Clouds are widespread across the Tennessee Valley this Saturday afternoon, and rain is not too far away. Showers and storms are as close as northwest Mississippi, southwest Tennessee, and another batch in west Alabama that is moving northward with time. None of these are severe. What we’re watching is how this northward/northeastward moving afternoon rain interacts with a wedge of cooler, drier, and stable air originating from Georgia and the Carolinas that extends over into our area. There’s a very real chance that the rain spreading up into this stable air mass currently over us may help reinforce it over our area and keep the severe storms later tonight off to our south. That’s been the most likely outcome all along, and it is trying to play out in reality. However, as we have also mentioned, it’s going to be a close call, and for your safety, we have to be cautious about it just in case.
The freshly issued outlook from the NWS Storm Prediction Center maintains a lower-end Level 2 of 5 risk of severe storms for tonight for areas along and south of a line from roughly Hohenwald to Lewisburg in Tennessee and then southward through northwest Alabama and northeast Mississippi. An even lower Level 1 of 5 risk of severe storms is maintained north of there in Tennessee. In both risk areas, this is a very uncertain and lower-end type risk. There is a very real potential that the severe storms stay to the south of our area tonight. However, because of the strength of the dynamics in the atmosphere with this weather system, we have to play it on the safe side. IF storms are able to become severe in our area, the main concerns would be spotty damaging wind gusts of 50-65 mph along the line of storms, along with the potential for an embedded tornado or two. In addition, heavy rain will likely cause localized street flooding, especially in low-lying and poor drainage areas. Small pea to dime size hail can’t be ruled out, but large hail is not a big concern in our local area with this system. Farther southwest of us, this remains a much different animal with a somewhat rare Level 4 of 5 risk of severe storms for central and south Mississippi, southwest Alabama, and north-central Louisiana. There have already been tornadoes in Texas and Louisiana today, and there could be a few long-tracked strong to potentially violent type tornadoes in those areas. That level of risk is WELL south of our local area here and will NOT be moving north towards us!
Above is an overall Futurecast type timeline projection of events using the HRRR model. It is doing a reasonably decent job at depicting things currently. As we head deeper into the late afternoon and early evening, moderate to heavy rain with embedded thunder from north Mississippi and west Alabama looks to spread northward into our area. This action will not be severe as it moves in. This is the rain that may actually help to reinforce the stable air mass over our area and reduce our local severe weather risk for the overnight. By 9:00-10:00, a more organized line of storms will begin to approach from the west and then move eastward across southern middle Tennessee and northwest Alabama from then on through 12:00-2:00am. IF there are going to be severe storms in our area tonight, it will be with this line of thunderstorms. Even if the storms are NOT severe, they will have a lot of lightning, will have heavy downpours, and will be capable of 30-45 mph wind gusts. However, we can’t rule out the potential for a few places in the line to produce 50-65 mph wind gusts or produce an embedded tornado or two. Notice, though, that the model never brings the temperatures up out of the upper 50s and lower 60s as the line moves through. This is telling me that there’s a very reasonable chance the stable air may stay in place and try to prevent these storms from doing something too rough. We just have to play it cautious and safe though, just in case! When you have an organized line of storms and a dynamic weather system like this, it takes very very VERY little surface-based instability to produce damaging winds or a spin-up tornado. Even if it feels cool outside, the dynamics from the storm system can sometimes overcome that. That’s why we have to be cautious and give this a little more attention than we otherwise probably would.
Even though there’s a very real chance the damaging stuff stays south of us overnight, it is critical that you are weather alert and ready to act if warnings are issued for your area. Make sure you have multiple reliable methods of hearing warnings, including something that will wake you out of your sleep since this will be an overnight threat. Know where you will shelter, now ahead of time while the weather is still calm, in the event a dangerous storm threatens your area. We will be staffed in the weather center overnight and ready to provide LIVE coverage should any severe storms threaten our area!
