the latest deadly outbreak of tornadoes in the heartland. authorities in oklahoma say the death toll from friday's storms could rise again as search for the missing continues. at least 13 people were killed. among victims, four children, five other kids are among the seven still missing. the torrential rain that came in the storms was too much for one section of road in oklahoma city. the rushing water opened a sinkhole that swallowed part of a highway. rescuers in boats had to pluck families from flooded homes in missouri. >> among 13 killed in the oklahoma twister were three men involved in tornado research. abc's ginger zee reports on the storm chasers who knew the risks. the tornados moved in quickly. second time in two weeks. they were deadly, the interstates packed with terrified families. drivers trying to escape before the tornados hit. they had just survived the tornado the week before. the mother and child killed, pulled from their car by the twister. and we have learned of three more lives lost.