The Supercell

Weather forecasting certainly has its challenges. I’ve said that many times. Most of the time we can know it’s going to rain. Then we have to forecast the amount. If you’re off a tenth or three no one really notices. You say it’s going to rain and it rains. Everyone is happy. Well, except for the ones who didn’t want the rain (ha).

Then, there’s the wintry precip. You know something will probably fall, but then you have to decide in what form that something will take as it falls, and then you have to decide how much of that something is going to fall. If you’re off an inch or two of snow everyone notices. By the way, that would only be a tenth or so of rain.

Sunny, windy, cloudy, foggy, frosty….so many things to forecast. But, it’s actually kinda fun and for those who love a challenge the atmosphere is chock full of challenges!

Billions of trillions of equations that change every second from the surface to about as high up as your eyes will let you see, all moving along a rigid surface that rotates on a big ball of blue and green that we call Earth. You want a forecast for that? Piece of cake.

Last night’s storm demonstrated that those equations can change too quickly and in a bad way. The Storm Prediction Center missed it. The National Weather Service missed it. Heck, even your own Meteorologist Mark missed it. No sense denying we all went to bed expecting “a strong storm or two” and woke up to damage in neighboring Putnam County that rivals some of the strongest tornadoes we’ve ever seen on our plateau.

And then there’s those who went to bed and woke up in the next life. That part really bothers me, so we’ll focus on the meteorology of it all for now.

All it takes is one storm. One. Single. Storm. The image below is of some of the storm reports from last night’s storm. Normally, with tornado situations we see multiple paths across the state, but not so with this situation. We just had that one storm to worry about. Look at that straight line of damage across the state.


In the end, I truly believe the cooler environment of the plateau did save us from a significant tornado. When I made my last forecast for last evening, I figured the cooler air would save us from any significant severe weather. My post stated,

“The main threat we would face is gusty winds and some small hail. In other words, perhaps a storm or two could still be on the strong side when it gets here. Temps decrease rapidly with height right now and that could lead to some small hail in the stronger storms.”

We certainly had a stronger storm slide across northern Cumberland and southern Fentress Counties. It was a small storm but fierce. I had a ton of hail at my house and winds of at least 50-60 mph. Don’t get me started on the lightning! Geez.

The storm formed a couple of counties west of Nashville. It formed alongside another supercell but it quickly became the dominant cell as it quickly slid east.

In the radar image below, the supercell in question is the darker reds you see over toward Knoxville (circled). What I want to point out is the absence of precip south of this big shield of rain. That unstable air was feeding right into the supercell as it slid along the southern edge of that precip shield. That one supercell traveled 275 miles in 4 hours and 15 minutes. Let that sink in a minute.


The map below shows the strength of the rotation as the storm moved along. The brighter blues represent stronger rotation. The map is centered on the Nashville area. Carthage is on the far right side of the map.


I was thinking a lot today about forecasts that went off the tracks in the past. I remembered the Blizzard of ’93 and how 4-6 inches of snow turned into 18-24 inches. I remembered the wet snowstorm we had in February 1998 and how a cold rain turned to 10 inches of destructive wet snow. I remembered May 3, 1999 and how, in the heart of Tornado Alley and where the best of the best experts reside, a forecast for a few severe storms turned into one of the worst tornado outbreaks in Oklahoma history. Chasers were told not to bother chasing as late as that afternoon. Nothing to see here, folks. Even the environment that produced Tennessee’s one and only F-5 in 1998 wasn’t THAT impressive. We knew severe storms were coming but an F-5? No way.

You know what concerns me about the things I just mentioned in the paragraph above? Even today, I’m not sure any of us would have “seen it coming”. And these are the BIG events. I dare say I would never forecast nearly two feet of snow in the middle of March. I doubt any of us would have seen a low pressure that would strengthen by leaps and bounds and pull cold air from the atmosphere above to make a wet snow. How does that even happen? I doubt any of us would predict May 3 even today (today’s computer models still don’t forecast that outbreak when given the data from that day).

Billions and trillions of equations changing every second on a rotating sphere with a rugged surface. It’s enough to make the brightest physicists cringe.

Yet, that’s what I have to make a forecast with. It’s what meteorologists do. We analyze, analyze, analyze and then we analyze some more. We get it right most of the time and that’s why you trust us.  That’s why it bothers us when we miss one, especially the big ones. We compromise your trust.

