Tornado ‘hot spots’ and what we’ve learned since April 27th

April 27 Anniversary
This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

LIMESTONE COUNTY, Ala. – It is more than a sense of déjà vu. History does repeat itself, especially when it comes to weather.

It’s obvious, just on the surface of Alabama’s history with tornadoes. Research has proven Alabama to be among the most tornado-prone regions of the country, but there are some spots within our state where that seems like an understatement.

Take Tanner, for example. 

Alabama’s tornado database only goes back to 1950.

In that seven decade span, though, 41 tornadoes have come within 10 miles of Tanner according to Storm Prediction Center data.

In the exact same time frame, only 23 tornadoes have come within 10 miles of Lester in the northwestern part of the county.

It’s obviously not random chance; there’s something more to this.

Is it the Tennessee River?

You may often hear, “it’s the river,” when tornado history comes up around here. It’s one thing to say it, but it’s quite another thing to prove that there’s a cause beyond some bad luck. 

Enter UAH research meteorologist Dr. Tim Coleman.

“I think there’s some combination of both,” he said. “You would need to prove it with absolute certainty. You would need hundreds of years of tornado data, but we know that there are physical processes that happen that are stationary. They’re related to things like mountains, friction, different types of land cover and heat.”

“Things like that that are stationary. We do see some theories and the tornado maximums, at least some of them, match the theory. So, some of the tornado minimums and maximums we can explain, but others, we look at them and say we really don’t know what’s going on here.”

Dr. Coleman says we have some understanding of why communities like Tanner seem to be in the bullseye so often; we just don’t know it all yet.  

“In southern Limestone County, the air blows over the Tennessee River, so it speeds up due to lower friction,” he said. “Then when it comes into the county, it goes over land and starts getting over the urban areas, around Athens and west Huntsville out near County Line Road, so it starts to slow down. That creates a convergence of the air and sometimes can be a trigger for a tornado.”

Surface roughness changes from the land to the smooth river may enhance shear, but it’s not the only reason southern Limestone County is a tornado ‘hot spot.’

Friction is resistance, and land surface changes produce friction when air blows over them: influencing the wind speed and direction. When wind speed and direction change over short horizontal distances and in the vertical that increases the shear available to a thunderstorm for tornado development: sometimes.

Model of tornado development in a thunderstorm

How does this help?

Researchers at UAH work on this problem daily with the goal of improving tornado warnings.

Dr. Coleman says research continues to be promising in identifying reasons why some places are more tornado-prone than others, and that will lead to better warnings from the National Weather Service.

The meteorologist issuing a tornado warning will have a better tool to know how a storm should behave moving into a particular environment, which, in turn, will give more lead time for real tornado-producing storms and reduce false alarms in other instances.

Information like this also helps us at News 19 in conveying urgent, local information when a tornado occurs.

Dr. Coleman’s work is more than identifying trouble in the here and now; he is also working on a new forecast index to better predict tornado-producing storms.

“I’m working on something called ‘SHAPE,’ which is kind of like instability, but it’s created by wind shear,” he said. “Sometimes in the winter time we have these events where there’s almost no instability, but we still have some tornadic lines of storms, so I’m working on a parameter to help predict those. We don’t stop. We’re always looking for new things.”

How concerned should you be if you are near a ‘hot spot?’

We know from living in the state, Alabama, in general, is a ‘hot spot’ for tornadoes. Dr. Coleman’s research shows none of us are ‘safe,’ but that does not necessarily mean we should live in fear.

“Any one location still has about a one in 200 chance, and this is in the highest risk areas of Alabama, about a one in 200 chance of actually being hit by a tornado,” he said. “On April 27, 2011, about 1.1 percent of the land cover of Alabama was hit. Now that’s a lot, but that means you had a 98.9 percent chance of NOT being hit by a tornado that day.”

In April 2014, Dr. Coleman and Dr. Grady Dixon defined a new ‘tornado alley’ in the South: Dixie Alley.

A region from near Jackson, Mississippi, northeast to near Decatur, Alabama, had the highest concentration of strong to violent tornadoes in the nation between 1973 and 2011.

Coleman & Dixon: Average annual path length of all significant (F-2 to F-5) tornadoes passing within 25 miles of a point between 1973 and 2011.

The heart of that zone is near Dr. Coleman’s property on the Walker-Jefferson County line in Central Alabama. One unpublished figure from the paper, An Objective Analysis of Tornado Risk in the United States, surprised Coleman, but it does not scare him.

He discovered that the highest probability of a tornado in Alabama is right at his house on the Warrior River, but Coleman says he does not live in fear, and neither should you.

“People think they’re safe on the side of a mountain or down in a valley,” he said. “None of that is true. You should never be cavalier about it even if you live in a tornado minimum. But if you live in a maximum you should not panic either!”

Arm yourself with knowledge, and be prepared with a plan. That’s how you can avoid panic.

A NOAA Weather Radio is the best, tried-and-true way to make sure you get a warning when severe weather approaches.

You can also get up-to-date, location-based alerts wherever you are on Live Alert 19: available on both iOS and Android devices.

It’s what you do with the information that matters. Your tornado safety plan should be simple but flexible. It needs to be flexible because we do not always have fifteen minutes of lead time, sometimes it’s less than five minutes.

Being prepared and informed is the key to handling severe weather.

Copyright 2021 Nexstar Media Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.