JUST ISSUED: High wind warning Thursday for Roanoke Valley and Blue Ridge westward to West Virginia state line, for possible 60 mph wind gusts. This was upgraded from a wind advisory.
Flirt with the freezing mark, and sometimes it falls on one side of the line, sometimes the other. Wednesday fell on the freezing side as wedge of cold air — displayed by forecast models for days, but varying greatly in strength — proved too much to overcome, and a wintry mix of rain, freezing rain, sleet and snow spread across the region, knocking out power to thousands and causing icy roads leading to accidents, at least one fatal. The storm has moved past now, though some light drizzle, freezing drizzle or snow showers may occur overnight, and some strong and gusty northwest winds on Thursday. Check out this early evening water vapor satellite photo of this powerful storm that has spread a blizzard from Arkansas to Michigan and spawned tornadoes across the South. You can clearly see where the strong jet-stream level winds are cutting out the deep trough (the dark “U-shaped” area).
There is another system coming down the pike rather quickly that, once again, will pose wintry precipitation possibilities for Southwest Virginia. For now, it appears to be the kind of fast-moving wave, lifting Gulf of Mexico moisture over cold air at the surface, that we see frequently during the winter months, and that often produce a quick-hitting light to moderate (1 to 4 inches, or so) snowfall. As the 12Z European model run for Saturday shows at left, there is something of a double-barrel look to the low-pressure system, one to the north and one to the south, and how these pieces of energy interact will determine much about how this storm evolves. For now, it does NOT appear this is likely to be a major winter storm in our region (or heavy rain producer, if it is not cold enough), and it also appears that the temperature structure will not be conducive for long-term sleet or freezing rain. In other words, this will probably either be mostly snow or mostly rain. Where exactly the rain/snow line sets up is very uncertain — in this model at left, the blue colors noting 0C/32F or colder temperatures about a mile up — a very rough indicator of where the rain/snow line might setup — lands well to the south in North Carolina. We should know a little more about this in the next 24-36 hours as the models latch on a little better to how strong the northern and southern low-centers are, and whether the jet stream will amplify at least a little with this energy and bring the storm more northward. Some amplification, or farther south and east amplification, could increase the threat of heavier snow here this weekend, but early or stronger amplification, as with this last storm, could lift it farther north and west and leave our region in mostly rain. The Hydrometeorological Prediction Center has drawn the northern half of Virginia as having the best shot at potential 4-plus inch snows on Saturday — but it is a very low end risk, coupled with a forecast discussion that begins with the words “There is still considerable uncertainty …” As I said above, this is the kind of setup that often brings us a few inches of snow, but the biggest question in my mind is not whether there will be sufficient moisture, but whether the temperature structure will be supportive of widespread snow. It may be easy for the storm draw in just enough milder air off the Gulf with the moisture influx to push the rain/snow line very near or even north of our region. It’s another tough call that hopefully will become clearer by Thursday evening or Friday morning, since precipitation may begin as early as Friday evening.
My best guess: I’m leaning to a 1-4-inch type snow event for most of, maybe all of, Southwest Virginia on Friday night and Saturday. But I’m not all that confident about it, at least yet.
Then we MIGHT be looking at a very similar system next Tuesday or so. It too may be a borderline call. The air mass has become just cold enough for wintry threats, but not cold enough to make them unambiguously snow a few days out.