A winter weather advisory is in effect through 10 a.m. Saturday for several counties north of Roanoke and along the Blue Ridge from Roanoke and Blacksburg southward, as patchy freezing drizzle and light freezing rain may redevelop, especially in higher elevations, overnight and early Saturday.
The murky winter of 2012-13 rolls on. Temperatures along some of the Blue Ridge and in some areas north of Roanoke in the Alleghany Highlands and southern Shenandoah Valley did not get above freezing today. Additional light rain or drizzle developing overnight as a low tracks northeastward to our south (not a bad path for a snow-making storm, were it not for the low over the Great Lakes sweeping in warm air aloft) may add a little bit to the ice in some of those places that didn’t get above freezing, especially at higher elevations. That’s why the National Weather Service continued/re-issued the winter weather advisory for the counties north of Roanoke and then along the Blue Ridge from Roanoke and Blacksburg southward. Roanoke city and probably even most of the New River Valley will probably stay above freezing overnight and Saturday morning.
The stubborn wedge may not fully break on Saturday – highs could struggle to reach into the 40s – but should by Sunday, as westerly winds behind a cold front trigger downslope warming (ironically) for a day with lots of highs in the 50s before somewhat colder weather returns early next week. The 12Z European model chart for Tuesday morning may look mighty familiar, with a low tracking well to our west and a dribble of colder air (the blue colors) slipping into western Virginia. This is a third system similar to last Tuesday’s and Friday morning’s that could spread some moisture over a cold-air wedge late Monday night and early Tuesday, and thereby create some possible snow or ice at the start of the precipitation. In this case, it appears the flow of warmth and moisture from the low will be too overwhelming, and the retreating cold high too ineffectual, for the cold to hold long, and this may even turn into a sizeable well-above-freezing rain situation.
The Tuesday storm is the caboose on the train of these lows that have tracked southwest to northeast from the southern Plains to the Great Lakes. This low will morph into a slow-moving upper-low over the eastern Great Lakes or southeast Canada that circulates cold air, relative to normal, through the southern and eastern U.S. High pressure building westward across the north Atlantic into eastern Canada will trap it there, and high pressure building in the western U.S. will also help pump in a cold period to start March in the southern and eastern U.S. A few disturbances squirting across the South will have to be monitored for winter weather potential, but models have very different ideas on exactly how the big features line up and what they do to these systems. For now, I’m doubting the big storm potential at least through March 3 in our region, as it appears the trough may be centered too far east and the low near the Great Lakes too far south and west to guide systems in the right manner to make that happen. But some smaller snow/ice situations are quite possible. And of course, things can change, either direction.