Three storm chasers, including well-known tornado researcher Tim Samaras, were killed in the latest violent storm to hit Oklahoma.
Samaras, 55, his 24-year-old son Paul, and fellow storm chaser Carl Young, 45, died while tracking a tornado on Friday night near El Rino.
The storm front is responsible at least 14 deaths from tornadoes and flash floods in Oklahoma, Arkansas and Missouri.
Ten people, including two children, were killed in the western suburbs of Oklahoma. Eight of the victims were on roads that were crowded with people trying to escape the howling winds.
Gov. Mary Fallin on Sunday said the death toll could rise as emergency workers search for missing people. She said 115 people in the state were injured in the storm.
A powerful EF-5 tornado that struck Moore, Okla. killed 26 people on May 20.
Samaras' brother, Jim Samaras, said on his Facebook page that Tim died doing what he loved and that "Carl and Tim were the best of friends."
The storm chaser had worked with National Geographic Channel and the Discovery Channel, presenting data from severe storms collected with equipment he had a hand in designing.
"We are deeply saddened by the loss of Tim Samaras, his son Paul, and their colleague Carl Young. Our thoughts and prayers go out to their families," Discovery Channel spokeswoman Laurie Goldberg said.
The exact circumstances of their deaths are not clear, but it appears they were killed in an EF-3 tornado that struck 55 kilometres west of Oklahoma City.
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Canadian weather journalist chaser Greg Johnson of Regina, whose truck was struck by debris during one of the Oklahoma tornadoes, knew Samaras.
"Tim was the type of person who was without ego. He was in it for the science. He's been doing it for 30 years and he was widely recognized as the Wayne Gretzky of storm chasing," Johnson told CBC News.
The violent weather system responsible for Friday's tornadoes expected to hit the U.S. East coast on Sunday. Forecasters say Washington, D.C. to northern Maine could be hit with hail and high winds, although a tornado is possible.