Tornado Survey Science: How Experts Tell The Difference Between Tornadoes And Straight Line Winds

Inside The Tornado Damage Survey Process

After a powerful storm tears through a community, a few big questions often follow: Was it really a tornado? And if so, how strong was it?

That answer doesn’t come instantly. Instead, meteorologists and storm survey teams begin a careful investigation to determine exactly what happened and how strong the winds were.

Meteorologist Rob Shackelford explains that the process starts with one important step: waiting.

“First off, people have to wait until the severe weather actually leaves the area. Oftentimes, people are waiting for that tornado report to come in, but they have to wait. They can't go out there until the storms have moved on," he warns.

Once the storm is gone and conditions are safe, survey teams head into areas where damage has been reported. They also look at where tornado warnings were issued and where meteorologists suspected a tornado may have touched down as the event unfolded.

When surveyors arrive, they begin inspecting the destruction, looking for things like broken roofs, downed trees, damaged buildings and power lines.

(MORE: What Is Tornado Alley?)

How Tornado Strength Is Measured

When you see an EF rating, it's not actually a measure of wind speed, but instead an estimated peak wind of the tornado. Take an EF3 storm for example: Even if most of the damage was EF2 rated, if the worst was considered to be EF3 strength, then that becomes the official designation.

Storm teams evaluate this by looking at what they call "damage indicators," or DIs. These can be buildings, power lines, trees or anything else with a structural integrity that could be measured against the weather.

Each structure is evaluated based on how badly it was damaged, called the "degree of damage," or DOD.

(MORE: Do You Know The Difference Between These Tornado Warnings?)

Not every storm investigation is straightforward, and sometimes the damage doesn’t tell the whole story. In those cases, meteorologists and survey teams turn to radar data and post-storm engineering analysis to confirm details that are unclear on the ground.

Tornado Or Straight-Line Winds?

One of the biggest goals of a damage survey is figuring out whether the damage was caused by a tornado or by straight-line winds.

“What tornado surveyors are most looking for is how the pattern of damage is looking. Should all the trees be falling in one direction, that's usually a straight line wind event," Shackelford explains. “When trees are converging, falling on each other, or in a very chaotic manner, more often than not, that's what a tornado is.”

This happens because tornadoes pull inward toward the center of the rotating vortex.

Many people assume tornadoes cause the strongest winds in storms. But that’s not always the case.

“Straight line winds can actually generate wind speeds that can be comparable to a tornado," Shackelford says. “Everyone always thinks that tornadoes are the ones that do the most damage.”

Unsung Heroes

Storm survey teams don’t just document damage. They also help communities understand what happened and how to prepare for future storms. Shackelford believes their work often goes underappreciated.

“People who do tornado reports do actually care about the communities. They go out and they try to help people get the community back on track as quickly as possible," he notes.

And by studying storms after they strike, these investigators play a key role in improving safety and awareness, helping people better understand the incredible power of severe weather.