Tuesday’s missed shot at light snow in the Roanoke and New River valleys was yet another example of how cold air just about never (here, at least) catches up to departing moisture in time for snow. BUT … the same cannot be said for moisture catching up to departing cold air. That happens quite often. It did Sunday for a significant ice storm, and probably will again late Friday into Saturday. In fact, the coming setup may have deeper cold air to work with, banked against the mountains, and moisture may arrive far enough ahead of the parent low pressure system that it won’t already be scouring out the cold air when the first moisture arrives. Moisture arriving into very cold, very dry air loft Friday night into Saturday will trigger evaporational cooling that will probably lead to a period of mixed frozen precipitation, possibly leaning to snow and sleet at first. What does not appear likely to happen is that a low will track south of us and go up the coast, keeping us in below-freezing air throughout the precipitation. The high pressure blocking does not exist downstream to either keep the cold air in or force the storm track to the south, for long. The initial low will likely track west of the Appalachians and transfer its energy to a new low along the coast north of our latitude, a pattern that with enough cold air sometimes lends itself to “hitting for the cycle” on precipitation — going snow to sleet to freezing rain to rain.
As with this past weekend, forecasts for the coming system are highly variable depending on various atmospheric details that can’t be fully discerned at this time. It is very possible this could move toward a cold rain with only a little ice/sleet to begin, or toward a more long-lasting winter storm.