We are entering a period of weather like we might not see again for a long time around here. There are two opportunities for accumulating snow in the Tennessee Valley this week, and both of them have potential to cause some real travel headaches starting tonight lasting through at least Thursday.
Let’s start with what we know for sure: the air is cold enough for this to happen. It’s not a question of rain or snow; it is a question of how much snow. Soil temperatures at a four-inch depth are around 34 to 38 degrees. That’s cold enough for accumulation, and today’s cold rain and drizzle will chill highways and bridges to the point that it will not take much before this precipitation moving into the area starts to create patchy ice this evening. The main problems start taking shape after midnight through midday Tuesday.
The big unknown with this first wave of winter weather is the exact northern extent of the precipitation. If you have followed the modeling, you’ve seen it swing back and forth from nothing to a little to a lot. This is the morning NAM’s snow accumulation chart; it may be a little overdone in spots because it is using a 10:1 snow-to-liquid ratio. Our ratio will be more like 8:1 tonight and Tuesday morning. It’s not a big change, but it will be the difference between 2″ of snow and 3″ of snow in some cases.
I’ve also noted the areas where there seems to be an error in the model – I do not think the snow misses US 72 completely as is displayed in the graphic:
Expect tough travel in the morning – especially in areas south of US 72 closer to US 278 in north central Alabama. Any areas that get more than 2″ of snow will probably not thaw at all on Tuesday leaving icy roads in place. Places that get a dusting or up to one inch will have a chance to thaw some on Tuesday afternoon as snow ends and temperatures rise just above freezing.
Another More Significant Storm? Tuesday morning’s snow is nothing to scoff at; it will cause some problems for us, so be ready for it. There is another system coming on Wednesday that could bring a much more substantial snowfall area-wide. It is more of a classic winter storm, and it is not out of the question that some of the higher terrain in northeast Alabama could have as much as 6 inches of snow or more between the two systems. This is the latest GFS plot showing the total accumulation between both snow events through Thursday morning:
We will be initiating a live blog soon so that all information will be found on one single link instead of multiple posts.
We need your reports to help piece all of this together. If you know of icy roads, have a photo, or have a snow depth to report, send it to us. The fastest way is through social media – on Twitter use the hashtag #valleywx. You can e-mail photos to firstname.lastname@example.org.