We begin with the extreme weather across the country tonight. The fast-moving wildfires in just a moment. First, the growing toll from those tornadoes. And that same system now on the move have... See More
We begin with the extreme weather across the country tonight. The fast-moving wildfires in just a moment. First, the growing toll from those tornadoes. And that same system now on the move have evening. From oklahoma to missouri, this family just outside st. Louis and all that's left of their home. Another moment near oklahoma city, a mother handing her 7-month-old baby over to a rescuer. The family brought to safety from their flooded neighborhood. Tonight, the death toll from the second wave of tornadoes is now at 13, as the search tonight for the missing goes on. This evening, among those lost, a veteran scientist, his son and their colleague. They've been devoted to helping improve warning systems and to better forecast these storms, even taking us along with them. Abc meteorologist, ginger zee, knew them well. And she's with us here tonight. Ginger, a difficult day for you. But we thank you for joining us and reporting on this tonight, ginger. Reporter: Thank you, david. It really has been a difficult day for those who have lost loved ones. For those who are now rebuilding. And certainly, tonight, as we learn of that loss that hits all-too close to home. The tornadoes moved in quickly. The second time in two weeks. And they were deadly. The interstate, packed with terrified families, drivers trying to escape before the tornadoes hit. They had just survived the tornado the week before. The mother and child killed, pulled from their car by the twister. Tonight, we learned of three more lives lost. Three veteran storm chasers now among the dead. Tim samaras, his son, paul, and their colleague, carl young, all trying to document the storm. Here's what we know -- tim was found, seat belted in his car. The others, pulled from the car by the tornado. One was found a half-mil 7:45. Large tornado. Reporter: Tim, who led the team, was an esteemed scientist. In the storm chasing community, he was known not only as one of the best, but as one of the most cautious. He showed genuine concern of our safety going in. And you know, we lost someone that probably already has saved countless lives with his research. Reporter: He chased because he wanted to learn, to improve warning systems and help meteorologists better forecast tornados in the future. documented one of his scientific expeditions. Tim and his son, taking us along. One of their many good-byes to his wife, kathy. See you later. Have a good trip. Yeah. Reporter: Much of his recent research, funded by national geographic. Tonight, in a statement, they said, we are shocked and deeply saddened. He was a courageous and brilliant scientist, who fearlessly pursued tornadoes and lightning, in an effort to better understand these phenomena.On our trip, he showed me his baby, the kahuna, what could be the fastest camera in the world. Actually, 82 cameras in 1. It helps him firsthand, studying the burst of a lightning strike. Our journey took us 800 miles in 4 states. But he also knew the real dangers of doing this. At times, I have mixed feelings about chasing these storms. On one hand, they're incredibly beautiful. On the other hand, these powerful storms can create devastating damage that change people's lives forever. Reporter: At the end of our chase, tim told me, it was his desire to know more, to inform us all, that fueled him to go out again. I don't know how many storms I've seen in my lifetime. But every single one of them, i still get pretty excited. The little boy in me just wants to come out here and just watch and stare. Ginger's back with us, now. Ginger, I know you studied a lot of tim's work. And a question that you often get, I'm sure, from members of your own family. Why do this? Why travel out there when it's so dangerous at those times? It's for the exact reason why tim did it. It's to learn. To research. And I think in his passing and for the others, I think a lot of storm chasers will dedicate even more research to this. It is not just for the thrill. It is to learn, to warn, and just to be a great man. And that's who tim and the others were. Well, his work is to be applauded. As he would want you to do, ginger, to move forward. So, what's the forecast tonight as the severe weather now moves? And that's exactly what we want to do. We want to warn. So, in the northeast tonight, this is who needs to take a look out and be ready for the warning. This afternoon and evening, obviously, we're having the bulk of it. You can see the area there, from maine, all the way into the mid-atlantic. Now, tomorrow the threat reinvigorates in parts of the plains. So, have your noaa radios on and do everything you can to protect yourself and your families.
This transcript has been automatically generated and may not be 100% accurate.