UPDATE 3:10 PM: WINTER WEATHER ADVISORIES expanded to include Roanoke, Botetourt and Rockbridge counties. Temperatures appear likely to be a little colder than earlier projected in the lower levels of the atmosphere, therefore a little more snow/sleet may fall in these areas with accumulations near 2 inches common and locally up to 4 inches. The advisory continues for counties to the west as well. END UPDATE
Winter weather advisories have been posted for the counties west of Roanoke (Craig, Montgomery, Floyd and westward) tonight and Saturday for the potential of 1-4 inches of snow/sleet mix as a rather complex but not-well-organized storm system lifts some moisture into marginallly cold air in the lower layer of the atmosphere. Wintry precipitation is not expected to be limited only to these counties, but is currently expected to accumulate an inch or less — below the advisory threshhold — in the counties farther east, including the Roanoke Valley. Forecast guidance overnight has lessened the available moisture slightly, and has emphasized the northern piece of the system more than the southern piece, which may allow it to pull a nose of slightly warmer air aloft from Roanoke and Blacksburg southward for a while that would introduce more sleet and some patchy freezing rain into the equation. It also may focus the chance of deeper snow more to the north, with the 2-4 inch amounts more likely north of the New River Valley, and the 1-2-inch side of things from the New River Valley south. Many areas may start as rain, and locations south and east of Roanoke may stay mostly rain.
Expect the arrival of precipitation around mid to late evening in Southwest Virginia. Much will depend on just how intense the stream of moisture from the Gulf is — heavier precipitation reaching our region or more of a southern stream influence with the storm could shift amounts higher and more toward snow. The plume of moisture is already visible in the lower Mississippi River Valley this morning on Radar / Future Cast (pulling back the magnification on bar at the left).
Temperatures will warm well above freezing Saturday afternoon in most of the region, so anything that falls will quickly melt. And there remain one or two more possible systems to watch next week, with borderline temperatures again likely for each of those.