There is no disputing that forecast guidance has moved more strongly in the direction of making this an I-64 and north snowfall on Wednesday, at least for the heaviest stuff. Some of the frequenters of the blog in the Lexington area up to Charlottesville may still be in line for about 6 inches, possibly more. Higher elevations toward Bath and Highland counties could go up to 10, under current thinking. Heaviest snow, possibly topping a foot, will likely fall in higher elevations of Shenandoah National Park and in the mountains of northwest Virginia west of Interstate 81. Storm dynamics are driving the boat in terms of temperature and precipitation rate, but a little boost in elevation can help with the surface temperatures, too.
In the Roanoke and New River valleys, and even farther south and west, it’s still far from a foregone conclusion that we will have bare ground come Wednesday morning. There are really two different facets to watch for possible snow. The first is how quickly cold air can catch up to the original rain shield moving across the area Tuesday afternoon into Wednesday morning. This will be developing ahead of a low-pressure system moving into the Ohio Valley. It may begin as a rain/sleet/snow mix, but is projected to go to mostly or all rain as milder air moves in aloft ahead of the low, and surface temperatures remain above freezing. Cold air in the mid and upper levels will begin advancing east overnight, and as it does so, will begin to change rain to snow from west to east and from higher elevations to lower ones. Honestly, I’m always a bit skeptical of these cold air catching rain shield setups for snow at least in the Roanoke Valley, because they seldom seem to work, but this will have a deepening low in North Carolina starting to pull cold air eastward. I think we could get 1-2 inches in the greater New River/Roanoke valleys from this if it pans out moderately well. The easiest way to get more snow than projected would be for it to simply be colder Tuesday night than expected and have snow for a much longer period of time. Locations northwest and northeast of Roanoke may have a better shot at this happening.
The second issue is how far southwest the snow shield spreads behind Wednesday’s deeper low that forms over North Carolina. This is the hardest issue to figure out. Even the northward North American Model has brought it into Southwest Virginia off and on during its last several runs. The Euro and Canadian models have been downright robust with this snow shield in Southwest Virginia at times. Locations that can get in this “deformation zone” snow shield for several hours could add quite a few inches to their snow totals. It appears I-64 and north stays in most of the day. Some forecast models bring it down to the U.S. 460 corridor (Blacksburg-Roanoke-Bedford-Lynchburg), and a few have even touched Interstate 77 or the Virginia-North Carolina border. This may well turn into a “nowcasting” situation that won’t be able to be ascertained very well until the event is ongoing.
Throwing out some educated guesstimates: Roanoke, Blacksburg, 2-3 inches; Botetourt, northern Bedford County, 3-5 inches; areas to south of Roanoke, Blacksburg, 0-2 inches; Rockbridge, Bath counties, 4-8 inches, locally 10+ in higher elevations. This is very fluid, even more than a typical snow situation, and these numbers could all easily bust in either direction.
Probability wise for Roanoke/Blacksburg: 1+ inch, 70 percent; 2+ inches, 55 percent; 4+ inches, 45 percent; 6+ inches, 35 percent; 8+ inches, 25 percent; 12+ inches, 15 percent. I see Roanoke/Blacksburg on the same plane with this event, as Blacksburg has elevation and westward advantage to get snow earlier in the initial precipitation shield, and Roanoke has a bit of a northeastward advantage to have a better chance of getting in the wraparound snow for a little longer.
Of course, it’s still possible that the vort digs farther south than expected, the low develops farther south and the snow shield on Wednesday is farther south. (Or, of course, it could happen even farther north, and leave us with little or no snow.) Weather is played out in the atmosphere, not in forecast models. Whatever happens Wednesday, we may be in the 60s by the weekend. March is upon us.