I love weather, I really do. I love the equations and I love the challenge! I love the power of nature and I love seeing it and experiencing it. I love telling you all what I think it’s going to do. And I really love it when what I tell you is going to happen….well, happens!

That’s a good day and I’m thankful for many of those.

But the bad days teach us. May we learn from the bad days.

Switching gears….

Super Tuesday is a special day for me. No, it has nothing to do with politics! (ha) I saw my first tornado on Super Tuesday of 2008 out in West Tennessee at Jackson. Super Tuesday was on February 5th that year (tornado season got off to a very early start!). Wow, what a day that was. A half-mile wide EF-4 roaring by. No drug or drink can compare. My first tornado was well forecasted. We KNEW big tornadoes were coming that day.

When I think about last night I wonder what I could have done differently? Even if I had stayed up long enough to see the tornado-warned storm coming into Nashville, I think it’s safe to say I would have downplayed it for us. We were 100 miles away and 48 degrees at 10:45. It was too cold for bad storms.  Right?

This storm didn’t need warmth. Even temps in Nashville were just in the lower 60s, with dewpoints in the upper 50s. That would support a strong storm, for sure, but not a violent tornado. Shear was really high but we see high shear events all the time this time of year around here. The amount of energy available (CAPE) was pitiful and certainly nothing that could support a long-track tornado. Right?


With the knowledge and tools we have in 2020 we missed something. Did we miss something we don’t have in our meteorology tool box yet? Is there another variable we haven’t learned yet? What did we miss?

There was a potent disturbance moving overhead. We call it a shortwave. I’ve seen these things create forecast surprises many times. Is that what happened?

I’m confident this storm will be studied very closely. It created it’s own environment and that is very, very rare. There’ll be conferences that feature a talk or three about the March 3, 2020 Tennessee Supercell. And yes, there’ll be papers published. It’s all but certain.

And we’ll learn from it and we’ll be better for it.

Let’s not forget we are in tornado season. Yes, it snowed just this past Thursday but this time of year is all about change. It’s March and March, April and May are our main severe weather months in Tennessee. Have you and yours practiced your severe weather plan to the point that you could do it with  your eyes closed? Could you do it at 2:00 a.m. with no power and hail slamming into the windows as the wind roars outside? Practice, practice, practice.

You’ve heard the spill…interior room, ground floor or basement, head protected (use that bicycle helmet!) and put as many walls as you can between you and the outside. It’s like a sick came of hide and seek where your life depends on how well you hide.

It’s spring. It’s tornado season. Get a weather radio. Do NOT rely on me for warnings. That’s not what I do. I’m one person and I have faults. You must get a weather radio. There are good phone apps out there too but you have to shop around for that. I use weatherTAP and so I’m not familiar with any others.

Have multiple ways of getting warnings! Download an app, have a weather radio, etc.

Understand what a warning is. That means a tornado is either occurring or is very, very possible. Understand the polygon! Warnings these days are issued by polygons, not by county. If there’s a tornado warning for Rinnie and the storm is moving east, why on earth would you panic if you live in Grassy Cove? If you’re not in the polygon, don’t stress out about it. Pay attention, yes, but don’t overreact if you’re not in the polygon.

In the example below, only those folks within the red polygon should be taking cover for a tornado. That’s why the NWS moved from county-wide warnings to polygon warnings many years ago.


I love giving you all the forecast and other educational weather information, not to mention my rocket launch coverage! I really, really do! I enjoy preparing you all for the weather that is coming. You just cannot rely on me for warnings. I do my best, that’s for sure, but I’d rather you hear the warning on your weather radio, take shelter, and THEN get online to see what I’m saying about it. That’s the ideal scenario. Get a weather radio. I’ll even help ya set it up if you bring it by weatherTAP.

This is the one most everyone gets. You can find others, of course, but this is definitely the one I recommend.


Finally, our hearts go out to all those who are hurting tonight. Some have lost a lot. Some have lost their everything. They need our love and they need our support.

I’ll end with something I saw today that makes this all bearable. Cookeville Regional Hospital issued a plea for blood donations. With so many injuries, there was a lot of need for life-saving blood. This is the hospital this afternoon. Lined up out the door. That’s my Tennessee.


You all have a good night.

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