- [man] Tornado's right behind us is crossing right here.

[debris falling] - Tornadoes are among the most violent natural phenomenon on earth.

And despite decades of study, there are still a lot of questions that have yet to be answered.

But what we can observe about them is fascinating.

They're found on every continent except Antarctica but the US has larger tornadoes and more of them than anywhere else on Earth.

And if you think you know where the riskiest areas are, pay attention because tornado frequency is actually shifting East from Texas towards the Southeast US.

In this episode, we'll visit a Kansas town hit by a super cell tornado, follow a storm chasing meteorologists, and as always learn what you can do to prepare your home and stay safe.

(tornado whirring) So, how does a tornado form?

First warm moist air near the earth's surface rises and develops into Cumulus clouds.

If the atmosphere is unstable, this warm air continues to rise and the cycle of cloud formation continues and a thunderstorm is formed.

When wind speeds and directions are different at different altitudes it's called wind shear.

And that wind shear can cause a horizontal rotating tube of air to form.

Then the rising warm air called an updraft can turn that horizontal tube vertical making the whole storm rotate.

At that stage, the storm is considered a Supercell.

Warm moist air pushes upward while cool dry air pushes down and these two forces tighten and the vortex is sent towards the ground.

While all supercells have the potential to produce a tornado.

Only one in five do end up creating one.

And exactly which ones will become a tornado and which ones won't remains a mystery and a weakness in our forecasting and warning systems.

But that's where the work of meteorologists like Nick Stewart comes in.

- So we're trying to figure out why one storm will produce a tornado and why another one will not.

And the biggest problem is we don't have data right around those tornadoes.

So what we're trying to do is place weather instruments out ahead of the storm, around the entire storm to see exactly what's happening with the temperatures the humidity values in those lowest levels of the storm.

- So on May 28th, 2019 We knew that there was gonna be severe weather in Eastern Kansas.

- [man] That blue right there, that's gotta be a trail on the ground.

- [Nick] We knew that it was a very strong tornado based on the radar.

We knew winds were easily 140 150 miles an hour, if not stronger.

And we knew it's very large, but we knew that we were in the perfect spot to put a weather instrument.

And you're basically playing a game of cat and mouse with tornadoes trying to make sure you get in the right spot at the right time.

On the far right side of this rain.

You can see the info tab blowing into it.

There's the very probably strong tornado is in all of that rain right there.

And we've never had a example of a tornado being that large before.

[winds blowing] - [man] Big time tornado, Nick hurry!

- And this tornado begins just accelerating towards us.

And at that point, you know the outer rain bands are basically right overhead of us.

And we need to go.

- [man] Hey we gotta go!

Nick we gotta go!

- [Nick] Go,go,go [rain pouring] - [Nick] And you can just see the tornado take almost a direct aim right at Linwood.

- [man] Tornadoes right behind us, its crossing right here.

If Linwood's next Linwood's gonna get it if it keeps that track.

- [Announcer] Residents of Linwood received tornado warnings and took shelter.

- [man] God, it's huge, too.

It's here, we're headed to the basement.

[winds blowing] - [woman] We're okay, we're okay - [man] Everything's good right now.

- [woman] Yup.

- We are okay.

- It's the pressure that was on your head.

It felt like it pushed your head in a quarter of an inch and then it blew back out.

And we knew when that blew back out that was the house coming apart.

- [Josh] Oh my God!

Well, we got out in basement right in time.

This is, this is what my parents' kitchen was.

I mean, we were a direct hit, but we're alive.

- [Maiya] In all, 19 houses were destroyed and 50 were damaged.

Tornadoes are rated on the Enhanced Fujita or EF-Scale.

EF-0's cause light damage and have winds of 65 to 85 miles an hour.

While EF-5's have winds over 200 miles an hour and cause incredible damage.

The tornado that hit Linwood was an EF-4 and it was a mile wide.

but because of early warnings, no lives were lost.

Elaina Sutley is a structural engineer whose goal is to prevent the kind of devastation that we saw in Linwood.

- So the tornado landed at about 6:00 PM on Tuesday, May 28th.

We were on the ground at 7:00 AM that Friday the 31st.

Our goal was to document and understand the extent of damage that happened along the path specifically from a structural engineering perspective.

And we paired off into our teams of two and we all had a map with the survey points on our map and everyone was assigned specific areas to go to.

In our damage assessment we consistently saw evidence of a lack of a continuous load path where the roof was not properly connected to the walls and the walls not being completely connected to the foundation.

In a few select cases we did see where interior walls were only glued to the foundation.

And when we approached this site the slab had been swept clean, and that all of the built structure had been completely lifted off and removed but there was just debris everywhere.

And so now they're rebuilding, there's still no adopted building code in Leavenworth County.

So this is their walk-out basement.

And if you have a basement, that's a great place to shelter.

But all of this subfloor down here had been lifted off by the tornado.

When you're reaching EF-4 intensity speed.

So you can still be sucked out of it.

And so at that point, you really need a safe room.

So the people who lived here did shelter in their safe room.

Had they been out here they probably would have been sucked up by the tornado and killed.

- [Elaina] Our building codes don't include tornado loads.

We do not design structures to withstand tornadoes.

So, we expect to see catastrophic damage when a tornado comes through.

This is hard for me to understand because we have more than 1200 tornadoes documented every single year in the United States and have a history of more than 4,300 documented in the state of Kansas.

But tornadoes are not in our building codes.

- The good news is that houses can be easily and affordably built to withstand many tornadoes and it's possible to retrofit existing structures.

You can really see why this matters by looking at research from our friends at IBHS.

If you've seen our episodes on fires or hurricanes you remember that they build and destroy homes in their labs to figure out weak points including creating tornado winds.

For your home to stay put, when it's faced with tornadic winds, it's all about the connections.

Your walls need to be bolted to the foundation.

The stories of your house need to be tied together.

And the roof needs to be tied down to the walls.

This might seem obvious, but without building codes you often find houses without any of these connections.

So to test this design, researchers at IBHS built two houses one included fortified standards, and one did not.

[wind blowing] - [Maiya] I think I know which one I'd rather be in during a tornado.

[debris thuds] Even if you live in a well-prepared home make sure you have a plan in place when tornado weather is coming your way.

- If a tornado watch is issued, that's when you want to make sure your weather radio is on.

You want to have a way to get multiple ways of getting warning.

If that warning is issued the biggest thing is respect the polygon.

If you're inside that tornado warning treat it as if it's coming your way.

- [Maiya] If you're able to afford it, a concrete safe room is the best option, as it should protect you from even the most powerful tornadoes.

But whatever your shelter make sure its cleaned out and that you have easy access to it.

- For most people, the basement's the best place to go.

The lowest level of your home, they'll protect you from any flying debris outside during a tornado.

If you don't have a basement, if you have like a closet or a bathroom or underneath stairs the biggest thing is just putting as many walls between you and the outside as possible.

- Finally, if you have a reasonably safe place.

Don't evacuate.

But if you live in a mobile home or similar structure make an evacuation plan.

Pay close attention to weather updates and go early to a predetermined place like a school, church, or a neighbor's house and give yourself plenty of time to get there and make absolutely sure that you have access to it when you need it.

The last thing you want is to be stuck in the car when a tornado is coming your way.