" Outside the rain began to pour in sheets, and the wind howled . Giant pieces of hail began to pelt the building— banging off the skylights so hard that Simpson worried the glass might shatter. Then, as it had earlier in the day, the wind briefly let up. It was then Simpson heard a sound she had dreaded —a sound she couldn’t believe she was actually hearing. It was 2: 40 P.M. and the tornado sirens in Moore started to wail. "

― , The Mercy of the Sky: The Story of a Tornado