The various National Weather Service offices that cover our area have a WINTER WEATHER ADVISORY in place for the entire region from the predawn hours of Thursday into the early evening as the latest winter weather event gets ready to take aim on the Tennessee Valley area. Accumulations of snow, sleet, and freezing rain look to be a good bet, and travel problems will be a significant issue.
Mostly sunny skies allow us to top out areawide in the lower 50s this afternoon, but winds are switching around behind this frontal boundary, and temperatures will drop quickly out of the 50s, through the 40s, into the 30s by the evening. After we get past midnight, temperatures over a large part of the area will be in the upper 20s to lower 30s. This will be setting the stage for the wintry precipitation to move in.
The latest run of Futurecast has things starting a little sooner, as early as 3:00-4:00 AM from west to east, with an expanding shield of snow, sleet, and freezing rain overspreading the area through the morning, into the midday and early afternoon. Things may start as a wintry mix of sleet, freezing rain, and even rain over northwest Alabama, but as the colder air deepens Thursday morning, the precipitation even over north Alabama will transition primary over to freezing rain and sleet and then sleet and snow as we work deeper into the morning. The winter weather settling in this early in the day and sticking around makes it more likely that our temperatures lock in below freezing, maybe even in the mid to upper 20s, and are then never able to warm. This, along with cloud cover and colder air continuing to move in during the afternoon, will mean there won't really be a chance for roads to improve much at all during the day. Temperatures drop well into the teens overnight, and if there is a decent snow pack on the ground, those temperatures could end up a little lower. We look to stay just below freezing all day Friday, making road recovery slow. Even with temperatures in the 20s, snow can melt off the roads if there is sun, but how much that happens Friday will be determined by how much clouds are able to clear out.
With the latest data trending earlier, colder, and wetter, we have bumped up some of the accumulation totals across middle Tennessee. We have now stretched the 1-3" snow are aback westward to include areas along and north of Highway 64 as far west as Savannah, TN. With higher confidence in a heavier and wetter snow band, we have added a 2-4" accumulation area along the Highway 412 corridor. It is important to pay attention to the full RANGE that is being projected, not just the upper-end of the range. Snow accumulations of 1 to as much as possibly 3 inches look a decent bet all the way down to the Highway 64 corridor of southern middle Tennessee, and there will likely be some light sleet and icing accumulations as well. In northeast Mississippi and northwest Alabama, these areas will be closer to the warmer air aloft, and these regions will likely stay sleet and freezing rain for longer. However, even here, we expect a changeover to snow during the late morning and midday if not sooner. Snow accumulations anywhere from a dusting to as much as 2 inches in isolated spots looks like a good bet as far south as Moulton and Decatur. South of there, we do still expect a wintry mix as far south as Highway 278, and there may be some light icing. However, a good portion of this will be rain there, and we expect little to no snow accumulations.
Another critically important part of this whole event will be dangerously cold wind chill values Thursday, and especially Thursday night and Friday morning. Wind chills will drop through the 20s into the teens as colder air moves in and winds increase on Thursday. As temperatures drop overnight, wind chill values look to drop into the single digits and may even bottom out near zero in places overnight and into daybreak on Friday! Even by midday, wind chill values on Friday look to still range from the mid 10s to the lower 20s. Prolonged exposure to the wind and cold temperatures will be dangerous to humans and pets, and it will be important to take precautions against these conditions.