Wise County and most of Southwest Virginia residents awoke to about eight to 10 inches of snow a few days ago, but Big Stone Gap didn’t learn about it until they watched the news or checked their smartphones. Big Stone Gap was spared from the snow, and many people wondered why.
Many took to social media to show snapshots of the hefty accumulation. Big Stone Gap residents posted photos of green lawns. Wayne Browning with the natural sciences department at UVa-Wise was not surprised at all. He had predicted it already.
“I have documented this many times in the past, and it is nothing new,” he said. “I was expecting it and plainly stated this on my forecast website. It is nearly impossible for the floor of Powell Valley, southwest of the valley head, to accumulate significant show on easterly flow streaming across the high country of the High Knob Massif.”
Browning correctly predicted that if that type of flow developed, most of the snow accumulation toward Big Stone Gap would occur after low-level flow shifts more northerly in direction late Sunday.
“I was not expecting Big Stone Gap to get hardly anything during this period of the storm, and only forecast a three to eight inch range (eight inch near the head of Powell Valley and three inches toward Big Stone Gap) given I was allowing for snow to develop on the backside of the storm in wrap-around flow beneath the upper level low.”
Browning said that period of the event was weaker and more to the south of the area, so Big Stone Gap ended up with essentially nothing and the head of Powell Valley had four inches or a bit more.
“I discovered a rather unique circulation that I named a Thermally Indirect Mesoscale (TIM) Circulation since instead of cold air sinking and warm air rising like is most typical in the atmosphere, cold air is forced to rise and milder air is forced to sink, forming an indirect circulation,” he said. “I discovered this in wake of the great January 1998 storm which buried the area (again, Big Stone Gap had very little to no snow). This event produced up to 40″ plus of snow in High Knob in only 21-hours (unofficially setting a new 24-hour snowfall record for Virginia), and while some snow did fall not associated with the TIM Circulation the bulk came when it was cranking.”
Browning said for the town of Big Stone Gap to get a big snow event, a SW flow must be able to stream up toward the massif of High Knob. If cross-contour turning occurs, called ageostrophic flow in meteorology, it must be to the right of mean motion and not to the left.
“A left-turning ageostrophic flow component will kill the SW snow and induce sinking again off the high country of the massif.” Browning said. “A right-turning component of the flow will, however, cause air to flow into the massif and converge over Big Stone Gap-Powell Valley to enhance snowfall. A weather event like we have just witnessed, in which feet of snow accumulates on High Knob and along its windward side in this case that was Scott County, which had the most severe impacts from this event and nothing in Big Stone Gap, is testimony to the greatness of the High Knob Massif and the location of Big Cherry Lake and its amazing watershed,” he said. It shows the massif of High Knob impacts weather across this region, with locations upstream of the massif getting the most snow or precipitation.”