UPDATE 9:50 PM: Snow has developed rapidly into much of the Roanoke Valley and some of the New River Valley this evening. The storm system appears to be developing faster than earlier expected. Will monitor the next few hours to see how quickly and where a dry slot forms in parts of Southwest Virginia. END UPDATE
Some snow has already begun in the I-64 corridor (reports in parts of Alleghany and Rockbridge counties) and northward. Earlier sleet and some snow were reported farther south, even into the Roanoke and New River valleys, mixed with rain as the initial wave of precipitation encountered dry air aloft and initiated evaporational cooling, but most of that has changed to rain. Later tonight and into early Wednesday morning, it is expected that cold air aloft will spread eastward and southeastward so that snow expands into more of the region, but it will be a race against time as to whether it will spawn significant snow farther south before the initial precipitation shield shifts eastward rather rapidly. Once low pressure begins to form along the North Carolina-Virginia border to our east, it will rotate a shield of wet snow over much of central and northern Virginia, where widespread 4+ and some 10+ amounts are projected. Most model guidance suggests the bulk of this will stay north of the U.S. 460 corridor (Blacksburg-Roanoke-Bedford-Lynchburg). So the Roanoke and New River valleys are very much on the rim of snow expectations tonight and early Wednesday, and that has made this an unusually difficult snow forecast. Forecasts have tended to drift into the mid range of 1-3 inches, but could easily go to minimal snow or larger amounts depending on how these factors play out.
So we’re very much in a “nowcasting” phase now. We’ll watch how it develop tonight and early Wednesday.