Locations in Texas that rarely see snow like San Antonio and Austin have turned white on this Thursday evening, and snow will spread across parts of the Deep South on Friday in lots of places that don't usually get a lot. The Carolinas and Virginia likely get in on the act, too, but will it snow appreciably in the Roanoke area? It's every bit as murky as I thought it would be a couple days ago.
It would be pointless in this space to give a summation of all the various model solutions for the possible but far-from-certain first measurable snowfall of the 2017-18 winter in this space. While the overall setup isn't super complicated -- waves of low pressure spreading moisture into Arctic air -- some of the details have created some complexities that mean a lot in terms of whether your particular location gets covered by snow, just gets some "conversational flakes" or watches it hit someone else to the east or south this time around.
Generally, locations to the south and east of Roanoke will have a better chance of seeing significant snowfall on Friday into early Saturday, though some of the forecast guidance has shifted considerably west with the snow potential over the past 24 hours, and the Roanoke and New River valleys are at least on the cusp of getting a fairly decent early December snowfall if a couple of things click just right (or wrong, depending on your perspective of snow). An inch or two of wet snow, mostly on grass and exposed objects, seems reasonable for Roanoke and New River valleys -- you can scroll down to see the high-end, low-end and reasonable middle scenarios.
Here is the way Friday and early Saturday may unfold:
* An initial wave of precipitation may work its way northward from the western Carolinas during the day on Friday, maybe as early as late morning. This will probably have some trouble saturating the atmosphere and reaching the surface, but some daytime flakes of snow are possible, especially south and east of Roanoke. An early heavier band could turn some places white, but it will take some intensity to do that, with surface temperatures likely climbing into the mid and upper 30s, limiting accumulation.
* A second wave of snow may develop and/or move into our region during the evening and overnight hours. An Alberta clipper system moving in from the northwest may interact with the coastal wave of low pressure, which could intensify it enough to throw moisture much farther west than the first wave, perhaps even to near the West Virginia border or beyond. This is the band that, if it cranks up to some of its highest potential, could leave snowfall in inches for our region, especially south and east of Roanoke. This snow may linger as late as mid-morning on Saturday.
So breaking it down by the high-end, low-end and the reasonable middle:
High-end scenario (if everything clicks for more snow): The region experiences both a wave of moderate snow for a couple hours during the day Friday and a long period of light to moderate snow, briefly heavy, Friday night into early Saturday with widespread 3-6 inches along and east of I-81 and 2-4 inches westward to the West Virginia line.
Low-end scenario (if everything clicks for less snow): A total miss to the east, as the first wave is shunted eastward and/or dries up and the second wave doesn't amplify as some models show. We get little or nothing if that happens. Still very much possible.
Reasonable expectation (my best-guess snowcast at this time): 1-2 inches for the Roanoke Valley, most of the New River Valley and generally along the I-81 corridor, mostly at night, tapering to an inch or less to the north and west near the West Virginia line. 1-3 inches along the Blue Ridge south of Roanoke, locally up to 4, and 2-4 inches (locally more) east of the Blue Ridge toward Smith Mountain Lake, Southside, Bedford and Lynchburg.
This outlook is going to require a lot of "nowcasting" and fine-tuning as the day develops. Right now I don't anticipate major widespread travel difficulties, as the roads still hold quite a bit of warmth, but some scattered slickness could develop after dark, especially if some of the heavier snow potential is realized.