Thirteen people are confirmed dead after a tornado outbreak this weekend in Oklahoma including three veteran storm chasers.

Tim Samaras, his son Paul Samaras and Carl Young were featured on the TV show “Storm Chasers” and founded TWISTEX (Tactical Weather Instrumented Stample in Tornadoes Experiment.) The men were killed in El Reno, Oklahoma by an EF-3 tornado that abruptly changed direction and caught them off guard.

“Samaras was a respected tornado researcher and friend … who brought to the field a unique portfolio of expertise in engineering, science, writing and videography,” the Storm Prediction Center in Norman, Oklahoma said in a statement. They said it is believed the deaths are the first of scientific researchers chasing tornadoes.

The Samaras family released a statement from Tim’s brother Jim regarding the tragedy.

“It truly is sad that we lost my great brother Tim and his great son, Paul. Our hearts also go out to the Carl Young family as well as they are feeling the same feelings we are today,” Jim Samaras wrote. “They all unfortunately passed away but doing what they LOVED. Chasing Tornado’s. I look at it that he is in the ‘big tornado in the sky…”