Wednesday Afternoon Severe Wx Update

WHAT: Strong to severe thunderstorms, with all modes of severe weather possible, including isolated tornadoes.

WHEN: Mainly in the 6:00pm – 6:00am timeframe (all night)

NOTE: I will tell you when we are in the clear, when that time comes.

Please note that my concern and confidence are unchanged from previous outlooks. Remember, my concern is high, in part, because of this being an overnight event. Darkness just adds one more risk factor when dealing with storms. That’s why it is SO important that you have a plan in place BEFORE the storms arrive, especially if it’s after dark. I have given you everything you need to know in previous blog posts.

We currently have light to moderate rain falling across the plateau. This is that warm front that we’ve been talking about for a few days now. The farther north it gets, the more unstable our atmosphere becomes. It still looks like it will get north of much of the plateau.

The one thing I want us to get away from is the idea of not having much/any sunshine makes everything better. We get many of our storms at night. IF storms come in the day, the sun matters. At night, when we get most of our severe weather, we pay more attention to wind shear. Remember, Baxter had a tornado at 1:00am. Tansi was hit in 2001 at 9:00 pm. See my point? Again, storms by day ARE enhanced by sun, so if we get any sun this afternoon and a storm pops up, be leery of those storms.

So, what is wind shear? Those of you who have taken my weather classes know all about this. Winds near the surface are usually slower than winds up high. The winds here at the surface are slowed by trees, buildings, etc. The winds up high have little to no obstruction. The faster winds that are on top of slower winds cause the air to roll. This is part of what we call “wind shear”. If a storm ingests that rolling motion, it can stand that rolling air up vertically, leading to a rotating updraft. Sometimes, that rotation reaches the ground. Most of the time, rotation never reaches the grounds. Tornadoes, even in the worst of outbreaks, are rare occurrences.

Pictured below is that rolling motion that results from faster winds aloft overrunning slower winds at the surface. Notice that wind motion makes the air roll.

The warm updraft of a storm may ingest that rolling motion, stand it vertical, and lead to an rotating updraft. Most rotating updrafts do not produce tornadoes. Some do. The image below is typical thunderstorm, with just updrafts and downdrafts. The updraft brings in the warm, moist air and the downdraft is the descending, rain-cooled air. All storms begin as just updrafts. As clouds build and become full of water droplets, the droplets fall, leading to the formation of a rain-cooled downdraft.

If the air is rolling, like mentioned above, the updraft may ingest that rolling air, stand it vertical, and then cause a rotating updraft, as seen below. Notice the tornado is the bottom of the updraft and often at the very rear of the storm, after the heavy rain, gusty straight-line winds, and hail have passed.

So, what does all of this mean? Tonight, it looks like we will have plenty of wind shear. Winds just up off the surface will be really fast, while winds here at the surface will be much slower. Any storm that can get strong enough (strong updraft) to pull that spinning air (rolling motion) upward will have the potential to rotate. That is something to be mindful of.

FYI…If you know anyone in Mississippi, West Tennessee, or Alabama this afternoon make sure they’re watching the weather. Things are getting very rough down there.

Know where you are. I have a county map below. We will watch for warnings for White and Putnam, if they have warnings issued, because those storms will move our way. Those of you in Fentress county will watch for Putnam and Overton Counties.

Make sure the weather radio is on! If it has static, try moving it around the house and see if it comes in better somewhere else. As for apps, the Red Cross Tornado app is good, as is the WATE-Weather app from Channel 6 in Knoxville. Have multiple ways to get warnings! Have someone call/text you if they know of something coming, as another way to get a warning.

You can rely on me for information (I hope you do!) but you will rely on the NWS for warnings. I can’t issue warnings, nor can anyone else.

If you message me, be patient. I am slammed with messages and many of them pertain to folks wanting to know how to set up their weather radio, where to find shelter, etc. In other words, they are very important questions. I had one person message me this morning and ask if I knew bad weather was coming!! Yeah…

So, let’s just all be weather aware. We will likely be placed under tornado watches tonight and there will likely be warnings issued all across Middle Tennessee. I’ll track it all and we’ll see if anything makes it to us.

I’ve just noticed that the warm front is, indeed, lifting more northward now and we will all soon be in the unstable warm sector behind the warm front. We may get a peak of sun but that doesn’t matter since most of these storms will come much later. The atmosphere will only become slowly more unstable as we go through the rest of the day and night. Be weather aware.

You all take care and please don’t hesitate to reach out and ask a question. I may refer you to previous blog posts but you will get an answer. In fact, most questions I get have already been answered in previous blog post, just an FYI. 🙂

I will update, as needed, so stay tuned. Tell your friends to follow this blog! I’ll keep you all as informed and safe as I can!

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