The Arkansas tornadoes on 11 April 1976 were investigated using regular 30 min interval GOES digital infrared data, rawinsonde observations, Doppler sounder records and radar summaries covering the 3 hour time period immediately preceding the touchdown of the tornadoes. Clouds associated with the tornado were compared to other clouds that were not associated with tornadoes. It appears as if the altitude to which the overshooting cloud top penetrates above the tropopause is the major factor that controls tornado formation. Gravity waves were first observed at ionospheric heights when the overshooting cloud top began to penetrate the tropopause. Rawinsonde and radar observations were used to establish the background meterological conditions.