The radar and balloon data of Gossard et al. (1970) for an event on August 6, 1969, are examined and calculations presented showing that the wavelike motions observed by the radar are Kelvin-Helmholtz instabilities; the layer of intense wind shear that surrounds the height of the radar returns is shown to be a critical layer for gravity waves themselves generated higher in the atmosphere. The observed wind and temperature profiles are used in a linear shear instability calculation that shows a narrow band of unstable wavelengths generated at a shear layer some 770 m above the surface; the wave are evanescent upward but transport momentum downward to the critical level at 300 m, where the absortion enhances the wind shear and the reduced Richardson number leads to Kelvin-Helmholtz instability. The results of the analysis further indicate that the properties of the Kelvin-Helmholtz instabilities are consistent with the strong wind shear that critical level absorption would produce, and that the motion of the radiosonde balloon can be accounted for by superposing on the mean flow a slowly growing unstable wave. Thus the observations show the entire history of a shear instability event, from generation to absorption at a critical level.