November ends on Saturday with the month averaging more than 3 1/2 degrees below normal at both Roanoke and Blacksburg. So much for the mild November many were projecting at the start of the month. One of the culprits in offsetting some other factors pointing to mild was likely the negative phase of the Eastern Pacific Oscillation, which meant high pressure in the northern Pacific (farther west than we would see with a Pacific-North America-positive pattern, though the two sometimes coincide) consistently dumping Arctic air through central Canada into the central and eastern U.S.
Keeping that in mind, we should be cautious of similar projections for a cold December being issued around the Internet — though I think those projections have some solid basis in available data. Over the next week or two, we are going to see to a huge dump of cold air into the Northern Rockies, slowly oozing south and east with time. The upper-air flow over us will turn southwesterly ahead of the cold air push, and this would often mean a significant warmup, but that may be resisted at least for a while by a tendency for high pressure off the East Coast to push in easterly and northeasterly surface winds. So we may only see a gradual moderation of temperatures to near normal (50s highs, 20s-30s lows) over the next several days, with a reinforcing cold front Monday or Tuesday knocking temperatures back just a little bit again. Perhaps sometime after that there may be a shoot-up into the 60s for a day or two. There has already been some model-driven speculation about the Dec. 8-10 period possibly producing a wet storm system that could be wintry in nature near us. About that time, the cold air may reach a point where it is bumping against milder air near or just south of us. The boundary between mild and cold is typically where the storm track sets up. It’s way too far out to pin too many details, including the exact advance of the Arctic air and even the existence of a potential early December wintry threat. But if the blocking in the North Atlantic and over the Arctic sets up in December as some models have hinted at, colder air may spread south and east with vigor and become locked in for a while. None of this would guarantee snow for us, but certainly would tilt the odds toward patterns that would favor potential wintry weather events (as long as the cold air push doesn’t become so extreme it suppresses the storm track into the Gulf of Mexico and Florida.) There is also some chance the cold air digs more into the southwest and we end up with milder southwest-to-northeast flow much of the first half of the month. The jury is out.
The next several days offer nothing particularly extreme or inclement for Southwest Virginia, with mostly dry weather and cool temperatures.