of I-64.
Again, projected amounts vary a little by source, but they are all at this point large snowfall totals that will create hazardous driving and sporadic power outages.
A regionwide 1-2-foot snowfall is a reasonable possibility on the high end of the envelope. Some forecast models show that. On the low end, having only about 3-4 inches with none near I-64 and still 6+ near the North Carolina line would be on the low end of the envelope of possibilities, if moisture flow or lift were significantly weaker than expected. This doesn't look to be an issue as of late Saturday night.
Most accumulating snow is probably over by mid-evening, with some lingering light snow beyond that. This will be a relatively fast but powerful punch of snow. Snowfall rates of 1-to-2-inches per hours may develop, maybe even 3 inches. Travel will become hazardous rapidly in the morning, and there will be some sporadic power outages, more of them in areas near the North Carolina state line with a wetter consistency of snow.
If you like snow, be sure to enjoy it on Sunday. If you don't, remember that it starts melting Monday and will likely be gone entirely by next weekend's mild rain.