The forecast for the next 24 hours is going to be a very interesting one, and even though we're now to the day of the "event", there are STILL questions and inconsistencies in some of the data. Rain is already starting to move into parts of the area from the southwest, and these showers will overspread the area into the midday and afternoon. There may be times when the rain is locally heavy, but storms or severe weather are not expected. Highs today climb up into the mid 40s, and then we watch the temperatures as we begin to head toward evening.
Colder air begins to filter into the area this evening from northwest to southeast as the surface low off to our south passes by and the upper-level low approaches overhead. Temperatures by evening start dropping into the upper 30s, and by late in the evening, we get down into the mid 30s. This is when we will have to begin watching for the potential for a mix of or changeover to light snow. Because temperatures right near the ground and in the lowest few hundred feet of the atmosphere are above freezing, it will take heavier precipitation to bring the snow down to the surface. We still expect that to occur in many areas across southern Tennessee and maybe down into northern Alabama.
However, the latest computer model runs overnight and early this morning have trended lighter and drier with the precipitation tonight. This would make it harder for the changeover to snow to sustain itself for a longer period of time. Because of this, our updated snow forecast for tonight is a slight scale downward, even though it is a very small change. For areas of southern middle Tennessee, especially from Lawrence and Lewis counties, eastward through Maury, Marshall, and Giles Counties, we are now forecasting a general dusting to maybe up to 1 inch in spots. Because it will take heavier precipitation to bring the snow to the surface, these totals will be scattered and won't be even across that entire area. Areas in lower elevations will see less, while areas on ridges and hilltops MIGHT stand to see a little more, simply because that elevation puts them closer to the cold air and the snowflakes have less time to melt before reaching the surface. For most of the rest of the viewing area, from Wayne and Hickman Counties west through southern west Tennessee, through northeast Mississippi, and north Alabama, we expect the potential for still light snow mixing in... but we don't really expect much in the way of accumulations. However, we can't rule out maybe a light dusting on car tops or the grass here either if it comes down heavy for a little bit. Most folks in these areas won't see much more than flurries though.
All this wraps up going into early Friday morning with decreasing clouds through the day. The weekend looks overall quiet with a mix of sun and clouds and highs hanging out between the upper 30s and low-mid 40s as we await the next weather system due in by Monday.
This is the weather system we've had our eye on for several days now. A strong trough of low pressure in the upper atmosphere ejects out across south central Texas on Sunday, spinning up a surface low in the northwest Gulf of Mexico. These track eastward going into Monday. On the outside looking in, this GENERAL setup is your classic "Gulf low" setup for accumulating snow in the Tennessee Valley. HOWEVER, it is the exact details of the setup that determine whether or not that actually plays out.
ALL of the computer models have been steadily coming into better agreement on a general idea that puts accumulating snow either here OR near here. The GFS, the Canadian, the UKMET, and the Euro all are coming into better agreement on that general idea. The Euro ensembles have actually increased the probability of 1 inch or greater of snow across our area for Monday to a 20-40% range, doubling what those numbers were just 36-48 hours ago. The trend in probabilities is up. Looking at the range of the individual Euro ensemble members, almost all of them show accumulating snow in both southern middle Tennessee and northwest Alabama by early next week. There is a good signal for the OVERALL IDEA.
HOWEVER, the devil is in the details, and it's those exact details that make or break this. It's also those exact details that we just have NO WAY of possibly knowing just let. The latest trends in all the models have been for the system to be stronger and to be wetter. This is usually a signal that there will be a heavy, wet accumulating snow somewhere, with the potential for significant snow totals just north of where the rain/snow line is. However, those same mechanisms that allow that are also trending toward warmer air nosing in across a large part of Alabama, except maybe the Shoals, but it might be a close call there... and we can't rule out those same issues in southern middle Tennessee as well. That would have a MAJOR impact on snow totals, or if we're even able to pull off accumulating snow in our EXACT area, or if it's just a close call for us and it happens near by. That's just something we have NO WAY of knowing just yet, and it's probably going to be another day or maybe two before we really start having a good handle on the details like that.
The main message right now about Monday is that there is increasing agreement on the general IDEA on what may be an appreciable winter storm... either somewhere nearby to us or possibly including us. There is NO way to know exact amounts or exact locations. We CANNOT tell you if heavy snow will include our viewing area or if it will be a near miss and be a few counties away. Regardless, it is definitely close enough of a situation that you need to stay in touch with the latest weather information as we go through the rest of the week and the weekend. Old information is bad information. Just like milk, weather information has a short expiration date. As we head into tomorrow and Saturday and the upper-level system begins to take shape over the western United States, we will start to have a better idea of how it will evolve as it comes eastward, and that will start to allow us to begin hammering out smaller-scale details like where and how much. Be sure to keep checking back with us as we continue to work out these details!