As you may have seen on the internet from the local National Weather Service or Nashville media outlets, yes, there is a low-end Level 1 of 5 risk of severe storms for late tonight (after 3-4am) across west Tennessee and then that expands across a large part of middle Tennessee for the rest of the morning hours of Wednesday. This is issued by the Storm Prediction Center office in Norman, Oklahoma. They are the national-level branch of the National Weather Service that not only issues tornado watches and severe thunderstorm watches, but also these severe weather outlook forecasts. So yes, this is official information. And no, they are not hyping up a big threat by any means, but after looking at everything CAREFULLY, our team thinks that even the low-end type threat has a very slim chance (if any at all) of verifying.
Heavy rain and embedded thunderstorms will still mainly be situated north/west of the I-40 area through 4-6am, although there could be a spotty shower or thundershower here overnight tonight. As we work past sunrise, that band of rain and storms gradually sinks southeastward into our area, entering our viewing area on the northwest side between 8-9am Wednesday morning and then working southeastward through the viewing area through the rest of the morning into the early afternoon. Notice, however, that there is a drastic weakening of the storms as they move into the area. This is despite temperatures warming well into the 60s ahead of the line as it approaches. That weakening continues as the activity shifts deep into north AL through the late morning and afternoon.
Above is a projection of the lightning activity with the storms from the Baron Futurecast model. This tells the story pretty clearly. Lightning is still pretty frequent northwest of I-40 before sunrise, but as the storms move into our area by mid/late morning, the lightning just collapses as the storms rapidly lose their intensity. This continues as the storms shift into north AL by late morning and the early afternoon. It’s not just the Baron model that shows this. The HRRR, the various WRF models, and the 3k NAM model all show a similar situation.
One main reason why the storms rapidly weaken and fall apart as they are modeled to do appears to be that the line orients itself parallel to the mid/upper level winds (the red arrows on the maps above) as it first organizes overnight to our northwest and then stays parallel to the mid/upper level winds as it gradually sinks into our area. This causes the storms within the line to be messy and all rain into their neighboring storms along the line. That helps push the rain-cooled outflow air from the storms out ahead of the line so that the line itself can’t tap into the warm, humid, and unstable air out ahead of it. We would have some concern for gusty winds if there were segments in the line that were getting themselves more angled to the mid/upper winds. That does not appear to be the case, and this is the type of storm evolution that you would expect from the type of setup we will have in place late tonight and tomorrow.
We will certainly still have eyes on radar, and there will be one or more meteorologists staffing the weather center tomorrow morning as the storms move in. We don’t ignore threats. However, we just can’t find any real reasons to be truly concerned about the storms tomorrow. Should you still pay attention in case a stray storm along the line does try to misbehave? Yes. Should you be worried or overly anxious about this weather system? That answer is a firm NO.
