GEOFF BENNETT: Here in the U.S., emergency responders and crews are continuing to search through the wreckage from a wave of tornadoes that hit the South.

At least 22 people were killed in this weekend's storms including four children.

Hundreds of thousands lost power.

And the storms cut brutal paths of destruction through many towns.

WOMAN: Cover your head!

Cover your head!

GEOFF BENNETT: Terrifying scenes during a weekend of tumultuous storms, and officials are warning of more dangerous weather to come.

Over the holiday weekend, tornadoes tore through four states in the south.

In Valley View, Texas, winds reached 135 miles per hour, killing at least seven people and injuring about 100 others.

More than 200 buildings were damaged, including the gas station where people were sheltering.

DAWN HARDIN, Tornado Survivor: It was scary.

I don't ever -- it's the most horrific thing I have ever gone through.

WOMAN: The floor is shaking.

GOV.

GREG ABBOTT (R-TX): I have just signed a disaster declaration.

GEOFF BENNETT: Nearly a third of all Texas counties are in a state of emergency.

Texas Governor Greg Abbott spoke shortly after seeing the devastation for himself in Valley View.

GOV.

GREG ABBOTT: Candidly, it has been a harrowing week with lives lost, property reduced to rubble.

The hopes and dreams of Texas families and small businesses have literally been crushed by storm after storm.

GEOFF BENNETT: Across Oklahoma, the strong winds uprooted trees and toppled power lines.

Earlier today, rescue efforts continued, as Arkansas Governor Sarah Huckabee Sanders toured ravaged areas.

GOV.

SARAH HUCKABEE SANDERS (R-AR): Thank you.

GEOFF BENNETT: Heavy rain lashed Northwest Arkansas throughout the night.

Trees down by the storm damaged cars and blocked access into neighborhoods.

In Kentucky, Governor Andy Beshear declared a state of emergency earlier today.

This morning, more than 187,000 Kentuckians were still without power.

GOV.

ANDY BESHEAR (D-KY): Right now, we're working to get different generators from our sources that we have here in the state and around it.

Right now, we're providing assistance from the state level to our counties.

GEOFF BENNETT: This weekend's turbulent weather came after a week of severe storms across the nation.

Last Tuesday, a tornado killed five people and injured dozens in Iowa.

Forecasters warned residents from Alabama to New York to stay on high alert as the storm moves east.

May and June tend to be the most active months for tornadoes in the U.S., but some experts say this tornado season is looking like the most active since 2017.

To get a better understanding of what's happening now and the concerns as hurricane season approaches we're joined by Jeff Berardelli, chief meteorologist for WFLA-TV in Tampa Florida.

Jeff, thanks so much for being with us.

So put this into context for us.

How intense is this season compared to seasons past?

JEFF BERARDELLI, Chief Meteorologist, WFLA-TV: We have seen a lot of tornadoes a lot of severe weather especially during the month of May.

In fact, it's the second most active we have seen since 2010.

We have seen a lot of tornadoes, somewhere close to about 1,000 tornadoes, across the United States.

And given what we have seen the past couple of decades or so, it certainly is a very active year.

And part of the reason is this really huge heat dome in Central America which really hasn't moved.

It's been very stubborn.

And so it's set up a front across Tornado Alley.

It's kind of just stuck there.

And as long as that front is stuck there, we have the jet stream and disturbances riding along that front over an area very prone for severe weather, because that's where the cold air in the Pacific Northwest, where it's actually been pretty cold, and the very hot air down in the Gulf meet a collide there.

And so it's been it's been excessively severe in that area.

GEOFF BENNETT: Do we know what's causing that front?

JEFF BERARDELLI: Yes, again there's this stagnation in weather patterns.

This heat dome across Mexico and Central America is epic.

I mean, Mexico City two days in a row broke their all-time record highs.

We're seeing temperatures over 115, 120 degrees in parts of the country, feels-like temperatures over 125 degrees.

So this really persistent extreme heat wave, which is partly fueled by human-caused climate change, is causing everything to stagnate in the atmosphere.

And this front and this jet stream is stuck across the Central and Southern U.S., and it just keeps creating rounds and rounds of severe weather and tornadoes.

GEOFF BENNETT: There's been some observation that, when we have tornadoes now, we tend to see a more concentrated series of them.

Do we have a good understanding of what accounts for that?

JEFF BERARDELLI: Yes, I hear what you're talking about.

You're talking about the fact that the atmosphere is more primed when we have outbreaks.

So we're talking about the climate change signal here.

There isn't necessarily a signal for more tornadoes or perhaps even more severe weather over the past 30 or 40 years.

But one thing we do notice and the computer models pick up on is that, when the atmosphere is primed, it's even more primed than it used to be because of climate change.

And, therefore, during outbreaks, the outbreaks tend to be bigger.

GEOFF BENNETT: And hurricane season, we should note, is also expected to be more intense.

We could see half-a-dozen hurricanes that are Category 3 or higher.

What should folks know about that?

JEFF BERARDELLI: Yes, so a couple of things are going on.

first of all, we're transitioning out of El Nino to La Nina.

And during La Nina seasons, we see something like around twice the number of hurricanes than we would see during El Nino.

So this summer is likely to be a La Nina.

That's number one.

Number two, what's going on across the Atlantic Basin is unprecedented heat.

Water temperatures all across the basin are at record levels, but not just all across the basin, in the main development region, so the Tropical Atlantic, also in the Caribbean and also in the Gulf of Mexico.

As you raise water temperatures, storms tend to have more high-octane fuel to get stronger.

And so we're expecting not only more numbers of storms, so more named storms this season, but also likely more hurricanes and probably significantly more major hurricanes this season, which we're concerned about.

GEOFF BENNETT: And that's connected to climate change as well?

JEFF BERARDELLI: To some degree, it is because climate change races the baseline temperatures of the Atlantic Ocean.

In fact, in the Atlantic and in the Tropics specifically, we have seen about a two-degree Fahrenheit to three-degree Fahrenheit increase in water temperatures over the past 50 years or so.

So when you have that much more high-octane fuel, you can get storms that are a lot stronger.

So some of it is a climate change signal.

Other part of it is natural variability, and which is that El Nino and La Nina cycle.

GEOFF BENNETT: Jeff Berardelli is chief meteorologist with WFLA-TV in Tampa, Florida.

Jeff, thanks so much for being with us this evening.

We appreciate it.

JEFF BERARDELLI: You're welcome.