Dangerous tornado outbreak threatening states across the South

A major storm system is threatening heavy rain and tornado outbreaks in the South. CBS News' David Begnaud reports on the damage so far, and CBS News meteorologist and climate specialist Jeff Berardelli joins CBSN to explain why climate change is having an impact on the threat.

Video Transcript

ELAINE QUIJANO: Millions of Americans are in the path of a dangerous weather system that includes hail, thunderstorms, and tornadoes. Several twisters have already touched down in Alabama, and warnings have been posted in states across the Southeast. David Begnaud is in the danger zone with the latest.

DAVID BEGNAUD: There was a tornado in Whistler, Mississippi that tore through this chicken farm today shredding almost every building in sight. It was part of the massive front promising to affect nearly 40 million people from the state of Texas to the state of Georgia. Twisters touched down in rural communities throughout Mississippi and Alabama. There were hundreds of kids at the University of Alabama in Tuscaloosa who were forced to shelter in place today.

- Literally like a tornado.

DAVID BEGNAUD: This driver got quite the surprise in his rear view mirror--

- It's so crazy going to [INAUDIBLE], man.

DAVID BEGNAUD: --as he drove past a tornado that touched down right after lunchtime. Meanwhile, the powerful storm produced heavy rains that shut down schools and vaccination sites across the Gulf Coast.

ELAINE QUIJANO: For more, let's bring in CBS News meteorologist and climate specialist Jeff Berardelli. Hi there, Jeff. So how severe has the tornado outbreak been so far?

JEFF BERARDELLI: It's been bad. I mean, we've already seen about 20 tornadoes confirmed, and we're only about halfway through this event. In total, we could end up with 40 plus tornadoes, which is about half of what we would normally see during the month of March. And we are a five out of five, as you mentioned, on the severe weather scale today. So it's high as it can possibly get. And tomorrow, we are still a four out of five as that threat moves to the Southeast coast.

So that's a look at the radar over the past six hours or so. Now I'm going to put the tornadoes on, and watch all those tornadoes develop. Some of these have been big and strong tornadoes in both Mississippi and also into Alabama and some other tornadoes that also formed way back here in parts of Arkansas and northern parts of Louisiana as well.

So this has been a rough system, and we still have some time to go. The worst is going to be as we head through the evening into the overnight hours because that jet stream, that speed right there, is going to be picking up over the next few hours or so.

At the same time, we have the spin from the upper level low. That is providing the spin for the tornadoes, and this humidity is providing the instability. That is all coming together for what is a banner severe weather outbreak. It's going to be a very dangerous night across the Southeast.

ELAINE QUIJANO: So that's the near term. Jeff, what else is in store? What's the forecast?

JEFF BERARDELLI: All right, so as we head through the evening hours and overnight tonight, we're going to see a strengthening low level jet stream. That is usually when we see the most powerful tornadoes begin to pick up. So as we head through the evening hours, you can see, first of all, the outline of the pink here. It's where the worst of the tornadoes could potentially be. So that's parts of Alabama and Mississippi.

As we head through the later part of the evening, that line, a second round, moves through Birmingham, and then by morning, it moves through Atlanta. Could be tornadoes at any time as this line moves to the East. Now the threat tomorrow is still there for tornadoes, but it becomes a little bit more of a straight line wind damage threat because you can see that line of storms right there is kind of straight. It's no longer-- you don't see as many of those isolated thunderstorms. So we start to see that threat switch from tornadoes to wind during the day tomorrow.

ELAINE QUIJANO: Well, tornadoes have been very destructive during March in recent years. How is tornado season changing?

JEFF BERARDELLI: Well, it is about 2 plus weeks earlier than it used to be a few decades ago. And also, we're seeing an increasing trend in tornadoes here in what we call Dixie Alley and a decreasing trend in what is traditionally Tornado Alley. So you can see that right there where the increasing trend is corresponds exactly where the highest risk was during the day today and will be overnight tonight as well.

Here's the reason we think. It could be partially natural variability, natural cycles in the pattern. But we also think, because of climate change, the desert air, which in the former climate was kind of confined to the desert Southwest, is actually beginning to expand. We expect deserts to expand with climate change. So this is consistent with climate change.

That desert air pushing further east makes it more stable in the plains states, and at the same time, it pushes the humidity further east. The Gulf of Mexico is warming up. So that's pushing warmer and more unstable air further to the north in adjacent areas from the Gulf of Mexico. This all makes sense. This is a signal of climate change that these systems and the propensity for tornadoes would be shifting east, and that's exactly what we're seeing.

Why we're concerned about this is take a look at this map. This is a nighttime map of the United States. You can see Michigan. You can see Florida. There's New York City. All these lights are the cities. Well, take a look at the population density in the plain states. It is much less populated in traditional Tornado Alley, much more densely populated in the Southeast where these tornadoes are hitting right now.

And if the overall trend, which it has been and it will probably continue to be over the next few decades, is to push more tornadoes towards the Southeast, that is not good news because the folks there are more vulnerable. It's more densely populated. The homes are not quite as sturdy, not prepared for the tornadoes like they are in the plains states land.

ELAINE QUIJANO: All right, Jeff Berardelli for us. Jeff, thank you.

JEFF BERARDELLI: You're welcome.