JOHN YANG: Good evening, I'm John Yang.

A second round of violent weather is barreling across the central and southern United States after a deadly and destructive Friday night.

The storms have spawned violent tornadoes and fanned wildfires and dust storms that have claimed at least 17 lives and destroyed scores of homes.

More than 200,000 people are without power across five states.

Many of the fatalities have been in Missouri where at least four tornadoes touched down.

The National Weather Service says there's a heightened threat of tornadoes tonight stretching from the Deep South to the Ohio River Valley.

Earlier I spoke with Matthew Cappucci, senior meteorologist at MyRadar.

He's in Mississippi tracking the storms.

I asked him how unusual a multiday tornado outbreak like this is.

MATTHEW CAPPUCCI, SENIOR METEOROLOGIST, MYRADAR: So either of these two different events would in and of themselves be very significant.

Last night we saw roughly 140 tornado warnings in a 24-hour period with numerous fatalities and at least 18 tornado warning simultaneously.

So last night was a big deal.

And yet that's the appetizer for what's been happening all day today into the evening hours.

We have a level five out of five, a high risk, which issued only less than 1 percent of the time.

And so it's a top tier event anyway.

The verbiage the National Weather Service is using is downright alarming when they say things like volatile, intense, long track tornadoes.

JOHN YANG: Long track tornadoes explain that and why they're so dangerous.

MATTHEW CAPPUCCI: So most tornadoes tend to be towards the lower end of the scale at EF01 or 2 on the 0 through 5 scale today, long track strong and violent tornadoes.

We're talking like EF3, EF4 plus winds of 160 plus miles per hour.

And the other thing too, these supercells, the parent rotating storms, will be self-sustained for a long time because the atmosphere is so favorable for that these tornadoes can stay on the ground for 15, 20, 30 minutes, maybe close to an hour in a few instances, leading to very long damage tracks.

JOHN YANG: What are the ingredients in the atmosphere and the environment that make this all so conducive?

MATTHEW CAPPUCCI: In essence, you need two ingredients.

You need cape or juice.

How warm and moist is the atmosphere?

And you need spin.

That spin comes from changing winds with height.

Now it's warm, it's humid.

We have Gulf moisture walking northwards right now, so the atmosphere is very juiced up.

But at the same time the winds at the surface are out of the south or southeast, but aloft they're more out of the southwest.

So any storm that grows tall enough will feel those changing winds and will rotate in some cases quite profusely.

JOHN YANG: This increase intensity and also the long lasting, these long lasting storms, how much of this is due to climate change or is any of it due to climate change?

MATTHEW CAPPUCCI: It's really not that closely linked to climate change.

You know, the spring months of every year tend to be a really rough time.

We have the insurgences of Gulf moisture and a little bit of leftover cold from winter.

And those two seasons kind of battle it out during March, April, May.

Realistically, if you're going to get big tornadoes, it'll be over Mississippi or Alabama this time of year.

That said, we do know that wintertime events when the atmosphere is warming a little bit more tend to be overachieving a bit more thanks to the warming atmosphere.

So there's a little bit of a role, but really it's the time of year.

JOHN YANG: What's your advice or what do you say to people who's living in those areas or maybe under tornado watches or warnings?

MATTHEW CAPPUCCI: In an episode like this, we want people to take action ahead of time.

Ordinarily, folks wait until a tornado warning issued before they seek shelter.

But on a day like today, a night like tonight, if people are in a tornado watch, it's probably a good idea to get to a site built location, someplace with a below ground shelter even before any warnings are issued.

You never want to be more than five minutes away from a shelter on a night like tonight.

So that way if a warning's issued, you can just duck and cover real quick and you don't have to worry about moving locations.

If you have elderly, family, friends, loved ones, check in with them, make sure they have a plan too.

It's one of those nights we have to be good neighbors.

JOHN YANG: And Matthew, to help people out, they hear all these watches, warnings and that's alerts and that sort of things.

What's the difference between a watch and a warning?

MATTHEW CAPPUCCI: So a watch means conditions are favorable for tornadoes to form.

Guys, that's the edge of the tornado right there.

A warning means that we're seeing one on radar or in person, something is imminent or occurring.

So watch.

This means hey, watch out.

A warning means take action right now, shelter right now.

The warnings are those ones that buzz on your phones.

Now the National Weather Service is calling this APBS for a particularly dangerous situation.

Those type of watches are only issued about 7 percent of the time, but you're three times more likely to be hit by a violent tornado.

JOHN YANG: Matthew Cappucci in Mississippi, thank you very much and be safe.

MATTHEW CAPPUCCI: Thank you.